1. Atomic radius increases as you go down a group.
2. This is caused by the addition of electron shells (principal energy levels), which increases the distance between the nucleus and the outermost electrons, outweighing the increased nuclear charge.
3. Atomic radius decreases as you go across a period.
4. This is caused by the increasing number of protons in the nucleus, which increases the effective nuclear charge, pulling the electrons closer to the nucleus. Electrons are added to the same shell, so there’s no significant increase in shielding.
5. a) Al b) S c) Br d) Na e) O f) Ca
6. Order: O < C < Sn < Sr. Explanation: O and C are in the same period (Period 2); O is further right, so it has a smaller radius than C. Sn and Sr are in Period 5; Sr is on the far left (Group 2), Sn is in Group 14, so Sr has a larger radius than Sn. Both Sn and Sr are much larger than C and O because they are in higher periods with more electron shells. Sr is larger than Sn because, within the same period, atomic radius decreases from left to right.
7. Electronegativity is the ability of an atom in a molecule to attract shared electrons to itself.
8. The ionic radius of a nonmetal is larger than its atomic radius because nonmetals gain electrons to form anions, increasing electron-electron repulsion and expanding the electron cloud.
9. Electronegativity decreases as you go down a group.
10. This is caused by increasing atomic size and greater shielding of the valence electrons by inner electron shells, reducing the nucleus’s ability to attract bonding electrons.
11. Electronegativity increases as you go across a period.
12. This is caused by increasing nuclear charge (more protons) without a corresponding increase in shielding (electrons are added to the same shell), resulting in a stronger pull on bonding electrons.
13. a) Ga b) O c) Cl d) Br e) Sr f) O
14. Group 1 (alkali metals)
15. Group 2 (alkaline earth metals)
16. Group 17 (halogens)
17. Group 18 (noble gases)
Parent Tip: Review the logic above to help your child master the concept of worksheet periodic trends answer key.
