Question

1. compared to a nitrogen atom, a n³⁻ ion has

a) more electrons and a larger radius
b) more electrons and a smaller radius
c) fewer electrons and a larger radius
d) fewer electrons and a smaller radius

1. which ionic compound dissolves in water to form a colored solution?

a) nano₃ c) co(no₃)₂
b) mg(no₃)₂ d) ca(no₃)₂

Explanation:

• Question 21:
• A nitrogen atom (\(N\)) has 7 electrons. The \(N^{3 - }\) ion is formed by gaining 3 electrons, so it has \(7 + 3=10\) electrons.
• When an atom gains electrons to form an anion, the electron - electron repulsion increases. Since the nuclear charge (number of protons, which is 7 for nitrogen) remains the same, the outermost electrons are less tightly held. According to the concept of ionic radius, anions are larger than their parent atoms. So, \(N^{3 - }\) has more electrons and a larger radius than \(N\).
• Question 23:
• Transition metal ions often form colored solutions.
• \(NaNO_{3}\) contains \(Na^{+}\) (an alkali metal ion). Alkali metal ions generally form colorless solutions.
• \(Mg(NO_{3})_{2}\) contains \(Mg^{2+}\) (an alkaline - earth metal ion). Alkaline - earth metal ions generally form colorless solutions.
• \(Co(NO_{3})_{2}\) contains \(Co^{2+}\), a transition metal ion. Transition metal ions can have partially filled \(d\) - orbitals. The absorption and emission of light in the visible region due to \(d - d\) electron transitions can make their solutions colored.
• \(Ca(NO_{3})_{2}\) contains \(Ca^{2+}\) (an alkaline - earth metal ion). Alkaline - earth metal ions generally form colorless solutions.

Answer:

1. a) more electrons and a larger radius
2. c) \(Co(NO_{3})_{2}\)