Chapter 8 Memory Bank

metal + nonmetal

usually ionic

nonmetal + nonmetal

covalent

bond-polarity charge direction

more electronegative atom gets δ^-; less electronegative atom gets δ^+

electronegativity trend

increases up and right; fluorine is highest

same atoms bonded together

nonpolar covalent

Lewis-structure electron count

count total valence electrons; add for negative charge and subtract for positive charge

single bond electron count

2 e^-

double bond electron count

4 e^-

triple bond electron count

6 e^-

octet exceptions

H wants 2 e^-; Be may have 4; B may have 6; Period 3+ atoms may expand the octet

formal-charge formula

FC = V - N - B/2

resonance rule

atoms stay fixed; only electrons or bonds move

bond-enthalpy equation

ΔH_rxn = Σ(bonds broken) - Σ(bonds formed)

ΔH < 0

exothermic

ΔH > 0

endothermic

atomic-radius trend

increases down and left

electronegativity trend review

increases up and right