Question

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?
b. why do you think the cl⁻ ion is larger than a neutral cl atom?
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 while the number of protons remains constant.
activity b: removing and adding electrons
get the gizmo ready: choose ionization energy from the drop - down menu.
question: how does the radius of an atom affect the ability of the protons in the nucleus to hold on to and attract electrons?

Explanation:

A. Sodium (Na) loses an electron to form a Na⁺ ion. When it loses an electron, there are fewer electrons in the electron - cloud. With the same number of protons in the nucleus, the remaining electrons are pulled in more tightly, reducing the size of the electron - cloud and thus making the Na⁺ ion smaller than the neutral Na atom.
B. Chlorine (Cl) gains an electron to form a Cl⁻ ion. When an extra electron is added, the number of electrons increases while the number of protons remains the same. The added electron increases electron - electron repulsions within the electron - cloud. Since the attractive force of the nucleus has to distribute its pull over more electrons, the electron - cloud expands, making the Cl⁻ ion larger than the neutral Cl atom.

Answer:

A. Sodium loses an electron, so remaining electrons are pulled in more tightly, making the ion smaller.
B. Chlorine gains an electron, increasing electron - electron repulsions and expanding the electron - cloud, making the ion larger.