Answer
a. $CO_2$ is carbon dioxide.
b. $Li_3N$ is lithium nitride.
Work Step by Step
a. Molecular compounds are those made from two nonmetals. We look at the list of elements we are given for an element in group 14, which is the vertical group that starts with the element carbon. We see that this element in group 14 is carbon (C).
We also need an element belonging to group 16, which is the vertical group that begins with oxygen (O). We see in our list that oxygen is listed.
The compound has the general formula $AB_2$, where $A$ is the group 14 element and $B$ is the group 16 element. The formula for the compound we are looking for is $CO_2$.
For molecular compounds, we name the element further left first, and then we add the name of the element that is further right and change its ending to $-ide$. We add prefixes to denote how many atoms of each element there are in the compound. The exception is if the number of atoms of the first element is $1$. This compound is named carbon dioxide.
b. Ionic compounds are those formed between a metal and a nonmetal. We are asked to find a group 1 element, which is the vertical group beginning with hydrogen (H). From our list, we see that lithium (Li) fits the description.
We are also asked to look for an element belonging to group 15, which is the vertical column beginning with nitrogen (N). We see that nitrogen is on the list.
The compound we are looking for has the general formula $C_3D$, where $C$ is the group 1 element and $D$ is the group 15 element. Therefore, the formula for the compound we are looking for is $Li_3N$.
For ionic compounds, the cation is listed first, and its name remains as-is. The anion follows, and its ending is replaced by $-ide$. No prefixes are needed. The name of this compound is lithium nitride.
