Covalent bond 2

Question 1

VSEPR Theory use

Answer 1

Valence shell electron pair repulsion theory

This theory is applied to predict the shape of a molecular species.

It states that the bonding atoms in a molecule will achieve a geometry (shape) around the central atom in the valence shell.

Question 2

electron domains

Answer 2

both bonding pairs and lone pairs of electrons around the central atom

Question 3

electron (domain) geometry

Answer 3

arrangement of all the electron domain regions
around the central atom.

Question 4

molecular geometry

Answer 4

arrangement of only bonding regions
around the central atom

→ The lone pairs on the central atom are only shown in diagrams.

Question 5

VSEPR THEORY

Answer 5

● Electron domains are arranged to achieve:
minimum repulsion and maximum separation

● Each multiple bond is treated as just one bond pair/ one bonding region

● The repulsion decreases in the following order:
lone pair–lone pair > lone pair–bonding pair >
bonding pair–bonding pair

Question 6

shape of molecules
2 electron domains

Answer 6

bonding regions: 2
lone pairs: 0
shape and bond angle: linear, 180

Question 7

shape of molecules
3 electron domains

Answer 7

bonding regions: 3
lone pairs: 0
shape and bond angle: trigonal planar, 120

bonding regions: 2
lone pairs: 1
shape and bond angle: bent , 117-119

Question 8

shape of molecules
4 electron domains

Answer 8

bonding regions: 4
lone pairs: 0
shape and bond angle: tetrahedral,109.5

bonding regions: 3
lone pairs: 1
shape and bond angle: trigonal pyramidal, 107

bonding regions: 2
lone pairs: 2
shape and bond angle: bent, 104.5

Question 9

determining shape of a molecule

Answer 9

1) Draw the Lewis structure.
2) Count the total number of electron domains on the central atom.
3) Determine the electron domain geometry as follows:
● 2 electron domains - linear
● 3 electron domains - triangular planar
● 4 electron domains - tetrahedral
4) Determine the molecular geometry from the number of bonding electron domains.
5) Consider the extra repulsion caused by the lone pairs and adjust the bond angles
accordingly.

Question 10

BCl4-

Answer 10

● 4 electron domains around the central atom B
● With 4 bonding pairs of electrons and no lone pairs
● Electron pairs repel in maximum separation
● tetrahedral shape with bond angle 109.5°

Question 11

h2o2

Answer 11

● 4 electron domains around the central atom O with 2 bonding
pairs of electrons and 2 lone pairs
● Electron pairs repel in maximum separation
● Lone-pair repulsion is greater than bond-pair repulsion
● H-O-O bond angle = 104.5°

Question 12

definition of electronegativity

Answer 12

Electronegativity: the ability of an atom to attract the shared pair of electrons in a covalent bond.

Question 13

formation of electronegativity

Answer 13

● Atoms share their valence
electrons to form a covalent bond.

● The sharing of electrons is equal
when the atoms of the same
element share pair(s) of electrons.

● When atoms of different elements
form a covalent bond, the sharing of
electrons may be uneven.

Question 14

polar covalent bonds

Answer 14

● The more electronegative atom will draw
the bonding pair of electrons towards
itself → it will have a partial negative
charge (δ-)

● The less electronegative atom will have a
partial positive charge (δ+)

● The pair of partial opposite charges is
known as a dipole.

Question 15

what determines the polarity of covalent bonds

Answer 15

● The greater the electronegativity difference between two elements, the more polar a covalent bond is.

● Dipole moment is used to quantitatively
measure the bond polarity or molecular polarity (units: Debye, D).

Question 16

Electronegativity difference and ionic bond

Answer 16

● If there is a large difference in electronegativity of the two atoms in a molecule, the least electronegative atom’s electron will transfer to the other atom.

● This in turn leads to an ionic bond.

equal or less than 0.4 = pure covalent bond
Larger than 0.4 to 1.7 = polar covalent
Larger than 1.7= ionic bond

Question 17

Do all molecules with polar bonds become polar molecules

Answer 17

● Not every molecule with polar bonds is polar itself.

● Dipoles have directions and they can cancel each other out when they are in opposite directions - no net dipoles.

● As a result, the molecule is non-polar.

Question 18

intermolecular forces

Answer 18

● The electrostatic attraction force between
molecules or non-metal atoms (noble
gases).

● They are much weaker when compared with
ionic bond and covalent bond.

● Its existence is independent of the strength
of covalent bond holding the bonding atoms
together within a molecule.

Question 19

types of intermolecular forces

Answer 19

● Intermolecular forces account for the physical states as well as some physical properties (e.g. melting and boiling points and density) of the
molecular substances.

● Categories of intermolecular forces:
1) Van der Waals force
a) Dipole-dipole attraction
b) London dispersion force

2) Hydrogen bonding

Question 20

London dispersion force

Answer 20

● Also called instantaneous dipole-induced dipole attraction.

● Electrostatic attraction in all molecules (no matter they are polar or non-polar) and non-metal atoms.

● Random movement of electrons causes a temporary dipole.

● The electron distribution of the nearby atom or molecule will be disturbed, causing an induced dipole.

Question 21

what determines London dispersion force

Answer 21

● Strength of London dispersion force depends on the number of electrons (or the molecular mass) of the molecule or the atom.

● Increasing number of electrons, more probable to form an instantaneous
dipole with a larger size, stronger London dispersion force.

Question 22

dipole-dipole attraction

Answer 22

● The electrostatic attraction between polar molecules.

● The more polar a molecule, the stronger this attraction.

● Stronger intermolecular force than London dispersion force.

Question 23

Determining the polarity of molecules

Answer 23

For molecules with same chemical bonds -
● Asymmetrical shapes with lone pair(s): polar molecule
● Symmetrical shapes (no lone pairs): non-polar molecule

For molecules with different chemical bonds -
○ Having at least one polar bond (ΔEN > 0.4): polar molecule
○ Having no polar bonds: non-polar molecule

Question 24

Hydrogen bonding

Answer 24

● A special type of dipole-dipole attraction that occurs when there is a hydrogen atom covalently bonded to a highly electronegative atom X (X can be N, O, or F) in the molecules.

● In this situation, the hydrogen atom becomes
highly electropositive, which strongly attracts
to the lone pair of electrons on atom X in the
other molecule

Question 25

strength of hydrogen bonding

Answer 25

● Hydrogen bonds are the strongest form of intermolecular force.

● Molecules with hydrogen bonding have boiling points significantly higher than that
would be predicted from their molar mass