CHEM115 Chemical Bonds

Ionic bond

Attractive forces between oppositely charged particles

Covalent bonds

When atoms share valence electrons in the region of space created by orbital overlap

May include up to three pairs of electrons

• two pairs form a double bond

• Three pairs form a triple bond

The octet rule

Atoms will lose or gain electrons in order to have 8 electrons surrounding them

What elements always obey the octet rule?

C, N, O, and F

2nd period elements ____ exceed the octet rule

Never

______ can have more than 8 electrons

3rd period elements and below

Duet rule

H and He only need 2 electrons

B needs ___ electrons

6

Be needs ___ electrons

4

What group of elements are exceptions to the octet rule

Transition metals

Sigma bonds

From head-on overlap

Lie along the bond axis

Account for the first bond

Pi bonds

From lateral overlap by adjacent p or d orbitals

Are perpendicular to the bond axis

Account for the second and third bonds in a multiple bond

Bond length

Distance between the nuclei of two atoms in a bond

Bond order

The number of electron pairs shared between atoms

As bond order increases, bond length _____, and bond energy _____

Decreases, increases

Sigma bonds are ____ than pi bonds

Stronger

Bond length and bond energy are _____ related

Inversely

Bond length formula

BL = R1 + R2

Chemical bonds

Net attractive forces that bind atomic nuclei and electrons together

Bond energies are always _____

Exothermic

Bond formation is always ____

Exothermic

Bond energy

Energy required to separate the bonded atoms to give neutral species

Single bond = _____

One sigma bond

Double bond = _____

One sigma + one pi

Triple bond = _____

One sigma + two pi

Calculate enthalpy change from bond energy

ΔHrxn = Σ bonds broken - Σ bonds formed