Chemical Bonding 02

Question 1

How does electronegativity change across the period and its reason.

Answer 1

Electronegativity increases across the period.
Across the period, effective nuclear charge increases, 1 and shielding effect remains relatively constant, 2 hence the attractive forces between the valence electrons and the nuclear are stronger. 3 Thus, there is a greater attraction between the nucleus and electrons of another nucleus, 4 hence the greater electronegativity of the atom.

Question 2

How does electronegativity change down a group and its reason.

Answer 2

Electronegativity decreases down a group.
Down the group, although the nuclear charge increases, 1 the increasing distance between the nucleus and the valence electrons, 2 hence the weaker forces of attractions between the nucleus and the electrons of another nucleus.

Question 3

What are the most electronegative atoms? In what order?

Answer 3

F>O>N

Question 4

What are the physical properties of metallic bonds?

Answer 4

malleable; ductile
high melting and boiling points, due to the strong forces of attraction
good electrical and thermal conductivity

Question 5

What are the factors affecting the strength of metallic bonding? hint: there are two!!

Answer 5

1. Number of Valence Electrons: the more the number of valence electrons contributed by the metal atom, the more the number of delocalised electrons, hence the stronger the bonding.
2. Charge, and radius of the metal cation: the higher the charge and the smaller the radius of the metal cation, the stronger of bonding (since the metal atom has a stronger force of attraction.)

Question 6

What are alloys and what are their uses?

Answer 6

alloys makes metals harder; the addition of a different metal atom disrupts the disorderly arrangement of the main metal atoms.
ornaments, hospital and chemical equipment

Question 7

What are the physical properties of ionic bonds?

Answer 7

high melting and boiling points (strong forces of attraction between oppositely charged ions)

good electrical conductivity (free moving ions that act as mobile charge carriers to carry charge)

hard and rigid but brittle (strong forces of attraction between oppositely charged ions, but since they are alternatively arranged, like charged ions repel each other when they align, hence they are brittle)

soluble in water insoluble in organic substances

Question 8

What are the factors affecting the strength of ionic bonding?

Answer 8

Lattice energy(which is ALWAYS NEGATIVE)

Question 9

What are the factors affecting Lattice Energy and what is the formula?

Answer 9

Charge of anion and cation and radius of cation and anion

q+xq- / r+ + r-

Question 10

What are the physical properties of covalent bonds?

Answer 10

melting and boiling points are relatively lower than metals and ionic compounds

no electrical conductivity (no free moving electrons or ions to carry charge)

Question 11

What are the two types of orbital overlaps?

Answer 11

Sigma bonds and Pi bonds.
Single bonds consist of a sigma-sigma bond
Double bonds consist of one sigma bond and one pi bond
Triple bond consist of one sigma bond and two pi bonds

Question 12

What are the factors affecting the strength of covalent bonds?

Answer 12

bond length (the distance between the nuclei of the bonded atoms)
bond order is the number of covalent bonds between a pair of atoms

Question 13

What kind of bonds do small atoms form?

Answer 13

Shorter and stronger bonds.

Question 14

How are multiple bonds different from single bonds?

Answer 14

They are stronger and shorter than single bonds

Question 15

How does bond length affect reactivity in covalent bonds?

Answer 15

A longer, hence weaker bond breaks and hence reacts more easily (MORE REACTIVE)

Question 16

What must be required for an atom to be a donor atom (provides both bonding electrons)?

Answer 16

It must have a lone pair of electrons

Draw the Lewis Dot Diagram to find out the direction of the arrows.

Question 17

What type of bond do dative bonds have?

Answer 17

They can be EITHER sigma or pi bonds.

Question 18

What are the exceptions of the octet rule? (i.e.: filled electron shell with eight electrons.)

Answer 18

Helium will only have two electrons in its outermost shell, as it only has two electrons that fill up the first orbital.
Electron deficient species such as BF3 and AlCl3 and BeCl2.

Question 19

VSEPR: What is the shape for the polyatomic ions with 2 electron pairs?

Answer 19

2 bond pairs, 0 lone pairs linear 180’

Question 20

What are the shapes for the polyatomic ions with 3 electron pairs?

Answer 20

3 bond pairs 0 lone pairs, trigonal planar 120’

2 bond pairs 1 lone pair bent 118’ [reduce angle by 2’]

Question 21

What are the shapes for the polyatomic ions with 4 electron pairs?

Answer 21

4 bond pairs 0 lone pairs tetrahedral 109.5’
3 bond pairs 1 lone pair trigonal pyramidal 107’ [reduce by 2’]
2 bond pairs 2 lone pairs bent 104.5 (105’)

Question 22

What are the shapes for the polyatomic ions with 5 electron pairs?

Answer 22

5 bond pairs 0 lone pairs trigonal bipyramidal 90’ and 120’ around the orbital
4 bond pairs 1 lone pair see saw [remove electrons from the orbital first to minimise repulsion]
3 bond pairs 2 lone pairs t-shape 90’ throughout
2 bond pairs 3 lone pairs linear

Question 23

What are the shapes for the polyatomic ions with 6 electron pairs?

Answer 23

6 bond pairs 0 lone pairs octahedral 90’
5 bond pairs 1 lone pair square pyramidal [remove from top and bottom]
4 bond pairs 2 lone pairs square planar

Question 24

How does a more electronegative atom affect electrons?

Answer 24

A more electronegative atom will attract electrons more strongly to itself.

Question 25

INTERMOLECULAR ATTRACTIONS: How are dispersion forces [induced dipole-induced dipole attractions] formed?

Answer 25

NON-POLAR; The constantly moving elections form an instantaneous dipole on a non-polar molecule, which induces a corresponding dipole in the neighbouring molecule. Hence, there is an attraction between both molecules, however it is temporary and weak due to the constant motions of the electrons.

Question 26

What are the factors affecting the strength of dispersion forces?

Answer 26

1. The number of electrons or size of electron cloud. The larger the number of electrons or electron cloud, the more polarisable it is (the valence electrons are less tightly held). Hence the fdisperson forces between the molecules will be stronger.
   dispersion forces are weaker for smaller molecules like h2 and stronger for bigger molecules like I2.
2. boiling point increases as the molecule is more spherical as the SA is less than a cylindrical shape.

Question 27

INTERMOLECULAR ATTRACTIONS: How are permanent dipole- permanent dipole attractions formed?

Answer 27

POLAR; stronger than id-id.

Caused by the electrostatic attraction between oppositely charged ends of the molecules.

Question 28

What are the factors affecting the strength of pd-pd forces?

Answer 28

size of electron cloud and the greater the dipole moment the stronger the pd-pd forces.

Question 29

INTERMOLECULAR ATTRACTIONS: How are hydrogen bonding formed and what are the requirements?

Answer 29

stronger than pd-pd

1. One molecule must contain a hydrogen atom bonded to a highly electronegative atom like F, O or N
2. The other molecule must contain an atom with a lone pair of electrons, on a F, O or N atom

Question 30

is hexane soluble in H2O?

Answer 30

since the pd-pd forces between water and hexane[which contains pd-pd forces] are weaker than the pd-pd forces between hexane molecules and the hydrogen bonding between water molecules, pd-pd forces cannot be broken.

Question 31

is ch3coch3 and water miscible?

Answer 31

since ch3coch3 and water form hydrogen bonds, which are stronger than pd-pd forces between ch3coch3 molecules, it is miscible in water.

Question 32

how does low temp and high pressure affect gas particles?

Answer 32

low temp: gas particles move more slowly and intermolecular forces become more significant. Hence the particles can no longer overcome the intermolecular forces, therefore it liquefies.

high pressure: the vol of gas sample in the container decreases. Hence the molecules become less distant from each other and the intermolecular forces m=become more significant. Therefore it liquefies.

Question 33

how does shape and surface area affect melting and boiling points

Answer 33

the straighter and larger surface the molecules, the stronger the dispersion forces, hence the higher the melting/boiling point.

Question 34

what type of intermolecular force does CH3CH2CH2CH3OH have?

Answer 34

Hydrogen bonds, since it is an alcohol.

Question 35

what type of intermolecular force does CH3CH2CH2CH3 have?

Answer 35

dispersion forces as its non polar

Question 36

what type of intermolecular force does CH3CH2COCH3 have?

Answer 36

permanent dipole-permanent dipole forces as it is polar

Question 37

number of pi and sigma bonds in: double bonds

Answer 37

one pi one sigma

Question 38

number of pi and sigma bonds in: triple bonds

Answer 38

two pi one sigma

Question 39

number of pi and sigma bonds in: single bond

Answer 39

two sigmas

Question 40

VSEPR theory

Answer 40

1. electron pairs around The Central atom of a molecule (or ion) arrange themselves as far apart as possible to minimise mutual repulsion.
2. The repulsion between electron pairs decreases in strength from lone pair-lone pair, lone pair-bonded pair, bonded pair-bonded pair