Question

question 23 (1 point)
how does atomic radius change from top to bottom in a group in the periodic table?
o a it first decreases, then increases.
o b it tends to increase.
o c it tends to decrease.
o d it first increases, then decreases.

question 24 (1 point)
how does atomic radius change from left to right across a period in the periodic table?
o a it first decreases, then increases.
o b it first increases, then decreases.
o c it tends to decrease.
o d it tends to increase.

question 25 (2 points)
what causes the shielding effect to remain constant across a period?
o a the charge on the nucleus is constant.
o b electrons are added to the same principal energy level.
o c electrons are added to different principal energy levels.
o d the atomic radius increases.

Explanation:

• Question 23: As we move from top to bottom in a group of the periodic table, new electron shells are added. Each new shell is farther from the nucleus, so the atomic radius increases.
• Question 24: Across a period (from left to right), the number of protons in the nucleus increases (nuclear charge increases), and electrons are added to the same principal energy level. The increased nuclear charge pulls the electrons closer to the nucleus, so the atomic radius tends to decrease.
• Question 25: Shielding effect is related to the number of inner - shell electrons. Across a period, electrons are added to the same principal energy level. The number of inner - shell electrons (which cause shielding) does not change (because we are not adding new shells, just filling the same shell), so the shielding effect remains constant.

Answer:

• Question 23: B. It tends to increase.
• Question 24: C. It tends to decrease.
• Question 25: B. Electrons are added to the same principal energy level.