exam 3- COVALENT BONDING

What atoms can have an insufficient octet?

Hydrogen-1, Helium-2, Boron-6

What atoms can have an expanded octet?

Period 3 or below

What is the energy change for breaking chemical bonds?

Breaking bonds is endothermic (requires energy)

What is the energy change for forming chemical bonds?

Forming bonds is exothermic (releases energy).

What causes bond polarity?

Bond polarity is caused by the difference in electronegativity that creates a dipole.

difference of electronegativity: >1.7

=ionic

difference of electronegativity: 0.5-1.7

=polar covalent

difference of electronegativity: <0.4

=nonpolar covalent

Whats the trend for increasing electronegativity? Why

up and to the right because of increased effective nuclear charge (Zeff)

How do you calculate ΔH based on #/types of bonds broken and bonds formed?

ΔH = ∑bonds broken (reactants) - ∑bonds formed (products)

What molecules are nonpolar

Symmetrical molecules, molecules with no lone pairs on the central atom, molecules with square planar geometry

What molecules are polar

Molecules with lone pairs on the central atom, asymmetrical molecules, and those with a significant difference in electronegativity between atoms.

Steps to drawing resonance Lewis structures

• only electrons can move, not atoms

• move the double bond to other equal atoms

• determine bond order of the combined structure and charge on terminal oxygens

Trend for bond length

single > double > triple

Trend for bond strength

triple > double > single

How is formal charge assigned to specific atoms in a compound

Formal Charge = normal # valence electrons - (# free electrons + ½ bonded electrons)

How are the number of sigma and pi bonds in a molecule counted

The number of sigma bonds are counted as all single bonds and one bond from double or triple bonds, while pi bonds are counted as the remaining bonds in double and triple bonds.

How to determine Bond Order

total # of bonds / # of resonance structure

how to determine the charge on terminal oxygens

charge/ # of atoms