Chemical Bonding Why do bonds form?to lower the potential energy between positive and negative...

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