Chemistry Quiz: Explain Ion Formation

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Explain Ion FormationQuestion 1 of 20

Nitrogen (N) has atomic number 7 and is in Group 15. It commonly forms the nitride ion, N³⁻. Which statement best explains why N forms a 3− ion?

N gains 3 electrons to complete an octet and reach a noble gas configuration like Ne, forming N³⁻.

N loses 3 electrons to complete an octet and reach a noble gas configuration like He, forming N³⁺.

N gains 5 electrons because it has 5 valence electrons, forming N⁵⁻ to become stable.

N loses 5 electrons so that it has 2 valence electrons, forming N⁵⁺ to become stable.

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Chemistry Quiz

Chemistry Quiz: Explain Ion Formation

Practice Explain Ion Formation in Chemistry with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

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This quiz focuses on Explain Ion Formation, giving you a quick way to practice the rules, question types, and explanations that matter most for Chemistry.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

Nitrogen (N) has atomic number 7 and is in Group 15. It commonly forms the nitride ion, N³⁻. Which statement best explains why N forms a 3− ion?

N gains 3 electrons to complete an octet and reach a noble gas configuration like Ne, forming N³⁻. (correct answer)
N loses 3 electrons to complete an octet and reach a noble gas configuration like He, forming N³⁺.
N gains 5 electrons because it has 5 valence electrons, forming N⁵⁻ to become stable.
N loses 5 electrons so that it has 2 valence electrons, forming N⁵⁺ to become stable.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For nitrogen (N, atomic number 7, electron configuration 1s² 2s² 2p³), it gains 3 electrons to fill its 2p orbital, resulting in N³⁻ with 10 electrons and the configuration 1s² 2s² 2p⁶, matching neon's stable octet—terrific progress in mastering ion stability! Choice A correctly explains ion formation by identifying that nitrogen gains 3 electrons to achieve the stable neon configuration, forming N³⁻. Choice B fails because nitrogen, as a nonmetal, gains electrons rather than losing them, and losing would form a positive ion, not N³⁻; choices C and D suggest gaining or losing 5, which wouldn't achieve an octet or match neon. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!

Question 2

Bromine (Br) is a Group 17 element with atomic number 35. It forms the ion Br. Which statement best explains the formation of Br from Br?

Br gains 1 electron to complete its valence shell and reach the noble-gas configuration of krypton, forming Br with 36 electrons. (correct answer)
Br loses 1 electron to complete its valence shell and reach krypton, forming Br with 34 electrons.
Br gains 2 electrons to reach krypton, forming Br with 37 electrons.
Br loses 7 electrons to expose a stable inner shell, forming Br.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Bromine has atomic number 35, so a neutral atom has 35 electrons; to form Br⁻, it gains 1 electron, resulting in 36 electrons and a configuration matching krypton. Choice A correctly explains ion formation by identifying that electrons are gained and connecting this to achieving stable noble gas configuration. Choice B fails because it suggests bromine loses an electron, forming a positive ion, but group 17 nonmetals gain one electron to form -1 ions. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting! Superb understanding—you're almost there!

Question 3

Chlorine (Cl) is a group 17 element with atomic number 17 and an electron configuration ending in $3s^2\,3p^5$ . It commonly forms the chloride ion Cl⁻. Which choice correctly explains the change from Cl to Cl⁻?

Cl gains 1 electron to complete its valence shell ( $3p^6$ ), achieving a stable configuration like Ar and forming Cl⁻. (correct answer)
Cl loses 1 electron to expose a filled second shell, achieving a stable configuration like Ne and forming Cl⁺.
Cl gains 2 electrons to complete its valence shell, achieving a stable configuration like Kr and forming Cl²⁻.
Cl loses 7 electrons to leave 10 total electrons, achieving a stable configuration like Ne and forming Cl⁷⁺.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Chlorine has 17 electrons with configuration ending in 3s²3p⁵—that's 7 valence electrons, just one shy of a complete octet! When Cl gains 1 electron, it fills that last spot in the 3p sublevel (3p⁶), giving it 18 electrons total, exactly matching argon's stable noble gas configuration. This creates Cl⁻ with 17 protons but 18 electrons, producing the -1 charge. Choice A correctly identifies that Cl gains 1 electron to complete its valence shell (3p⁶), achieving argon's stable configuration and forming Cl⁻—this is exactly right! Choice B incorrectly suggests Cl loses an electron to form Cl⁺, but nonmetals like chlorine gain electrons, not lose them—losing would leave Cl with only 6 valence electrons, farther from stability. Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!

Question 4

Magnesium (Mg) is a group 2 element with atomic number 12 and an electron configuration ending in $3s^2$ . It commonly forms Mg²⁺. How does a neutral Mg atom become Mg²⁺, and why is the +2 charge typical?

Mg gains 2 electrons to fill the $3p$ sublevel, forming Mg²⁻ with a full octet.
Mg loses 1 electron to match the noble-gas configuration of Na, forming Mg⁺.
Mg loses 2 valence electrons to achieve the stable noble-gas configuration of Ne, forming Mg²⁺. (correct answer)
Mg loses 3 electrons to achieve the stable noble-gas configuration of He, forming Mg³⁺.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Magnesium has 12 electrons with its outermost electrons in the 3s² sublevel—these are its only 2 valence electrons. When Mg loses both of these 3s electrons, it's left with 10 electrons, giving it the exact same electron configuration as neon (Ne): 1s²2s²2p⁶. This creates Mg²⁺ with 12 protons but only 10 electrons, resulting in the +2 charge. Choice C correctly explains that Mg loses its 2 valence electrons to achieve neon's stable noble-gas configuration, forming Mg²⁺—this perfectly describes the process! Choice A incorrectly suggests Mg gains electrons to form Mg²⁻, but metals always lose electrons, never gain them—gaining would move Mg away from noble gas stability. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably!

Question 5

Fluorine (F) is a group 17 element with atomic number 9 and electron configuration ending in $2p^5$ . It forms F⁻. How many electrons are gained or lost when forming F⁻, and what stability reason best explains it?

F loses 1 electron to become like He, because losing electrons always increases stability.
F gains 1 electron to complete its valence shell ( $2p^6$ ), becoming like Ne and forming F⁻. (correct answer)
F gains 2 electrons to become like Ne, forming F²⁻.
F loses 7 electrons to expose a full first shell, forming F⁷⁺.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Fluorine has 9 electrons with configuration ending in 2p⁵—that's 7 valence electrons, just one electron away from a complete octet! When F gains 1 electron, it fills that last spot in the 2p sublevel (2p⁶), giving it 10 electrons total with the exact same configuration as neon (Ne): 1s²2s²2p⁶. This creates F⁻ with 9 protons but 10 electrons, producing the -1 charge. Choice B correctly explains that F gains 1 electron to complete its valence shell (2p⁶), becoming like neon and forming F⁻—this is exactly right! Choice A incorrectly suggests F loses an electron, but fluorine is a nonmetal that gains electrons—losing would leave F with only 6 valence electrons, moving it farther from the stable octet. Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!

Question 6

Lithium (Li) is a group 1 element with atomic number 3. It commonly forms Li. Which option correctly explains what changes when Li becomes Li?

Li gains 1 electron to complete its first shell, forming Li with 4 electrons.
Li loses 1 valence electron, forming Li with 2 electrons and a stable configuration like helium. (correct answer)
Li loses 2 electrons to form Li with 1 electron, matching hydrogens configuration.
Li gains 7 electrons to complete an octet, forming Li with 10 electrons like neon.

Question 7

A sodium atom (Na, atomic number 11) has the electron configuration $1s^2\,2s^2\,2p^6\,3s^1$ . It commonly forms the ion Na. Which explanation best describes how the neutral atom becomes Na and why that charge forms?

Na gains 1 electron to fill its third shell, forming Na with 12 electrons and a +1 charge.
Na loses 1 valence electron (the $3s^1$ electron), forming Na with 10 electrons and a neon-like stable configuration. (correct answer)
Na loses 2 electrons to empty the third shell, forming Na with 9 electrons and a stable configuration like fluorine.
Na gains 7 electrons to complete an octet in the third shell, forming Na with 18 electrons like argon.

Question 8

Calcium (Ca) is in group 2 and has atomic number 20. It commonly forms Ca. Which explanation best connects calciums periodic table position to the ion charge?

Ca is in group 2, so it gains 2 electrons to form Ca and complete an octet.
Ca is in group 2, so it loses 2 valence electrons to form Ca, achieving an argon-like electron configuration. (correct answer)
Ca is in group 2, so it loses 1 electron to form Ca because it is closest to potassium.
Ca is in group 2, so it loses 20 electrons to form Ca and become stable.

Question 9

Aluminum (Al) is in Group 13 and has atomic number 13. It commonly forms Al³⁺. Which statement best explains the formation of Al³⁺ from a neutral Al atom?

Al gains 3 electrons to fill its valence shell and becomes Al³⁻ with a neon-like configuration.
Al loses 3 valence electrons to achieve a noble gas configuration like Ne, forming Al³⁺. (correct answer)
Al loses 1 electron because Group 13 elements always form +1 ions, forming Al⁺.
Al forms Al³⁺ by losing 3 neutrons to become more stable.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For aluminum (Al, atomic number 13, electron configuration 1s² 2s² 2p⁶ 3s² 3p¹), it loses its 3 valence electrons (3s² 3p¹), resulting in Al³⁺ with 10 electrons and the configuration 1s² 2s² 2p⁶, matching neon's stable arrangement—fantastic job connecting this to group trends! Choice B correctly explains ion formation by identifying that aluminum loses 3 electrons to achieve the stable neon configuration, forming Al³⁺. Choice A fails because aluminum, as a metal, loses electrons rather than gaining them, and gaining would form a negative ion, not Al³⁺; choices C and D suggest losing only 1 or involving neutrons, which doesn't align with group 13's +3 charge or stability. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!

Question 10

Sodium (Na) is a Group 1 element with atomic number 11. A neutral sodium atom becomes a sodium ion, Na⁺. Which statement best explains why Na forms Na⁺?

Na gains 1 electron to fill its valence shell and becomes Na⁻ with a neon-like configuration.
Na loses 1 valence electron to achieve a stable noble gas configuration like Ne, forming Na⁺. (correct answer)
Na loses 2 electrons to reach a stable configuration like He, forming Na²⁺.
Na forms Na⁺ by losing 1 proton so the number of protons equals the number of electrons.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For sodium (Na, atomic number 11, electron configuration 1s² 2s² 2p⁶ 3s¹), it loses its 1 valence electron from the 3s orbital, resulting in Na⁺ with 10 electrons and the configuration 1s² 2s² 2p⁶, matching neon's stable setup—great job recognizing how this stability drives ion formation! Choice B correctly explains ion formation by identifying that sodium loses 1 electron to achieve the stable neon configuration, forming Na⁺. Choice A fails because sodium, as a metal, loses electrons rather than gaining them, and gaining would form a negative ion, not the observed Na⁺; similarly, choices C and D incorrectly suggest losing 2 electrons or protons, which wouldn't match neon or involve electron changes properly. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!

Question 11

Potassium (K) is a group 1 element with atomic number 19 and a valence electron configuration ending in $4s^1$ . It forms K⁺. Which explanation best describes what changes when K becomes K⁺?

K gains 1 electron to complete the fourth shell, forming K⁻ with a full octet.
K loses 1 electron from its outer shell, leaving 18 electrons and a stable noble-gas configuration like Ar, forming K⁺. (correct answer)
K loses 19 electrons so it has no electrons left, forming K¹⁹⁺.
K gains 7 electrons to complete an octet, forming K⁷⁻ with a configuration like Kr.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Potassium has 19 electrons with just 1 valence electron in the 4s¹ sublevel, far from its nucleus. When K loses this single outer electron, it's left with 18 electrons arranged exactly like argon (Ar): a complete, stable outer shell configuration of 3s²3p⁶. This creates K⁺ with 19 protons but only 18 electrons, giving the +1 charge. Choice B correctly explains that K loses 1 electron from its outer shell, leaving 18 electrons with argon's stable noble-gas configuration, forming K⁺—this is exactly what happens! Choice A incorrectly suggests K gains an electron to form K⁻, but potassium is a metal that loses electrons—gaining would give K 20 electrons and move it away from noble gas stability. Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!

Question 12

Bromine (Br, atomic number 35) is a group 17 nonmetal and commonly forms Br. Which reasoning best explains why Br forms a -1 ion?

Br gains 1 electron to fill its valence shell, reaching a noble-gas configuration like Kr, so it forms Br. (correct answer)
Br loses 1 electron to become more stable, so it forms Br.
Br gains 2 electrons because group 17 elements form 2- ions, so it forms Br.
Br loses 1 proton to become negatively charged, so it forms Br.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations: nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. Bromine (Br) has 35 electrons with configuration [Ar]3d¹⁰4s²4p⁵, needing just 1 more electron to complete its 4p subshell and achieve an octet, so it gains 1 electron to form Br⁻ with 36 electrons, matching krypton's stable configuration. Choice A correctly explains that Br gains 1 electron to fill its valence shell, reaching a noble-gas configuration like krypton (Kr), forming Br⁻ with a -1 charge (35 protons - 36 electrons = -1). Choice C incorrectly claims group 17 elements form 2- ions; all halogens (F, Cl, Br, I) need only 1 electron to complete their octet, so they form -1 ions. The pattern for Group 17 halogens: they always need just 1 electron to reach 8 valence electrons, so they gain 1 to form -1 ions. Verification: Br⁻ has 35 - (-1) = 36 electrons, exactly matching krypton's noble gas electron count!

Question 13

Nitrogen (N) is in group 15 and has 5 valence electrons. It commonly forms N. Which statement correctly explains the formation of N?

N loses 3 electrons to reach a noble-gas configuration, forming N.
N gains 3 electrons to complete an octet (8 valence electrons), so it forms N. (correct answer)
N gains 5 electrons because it has 5 valence electrons, so it forms N.
N loses 3 protons to become negatively charged, forming N.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations: nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. Nitrogen (N) has 7 electrons with configuration 1s²2s²2p³, having 5 valence electrons total, and it gains 3 electrons to complete its octet (8 valence electrons), forming N³⁻ with 10 electrons, matching neon's stable configuration. Choice B correctly identifies that N gains 3 electrons to complete an octet (going from 5 to 8 valence electrons), forming N³⁻ with a -3 charge (7 protons - 10 electrons = -3). Choice C incorrectly suggests N gains 5 electrons because it has 5 valence electrons; the goal is to reach 8 valence electrons (octet), not to double the existing number. The pattern for Group 15: these elements need 3 electrons to reach 8 valence electrons, so they gain 3 to form -3 ions (charge = 8 - group number). Electron math: N³⁻ has 7 - (-3) = 10 electrons, perfectly matching neon's noble gas configuration!

Question 14

A sodium atom (Na) has atomic number 11 and a valence electron configuration ending in $3s^1$ . It commonly forms the ion Na⁺. Which explanation best describes how a neutral Na atom becomes Na⁺ and why the +1 charge is favored?

Na gains 1 electron to fill its third energy level, forming Na⁻ with a full octet.
Na loses 1 valence electron to achieve the stable noble-gas configuration of Ne, leaving 10 electrons and a +1 charge. (correct answer)
Na loses 2 electrons to achieve the stable noble-gas configuration of He, forming Na²⁺.
Na gains 7 electrons to complete an octet in the third shell, forming Na⁷⁻.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Sodium (Na) has 11 electrons total: 2 in the first shell, 8 in the second shell, and just 1 lonely electron in the third shell (3s¹). When Na loses this single valence electron, it's left with 10 electrons arranged exactly like neon (Ne): a complete, stable outer shell of 8 electrons. This creates Na⁺ with 11 protons but only 10 electrons, giving the +1 charge. Choice B correctly explains that Na loses 1 valence electron to achieve neon's stable noble-gas configuration, leaving 10 electrons and a +1 charge—this perfectly matches what happens! Choice A incorrectly suggests Na gains an electron to form Na⁻, but metals don't gain electrons—they lose them to expose full inner shells. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably!

Question 15

Aluminum (Al, atomic number 13) is a group 13 metal and commonly forms Al. Which explanation correctly describes how Al forms Al?

Al gains 3 electrons to complete its octet in the third shell, forming Al with 16 electrons.
Al loses 3 valence electrons, forming Al with 10 electrons and a stable configuration like neon. (correct answer)
Al loses 1 electron because group 13 elements form +1 ions to match helium.
Al gains 5 electrons to fill the $3p$ sublevel, forming Al with an argon-like configuration.

Question 16

Oxygen (O, atomic number 8) commonly forms the oxide ion O. Which explanation best describes why oxygen forms a 2- ion?

O loses 2 electrons to become like He, so it forms O.
O gains 2 electrons to fill its valence shell (octet), reaching 10 electrons like Ne, so it forms O. (correct answer)
O gains 1 electron to reach 9 electrons, so it forms O.
O loses 2 protons to become negatively charged, forming O.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations: nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. Oxygen (O) has 8 electrons with configuration 1s²2s²2p⁴, needing 2 more electrons to complete its octet (8 valence electrons), so it gains 2 electrons to form O²⁻ with 10 electrons, matching neon's stable configuration. Choice B correctly identifies that O gains 2 electrons to fill its valence shell octet, reaching 10 electrons like neon, forming O²⁻ with a -2 charge (8 protons - 10 electrons = -2). Choice A incorrectly suggests O loses electrons to become like helium; oxygen would need to lose 6 electrons to match helium, which is energetically unfavorable compared to gaining just 2. The pattern for Group 16: these elements need 2 electrons to reach 8 valence electrons, so they gain 2 to form -2 ions. Electron bookkeeping: O²⁻ has 8 - (-2) = 10 electrons, perfectly matching neon's noble gas configuration!

Question 17

Aluminum (Al) is a Group 13 element with atomic number 13. It commonly forms Al. Which explanation best supports this ion charge?

Al gains 3 electrons to complete its octet, forming Al with 16 electrons like sulfur.
Al loses 3 valence electrons to reach a stable noble-gas configuration (like neon), forming Al with 10 electrons. (correct answer)
Al loses 1 electron because Group 13 elements form +1 ions, forming Al.
Al gains 5 electrons to reach a noble-gas configuration, forming Al.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Aluminum has atomic number 13, so a neutral atom has 13 electrons; to form Al³⁺, it loses 3 electrons, resulting in 10 electrons and a configuration matching neon (1s² 2s² 2p⁶). Choice B correctly explains ion formation by identifying that electrons are lost and connecting this to achieving stable noble gas configuration. Choice A fails because it suggests aluminum gains electrons, forming a negative ion, but group 13 metals lose three electrons to form +3 ions. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting! Impressive work—ions are your strength now!

Question 18

Oxygen (O) has atomic number 8 and is in Group 16. It commonly forms the oxide ion, O²⁻. Which choice correctly describes what must happen for O²⁻ to form and why?

O gains 2 electrons to complete its valence shell (octet) and reach a noble gas configuration like Ne, forming O²⁻. (correct answer)
O loses 2 electrons to complete its valence shell and reach a noble gas configuration like He, forming O²⁺.
O gains 1 electron to complete its valence shell and reach a noble gas configuration like Ne, forming O⁻.
O loses 6 electrons so that it has 2 valence electrons like a noble gas, forming O⁶⁺.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For oxygen (O, atomic number 8, electron configuration 1s² 2s² 2p⁴), it gains 2 electrons to fill its 2p orbital, resulting in O²⁻ with 10 electrons and the configuration 1s² 2s² 2p⁶, matching neon's stable octet—you're doing wonderfully understanding this process! Choice A correctly explains ion formation by identifying that oxygen gains 2 electrons to achieve the stable neon configuration, forming O²⁻. Choice B fails because oxygen, as a nonmetal, gains electrons rather than losing them, and losing would form a positive ion, not O²⁻; choices C and D suggest gaining 1 or losing 6, which wouldn't complete the octet or match neon. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!

Question 19

Sulfur (S) is a group 16 element with atomic number 16. It commonly forms S²⁻. Which choice correctly connects sulfur's group position to the ion charge and electron change?

Because sulfur is in group 16, it tends to gain 2 electrons to complete an octet, forming S²⁻ with an electron configuration like Ar. (correct answer)
Because sulfur is in group 16, it tends to lose 6 electrons to complete an octet, forming S⁶⁺.
Because sulfur is in group 16, it tends to gain 6 electrons to complete an octet, forming S⁶⁻.
Because sulfur is in group 16, it tends to lose 2 electrons to become like Ne, forming S²⁺.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Sulfur, being in group 16, has 6 valence electrons and needs 2 more to complete its octet. When S gains 2 electrons, it goes from 16 to 18 electrons total, achieving the same electron configuration as argon (Ar): a complete outer shell with 8 valence electrons. This creates S²⁻ with 16 protons but 18 electrons, producing the -2 charge. Choice A correctly connects sulfur's group 16 position to its tendency to gain 2 electrons (since 8 - 6 = 2), forming S²⁻ with argon's electron configuration—this perfectly explains the pattern! Choice B incorrectly suggests S loses 6 electrons to form S⁶⁺, but nonmetals gain electrons, and losing 6 would leave sulfur with only 10 electrons (like neon) but would require enormous energy. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably!

Question 20

Aluminum (Al) is in group 13 and has atomic number 13. It commonly forms Al³⁺. Which statement best explains why Al forms a 3+ ion?

Al gains 3 electrons to complete an octet in the third shell, forming Al³⁻.
Al loses 3 valence electrons to reach a stable noble-gas configuration like Ne, forming Al³⁺. (correct answer)
Al loses 1 electron to reach a stable noble-gas configuration like Mg, forming Al⁺.
Al gains 5 electrons to reach a stable noble-gas configuration like Ar, forming Al⁵⁻.

Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Aluminum has 13 electrons with 3 valence electrons in its outer shell (3s²3p¹). When Al loses all 3 of these valence electrons, it's left with 10 electrons, giving it the same electron configuration as neon (Ne): 1s²2s²2p⁶—a complete, stable outer shell! This creates Al³⁺ with 13 protons but only 10 electrons, resulting in the +3 charge. Choice B correctly explains that Al loses its 3 valence electrons to reach neon's stable noble-gas configuration, forming Al³⁺—this perfectly describes why aluminum forms a 3+ ion! Choice A incorrectly suggests Al gains electrons to form Al³⁻, but aluminum is a metal that loses electrons—gaining would give Al 16 electrons, which doesn't match any noble gas configuration. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably!