chemistry 2.2

the covalent model :)

electron domains

areas of electron density around a central atom

bond dipole

unequal charge distrbution

how we know relative polarity of molecules

charge distribution and molecular geometry

when covalent molecules are stabilised

when the forces of attraction between nuclei and shared electrons are balanced by the forces of repulsion between the nuclei

what holds atoms in a covalent bond at a fixed distance apart

forces of repulsion between two nuclei

energy of two separate atoms when close

low

energy of two separate atoms when far apart

high

when covalent bond forms in terms of energy

when energy is at minimum

octet rule def

tendency of atoms to gain a valence shell with a total of eight electrons

exceptions to the octet rule

small atoms such as beryllium and boron (fewer than eight electrons in its valence shell) = incomplete octet

bond length

measure of distance between the two bonded nuclei

bond strength

usually described in terms of bond enthalpy, a measure of energy required to break the bond

atomic radius evolution down a group

increases, due to added valence shells

enthalpy, as bond length increases

decreases

why multiple bonds have higher bond enthalpy

due to a larger number of shared electrons= stronger force of electrostatic attraction to the bonded nuclei= shorter and stronger bonds

double bonds strength relative to single bonds

not quite double, due to one bond being a weaker pi bond

coordination bonds

bonds in which both of the shared electrons come from one atom

species that can accept a pair of electrons in a reaction

lewis acids

species that can donate a pair of electrons in a reaction

lewis bases

transition element complex

aqueous transition element ion accepts electron pairs from another reactant in a solution

bases in transition element complex

ligands

repulsive forces decrease in order…

non bonding pair> multiple bond> single bond

species with two electron domains

linear shape, 180°

species with three electron domains