Chemistry Quiz: Describe Atomic Structure
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Describe Atomic StructureQuestion 1 of 20

An element has atomic number Z=13Z=13 and mass number A=27A=27 (a neutral atom). How many neutrons does it have?

13
14
27
40
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Chemistry Quiz

Chemistry Quiz: Describe Atomic Structure

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

What this quiz covers

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

How to use this quiz

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

An element has atomic number Z=13Z=13 and mass number A=27A=27 (a neutral atom). How many neutrons does it have?

  1. 13
  2. 14 (correct answer)
  3. 27
  4. 40
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), 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). The key formulas: protons = atomic number, neutrons = mass number - atomic number, electrons = protons for neutral atoms! For this atom with Z=13 and A=27, neutrons = 27 - 13 = 14 (protons=13, and as neutral, electrons=13). Choice B correctly determines the number of neutrons by properly using the formula A - Z. Choice A fails by not subtracting correctly, perhaps confusing Z with neutrons and giving 13 instead of 14. 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 this example: 27 - 13 = 14 neutrons. (3) ELECTRONS: For neutral atoms, electrons = protons. Quick checks to verify your answer: (1) Proton count should match atomic number exactly. (2) For neutral atoms, protons should equal electrons. (3) Mass number should equal protons plus neutrons (check: 13 + 14 = 27, correct!). These verification steps catch most errors before you finalize your answer!

Question 2

A neutral atom has 17 protons and mass number 37. How many electrons does it have?

  1. 17 (correct answer)
  2. 20
  3. 37
  4. 54
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 17 protons is chlorine), 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: 17 protons means atomic number = 17 (this is chlorine); mass number = 37; neutrons = 37 - 17 = 20 neutrons; since it's neutral, electrons must equal protons, so electrons = 17. Choice A correctly identifies 17 electrons because neutral atoms always have equal numbers of protons and electrons for charge balance. Choice B incorrectly gives 20 electrons (confusing with neutron count), choice C gives 37 (confusing with mass number), and choice D gives 54 (adding various numbers incorrectly). The key principle for neutral atoms: electrons ALWAYS equal protons—this maintains electrical neutrality. So with 17 protons, a neutral atom must have exactly 17 electrons. The mass number and neutron count don't affect electron count in neutral atoms!

Question 3

A neutral atom has 9 electrons. What is its atomic number (ZZ)?

  1. 9 (correct answer)
  2. 0
  3. 18
  4. 19
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 ZZ and defines which element it is), neutrons (neutral/no charge, also in nucleus, number equals mass number AA minus atomic number ZZ, so neutrons = A−ZA - Z), and electrons (negative charge, in electron cloud around nucleus, equal to protons in neutral atoms for charge balance). The key formulas: protons = atomic number ZZ, neutrons = mass number - atomic number, electrons = protons for neutral atoms! For this neutral atom with 9 electrons, since it's neutral, protons = electrons = 9, so Z=9Z=9 (the element is fluorine). Choice A correctly determines the atomic number as 9 by equating it to the electron count in a neutral atom. Choice C fails by perhaps doubling it or confusing with mass, giving 18 instead of 9. 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−ZA - Z). (3) ELECTRONS: For neutral atoms, electrons = protons, so ZZ = electrons. Quick checks to verify your answer: (1) Proton count should match atomic number exactly. (2) For neutral atoms, protons should equal electrons (check: 9 protons = 9 electrons, correct!). These verification steps catch most errors before you finalize your answer!

Question 4

A neutral atom of oxygen-16 (O-16) is given. How many protons, neutrons, and electrons does it have?

  1. 8 protons, 8 neutrons, 10 electrons
  2. 8 protons, 8 neutrons, 8 electrons (correct answer)
  3. 16 protons, 8 neutrons, 8 electrons
  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—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 oxygen-16: the atomic number of oxygen is 8 (this defines it as oxygen), so it has 8 protons; the mass number is 16, so neutrons = 16 - 8 = 8 neutrons; since it's neutral, electrons = protons = 8 electrons. Choice B correctly identifies 8 protons, 8 neutrons, and 8 electrons by properly applying these relationships. Choice A incorrectly gives 10 electrons (this would make it O²⁻), while choices C and D confuse the roles of mass number and atomic number. 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 neutral atoms, electrons = protons. Quick checks to verify your answer: protons should equal 8 (oxygen's atomic number), electrons should equal protons for neutral atoms, and mass number should equal protons plus neutrons (8 + 8 = 16, correct!).

Question 5

The ion O2−\text{O}^{2-} is oxygen with a −2-2 charge. If the isotope is oxygen-16 (16O^{16}\text{O}), how many electrons does 16O2−^{16}\text{O}^{2-} have?

  1. 6
  2. 8
  3. 10 (correct answer)
  4. 16
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⁻ has 8 protons but 10 electrons, having gained 2). For ¹⁶O²⁻: oxygen's atomic number is 8 (protons = 8), and with a -2 charge, electrons = 8 - (-2) = 8 + 2 = 10 electrons (gained 2 electrons to form the 2- ion). Choice C correctly identifies 10 electrons by properly accounting for the -2 charge. Choice B incorrectly states 8 electrons, which would be neutral oxygen, not O²⁻—the 2- charge means it has gained 2 extra electrons beyond the neutral atom's 8. 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). (3) ELECTRONS: For neutral atoms, electrons = protons. For ions, electrons = protons - charge (if charge is +2, subtract 2 electrons; if charge is -2, add 2 electrons—the negative sign in subtraction handles this!). Example: O²⁻ has 8 protons (atomic number), so 8 - (-2) = 10 electrons. Quick check to verify: the charge should equal protons minus electrons (check: 8 protons - 10 electrons = -2 charge for O²⁻, correct!).

Question 6

Carbon-14 (¹⁴C) is an isotope of carbon. How many protons and neutrons are in the nucleus of ¹⁴C?

  1. 6 protons and 6 neutrons
  2. 6 protons and 8 neutrons (correct answer)
  3. 8 protons and 6 neutrons
  4. 14 protons and 0 neutrons
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 carbon atoms have exactly 6 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 carbon-14 (¹⁴C), protons = 6 (Z for carbon), neutrons = 14 - 6 = 8. Choice B correctly determines the protons and neutrons by using carbon's atomic number and subtracting from the mass number. A distractor like choice A might assume equal protons and neutrons like in carbon-12, but isotopes vary in neutrons—always calculate A - Z! The particle counting recipe: (1) PROTONS: Atomic number (6). (2) NEUTRONS: A - Z (8). Quick checks: Mass = protons + neutrons (6 + 8 = 14, correct). These verifications make it easy to spot mistakes!

Question 7

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 8

An ion has 13 protons, 14 neutrons, and 10 electrons. What is the charge of the ion?

  1. $3-$
  2. $1-$
  3. 3+3+ (correct answer)
  4. 1+1+
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), 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, the charge is protons minus electrons: here, 13 protons - 10 electrons = +3 charge (neutrons=14 is given but not needed for charge). Choice C correctly determines the charge as 3+ by calculating protons - electrons = 3. A distractor like choice A might reverse the subtraction, but remember, positive charge means fewer electrons—charge = protons - electrons! The particle counting recipe: (1) PROTONS: 13. (2) ELECTRONS: 10. (3) CHARGE: 13 - 10 = +3. Quick checks: Mass = protons + neutrons (13 + 14 = 27, consistent if A=27). These steps confirm your answer perfectly!

Question 9

An element has atomic number Z=8Z = 8 and mass number A=16A = 16 and is neutral. How many neutrons does this atom have?

  1. 8 (correct answer)
  2. 16
  3. 24
  4. 0
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 element with atomic number 8 is oxygen, having 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 this atom with atomic number Z = 8 and mass number A = 16, we can calculate: protons = 8 (given as atomic number), neutrons = 16 - 8 = 8, and electrons = 8 (equals protons since it's neutral). The question specifically asks for the number of neutrons, which is 8. Choice A correctly identifies 8 neutrons by using the formula neutrons = mass number - atomic number = 16 - 8 = 8. Choice B incorrectly states 16 neutrons, which is a common error of confusing mass number (16) with neutron count—if there were 16 neutrons, the mass number would be 8 + 16 = 24, not 16. 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 this oxygen-16: mass 16, atomic number 8, so 16 - 8 = 8 neutrons. (3) ELECTRONS: For neutral atoms, electrons = protons. Quick checks to verify your answer: Mass number should equal protons plus neutrons (check: 8 + 8 = 16, correct!). This verification step ensures you've correctly calculated the neutron count!

Question 10

An ion has 9 protons and 10 electrons. What is the charge on the ion?

  1. +1+1
  2. −1-1 (correct answer)
  3. +9+9
  4. −10-10
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 ion 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 ions, the charge equals the number of protons minus the number of electrons: positive charge means fewer electrons than protons, negative charge means more electrons than protons. For this ion: 9 protons and 10 electrons; charge = protons - electrons = 9 - 10 = -1. Choice B correctly identifies the -1 charge using the formula charge = protons - electrons. Choice A incorrectly gives +1 (reversing the subtraction), choice C gives +9 (using only protons), and choice D gives -10 (using only electrons). The charge calculation is straightforward: always subtract electrons from protons—if you have more electrons than protons, you get a negative charge; if you have fewer electrons than protons, you get a positive charge. Here, having one extra electron (10 vs 9) gives a -1 charge, making this a fluoride ion (F⁻).

Question 11

A chloride ion is written as 35Cl−^{35}\text{Cl}^-. How many electrons are in this ion?

  1. 17
  2. 18 (correct answer)
  3. 35
  4. 16
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). The key formulas: protons = atomic number, neutrons = mass number - atomic number, electrons = protons for neutral atoms or protons - charge for ions! For ^{35}Cl^-, the atomic number Z is 17, so protons = 17; with -1 charge, electrons = 17 - (-1) = 18 (adding 1 for the negative charge). Choice B correctly determines the number of electrons by properly using atomic number and charge relationships. A distractor like Choice A might forget to add an electron for the negative ion, but remember for anions, electrons = protons + |charge|—keep building that intuition! 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). (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: 17 - 18 = -1 for Cl⁻, correct!). (4) Mass number should equal protons plus neutrons. These verification steps catch most errors before you finalize your answer!

Question 12

A magnesium ion is Mg2+\mathrm{Mg^{2+}} and the isotope is magnesium-24 (24^{24}Mg). How many electrons are in 24Mg2+\mathrm{^{24}Mg^{2+}}?

  1. 12
  2. 10 (correct answer)
  3. 14
  4. 24
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+Mg^{2+} 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 - charge for ions! For ^{24}Mg^{2+}, protons = 12 (Z=12), and electrons = 12 - (+2) = 10 (mass number isn't needed here but neutrons would be 24-12=12). Choice B correctly determines the number of electrons by properly using atomic number and charge relationships. Choice A fails by not subtracting the charge, giving protons (12) instead of reducing for the +2 ion. 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). (3) ELECTRONS: For ions, electrons = protons - charge (if charge is +2, subtract 2 electrons). Example: Mg^{2+} has 12 protons, so 12 - (+2) = 10 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: 12 - 10 = +2, correct!). These verification steps catch most errors before you finalize your answer!

Question 13

A neutral atom has 17 protons and 18 neutrons. What is the element?

  1. Sulfur (S)
  2. Chlorine (Cl) (correct answer)
  3. Argon (Ar)
  4. Potassium (K)
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—the element is determined solely by Z), 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). The key formulas: protons = atomic number Z, neutrons = mass number - atomic number, electrons = protons for neutral atoms! For this neutral atom with 17 protons and 18 neutrons, Z=17 which is chlorine (Cl), A=17+18=35, and electrons=17. Choice B correctly identifies the element as chlorine based on the proton count of 17. Choice A fails by perhaps miscounting protons as 16 for sulfur, not matching the given 17. The particle counting recipe: (1) PROTONS: Always equal atomic number (look it up or given). This never changes—element identity depends on proton count (17=Cl). (2) NEUTRONS: Subtract atomic number from mass number (A - Z), or add to protons for A. (3) ELECTRONS: For neutral atoms, electrons = protons. Quick checks to verify your answer: (1) Proton count should match atomic number exactly. (2) For neutral atoms, protons should equal electrons. (3) Mass number should equal protons plus neutrons (check: 17 + 18 = 35, correct!). These verification steps catch most errors before you finalize your answer!

Question 14

A neutral atom has 11 protons and 12 neutrons. What is its mass number (AA)?

  1. 1
  2. 11
  3. 12
  4. 23 (correct answer)
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), 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). The key formulas: protons = atomic number, neutrons = mass number - atomic number, electrons = protons for neutral atoms, and mass number A = protons + neutrons! For this neutral atom with 11 protons and 12 neutrons, A = 11 + 12 = 23 (electrons=11 since neutral). Choice D correctly determines the mass number by adding protons and neutrons. Choice C fails by perhaps only counting neutrons as A, giving 12 instead of adding protons. 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), or here, add to protons for A. For this: 11 protons + 12 neutrons = 23 for A. (3) ELECTRONS: For neutral atoms, electrons = protons. Quick checks to verify your answer: (1) Proton count should match atomic number exactly. (2) For neutral atoms, protons should equal electrons. (3) Mass number should equal protons plus neutrons (check: 11 + 12 = 23, correct!). These verification steps catch most errors before you finalize your answer!

Question 15

A neutral atom has 9 protons and a mass number of 19. What element is it, and how many neutrons does it have?

  1. Oxygen, 10 neutrons
  2. Fluorine, 10 neutrons (correct answer)
  3. Fluorine, 9 neutrons
  4. Neon, 10 neutrons
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), 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. The key formulas: protons = atomic number, neutrons = mass number - atomic number, electrons = protons for neutral atoms or protons - charge for ions! With 9 protons, the element is fluorine (Z=9); mass number A=19, so neutrons=19-9=10. Choice B correctly identifies the element as fluorine with 10 neutrons by using atomic number and mass number properly. A distractor like Choice A might miscount neutrons or confuse elements, but remember Z=8 is oxygen, and neutrons=A-Z=19-9=10 for Z=9—nice work! 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 this atom: mass 19, atomic number 9, so 19 - 9 = 10 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. (4) Mass number should equal protons plus neutrons (check: 9 + 10 = 19, correct!). These verification steps catch most errors before you finalize your answer!

Question 16

A neutral atom of carbon-12 (C-12) is given. How many protons, neutrons, and electrons does it have?

  1. 6 protons, 6 neutrons, 6 electrons (correct answer)
  2. 12 protons, 0 neutrons, 12 electrons
  3. 6 protons, 12 neutrons, 6 electrons
  4. 6 protons, 6 neutrons, 12 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 carbon atoms have exactly 6 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 carbon-12, the atomic number is 6 (all carbon atoms have 6 protons), the mass number is 12 (the '12' in carbon-12), so neutrons = 12 - 6 = 6 neutrons, and since it's neutral, electrons = protons = 6 electrons. Choice A correctly identifies 6 protons, 6 neutrons, and 6 electrons by properly using these relationships. Choice B incorrectly assumes all 12 particles are protons with no neutrons, misunderstanding that mass number includes both protons and neutrons. 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 carbon-12: mass 12, atomic number 6, so 12 - 6 = 6 neutrons. (3) ELECTRONS: For neutral atoms, electrons = protons. Quick checks to verify your answer: (1) Proton count should match atomic number exactly (6 for carbon). (2) For neutral atoms, protons should equal electrons (6 = 6, check!). (3) Mass number should equal protons plus neutrons (6 + 6 = 12, correct!).

Question 17

A calcium ion is 40Ca2+^{40}\text{Ca}^{2+}. Calcium has atomic number 20. How many electrons does this ion have?

  1. 20
  2. 22
  3. 18 (correct answer)
  4. 40
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 calcium atoms have exactly 20 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 (Ca²⁺ has 20 protons but 18 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 ^{40}Ca^{2+}, Z=20, charge +2, so electrons=20 - (+2)=18. Choice C correctly determines the number of electrons by properly using atomic number and charge. A distractor like Choice A might forget to subtract for the positive charge, but for cations, electrons = protons - charge—great effort! 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). (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: 20 - 18 = +2 for Ca²⁺, correct!). (4) Mass number should equal protons plus neutrons. These verification steps catch most errors before you finalize your answer!

Question 18

An atom has atomic number Z=12Z=12 and mass number A=24A=24, and it is neutral. How many neutrons does it have?

  1. 12 (correct answer)
  2. 24
  3. 36
  4. 10
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=12 has exactly 12 protons, making it magnesium), 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 atom: atomic number Z = 12 means 12 protons; mass number A = 24; therefore neutrons = A - Z = 24 - 12 = 12 neutrons; since it's neutral, electrons = protons = 12 electrons. Choice A correctly identifies 12 neutrons using the formula neutrons = mass number - atomic number. Choice B incorrectly gives 24 neutrons (confusing mass number with neutron count), choice C gives 36 (adding instead of subtracting), and choice D gives 10 (subtracting in the wrong direction). The neutron calculation is straightforward: neutrons = mass number - atomic number = 24 - 12 = 12. Quick verification: mass number should equal protons plus neutrons (12 + 12 = 24, correct!). This formula works for all atoms and isotopes—just subtract atomic number from mass number to find neutrons!

Question 19

A neutral atom is written as 14N^{14}\text{N} (nitrogen-14). How many neutrons are in its nucleus?

  1. 7 (correct answer)
  2. 14
  3. 21
  4. 6
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 nitrogen atoms have exactly 7 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. The key formulas: protons = atomic number, neutrons = mass number - atomic number, electrons = protons for neutral atoms or protons - charge for ions! For ^{14}N, Z=7, A=14, so neutrons=14-7=7. Choice A correctly determines the number of neutrons by subtracting atomic number from mass number. A distractor like Choice B might confuse mass number with neutrons, but neutrons = A - Z, not A— you're on the right track! 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 nitrogen-14: mass 14, atomic number 7, so 14 - 7 = 7 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. (4) Mass number should equal protons plus neutrons (check: 7 + 7 = 14, correct!). These verification steps catch most errors before you finalize your answer!

Question 20

A chloride ion is 35Cl−^{35}\mathrm{Cl}^-. How many electrons are in this ion?

  1. 17
  2. 18 (correct answer)
  3. 35
  4. 16
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 (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, so it has 17 protons; the -1 charge means it gained 1 electron, so electrons = 17 - (-1) = 17 + 1 = 18 electrons. Choice B correctly identifies 18 electrons by properly accounting for the negative charge (gaining an electron). Choice A incorrectly gives 17 electrons (that would be neutral Cl), choice C confuses mass number with electron count, and choice D suggests losing an electron instead of gaining one. The key insight for negative ions: they gain electrons! For Cl⁻, start with 17 protons (atomic number), then add 1 electron because of the -1 charge, giving 18 electrons total. Quick verification: charge equals protons minus electrons (17 - 18 = -1, correct!).