CEM 141 MSU: Study Guide with 100+ Answered Questions
Atomic Structure & Periodic Trends
1. What are the three fundamental subatomic particles, and what are their
charges?
ANSWER ✓ Proton (+1), Neutron (0), Electron (-1).
2. Where is most of the mass of an atom located?
ANSWER ✓ In the nucleus, which contains the protons and neutrons.
3. How is the atomic number (Z) defined?
ANSWER ✓ The number of protons in the nucleus of an atom. It defines the element.
4. What does the mass number (A) represent?
ANSWER ✓ The sum of the number of protons and neutrons in an atom's nucleus (A = Z
+ N).
5. What are isotopes?
ANSWER ✓ Atoms of the same element (same Z) that have different numbers of
neutrons (different A).
6. How do you calculate the average atomic mass shown on the periodic table?
ANSWER ✓ It is a weighted average of the masses of all naturally occurring isotopes:
(Fractional Abundance₁ × Mass₁) + (Fractional Abundance₂ × Mass₂) + ...
7. Who organized the periodic table based on increasing atomic mass and noticed
periodic properties?
ANSWER ✓ Dmitri Mendeleev.
8. How is the modern periodic table organized?
ANSWER ✓ By increasing atomic number (Z).
9. What is a period on the periodic table?
ANSWER ✓ A horizontal row. Elements in the same period have the same number of
electron shells (principal quantum number).
10. What is a group (or family) on the periodic table?
ANSWER ✓ A vertical column. Elements in the same group have the same number of
valence electrons and similar chemical properties.
, 11. What are the main group elements?
ANSWER ✓ Elements in Groups 1, 2, and 13-18 (the s- and p-blocks).
12. What is the trend for atomic radius across a period (left to right)?
ANSWER ✓ Atomic radius decreases. Increased effective nuclear charge pulls electrons
closer.
13. What is the trend for atomic radius down a group?
ANSWER ✓ Atomic radius increases. Electrons occupy higher principal energy levels
(larger electron shells).
14. What is ionization energy?
ANSWER ✓ The energy required to remove one electron from a gaseous atom or ion.
15. What is the trend for first ionization energy across a period (left to right)?
ANSWER ✓ Ionization energy generally increases. Higher effective nuclear charge makes
electrons harder to remove.
16. What is the trend for first ionization energy down a group?
ANSWER ✓ Ionization energy decreases. The outermost electron is farther from the
nucleus and shielded by inner shells.
17. What is electron affinity?
ANSWER ✓ The energy change when an electron is added to a gaseous atom.
18. What is the trend for electron affinity across a period (left to right)?
ANSWER ✓ Generally becomes more negative (releases more energy), meaning the
atom more readily accepts an electron. Halogens have the most negative values.
19. What is electronegativity?
ANSWER ✓ The ability of an atom in a molecule to attract shared electrons to itself.
20. What is the trend for electronegativity across a period?
ANSWER ✓ Electronegativity increases.
21. What is the trend for electronegativity down a group?
ANSWER ✓ Electonegativity decreases.
22. Which element has the highest electronegativity?
ANSWER ✓ Fluorine (F), with a value of 4.0 on the Pauling scale.
Atomic Structure & Periodic Trends
1. What are the three fundamental subatomic particles, and what are their
charges?
ANSWER ✓ Proton (+1), Neutron (0), Electron (-1).
2. Where is most of the mass of an atom located?
ANSWER ✓ In the nucleus, which contains the protons and neutrons.
3. How is the atomic number (Z) defined?
ANSWER ✓ The number of protons in the nucleus of an atom. It defines the element.
4. What does the mass number (A) represent?
ANSWER ✓ The sum of the number of protons and neutrons in an atom's nucleus (A = Z
+ N).
5. What are isotopes?
ANSWER ✓ Atoms of the same element (same Z) that have different numbers of
neutrons (different A).
6. How do you calculate the average atomic mass shown on the periodic table?
ANSWER ✓ It is a weighted average of the masses of all naturally occurring isotopes:
(Fractional Abundance₁ × Mass₁) + (Fractional Abundance₂ × Mass₂) + ...
7. Who organized the periodic table based on increasing atomic mass and noticed
periodic properties?
ANSWER ✓ Dmitri Mendeleev.
8. How is the modern periodic table organized?
ANSWER ✓ By increasing atomic number (Z).
9. What is a period on the periodic table?
ANSWER ✓ A horizontal row. Elements in the same period have the same number of
electron shells (principal quantum number).
10. What is a group (or family) on the periodic table?
ANSWER ✓ A vertical column. Elements in the same group have the same number of
valence electrons and similar chemical properties.
, 11. What are the main group elements?
ANSWER ✓ Elements in Groups 1, 2, and 13-18 (the s- and p-blocks).
12. What is the trend for atomic radius across a period (left to right)?
ANSWER ✓ Atomic radius decreases. Increased effective nuclear charge pulls electrons
closer.
13. What is the trend for atomic radius down a group?
ANSWER ✓ Atomic radius increases. Electrons occupy higher principal energy levels
(larger electron shells).
14. What is ionization energy?
ANSWER ✓ The energy required to remove one electron from a gaseous atom or ion.
15. What is the trend for first ionization energy across a period (left to right)?
ANSWER ✓ Ionization energy generally increases. Higher effective nuclear charge makes
electrons harder to remove.
16. What is the trend for first ionization energy down a group?
ANSWER ✓ Ionization energy decreases. The outermost electron is farther from the
nucleus and shielded by inner shells.
17. What is electron affinity?
ANSWER ✓ The energy change when an electron is added to a gaseous atom.
18. What is the trend for electron affinity across a period (left to right)?
ANSWER ✓ Generally becomes more negative (releases more energy), meaning the
atom more readily accepts an electron. Halogens have the most negative values.
19. What is electronegativity?
ANSWER ✓ The ability of an atom in a molecule to attract shared electrons to itself.
20. What is the trend for electronegativity across a period?
ANSWER ✓ Electronegativity increases.
21. What is the trend for electronegativity down a group?
ANSWER ✓ Electonegativity decreases.
22. Which element has the highest electronegativity?
ANSWER ✓ Fluorine (F), with a value of 4.0 on the Pauling scale.
