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Chemistry Help: Describe Atomic Structure

Review real example questions for Describe Atomic Structure in Chemistry.

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A magnesium atom (Mg) loses 2 electrons to form Mg2+\text{Mg}^{2+}. Magnesium has atomic number 12 and the isotope is magnesium-24 (24Mg^{24}\text{Mg}). How many protons, neutrons, and electrons are in 24Mg2+^{24}\text{Mg}^{2+}?

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Question 1

A magnesium atom (Mg) loses 2 electrons to form Mg2+\text{Mg}^{2+}. Magnesium has atomic number 12 and the isotope is magnesium-24 (24Mg^{24}\text{Mg}). How many protons, neutrons, and electrons are in 24Mg2+^{24}\text{Mg}^{2+}?

  1. 12 protons, 12 neutrons, 10 electrons (correct answer)
  2. 12 protons, 10 neutrons, 12 electrons
  3. 24 protons, 12 neutrons, 22 electrons
  4. 12 protons, 12 neutrons, 14 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all magnesium atoms have exactly 12 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: positive ions (cations) have fewer electrons than protons because they've lost electrons (Mg²⁺ has 12 protons but 10 electrons, having lost 2), and negative ions (anions) have more electrons than protons because they've gained electrons. The key formulas: protons = atomic number, neutrons = mass number - atomic number, electrons = protons for neutral atoms or protons - charge for ions! For ^{24}Mg^{2+}, Z=12 so protons=12; A=24 so neutrons=24-12=12; charge +2 so electrons=12 - (+2)=10. Choice A correctly determines the number of protons, neutrons, and electrons by properly using atomic number, mass number, and charge relationships. A distractor like Choice D might add instead of subtract for electrons, but for positive ions, subtract the charge from protons to find electrons—keep practicing, you're improving! The particle counting recipe: (1) PROTONS: Always equal atomic number (look it up or given). This never changes—element identity depends on proton count. (2) NEUTRONS: Subtract atomic number from mass number (A - Z). For magnesium-24: mass 24, atomic number 12, so 24 - 12 = 12 neutrons. (3) ELECTRONS: For neutral atoms, electrons = protons. For ions, electrons = protons - charge (if charge is +2, subtract 2 electrons; if charge is -1, add 1 electron—the negative sign in subtraction handles this!). Quick checks to verify your answer: (1) Proton count should match atomic number exactly. (2) For neutral atoms, protons should equal electrons. (3) For ions, the charge should equal protons minus electrons (check: 12 - 10 = +2 for Mg²⁺, correct!). (4) Mass number should equal protons plus neutrons (check: 12 + 12 = 24, correct!). These verification steps catch most errors before you finalize your answer!

Question 2

A potassium ion is written as ³⁹K⁺ (potassium-39 with a 1+1+ charge). How many electrons does ³⁹K⁺ have?

  1. 18 (correct answer)
  2. 19
  3. 20
  4. 39

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all potassium atoms have exactly 19 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: positive ions like K⁺ have fewer electrons (19 protons but 18 electrons, lost 1). For ³⁹K⁺, electrons = 19 - (+1) = 18. Choice A correctly determines the electrons by subtracting the positive charge from the proton count. A distractor like choice B might use the atomic number without adjusting for charge, but always apply electrons = protons - charge for ions! The particle counting recipe: (1) PROTONS: 19. (2) ELECTRONS: 19 - 1 = 18. Quick checks: Charge = protons - electrons (19 - 18 = +1, correct). Great job verifying!

Question 3

Chlorine-35 is written as ³⁵Cl. If it forms a chloride ion, Cl⁻, how many neutrons and electrons does the ion have?

  1. 18 neutrons and 17 electrons
  2. 17 neutrons and 18 electrons
  3. 18 neutrons and 18 electrons (correct answer)
  4. 35 neutrons and 18 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all chlorine atoms have exactly 17 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: negative ions like Cl⁻ have more electrons than protons because they've gained one (17 protons but 18 electrons). For ³⁵Cl⁻, neutrons = 35 - 17 = 18, electrons = 17 - (-1) = 18. Choice C correctly determines the neutrons and electrons by using A - Z for neutrons and adding 1 for the 1- charge on electrons. A distractor like choice B might swap the numbers or forget to add for the negative charge, but remember, neutrons don't change in ions—only electrons do! The particle counting recipe: (1) PROTONS: Atomic number (17). (2) NEUTRONS: A - Z (18). (3) ELECTRONS: Protons - charge (18 for Cl⁻). Quick checks: Charge = protons - electrons (17 - 18 = -1, correct); mass = protons + neutrons (17 + 18 = 35, correct). You're doing great—keep verifying!

Question 4

The ion  23Na+\,^{23}\mathrm{Na}^{+} (sodium-23 with a +1 charge) is given. How many protons, neutrons, and electrons does this ion have?

  1. 11 protons, 12 neutrons, 11 electrons
  2. 11 protons, 12 neutrons, 10 electrons (correct answer)
  3. 23 protons, 0 neutrons, 22 electrons
  4. 10 protons, 13 neutrons, 11 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all sodium atoms have exactly 11 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: positive ions (cations) have fewer electrons than protons because they've lost electrons (Na⁺ has 11 protons but 10 electrons, having lost 1). For ²³Na⁺: sodium has atomic number 11 (11 protons), mass number 23, so neutrons = 23 - 11 = 12 neutrons, and with +1 charge, electrons = 11 - 1 = 10 electrons. Choice B correctly determines 11 protons, 12 neutrons, and 10 electrons by properly accounting for the positive charge. Choice A incorrectly keeps 11 electrons, forgetting that the +1 charge means one electron was lost. The particle counting recipe for ions: (1) PROTONS: Always equal atomic number—sodium is always 11 protons. (2) NEUTRONS: Mass number minus atomic number: 23 - 11 = 12 neutrons. (3) ELECTRONS: For ions, electrons = protons - charge; for Na⁺: 11 - (+1) = 10 electrons. Quick verification: charge = protons - electrons = 11 - 10 = +1, which matches Na⁺ perfectly!

Question 5

Oxygen-16 can exist as a neutral atom  16O\,^{16}\mathrm{O} or as the oxide ion O2−\mathrm{O}^{2-}. Compared to the neutral oxygen atom, how does the number of electrons change when forming O2−\mathrm{O}^{2-}?

  1. It decreases by 2 electrons.
  2. It increases by 2 electrons. (correct answer)
  3. It stays the same because the mass number is unchanged.
  4. It increases by 8 electrons.

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all oxygen atoms have exactly 8 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: negative ions (anions) have more electrons than protons because they've gained electrons. Neutral ¹⁶O has 8 protons and 8 electrons; O²⁻ has 8 protons but 8 - (-2) = 8 + 2 = 10 electrons, having gained 2 electrons. Choice B correctly states the number of electrons increases by 2 when forming O²⁻ from neutral oxygen. Choice A incorrectly suggests electrons decrease, which would create a positive ion, not the negative O²⁻ we're forming. The key concept: forming negative ions means gaining electrons—the 2- charge on O²⁻ tells us oxygen gained 2 electrons. Think of it this way: to get a 2- charge, we need 2 more negative particles (electrons) than positive particles (protons). Verification: O²⁻ has charge = protons - electrons = 8 - 10 = -2, confirming our oxide ion!

Question 6

An atom has atomic number Z=8Z=8 and mass number A=16A=16, and it is neutral. How many protons, neutrons, and electrons does it have?

  1. 8 protons, 8 neutrons, 16 electrons
  2. 16 protons, 8 neutrons, 8 electrons
  3. 8 protons, 8 neutrons, 8 electrons (correct answer)
  4. 8 protons, 16 neutrons, 8 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—an atom with Z=8 has exactly 8 protons, making it oxygen), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For this neutral atom with Z=8 and A=16: protons = atomic number = 8, neutrons = mass number - atomic number = 16 - 8 = 8 neutrons, and since it's neutral, electrons = protons = 8 electrons. Choice C correctly identifies 8 protons, 8 neutrons, and 8 electrons using the fundamental relationships. Choice D incorrectly calculates 16 neutrons, perhaps confusing mass number (16) with neutron count, when neutrons = A - Z = 16 - 8 = 8. The particle counting recipe: (1) PROTONS: Equal to atomic number Z = 8. (2) NEUTRONS: Mass number minus atomic number: A - Z = 16 - 8 = 8 neutrons. (3) ELECTRONS: For neutral atoms, electrons = protons = 8. Quick verification: mass number = protons + neutrons = 8 + 8 = 16 (correct!), and charge = protons - electrons = 8 - 8 = 0 (neutral, as stated!).

Question 7

The ion Cl−\text{Cl}^- is chlorine with a −1-1 charge. If the isotope is chlorine-35 (35Cl^{35}\text{Cl}), how many protons, neutrons, and electrons does 35Cl−^{35}\text{Cl}^- have?

  1. 17 protons, 18 neutrons, 17 electrons
  2. 35 protons, 0 neutrons, 36 electrons
  3. 17 protons, 18 neutrons, 18 electrons (correct answer)
  4. 18 protons, 17 neutrons, 18 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all chlorine atoms have exactly 17 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: positive ions (cations) have fewer electrons than protons because they've lost electrons, and negative ions (anions) have more electrons than protons because they've gained electrons (Cl⁻ has 17 protons but 18 electrons, having gained 1). For ³⁵Cl⁻: chlorine's atomic number is 17 (protons = 17), mass number is 35, so neutrons = 35 - 17 = 18, and with a -1 charge, electrons = 17 - (-1) = 17 + 1 = 18 electrons. Choice C correctly identifies 17 protons, 18 neutrons, and 18 electrons by properly accounting for the negative charge. Choice A incorrectly keeps 17 electrons, forgetting that the -1 charge means the ion has gained an electron—neutral Cl has 17 electrons, but Cl⁻ has 18. The particle counting recipe: (1) PROTONS: Always equal atomic number (look it up or given). This never changes—element identity depends on proton count. (2) NEUTRONS: Subtract atomic number from mass number (A - Z). For chlorine-35: mass 35, atomic number 17, so 35 - 17 = 18 neutrons. (3) ELECTRONS: For neutral atoms, electrons = protons. For ions, electrons = protons - charge (if charge is +2, subtract 2 electrons; if charge is -1, add 1 electron—the negative sign in subtraction handles this!). Example: Cl⁻ has 17 protons (atomic number), so 17 - (-1) = 18 electrons. Quick checks to verify your answer: the charge should equal protons minus electrons (check: 17 protons - 18 electrons = -1 charge for Cl⁻, correct!).

Question 8

A neutral atom has 9 protons and a mass number of 19. How many neutrons and electrons does it have?

  1. 10 neutrons and 9 electrons (correct answer)
  2. 19 neutrons and 9 electrons
  3. 10 neutrons and 19 electrons
  4. 9 neutrons and 10 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—an atom with 9 protons is fluorine), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For this neutral atom with 9 protons and mass number 19: protons = 9 (given), neutrons = mass number - protons = 19 - 9 = 10 neutrons, and since it's neutral, electrons = protons = 9 electrons. Choice A correctly identifies 10 neutrons and 9 electrons using the fundamental relationships. Choice B incorrectly states 19 neutrons, confusing the mass number (19) with the neutron count, when neutrons = mass number - protons = 19 - 9 = 10. The particle counting recipe: (1) PROTONS: Given as 9. (2) NEUTRONS: Mass number minus protons: 19 - 9 = 10 neutrons. (3) ELECTRONS: For neutral atoms, electrons = protons = 9. Verification check: mass number = protons + neutrons = 9 + 10 = 19 (correct!), confirming our calculation!

Question 9

An oxide ion is written as O2−\mathrm{O^{2-}}, and the isotope is oxygen-16 (16^{16}O). How many protons, neutrons, and electrons does 16O2−\mathrm{^{16}O^{2-}} have?

  1. 8 protons, 8 neutrons, 8 electrons
  2. 8 protons, 8 neutrons, 10 electrons (correct answer)
  3. 16 protons, 0 neutrons, 18 electrons
  4. 8 protons, 16 neutrons, 6 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all oxygen atoms have exactly 8 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: positive ions (cations) have fewer electrons than protons because they've lost electrons, and negative ions (anions) have more electrons than protons because they've gained electrons (O2−O^{2-} has 8 protons but 10 electrons, having gained 2). The key formulas: protons = atomic number, neutrons = mass number - atomic number, electrons = protons - charge for ions! For the oxide ion ^{16}O^{2-}, protons = 8 (Z=8), neutrons = 16 - 8 = 8, and electrons = 8 - (-2) = 10. Choice B correctly determines the number of protons, neutrons, and electrons by properly using atomic number, mass number, and charge relationships. Choice A fails by not accounting for the ion's charge, treating it as neutral with 8 electrons instead of adding 2 for the 2- charge. The particle counting recipe: (1) PROTONS: Always equal atomic number (look it up or given). This never changes—element identity depends on proton count. (2) NEUTRONS: Subtract atomic number from mass number (A - Z). For oxygen-16: mass 16, atomic number 8, so 16 - 8 = 8 neutrons. (3) ELECTRONS: For ions, electrons = protons - charge (if charge is -2, subtract -2 which adds 2 electrons). Quick checks to verify your answer: (1) Proton count should match atomic number exactly. (2) For ions, the charge should equal protons minus electrons (check: 8 - 10 = -2, correct!). (3) Mass number should equal protons plus neutrons (check: 8 + 8 = 16, correct!). These verification steps catch most errors before you finalize your answer!

Question 10

A magnesium atom loses 2 electrons to form Mg2+\mathrm{Mg}^{2+}. If the magnesium isotope is magnesium-24 (Mg-24), how many protons, neutrons, and electrons are in Mg2+\mathrm{Mg}^{2+}?

  1. 12 protons, 12 neutrons, 12 electrons
  2. 12 protons, 12 neutrons, 10 electrons (correct answer)
  3. 10 protons, 14 neutrons, 12 electrons
  4. 12 protons, 24 neutrons, 10 electrons

Explanation: This question tests your understanding of atomic structure—how protons, neutrons, and electrons are arranged in atoms and ions, and how atomic number and mass number relate to these subatomic particles. Every atom consists of three types of subatomic particles: protons (positive charge, in the nucleus, number equals atomic number Z and defines which element it is—all magnesium atoms have exactly 12 protons), neutrons (neutral/no charge, also in nucleus, number equals mass number A minus atomic number Z, so neutrons = A - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). For ions, electrons change while protons stay the same: positive ions (cations) have fewer electrons than protons because they've lost electrons (Mg²⁺ has 12 protons but 10 electrons, having lost 2). For Mg²⁺ from magnesium-24: magnesium has atomic number 12 (12 protons), mass number 24, so neutrons = 24 - 12 = 12 neutrons, and with +2 charge, electrons = 12 - 2 = 10 electrons. Choice B correctly determines 12 protons, 12 neutrons, and 10 electrons by properly accounting for the 2+ charge. Choice A incorrectly keeps 12 electrons, forgetting that forming Mg²⁺ means losing 2 electrons. The particle counting recipe: (1) PROTONS: Magnesium always has 12 protons. (2) NEUTRONS: 24 - 12 = 12 neutrons. (3) ELECTRONS: For Mg²⁺, electrons = protons - charge = 12 - (+2) = 10 electrons. Verification: charge = protons - electrons = 12 - 10 = +2, confirming our Mg²⁺ ion!