Topic 3 Chemical Bonding

3 Chemical Bonding

3.1 Ionic bonding

Candidates should be able to:

(a) describe ionic (electrovalent) bonding as exemplified by NaCl and MgCl2. other ionic compounds: NaCl, KF, BaO, Na2O, MgBr2, MgCl2, Al2O3, BaCl2, CaO

3.2 Covalent bonding

Candidates should be able to:

(a) draw the Lewis structure of covalent molecules (octet rule as exemplified by NH3, CCl4, H2O, CO2, N2O4 and exception to the octet rule as exemplified by BF3, NO, NO2, PCl5, SF6);
(b) draw the Lewis structure of ions as exemplified by SO42-, CO32-, NO3- and CN-;
(c) explain the concept of overlapping and hybridisation of the s and p orbitals as exemplified by BeCl2, BF3, CH4, N2, HCN (or CN-), NH3 and H2O molecules;
(d) predict and explain the shapes of and bond angles in molecules and ions using the principle of valence shell electron pair repulsion, e.g. linear, trigonal planar, tetrahedral, trigonal bipyramid, octahedral, V-shaped, T-shaped, seesaw and pyramidal;
(e) explain the existence of polar and non-polar bonds (including CCl, CN, CO, CMg) resulting in polar or/ and non-polar molecules;
(f) relate bond lengths and bond strengths with respect to single, double and triple bonds;
(g) explain the inertness of nitrogen molecule in terms of its strong triple bond and non-polarity;
(h) describe typical properties associated with ionic and covalent bonding in terms of bond strength, melting point and electrical conductivity;
(i) explain the existence of covalent character in ionic compounds such as Al2O3, Ali3 and LiI;
(j) explain the existence of coordinate (dative covalent) bonding as exemplified by H3O+, NH4+, Al2Cl6 and [Fe(CN)6]3 (or CN-).

3.3 Metallic bonding

Candidates should be able to:

(a) explain metallic bonding in terms of electron sea model.

3.4 Intermolecular forces: van der Waals forces and hydrogen bonding

Candidates should be able to:

(a) describe hydrogen bonding and van der Waals forces (permanent, temporary and induced dipole);
(b) deduce the effect of van der Waals forces between molecules on the physical properties of substances;
(c) deduce the effect of hydrogen bonding (intermolecular and intramolecular) on the physical properties of substances.

3 Chemical Bonding

Puppies demonstrating covalent bonding (A) The two puppies represent atoms, their bones represent one of their electrons. (B) Both puppies share both bones. Image by Byron Inouye

In a reaction, there is a change in chemical bonding.
Some of the bonds in the reactants are broken, and new bonds are made to form the products.
It costs energy to break bonds, but energy is released when new bonds are made.

covalent bond, electronegativity, polar covalent

covalent compound / molecule
H2
Cs2
Cs2
Br2
NH3
H2O
CCl4
Cl2
HF
SiH4
I2
SiO2
N2H2

3.1 Ionic bonding

Candidates should be able to:

(a) describe ionic (electrovalent) bonding as exemplified by NaCl and MgCl2. other ionic compounds: NaCl, KF, BaO, Na2O, MgBr2, MgCl2, Al2O3, BaCl2, CaO

ionic compounds/  molecules

KF
BaO
Na2O
MgBr2
Al2O3
BaCl2
CaO

3.2 Covalent bonding

Candidates should be able to:

(a) draw the Lewis structure of covalent molecules (octet rule as exemplified by NH3, CCl4, H2O, CO2, N2O4 and exception to the octet rule as exemplified by BF3, NO, NO2, PCl5, SF6);

NH3,

 

CCl4,

H2O,

CO2,

N2O4

exception

BF3,

 

Exception:

(b) draw the Lewis structure of ions as exemplified by SO42-, CO32-, NO3- and CN-;

incomplete: BeCl2, BeF2
expanded: SF6, SF4 , PCl5,
odd: NO , NO2
SO4 2-,
CO3 2-,
NO3-,
CN-;

incomplete: BeCl2

BeCl2. 1 Be × 2e- = 2e- 2 Cl × 7e- = 14e- 16e- Cl Be Cl. – 4e- 12e-

BeF2

 

expanded:

SF6,

 

SF4 ,

PCl5,

 

 

odd: NO , NO2

NO,

The valence electrons you have available are: 1 N + 1 O = 1×5 + 1×6 = 11.
With an odd number of electrons (11), we cannot give every atom an octet. We can write two possible structures. The formal charge on each atom is:

Top structure: N = 5 – 3 – ½(4) = 0; O = 6 – 4 – ½(4) = 0
Bottom structure: N = 5 – 4 – ½(4) = -1; O = 6 – 3 + ½(4) = +1

The “best” Lewis structure is one that has the fewest formal charges — the top structure.

NO2,

 

(c) explain the concept of overlapping and hybridisation of the s and p orbitals as exemplified by BeCl2, BF3, CH4, N2, HCN (or CN-), NH3 and H2O molecules;

BeCl2

BF3

CH4

N2

HCN (or CN-)

NH3

H2O

(d) predict and explain the shapes of and bond angles in molecules and ions using the principle of valence shell electron pair repulsion, e.g. linear, trigonal planar, tetrahedral, trigonal bipyramid, octahedral, V-shaped, T-shaped, seesaw and pyramidal;

e.g. linear, trigonal planar, tetrahedral, trigonal bipyramid, octahedral,
V-shaped, T-shaped, seesaw and pyramidal;
linear,
trigonal planar,
tetrahedral,
trigonal bipyramid,
octahedral,
V-shaped,
T-shaped,
seesaw,
pyramidal;

(e) explain the existence of polar and non-polar bonds (including CCl, CN, CO, CMg) resulting in polar or/ and non-polar molecules;

http://www.softschools.com/quizzes/chemistry/polarity_electronegativity/quiz941.html

CCl ,
CO,
CMg

(f) relate bond lengths and bond strengths with respect to single, double and triple bonds;

(g) explain the inertness of nitrogen molecule in terms of its strong triple bond and non-polarity;

(h) describe typical properties associated with ionic and covalent bonding in terms of bond strength, melting point and electrical conductivity;

(i) explain the existence of covalent character in ionic compounds such as Al2O3, Ali3 and LiI;

(j) explain the existence of coordinate (dative covalent) bonding as exemplified by H3O+, NH4+, Al2Cl6 and [Fe(CN)6]3 (or CN-).

 

H3O+,
NH4+,
Al2Cl6
[Fe(CN)6]3 (or CN-).

3.3 Metallic bonding

Candidates should be able to:

(a) explain metallic bonding in terms of electron sea model.

 

3.4 Intermolecular forces: van der Waals forces and hydrogen bonding

Candidates should be able to:

(a) describe hydrogen bonding and van der Waals forces (permanent, temporary and induced dipole);

two types of van der Waals forces:
1. permanent dipole forces (dipole-dipole), (polar molecules).
2. temporary dipole-induced dipole forces (London dispersion), (temporary polar molecules).
3. permanent induced dipole-induced dipole (London dispersion) (non-polar molecules)

1. permanent dipole forces (dipole-dipole), (polar molecules).
2. temporary dipole-induced dipole forces (London dispersion), (non-polar molecules).

3. permanent induced dipole-induced dipole (London dispersion) (non-polar molecules)

Summary of permanent, temporary and induced dipole

(b) deduce the effect of van der Waals forces between molecules on the physical properties of substances;

(c) deduce the effect of hydrogen bonding (intermolecular and intramolecular) on the physical properties of substances.
electronegativity
Other links for online notes
http://www.softschools.com/quizzes/chemistry/polarity_electronegativity/quiz941.html

ionic compound / molecule

KF
BaO
Na2O
MgBr2
Al2O3
BaCl2
CaO

covalent compound / molecule

H2
Br2
NH3
H2O
CCl4
Cl2
HF
SiH4
I2
SiO2
N2H2

multiple covalent bond

double bond: O2 , CO2 , N2O4 ,
triple bond: N2 , C2H2 , HCN (or CN-)

ions covalent bond

ClO2-
CN-
NO2-
CO3 2-
SO4 2-
NO3-
H3O+
OH-

dative / coordinate bond

NH4+
Al2Cl6
[Fe(CN)6]3- (or CN-)
CO

exception to the octet rule

1. incomplete octet

2. Expanded octet

3. Odd electron molecules

incomplete octet

BeCl2
BF3

Expanded octet

PCl5
SF6

Odd electron molecules

NO
NO2

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