Exam 1: Bonding and Structure Flashcards
Octet rule
main group elements bond in such a way that each atom has eight electrons (a completed valence)
EXCEPTIONS:
- hydrogen (2 electrons)
- boron (6 electrons)
- aluminum (6 electrons)
- expanded octets (go above a total of 8 electrons)
chemical bonds
atoms form bonds to lower their potential energies by allowing unpaired electrons to become paired
ionization energies
metals have low ionization energies and want to form cations
electron affinity
nonmetals have negative (favorable) electron affinities and want to form anions (-)
ionic bonds
electrons are TRANSFERRED from one entity to the other (based off ionization energies and electron affinities)
covalent bonds
electrons are SHARED between atoms (no charges formed); two types
polar covalent
electrons are not shared equally with the electron density residing towards the more electronegative atom
non polar covalent
electrons are essentially shared equally between the atoms
lewis structure
- empirically based method of drawing molecular structures
- valence electrons are represented as dots around the atom
- bonds are represented as lines between atoms
STEPS:
1) determine number of valence electrons
2) draw chemical symbol
3) place one dot on each side of chemical symbol
4) any remaining electrons are paired until no electrons remain
expanded octets
- 10 or 12 electrons are possible
- only occurs in period 3 elements or higher
- all thanks to d-orbitals (close enough energy in the outer shell and can accept some electrons)
molecular compounds lewis structure (steps)
1) count the total number of electrons available
2) draw skeletal structure (central atom - lowest electronegativity + peripheral atoms + bonds)
3) fill octets of peripheral atoms by adding lone pair electrons
4) add any remaining electrons to the central atom as lone pair electrons
5) calculate any formal charges
6) adjust structure to minimize formal charges
how many electrons is a single bond?
2 electrons
how many electrons is a double bond?
4 electrons
how many electrons is a triple bond?
6 electrons
formal charges
- an electron counting system used to determine the best lewis structure
- takes into account the different types of electrons involved with an atom (valence electrons, lone pair electrons, bonding electrons)
FC = # valence - lone pair - 1/2(bonding)
valence shell electron pair repulsion theory (VSPER)
- extension of Lewis Theory
- based on the idea that electron groups (lone pairs, single bond, multiple bonds, single electrons) repel one another
- achieve MAXIMUM SEPARATION
- having one central atom geometry depends on (1. # of electron groups, and 2. how many of the groups are bonding groups vs lone pairs)
AXE Nomenclature
-A = central atom
-X = peripheral atom
-E = lone pair electrons
AX2
TWO ELECTRON GROUP
- electron geometry = AX2
- molecular geometry = AX2
- shape = linear
- bonding angle = 180
AX3
THREE ELECTRON GROUP
- electron geometry = AX3
- molecular geometry = AX3
- shape = trigonal planar
- bonding angle = 120
AX2E
THREE ELECTRON GROUP
- electron geometry = AX3
- molecular geometry = AX2E
- shape = bent
- bonding angle = < 120
AX4
FOUR ELECTRON GROUP
- electron geometry = AX4
- molecular geometry = AX4
- shape = tetrahedral
- bonding angle = 109.5
AX3E
FOUR ELECTRON GROUP
- electron geometry = AX4
- molecular geometry = AX3E
- shape = trigonal pyramidal
- bonding angle = < 109.5
AX2E2
FOUR ELECTRON GROUP
- electron geometry = AX4
- molecular geometry = AX2E2
- shape = bent
- bonding angle = < 109.5
AX5
FIVE ELECTRON GROUP
- electron geometry = AX5
- molecular geometry = AX5
- shape = trigonal bipyramidal
- bonding angle = 180, 120, 90
