Question

how many total valence electrons are present in a carbonate ion (co₃²⁻)?
22
24
18
26
in the lewis structure for the ammonium ion (nh₄⁺), how many covalent bonds are present?
4
2
5
3
what is the formal charge on the nitrogen atom in the ammonium ion (nh₄⁺), assuming each hydrogen atom contributes one electron and nitrogen contributes five?

Explanation:

Step1: Find valence - electrons of atoms in carbonate ion

Carbon has 4 valence electrons, oxygen has 6 valence electrons. For $CO_{3}^{2 -}$, there is 1 carbon atom and 3 oxygen atoms. The total valence - electrons from neutral atoms is $4+(6\times3)=22$. The 2 - charge means we add 2 more electrons. So the total number of valence electrons is $22 + 2=24$.

Step2: Determine covalent bonds in ammonium ion

In the ammonium ion $NH_{4}^{+}$, nitrogen is the central atom. Nitrogen forms a covalent bond with each of the 4 hydrogen atoms. So there are 4 covalent bonds.

Step3: Calculate formal charge of nitrogen in ammonium ion

The formula for formal charge is $FC = V - N_{b}-\frac{B}{2}$, where $V$ is the number of valence electrons of the neutral atom, $N_{b}$ is the number of non - bonding electrons, and $B$ is the number of bonding electrons. For nitrogen in $NH_{4}^{+}$, $V = 5$, $N_{b}=0$, and $B = 8$. So $FC=5 - 0-\frac{8}{2}=5 - 4 = 1$.

Answer:

The total number of valence electrons in a carbonate ion ($CO_{3}^{2 -}$) is 24.
The number of covalent bonds in the ammonium ion ($NH_{4}^{+}$) is 4.
The formal charge on the nitrogen atom in the ammonium ion ($NH_{4}^{+}$) is 1.