CHEM 1151 Lecture Notes - Lecture 2: Valence Electron, Octet Rule, Roman Numerals
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Unit 2 Notes
• Chemical bonds
o Ionic bonds: bonds formed between positive and negative ions
▪ High melting points
▪ Conduct electricity in solution
▪ Usually formed between metals and nonmetals
o Covalent bonds: bonds formed by atoms sharing electricity
▪ Can be gases, liquids, or solids
o Valence electrons: the electrons in the outermost energy level
▪ The only electrons that are involved in bonding
o Ions
▪ Cations: positive ions; atoms that lose electrons
• Usually metals
▪ Anions: negative ions ;atoms that gain electrons
• Usually nonmetals
▪ Octet rule: atoms will gain or lose electrons in order to get 8 valence
electrons
• Charges of ions based on PT location
Group
Valence e-
Gain/lose e-
Ionic Charge
1
1
lose 1
+1
2
2
lose 2
+2
13
3
lose 3
+3
14
4
tweener
varies
15
5
gain 3
-3
16
6
gain 2
-2
17
7
gain 1
-1
18
8
neither
0
• Writing formulas of ionic compounds
o Write positive ion followed by negative ion
o Cross charges to give subscripts
o If the subscript is 1, drop it
o If more than 1 polyatomic ion is needed, use parenthesis around the polyatomic
ion, then use the subscript
o Reduce the subscripts (outside of the parenthesis) to lowest whole number
• Polyatomic ions
NH4+1
ClO3-1
C2H3O2-1
OH-1
NO3-1
CO3-2
SO4-2
PO4-3
• Ions with a Roman Numeral
Copper (I or II)
Chromium (II or III)
Iron (II or III)
Cobalt (II or III)
Nickel (II or III)
Manganese (II or III)
Lead (II or III)
Tin (II or IV)
• Naming ionic compounds
o Learn the names/forumlas and charges
o Give the name of the positive )if the positive ion has more than 1 charge, include
a roman numeral in the name)
o Give the name of the negative ion
▪ If monatomic ion: usually ends in -ide
▪ If polyatomic ion: usually ends in -ate
Prefix
Meaning
mono-
1
di-
2
tri-
3
tetra-
4
penta-
5
hexa-
6
hepta-
7
octa-
8
nona-
9
deca-
10
• Naming covalent compounds
o Use a prefix and the name of the first element
o Use a prefix and the name of the second element
▪ The second element ends in -ide
▪ Do not use the prefix
CO2: carbon dioxide
P4O10: tetraphosphorus decoxide
S2Cl2: disulfur dichloride
• Lewis Dot Diagrams/Lewis Strutures (LDD)
o Shows only the valence electrons
o LDD for compounds
o Steps:
i. Count total valence e- in molecule
ii. Show LDD for each diagram
iii. Determine CBA for each molecule
iv. Arrange LDD for atoms around the CBA so that single e-are next to each
other
v. Form bonds between atoms sharing e- one for each atom
1. Share 1 pair e- = single bond
2. Share 2 pair e- = double bond
3. Share 3 pair e- = triple bond
vi. Try to get 8 e- around each atom