Transcript Unit 4: Chemical Bonding

Chapter 6:
Chemical Bonding
Introduction to Chemical Bonding
Chemical Bonds
 A mutual electrical attraction between the nuclei and
valence electrons of different atoms that binds the
atoms together.
 Atoms combine to minimize potential energy, which
makes them more stable.
 It is in the breaking and forming of chemical bonds
that the vast majority of Chemistry takes place.
Types of Chemical Bonds
 Ionic Bonds – between a metal ion and a non-metal ion
where a transfer of valence electrons takes place;
 The electrical attraction between large numbers of
cations and anions
 Covalent Bonds – between two or more non-metal
atoms where valence electrons are shared in pairs;
 Non-Polar - balanced distribution of shared electrons
 Polar – uneven distribution of shared electrons
 Metallic Bonds – between metal atoms of the same
element where valence electrons are shared in an
electron sea
Types of Chemical Bonds-Ionic Bonds
Types of Chemical BondsCovalent Bonds
Types of Chemical BondsMetallic Bonds
Relative Strengths of Bonds
Ionic Bond
Strongest
Covalent Bond
Metallic Bond
Weakest
Metallic Bonding
 Characterized by an “electron sea” using the atoms of multiple
neighboring atoms of the same element
 The valence electrons are constantly associating with random metal
atoms through a complex swapping of highly mobile, delocalized
electrons
 Metallic bonds are relatively weak, but the highly mobile valence
electrons quickly reform new bonds
 The nature of the metallic bonds result in:




Relatively high melting points
Malleability – the ability to be rolled or hammered into thin sheets
Ductility – the ability to be pulled into thin wire
Conductivity – the ability to pass an electrical current and transfer heat
Metallic Bonding
(Electron Sea)
Ions
An atom that has an electrical charge as the result of
gaining or losing one or more valence electrons
If an atom loses electrons, it becomes positive
 Cation
If an atom gains electrons, it becomes negative
 Anion
Octet Rule
 Atoms gain, lose, or share electrons in order to
have 8 electrons in their outermost energy level (s
and p orbitals)—an “octet” of electrons
 Metals tend to lose electrons to achieve a stable
octet.
 Nonmetals tend to gain electrons to achieve a
stable octet.
Oxidation Numbers
 The oxidation number of an atom of an element is
zero
 The oxidation number of an ion is equal to the
charge of the ion
 Metals tend to lose electrons and become +
 Nonmetals tend to gain electrons and become  Examples
 Calcium loses 2 electrons and becomes Ca2+, with an
oxidation number of +2
 Bromine gains 1 electrons and becomes Br-1, with an
oxidation number of -1
Oxidation Numbers
Oxidation Numbers
2
1
IIA
2
IIIA
13
IVA
14
VA
15
VIA
16
VIIA
17
He
3
4
5
6
7
8
9
10
Li
Be
B
C
N
O
F
Ne
+1
+2
+3
+2,4
-2,4
-3
-1
0
+2,3,4,5
-2
-1,+1
14
15
16
17
18
Al
Si
P
S
Cl
Ar
+3
+2,4
-3
+3,4,5
-2
+2,4,6
-1
0
+1,3,5,7
H
+1
-1
11
12
Na
Mg
+1
+2
3
13
4
22
5
23
6
24
7
25
8
26
9
19
20
21
27
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
+1
+2
+3
+3,4
+2,3,4,5
+2,3,6
+2,3,4,
6,7
+2,3
+2,3
37
38
39
40
41
42
43
44
45
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
+1
+2
+3
+4
+3,5
+2,3,4,5
,6
+7
+2,3,4,
6,8
55
56
57
72
73
74
75
76
77
Cs
Ba
La
Hf
Ta
W
Re
Os
+1
+2
+3
+4
+5
+2,3,4,5
,6
+2,4,6,7
-1
+2,3,4,
6,8
10
28
11
12
0
29
30
31
32
33
34
35
36
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
+2,3
+1,2
+2
+3
+4
-3
+3,5
-2
+2,4,6
-1
+1,5,7
0,2
46
47
48
49
50
51
52
53
54
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
+2,3,4
+2,4
+1
+2
+3
+2,4
-3
+3,5
-2
+2,4,6
-1
+1,5,7
0,2,4,6
78
79
80
81
82
83
84
85
86
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
+2,3,4,
6
+2,4
+1,3
+1,2
1, +3
+2,4
+3,5
+2,4,6
-1
0,2
+1,3,5,7
87
88
89
104
105
106
107
108
109
110
111
112
114
116
118
Fr
Ra
Ac
Rf
Db
Sg
Bh
Hs
Mt
Uun
Uuu
Uub
Uuq
Uuh
Uuo
+1
+2
+3
Ionic Bonding
 Transfer of electrons
 From metal → non-metal
 Results from the electrostatic charge between a metal ion
(cation - positive charge) and a non-metal ion (anion – negative
charge)
 The difference in electronegativity between the ions is
generally greater than 2.0
 Atoms completely give up electrons to other atoms
 The overall number of negative and positive charges must be
the same – the algebraic sum of the oxidation numbers of
the positive and negative ions must equal zero
Ionic Bond
(Transferring of valence e-)
Metal
+
Non-Metal
Structure of Ionic Bonds
 Positive and negative ions are strongly
attracted to each other as a result of the
electrostatic forces involved
 Crystalline in Structure – Form lattices
 Relatively high melting and boiling points
 Brittle – the lattice can be broken if enough
external force applied
 Conduct electricity only when melted or
dissolved in water
Used courtesy of: http://ibchem.com/IB/ibnotes/full/bon_htm/4.1.htm
Covalent Bonding
 Sharing of electrons
 between two or more non-metal atoms to fill the outermost
energy levels of the atoms to become stable
 The filling of the outermost s and p orbitals to become stable
is known as the octet rule
 The resulting group of atoms forming compounds are neutral
(with the exception of polyatomic ions which are covalent
compounds with an overall charge that act as ions in forming
ionic bonds)
 Covalent compounds are referred to as molecular compounds
 The difference in electronegativity between the atoms is
generally less than 2.0
Covalent Bond
(Sharing of Valence e )
Two Non-metals
Covalent Bonding
 Relatively low boiling points and melting points
 Molecular compounds take multiple forms
structurally, but many are liquids or gases at room
temperature.
 Not conductive in water because they do not break
into ions
Key Terms
 Chemical bond: an attraction between atoms or
molecules that allows the formation of chemical
compounds
 Covalent bond: a chemical bond that involves sharing a
pair of electrons between atoms in a molecule
 Ionic bond: chemical bond in which one atom loses an
electron to form a positive ion and the other atom gains
an electron to form a negative ion
 Metallic bond: the electromagnetic interaction between
delocalized electrons
 Octet rule: atom tends to lose, gain or share electrons so
that it is surrounded by eight valence electrons
 Oxidation number: represents the number of electrons
lost or gained by an atom