Chemistry Unit E Test Review

How to name Covalent Compounds and writing formulas

When naming compounds remember prefixes and suffixes (only for the last element).

Ex: Disulfur Tetraphosphide or Hydrogen Dioxide

When writing formulas, remember prefixes to know how many atoms of an element there is.

Ex: Tetra means 4 so Tetraoxide would be 4 atoms of Oxygen

How to determine number of valence electrons

Look at group number (disregard d block elements). Groups 1-2, 13-18 have 1-8 valence electrons.

What happens to potential energy when an atomic bond is formed?

Energy decreases and atoms become more stable.

Bond Energy and Length

Single Bonds have the longest length and the lowest energy. Triple Bonds have the shortest length.

Uneven Distribution of Charge (Polar or Not?)

- Asymmetrical means polar

- Lone pairs means Polar!

- Number of bonds (check flowchart)

- Direction of dipoles (check flowchart)

Lewis Dot Structure

Number of dots surrounding the element symbol represents number of valence electrons

What is VSEPR?

Valence Shell Electron Pair Repulsion predicts molecular geometry/shape based on amount of bonds
Ex: Tetrahydral, Trigonal Planar, Bent, etc.

Intramolecular

Force within a molecule, stronger than Intermolecular. Strongest Intramolecular force is Triple Bonds.

Intermolecular

Force between molecules. Weaker than Intramolecular. Strongest to weakest intramolecular forces are: Hydrogen-Bonding, Dipole to Dipole, and the weakest force is London Dispersion Forces. London Dispersion forces occur in all compounds but not all compounds have Hydrogen Bonding.

What is a Polar Bond

Bond with polarity, difference in charges

Difference in Electronegativity

<0.3 = Non Polar

0.3-1.7 = Polar

1.7> = Ionic

Large difference in electronegativity is ionic

Octet Rule

Most elements are stable with 8 valence electrons in their valence electron shell.

Exceptions:

- Hydrogen only needs two valence electrons

- Boron only needs six valence electrons

- Beryllium only needs four valence electrons

How to check for correct Lewis Structure Models

- Add up number of valence electrons total in the compound and check them off when making the structure

- Count number of electrons and bonds each element has (most elements need 8 valence electrons)

- No lone pairs on Carbon

- Nitrogen likes to triple bond, most commonly with another Nitrogen atom (N2)