Chemical Bonding

Why do bonds form? to lower the potential energybetween positive and negative charges

positive charges protonscations

negative charges electronsanions

metals

Periodic Tablelose e-

non-metalsgain e-

metal + non-metal

Ionic bonding

Groups 1 and 2 Groups 6 and 7

low Ionization Energy

lose 1 or 2 valence e-

high Electron Affinity

gain e-

electron transfer takes place

electrostatic attraction between cation and anion

formula = ratio of anions to cations

e-

+-

+ non-metalnon-metal

Covalent bonding

electrons shared between atoms

high Ionization Energies

high Electron Affinities

electron density between the atoms

distance between atoms = bond length

formula = actual # atoms

metal + metalMetallic Bonding

metals valence e- well shielded

low Ionization Energy

low Electron Affinities

share valence e- not localized between atoms

delocalized

move freely throughout metal

Nae- “sea”

(nucleus and core e-)(valence e-)

metal + non-metal

Ionic bonding

http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA0/Movies/NACL1.html

Na (s)2 + Cl2 (g) NaCl (s)2

exothermic heat given off

Ionization Energy Na + 496 kJ/mol

Electron Affinity Cl -349 kJ/mol

Lattice Energy

Na+

Cl-

E =d

-504 kJ/mol

Na++ Cl- NaCl

negative

Coulomb’s law

k Q1Q2

Lewis electron-dot symbols

element symbol = nucleus + core e-

one “dot” = valence e-

metals dot = e- it loses to form cationnon-metal unpaired dot = e- paired through

e- gain or sharing

metal + non-metal

Ionic bonding

Na (s)2 + Cl2 (g) NaCl (s)2

[Ne] [Ne] [Ne] [Ar]

Ca O: :..

..

[Ar]4s2[He]2s2 2p4

Ca2+ O2-

[Ar] [Ne]

Ca(s)2 2+ O2(g) CaO (s)

Sn, Pb, Bi and Tl exceptions

Na. + Cl-::

::+ Cl:

:: . Na+

3s1 3s23p5

Ionic sizes

isoelectronic series

46 e-

+49 +50 +51 ions get smaller

same # electrons

+-

e-

+ non-metalnon-metal

Covalent bonding

H. + H . H ..H1s1 1s1 [He]

F.: ::

:F.:

:

+ .

: :F .:

:

F:

:

[He]2s22p5 [Ne]

F:

:: F:

::

e- not used in bonding lone pairs

Lewis structure

shared equally between F

H O.

::. .

:O:

. .H. H.

oxygen 2 lone pairsbonding pair

1s1 [He]2s22p4

[He]

shared e- bonding pair

not shared equally

[Ne]

Electronegativity

ability of an atom in a moleculeto attract e- to itself

related to Ionization EnergyElectron Affinity

Pauling scale

non-polar covalent 0.4polar covalent 0.5-1.8

NaCl 2.1 ionic 801oC

AlCl3 1.5 polar covalent 178oCPCl3 0.9 polar covalent 76oCCl2 0.0 covalent

ionic > 1.8

C HC O-+

Li2O

BeCl2 1.5 polar covalent 405oC