UNIT 7: CHEMICAL BONDING & MOLECULAR GEOMETRY
IONIC BONDING
Transfer of electrons between a metal (cations) and nonmetal (anions).
CATIONS: lost of electrons, resulting in a
➕
charge (more protons than e-)
ANIONS: gain of electrons, resulting in a
➖
charge (more e- than protons)
PREDICTING CHARGES OF ELEMENTS:
Metals (cations):
- Group 1 (alkaline) ALWAYS FORM
1+ ions
- Group 2 ALWAYS FORM 2+ ions
Nonmetals (anions):
- Group 16 (chalcogens) ALWAYS
FORM 2- ions
- Group 17 (halogens) ALWAYS
FORM 1- ions
COVALENT BONDING
Sharing of electrons between 2 nonmetal atoms
POLAR: bonds are POLAR when…
1. Electronegativity is 0.4 - 1.8
2. Has LONE PAIRS
3. Electrons shared UNEQUALLY
(results in partial charges δ+, δ−)
4. Angles are NOT EQUAL
(NON-SYMMETRICAL)
NON-POLAR: bonds are NONPOLAR
when…
1. Electronegativity is 0 to < 0.4
2. Electrons shared EQUALLY
3. Angles are typically EQUAL
(SYMMETRICAL)
LEWIS STRUCTURES
STEPS:
1. Count total # of valence electrons:
- For polyatomic ions, add electrons for negative charges and subtract for positive
charges.
2. Connect all atoms with single bonds
- Aim for symmetry
- Least electronegative atoms tend to be in the center
- Carbon is always in the middle
