CHEM 121 Ch.7 Chemical Bonding and Molecular Geometry

3 types of bonding

ionic bonds, covalent bonds, metallic bonds

ionic bonds

metal + nonmetal; electrostatic

covalent bonds

nonmetals; shared electrons

metallic bonds

metals; free moving electrons

cations

formed from atoms losing electrons

anions

formed from atoms gaining electrons

energy is ______ when ions come together

released

usually elements in the “s block” are _____, so they lose electrons

metals

usually elements in the “p block” are ______, so they gain electrons

nonmetals

pure covalent bond

formed by identical atoms (ex. H2 or Cl2)

polar covalent bond

formed by different atoms, unequal electron distrubition

electronegativity

a measure of the tendency of an atom to attract electrons towards itself

more electronegative atoms attracts _____ to them

stronger

a smaller electronegativity is a

metal

a larger electronegativity is a

nonmetal

Lewis symbols

dots for valence electrons + element symbol

octet rule

atoms gain, lose, or share electrons until they’re surrounded by 8 electrons

lewis structures

drawing that describes chemical bonding in molecules and polyatomic ions

single bond

1 single shared pair of electrons

steps of drawing lewis structures

1. draw a picture

2. count valence electrons

3. give out atom lone pairs

4. count number of electrons used, still available

5. still available = lone pairs on central atom

6. central atom octet? if yes, done. if no, outer atoms share lone pairs

3 exceptions to lewis structures

1. molecules and polyatomic ions containing an odd # of electrons

2. molecules and polyatomic ions in which an atom has fewer than 8 electrons

3. molecules and polyatomic ions in which an atom has more than 8 electrons

hypervalent molecules

formed only for central atoms from period 3 and below in periodic table

what are the exceptions for odd # of electrons

ClO2, NO, NO2, O2-

exceptions for less than 8 electrons

H, He, Li, Be, B, Al

what elements are more stable with more electrons?

rows 3-7 and beyond

formal charge

the hypothetical charge assigned to an atom in a molecule, calculated by assuming all electrons in chemical bonds are shared equally, regardless of the atoms' electronegativity.

formal charge formula

number of valence shell electrons - # of lone pairs - ½ of bonding electrons

is breaking chemical bonds exothermic or endothermic?

endothermic

is the formation of bonds endothermic or exothermic?

exothermic

what is the order of electronegativity in periodic table.

increases from bottom to top in a group and from left to right across a period

what is the underlying principle of the born-harber cycle 

Hess’ law

electron geometry

is the 3D arrangement of all electron regions (bonds and lone pairs) around a central atom

molecular geometry

the 3D shape of the molecule based on the arrangement of only the bonded atoms

how to determine if a molecule is polar

A molecule is polar if it has an asymmetrical shape or contains lone pairs on the central atom, which results in an uneven distribution of electron density.

how to determine if a molecular is nonpolar

A molecule is nonpolar if it is symmetrical and does not have lone pairs on the central atom, which causes the bond polarities to cancel each other out.