Covalent Bonding NotesFORMED ONLY BETWEEN 2 OR MORE NONMETALS

Electronegativity

Less electronegative goes first followed be the more electronegative.•Electronegativity: atom’s ability to attract electrons in a chemical bond. (higher electronegativity means the atom wants electrons more)Example: HF (Hydrogen Flouride)• H (2.1) and F(4.0)

How do you know which nonmetals to write first?

Yes, there are 2 kinds of covalent bonds!

• Polar covalent: the electrons are shared, but one atom is pulling on the electrons a lot more. The electrons spend more time around that atom.

• Nonpolar covalent: the electrons are evenly shared between the two atoms. Ex. Cl2, H2

O(3.5) – O (3.5) = 0Nonpolar covalent bond

O2

• The electronegativity difference is zero.• The electrons are equally shared between two

oxygen atoms forming a nonpolar covalent bond.

O(3.5) – H (2.1) = 1.4Polar covalent bond

H2O

Properties of Covalent Compounds

1) Covalent compounds generally have much lower melting and boiling points than ionic compounds. 2) Covalent compounds are soft and squishy (compared to ionic compounds, anyway).

Properties, Cont’d

• 3) Covalent compounds tend to be more flammable than ionic compounds.

– There are exceptions to this rule!

• 4) Covalent compounds don't conduct electricity in water.

How to Name Covalent Compounds

• 1. Name the first element (normal name)

• 2. Name the second element (root name + “-ide”)

• 3. Add prefixes to indicate how many atoms of each element are in the molecule

(Subscripts)• Exception: no need to use “mono” for first element.

Example: CO2 = carbon dioxide

Prefixes

Subscript prefix1 Mono2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-7 Hepta-8 Octa-9 Nona-10 Deca-

Diatomics• Diatomic elements are elements that do not

exist singularly in nature because they are highly reactive.

“Which elements are the diatomics?”“HON, it’s the halogens!”

• H2, O2, N2, F2, Cl2, Br2, I2

Ionic vs Covalent Bonding

• Ionic: electron(s) leave one atom & gained by another atom to satisfy both atoms’ octets, this results in the formation of ions. The resulting opposite charges attract each other.

• Covalent: electrons are shared by two or more atoms to satisfy their octets.

How can you tell if a bond is IONIC or COVALENT?

• Subtract the two electronegativity values (look at an electronegativity chart p. 263).

>1.7 to 4.0: Ionic >0.4 to 1.7: Polar Covalent 0.0 to 0.4: Non-Polar Covalent

How can you tell if a bond is IONIC or COVALENT?

• Easy way:

All metals = metallic bondNonmetals and Metals = ionic bondAll nonmetals = covalent bond

• The closer the elements are on the periodic table, their electronegativities are more similar… more likely to form covalent bonds

• Farther away… greater difference in electronegativity… more likely to form ionic bonds.

• Metal + nonmetal = usually ionic• Nonmetal + nonmetal = usually covalent.

Bond Dissociation Energy

• Bond dissociation energy = energy required to break a covalent bond.

Highest bond energy Lowest bond energyHardest to break Easiest to break

Triple Double Single Bond Bond BondShortest bond length Longest bond lengthStrongest Weakest

Memorize these exceptions

Chemical formula name

H2O water

CH4 Methane

NH3 ammonia

MEMORIZE THESE ACID NAMES

Acid Name

HCl Hydrochloric acid

H2SO4 Sulfuric acid