Chapter 3. Chemical Bonding

Question 1

What is electronegativity

Answer 1

The tendency of an atom to attract electrons towards it

Question 2

State and explain the trends in electronegativity on the elements of the periodic table

Answer 2

1. Electronegativity decreases down a group because atoms get larger and the distance between the nucleus and the outer electrons gets increased and there is more shielding hence a decrease in electronegativity
2. Electronegativity increases across a period because atoms become smaller and nuclear charge increases

Question 3

What are the factors that electronegativity depends on

Answer 3

1. Nuclear charge - the higher the charge the higher the electronegativity
2. Atomic radii- the bigger the radius the lower the electronegativity
3. Shielding - decreases nuclear charge

Question 4

Exam tip

Answer 4

A difference in electronegativity of 2.1 is considered ionic bonding

Question 5

What is covalent bonding

Answer 5

The electrostatic attraction between the nuclei of two atoms and a shared pair of electrons

Question 6

What are the actual bond angles of ethene and explain why?

Answer 6

C-H-C 118⁰ and H-C-C 121⁰ because the four electrons in the double bond repel more than the two electrons in the single bond.

Question 7

What is the shape and bond angles of NH₃?

Answer 7

Triangular pyramid with 107⁰ N-H angle.

Question 8

What is the shape and bond angles of water?

Answer 8

non-linear 104.5⁰ bond angle.

Question 9

What are the three van der Waals forces and order them in terms of increasing strength?

Answer 9

“1.London dispersion forces
2. Dipole-dipole forces
3. Hydrogen bonding”

Question 10

How do dipole-dipole forces form?

Answer 10

If molecules with dipoles are not symmetrical they have a net charge on either sides so this are attracted to other molecules with dipoles aswell.

Question 11

How do instantaneous dipole induced dipole forces form?

Answer 11

Electrons are not stationary hence their positions can change any time and when they are crowded one side they create a dipole while induces a dipole in the surrounding atoms/molecules creating a London dispersion forceforce.

Question 12

What are the conditions necessary for a hydrogen bond to form?

Answer 12

A very electronegative atom

Question 13

Why are hydrogen bonds stronger than dipole dipole forces?

Answer 13

There are lone pairs of electrons in hydrogen bonding and the hydrogen atoms are highly electron deficient as the other atoms has a high electro-negativity and the hydrogen atoms are small so they have a very strong electric field.

Question 14

What is a covalent bond?

Answer 14

covalent bond is defined as the electrostatic attraction between the nuclei of two atoms and a shared pair of electrons.

Question 15

State electron domains and their shape and their hybridisation type of the central atom

Answer 15

Electron Domains, Hybridisation of central atom, Electron domain geometry
2, sp, linear
3, sp², trigonal planar
4, sp³, tetrahedral
5, sp³d, trigonal bipyramidal
6, sp³d², octahedral

Question 16

Define ionic bonding

Answer 16

The electrostatic attraction between oppositely charged particles.

Question 17

What are the conditions required for ionic compounds to conduct electricity?

Answer 17

they have to be molten or dissolved

Question 18

What does delocalised mean?

Answer 18

not tied to a particular atom.

Question 19

Define metallic bonding

Answer 19

Positive ions in a sea of delocalised ions.

Question 20

What holds covalent bonds?

Answer 20

Electrostatic force between the nuclei and shared electrons.

Question 21

What are the two types molecular orbitals?

Answer 21

1. Sigma orbital s to s, s to p and p to p.
2. Pi orbital p to p parallelly. A double bond.

Question 22

Explain how an sp³ is formed.

Answer 22

A 2s orbital raises its energy level to 2p. The 2p will be having two electrons only so the 2s brings 2 electrons and creates an sp3 orbital

Question 23

What are the angles of the hybrid orbitals?

Answer 23

-sp³ 109.5⁰
-sp² 120⁰
-sp 180⁰

Question 24

Which orbital is weaker and why?

Answer 24

A pi bond is weaker than a sigma bond because there is more overlap of orbitals in forming a sigma bond.

Question 25

Which atoms are electronegative enough to form hydrogen bonds?

Answer 25

“Oxygen, Nitrogen and Fluorine.”

Question 26

What is the shape of a hydrogen bond?

Answer 26

Linear because the electron in the covalent bond repel those in the hydrogen bond.

Question 27

Why does water have a higher boiling point as compared to methane with a comparable Mr?

Answer 27

Water has hydrogen bonds.

Question 28

Why is ice less dense than liquid water.

Answer 28

In liquid water the hydrogen bonds can easily be broken and reformed whereas in ice the molecules are not free to move about and the hydrogen bonds hold the molecules together in a 3-dimensional structure that resembles the structure of diamond. In order to fit into this structure the molecules are slightly less closely O packed than in liquid water which causes the ice to be less dense.

Question 29

What are intramolecular forces?

Answer 29

Forces within molecules i.e covalent bonding. These govern the chemical properties of a compound

Question 30

What are intermolecular forces?

Answer 30

relatively weak forces that exist between molecules. They govern the physical properties of a compound such as melting point

Question 31

What is electronegativity?

Answer 31

Electronegativity is the ability of a particular atom

Question 32

What are the trends of electronegativity?

Answer 32

It increases across a period and it decreases down a group

Question 33

What is bond energy?

Answer 33

Bond energy is the average amount of energy absorbed when one mole of a particular bond is broken in 1 mole of gaseous molecules

Question 34

What is bond length?

Answer 34

The covalent bond length is the distance between the nuclei of the two atoms in the bond

Question 35

What is the range for polar covalent compounds in terms of electronegativity?

Answer 35

0.3 to 1.7

Question 36

Factors that increase the strength of id-id forces?

Answer 36

1. Increasing number of electrons per molecule.
2. increasing number of contact points between the molecules.

Question 37

Three facts to count when showing hydrogen bonding

Answer 37

(i) Show two dipoles
(ii) Show a lone pair of electrons on NOF
(iii) Show hydrogen bonding between the hydrogen atom and the lone pair.