Download Chapter 8: Chemical Bonding

Chapter 8: Chemical Bonding
Three general types of chemical bonds:
Ionic
Covalent
Metallic
Ionic bond
Electrostatic force between particles
of opposite charge
Generally involves metal and a
nonmetal
Covalent bond
Results from sharing of e- between
atoms
Generally involves two nonmetals
Metallic bond
Found in metals, e.g. Fe/Al/Cu
Bonding e- are free to ‘move’
How do we discuss the arrangement of electrons when
atoms form compounds?
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Lewis symbols: the octet rule
Valence: capacity of an element to form chemical
bonds
Valence e-: electrons which take part in chemical
bonding
Reside in outermost (or valence) shell, e.g.,
C: [He]2s22p2
4 valence e-
Cl: [Ne]3s23p5 7 valence e-
Representing valence electrons: Lewis symbols
Lewis symbol: symbol for element plus a dot for each
valence e-, e.g.,
Be: [He]2s2
N: [He]2s22p3
S: [Ne]3s23p4
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Electron dots are placed in 4 "regions" around the symbol
Each region can accommodate an e- pair (USE HUND'S
RULE!!!)
e.g. draw Lewis symbols for
Mg
Sc3+
B
Note: The number of valence e- for the s and p-block
elements is given by the element's group number!
The octet rule
Atoms tend to gain, lose or share e- to get to the nearest
noble gas configuration
Noble gases: all (except He) have s2p6 valence shells (8 e-)
Hence: atoms tend to be surrounded by 8 valence e- - this
is the reason that group 1 atoms form +1 ions, group 6
atoms form -2 ions, etc
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How does the octet rule influence the number of bonds
that an atom will form in a compound?
Let us look at ionic and covalent bonding in term of the
octet rule….
Ionic Bonding
What happens in a reaction if the atoms involved
differ greatly in attraction for e-? e.g.
Na(s) + ½Cl2(g)  NaCl(s)
Na: low I1; Cl: very negative EA
Write the above reaction with electron-dot symbols:
e- is transferred from Na to Cl; do both species
have an octet of e- ?
Ionic bonds result from a transfer of electrons from the
metal to the nonmetal such that both obtain an octet
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e.g. Which ionic compound is expected to form from:
Rb and O
Ba and I
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