Unit 2

electronegativity

electronegativity

the ability of an atom to attract electrons closer to itself when in a bond; stronger across periods, weaker down groups

polarity

measure of how electrons are shared in a bond; nonpolar = shared equally, polar = shared unequally (difference in electronegativities)

dipole arrow

points towards more electronegative atom in a bond

metallic bonds

delocalized electrons move freely within cations, strong but nondirectional

conductivity

free electrons in metallic bonds; as electrons pushed into a wire, can be pushed out other end, creating flow of electricity

malleability

free electrons can move with the protons when shape of metal is changed (bends instead of breaks)

luster

free electrons absorb photons, making metal opaque; electrons on the surface bounce back light, making metal shiny

intermolecular force graph

at lowest point, x is bond length, y is energy released (-)/formed (+) when bond forms/breaks; deeper low point = stronger bond

factors that influence bond length

atomic radius (bigger atoms = longer bond), bond order (single > double > triple)

covalent bond

between nonmetals

ionic bond

between metals and nonmetals

factors affecting strength of ionic bonds

smaller radius = stronger bond

larger product of charges = stronger bond

lattice energy

energy required to break an ionic solid and convert atoms into gaseous ions (+) or bind ions to form ionic solid (-); stronger with smaller radii or greater product of charges

how ionic crystals arrange

to minimize repulsive forces and maximize attractive forces

substitutional alloys

form between atoms of similar radius (<15% difference), one atom substitutes for the other in the lattice

interstitial alloys

form between atoms of different radius (>15% difference), where smaller atoms fill in spaces between larger atoms; stronger metal bc less space to move

elements that can exceed octet

3rd row and heavier

elements that can have less than 8 valence electrons in lewis structure

B, Be

formal charge rules

minimize the number of formal charges, negative charge goes on most electronegative atom, sum of formal charges is charge of molecule

how to calculate formal charge

+2 for each lone pair, +1 for each bond, compare to value on periodic table

net dipole moment

overall dipoles in molecule don’t cancel out

how to calculate hybridization

find steric number (number of bonds + lone pairs), hybridization is one less

sigma bond

exist in regions between two bonded atoms

pi bonds

exist in regions above/below a line drawn between 2 bonded atoms