Chem Unit: 6 molecular geometry (part 3)

how do you determine the number of electron domains in a lewis structure.

1) bonds on the central atom 2) lone pairs on the central atom double bonds count as one domain and triple bonds act as one domain

lone pair electron region

Places around the central atom where electrons are not bonded with other atoms

electron region

a place around the central atom where electrons are found (either bonded or lone pairs) - the number determines the bond angle ex. molecules with bond angles of 105 - 109 will have four total electron regions; any molecules that has bond angles of approximately 120 will have three total electron regions; and any molecules with bond angles of approximately 180 will have two total electron regions

wedge and dash notation

assits in representing the actual three dimensional shape of a molecule when drawing it on a flat surface such as paper. - used when dealing with tetrahedral, trigonal pyramidal, trigonal bipyramidal, and octahedral geometries

hybridization

during chemical bonding, different atomic orbitals undergo hybridization. Atomic orbitals mix and form new identical hybrid orbitals

VSEPR main concept 1

electron domains (bonding or lone) must stay near the nucleus, but otherwise they get as far apart as possible. - electron pairs (or domains) will push away from each other to form the largest possible bond angle. this minimizes the repulsive forces between shared/ unshared valence electrons pairs around the central atom

why is the shape of a molecule important

it is important to the taste, smell,l development of enzymes, drugs, new materials ect.

VSEPR main concept 2

lone pairs of electrons around the central atom occupy greater space than shared electron pairs. Lone pairs "push" the bonded pairs closer together. (bond angles decrease)

Do bonds or lone pairs take up more room

lone pairs take up more space because they have a greater repulsion; no atoms near them. Lone pairs cause atoms to squeeze closer together creating smaller bond angles

bonding electron regions

places around the central electrons where electrons are shared

electron domains

regions where shared or unshared electrons pairs reside around the central atom. note: double bonds count as one electron remain (not 2). triple bonds count as one electron domain as well.

pairs of electrons (attract/ repel) each other two bonds on the same atom will try to get as (close/ far) from each other as possible a lone pair of electrons and a bonded pair of electrons will (push away from/ or move toward) each other

repel far from push away from

valence shell electron pair repulsion model

the VSEPR is used to predict the bond angles allowing scientists to determine the shapes of molecules in real life (3D). this model is supported by experimental evidence

linear shape

total # of electron regions: 2 # of boding electron regions: 2 # of lone pair electron regions bonding angle: 180 ex. carbon dioxide CO2

trigonal planar shape

total # of electron regions: 3 # of bonding electron regions: 3 # of lone pair of electron regions: 0 bonding angle: 120 ex. carbonate, (CO3) -2

bent shape (2)

total # of electron regions: 3 # of bonding electron regions: 2 # of lone pairs of electron regions: 1 bonding angle: 118.6 ex. ozone, O3

bent shape

total # of electron regions: 4 # of bonding electron regions: 2 # of lone pair of electron regions: 2 bondig angle: 104.5 ex. water, H2O

trigonal pyramidal

total # of electron regions: 4 # of bonding electron regions: 3 # of lone pair electron regions: 1 bonding angle: 107 ex. ammonia, NH3

tetrahedral shape

total # of electron regions: 4 # of bonding electron regions: 4 # of lone pairs: 0 bonding angle: 109.5 ex. methane, CH4

wedge

use to show an atom that is coming towards you.

normal line

used for atoms that are on the same plane.

dash

used to show an atom that is away from you.