SECTION 3 - LEWIS THEORY Flashcards
Ionic bond
Electrons TRANSFERRED from 1 atom to another (non metal + metal)
Covalent bond
Electrons SHARED from 1 atom to another (2 nonmetal)
Lewis theory
Lewis stated that atoms combine to acquire electron configuration of noble gasses and valence electrons are shared/transferred
Lewis symbol
Dots around symbol (representing valence electrons)
Octet rule
When electrons are shared in a way that each atom acquires filled outershell of 8 valence electrons
Duet rule
H fills 1s level with 2 electrons
Single bond
2 bonding electrons
Double bond
4 bonding electrons
Nonpolar covalent bond
Electrons shared EQUALLY between atoms of bond (no separation of charge)
Polar covalent bond
Electrons shared UNEQUALLY between atoms of bond (separation of charge)
Electronegativity
Describes an atom’s ability to compete for electrons with another atom which its bonded (measure of pull of electron). Higher the electronegativity, the stronger
Electronegativity trend periodic table
Increase across period left to right and increase up a group
Dipole arrows
- Arrows go from S+ to S-
- The more electronegative one is S-
Electronegativity trend
- Difference less than 0.4 = non polar covalent bond
- Difference between 0.4-2.0 = polar covalent bond
- Difference greater than 2.0 = ionic bond
Opposite dipoles (CO2)
Cancel each other out. Bonds between C-O are polar, but since the arrows are opposite, they cancel out and the molecule is non polar
Formal charge
Valence electrons - non bonding electrons - number of bonds.
- Formal charge has to be on the most electronegative atom in a resonance structure if there has to be a - charge, and + charge on least electronegative atom
Non bonding electron
Valence electron -8(n)/2
- n is the number of atoms that is not central
Reasonance structure
Occurs when you can draw 2 or more plausible lewis structures with equal correctness. The only thing that changes is the location of multiple bonds
Reasonance bond rules
- Single bond between atom means 3 LP (6 electron on terminal)
- Double bonds between atom means 2 LP (4 electron on terminal)
- Triple bonds between atom means 1 LP (3 electron on terminal)
- Can only move electrons in P orbitals
Exceptions on octet rules
- Free radicals: Molecules with unpaired electrons
- Incomplete octet: Some atoms (B, Al, Be) form 3 bones instead of 4 and are satisfied
- Expanded valence shell: Elements in 3rd row and below CAN have more than an octet
