chem unit 6 - chemical bonds

* don't need to know angles

chemical bonds and octet rule

• attractive force between atoms or ions that binds them together as one unit

• bonds form to increase stability (octet rule - atoms want 8 valence electrons)

• only valence electrons

ionic bond properties

• metal + nonmetal

• electrons transferred from metal to nonmetal

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• structure: crystal lattice

• state: solid (hard/brittle)

• melting point: high

• soluble in water: yes

• electric conductivity: yes if solution or molten

• covalent bond properties

• nonmetal + nonmetal

• a pair of electrons is shared between atoms

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• structure: true molecules

• state: liquid or gas

• melting point: low

• soluble in water: not usually

• electric conductivity: no

• other properties: odorous

electron dot diagrams

crystal lattice

covalent bonding

• can form single (2e-), double (4e-), or triple (6e-) bonds

• unshared pairs are pairs of unbonded valence electrons

• each atom still needs a full outer shell

drawing covalent lewis dot structures

• count total valence electrons

• connect all atoms with single bonds

• “single” atom is center

• “multiple” atoms on the outside

• C is always the center, H is always outside

• check for multiple centers

• full octet? if not then add multiple bonds

• extra electrons? put on central atom

usual number of bonds for C, O, H, N, and halogens

• C - 4

• O - 2

• H - 1

• N - 3

• halogens - 1

octet exceptions

• H - 2

• Be - 4

• B - 6

• P - 10

• S - 12

polyatomic ions

linear

• 0 lone pairs

• 2 bonding pairs

trigonal planar

• 0 lone pairs

• 3 bonding pairs

tetrahedral

• 0 lone pairs

• 4 bonding pairs

trigonal pyramidal

• 1 lone pair

• 3 bonding pairs

bent

• 2 lone pairs

• 2 bonding pairs

trigonal bipyramidal

• 0 lone pairs

• 5 bonding pairs

octahedral

• 0 lone pairs

• 6 bonding pairs

polar molecules

• unequally share electrons

• 2 requirements:

  • polar bonds

  • symmetry can’t cancel out polar bond effects

bond polarity

• 0-0.4 nonpolar

• 0.5-2.0 polar covalent

• 2.1-3.3 ionic

dipole

• arrow points towards the more electronegative atom

symmetry

• nonpolar molecules are symmetrical

metallic solids

• metallic bonding

• atoms held together by electrons