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Chemistry Exam 2: Unit 5 Cheat Sheet (DRAFT) by

Chemistry cheat sheet for Exam #2

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Prefer­ential Bonding

*Note: all elements in the first two periods (rows) on the periodic table can NOT have an expanded octet
H - doesn't have prefer­ential bonding because it can only bond one way (only has one bond)
C - atoms with 4 valence electrons, like carbon, can bond in 4 ways
N - atoms with 5 valence electrons, like nitrogen, can bond in 3 ways (3 total bonds and one lone pair - in any config­ura­tion)
O - atoms with 6 valence electrons, like oxygen, can bond in two ways (double bond with two lone pairs, or two single bonds and two lone pairs)
Halogens (F, Cl, Br, I) - halogens prefer to have one bond and 3 lone pairs. F can NEVER have more than one bond. Cl, Br, and I can have expanded octets, so they have more options for bonding.

Naming Covalent Compounds

Rules:
1. Name the first nonmetal by it's element name
2. Name the second nonmetal using the suffix -ide
3. Add prefixes to indicate the number of atoms of each element
 
only use prefixes for covalent compounds

Prefixes

Mono
1
Di
2
Tri
3
Tetra
4
Penta
5
Hexa
6
Hepta
7
Octa
8
Nona
9
Deca
10
 

Octet Rule

main group atoms tend to form chemical bonds to achieve eight electrons in their valence shell, making them as stable as noble gases

Exceptions to the Octet Rule

Less e- than an octet
Ex. - Boron (3 ve-), He, Li, H
More e- than an octet (expanded octet)
Ex. - Sulfur and Phospo­horus: 8, 10, or 12 ve-

Identi­fying Central Atoms

Central atom - atom that is bound to two or more other atoms
C - prefers to be central all the time
N - prefers to be central sometimes
O - can be central or not central
F and H - never central because they can only have one bond each
 

Polyatomic Ions

Polyatomic Ions
a group of two or more atoms covalently bonded together that carries an overall net electric charge (positive or negative)
Polyatomic Cation
covalent molecule with an overall positive charge
Polyatomic Anion
covalent molecule with an overall negative charge
Examples:
H3O+
Hydronium ion
NH4+
Ammonium ion
SO4-2
Sulfate
Suffixes:
- ate (most common suffix)
ion with more oxygen atoms
- ite
ion with less oxygen atoms
Examples:
NO3-
Nitrate (3 oxygen atoms)
NO2-
Nitrite (2 oxygen atoms)
 

Covalent Compound Examples

NO2
Nitrogen Dioxide
CO
Carbon monoxide
N2O4
Dinitrogen Tetroxide
SiF4
Silicon Tetraf­luoride
P2O5
Diphos­phorus Pentoxide
SiO2
Silicon Dioxide
N2O3
Dinitrogen Trioxide