What are Covalent Compounds?
Covalent compounds are called molecules. Ionic compounds are not called molecules, they are called ionic compounds. Remember, in ionic bonds, metals transfer their valence electrons to nonmetals. In a covalent bond two non-metals share their valence electrons.
- Ionic Bond: Transfer of electrons
- Covalent Bond: Sharing of electrons
Also, the octet rule is still followed.
- Octet Rule: Atoms wants a full outer shell of electrons.
- Single covalent bond = 2 electrons
Naming Covalent Compounds
There are a set of rules that are used for naming covalent compounds. Here are the rules:
- List elements in order of increasing group number.
- Add prefixes to show how many atoms of each element are present
- mono- = 1 (Note: you only use mono- on the second element. You do not use it on the first element)
- di- = 2
- tri- = 3
- tetra- = 4
- penta- = 5
- hexa- = 6
- hepta- = 7
- octa- = 8
- nona- = 9
- deca- = 10
- Add the suffix -ide to the second element.
- Note: The final "o" or "a" of a prefix is often dropped when the elements begins with a vowel. For example, for CO the name will be carbon monoxide NOT carbon monooxide. The final "o" of mono is dropped. Watch the following video:
Writing Covalent Formulas
There are a set of rules that are used for writing formulas for covalent compounds. Let's look at how to write the formula for dihydrogen monoxide.
- Step 1: Identify the element symbols for each element name.
- Hydrogen = H
- Oxygen = O
- Step 2: Identify the meaning of each prefix.
- Di- =2
- Mono- = 1
- Step 3: Write the element symbol for the first element in the name. Then add the prefix number as the subscript.
- Step 4: Add the symbol for the second element/ Then add the prefix number as a subscript.
- Step 5: If there are any ones, eliminate them.
The formula for Dihydrogen Monoxide is the following:
Watch the following video:
Examples of Covalent Names and Formulas
Polar Versus Nonpolar Covalent Bonds
Covalent bonds form when electrons are shared between non-metals, but there are two types of covalent bonds:
- Nonpolar Covalent Bond: This bond occurs between nonmetal atoms. In this bond, the electrons are shared equally due to having almost no electronegativity difference.
- Polar Covalent Bond: This bond occurs between two nonmetal atoms. In this bond, the electrons are shared unequally. The more electronegative atom attracts more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge. This is due to the electronegativity difference being moderate.
- Ionic Bonds occur between
- a metal and a nonmetal
- a metal and a negative polyatomic ion
- a positive polyatomic ion and a nonmetal
- a positive polyatomic ion and a negative polyatomic ion
- Ionic Bond: This type of bond is the results of electron transfer due to a large electronegativity difference
If you wanted to determine if you have a polar covalent bond, a nonpolar covalent bond, or an ionic bond, you can calculate it.
- Example 1: If you had N and H, you could look up their electronegativities:
- N= 3.0
- Electronegativity difference = 3 - 2.1 = 0.9
- This is a moderately polar covalent bond.
- Example 2: Of you had F and F, you could look up their electronegativities:
- F= 4.0
- F = 4.0
- Electronegativity difference = 4.0 - 4.0 =0
- This is a nonpolar covalent bond.
- Example 3: If you had Ca and Cl, you could look up their electronegativities:
- Ca = 1.0
- Cl = 3.0
- Electronegativity difference = 3 -1 =2
- This is an ionic bond