Question

1. analyze: consider how the number of protons might affect the size of the electron cloud.

a. as you move across a period, are new energy levels added? no
b. what happens to the number of protons in the nucleus as you move from one element to the next across a period? increase by 1
c. if the proton number increases while the number of energy levels remains constant, what happens to the attractive force between the nucleus and the electrons? the attractive force between the nucleus and the electrons increases
d. how does your answer to the previous question explain the trend in radii across a period?

1. extend your thinking: the gizmo enables you to examine ions, or atoms that have gained or lost electrons. select na and turn on show ion. compare the radius of the neutral atom to that of the ion. repeat with cl. then look at other ions. see if you can find a pattern.

a. why do you think the na⁺ ion is smaller than a neutral na atom? sodium loses an electron
b. why do you think the cl⁻ ion is larger than a neutral cl atom? chlorine gains an electron
unlike neutral atoms, ions have a different number of electrons than protons. the electrons are attracted to the protons and repelled by other electrons. if another electron is added, the repulsion between electrons increases while the attractive force of the nucleus stays the same. as a result, the electron cloud expands. if an electron is lost, the cloud is pulled in more tightly. electron repulsions decrease

Explanation:

10.D. As the attractive force between the nucleus and electrons increases (due to more protons and constant energy - levels), the electrons are pulled closer to the nucleus, causing the atomic radius to decrease across a period.

1. When sodium forms a $Na^+$ ion, it loses an electron, reducing electron - electron repulsion and allowing the remaining electrons to be pulled closer to the nucleus, making the ion smaller. Chlorine gains an electron to form $Cl^-$ ion. The added electron increases electron - electron repulsion, causing the electron cloud to expand and making the ion larger.

Answer:

10.D. As the attractive force between the nucleus and electrons increases, the electrons are pulled closer to the nucleus, resulting in a decrease in atomic radius across a period.
11.A. Sodium loses an electron, reducing electron - electron repulsion and making the ion smaller.
11.B. Chlorine gains an electron, increasing electron - electron repulsion and making the ion larger.