Chemical Bonding

Question 1

Name the shapes of molecules with:
1 lone pair + 2 bonded pair
1 lone pair + 3 bonded pair
2 bonded pair
3 bonded pair
4 bonded pair
2 lone pair + 2 bonded pair
6 bonded pair
5 bonded pair

Answer 1

1 lone pair + 2 bonded pair = non- linear (104.5°)

1 lone pair + 3 bonded pair = trigonal pyramidal (107°)

2 bonded pair = linear (180°)

3 bonded pair = trigonal planar (120°)

4 bonded pair = tetrahedral (109.5°)

2 lone pair + 2 bonded pair = non-linear (104.5°)

6 bonded pair = octahedral (90°)

5 bonded pair = trigonal bipyramidal (90° & 120°)

Question 2

Which element is the most electronegative?

Answer 2

Fluorine.

Question 3

Define electronegativity.

Answer 3

the power of a particular atom that is covalently bonded to another atom to attract the bonding pair of electrons towards itself.

Question 4

What is atomic radius?

Answer 4

The distance between the nucleus and the electrons in the outermost shell.

Question 5

Factors affecting electronegativity.

Answer 5

1. Nuclear charge
   A greater nuclear charge is more likely to attract the bonded pair of electrons towards itself.
2. Atomic radius
   If the outer shell electrons are further away from the nucleus, the electronegativity of that atom decreases as the pull of the positive nuclear charge on the bonded pair of electrons is lower.
3. Shielding effect
   When the number of shells and subshells increases, electronegativity decreases as the inner shells reduce the effect of nuclear charge on the bonded pair of electrons.

Question 6

How does the increase in nuclear charge increase electronegativity of an atom?

Answer 6

Attraction exists between the positively charged protons in the nucleus and negatively charged electrons found in the energy levels of an atom. An increase in the number of protons leads to an increase in nuclear attraction for the electrons in the outer shells. Therefore, an increased nuclear charge results in an increased electronegativity.

Question 7

How does an increase in atomic radius decrease electronegativity of an atom?

Answer 7

Electrons closer to the nucleus are more strongly attracted towards its positive nucleus. Those electrons further away from the nucleus are less strongly attracted towards the nucleus. Therefore, an increased atomic radius results in a decreased electronegativity

Question 8

How do more inner shells and subshells decrease electronegativity of an atom?

Answer 8

Filled energy levels can prevent the outermost electrons from experiencing the full attractive forces of the nucleus. This causes the outer electrons to be less attracted to the nucleus and thus decreases electronegativity.

Question 9

Why are some bond lengths shorter than others? How is the bond length related to the bond energy?

Answer 9

Greater forces of attraction between the bonded electrons and nuclei, the bond length decreases as the atoms are pulled closer to each other. It also means that the covalent bond is stronger and therefore needs more energy to be broken. Hence, bond energy increases.

Question 10

Why is the triple covalent bond the strongest?

Answer 10

Triple bonds are the shortest and strongest covalent bonds due to the large electron density between the nuclei of the two atoms. This increases the forces of attraction between the electrons and nuclei of the atoms. As a result of this, the atoms are pulled closer together causing a shorter bond length and the increased forces of attraction results in a stronger covalent bond.

Question 11

How can some insects skate on water?

Answer 11

Each water molecule is very strongly attracted to other water molecules. At the surface of the water, the air molecules and water molecules have hardly any attraction. So, the strong attraction between the water molecules on the surface creates a downward force on the surface causing the surface to be pulled inwards. This is called surface tension. This surface tension allows insects to skate on water.

Question 12

What are the types of van der Waals forces?

Answer 12

1. Dipole (instantaneous dipole-induced dipole) forces
2. Permanent dipole-permanent dipole forces
3. Hydrogen bonding (also a type of pd-pd forces but stronger)

Question 13

Another name for ionic bond.

Answer 13

Electrovalent bond.

Question 14

What is an ionic bonding?

Answer 14

The electrostatic attraction between oppositely charged ions.

Question 15

Why is ionic bonding stronger than any other bond?

Answer 15

Due to the complete transfer of electrons, ionic bonds are stronger than any other bonding.

Question 16

Define covalent bond.

Answer 16

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

Question 17

Name the covalent compounds that do not have the noble gas configuration.

Answer 17

1.Boron trifluoride, BF3:
6 electrons - electron deficit

2.Sulfur hexafluoride, SF6:
12 electrons - expanded octet

3. Phosphorus(V) chloride, PCl5:
   10 electrons - expanded octet
4. Sulfur dioxide, SO2:
   10 electrons - expanded octet

Question 18

What is co-ordinate/ dative covalent bonding?

Answer 18

The sharing of a pair of electrons between two atoms where both the electrons in the bond come from the same atom.

Question 19

What is meant by lone pairs?

Answer 19

Pairs of electrons in the outer shell of an atom that are not involved in bonding.

Question 20

How is dative covalent bond represented in a displayed formula?

Answer 20

With an arrow.
Arrow head points away from the lone pairs.

Question 21

Examples of dative covalent bonds.

Answer 21

Ammonium ion.

Aluminum chloride:
At higher temperature, AlCl3 forms which has electron deficit. Ta lower temperature, two AlCl3 combines to form Al2Cl6.

Question 22

Define bond energy. What is the unit?

Answer 22

The energy required to break one mole of a particular covalent bond in the gaseous state.
Unit: kilojoules per mole

Question 23

Define bond length.

Answer 23

The distance between the nuclei of two covalently bonded atoms.

Question 24

How is bond length and bond energy related?

Answer 24

Shorter bond lengths have higher bond energy and vice versa.

Question 25

Why does a double covalent bond have shorter bond length than a single covalent bond?

Answer 25

Because double covalent bonds have a greater quantity of negative charge between the two atomic nuclei. The greater forces of attraction between the electrons and the nuclei pulls the atoms closer together.

Question 26

Factors that influence the reactivity of molecules.

Answer 26

1. Bond strength
2. Polarity of the bond
3. Whether it is a sigma bond or a pi bond

Question 27

Most to least repulsion between pairs of electrons.

Answer 27

Lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

Question 28

Why is metallic bonding strong?

Answer 28

Because the ions are held together by the strong electrostatic between their positive charges and the negative charges of the delocalized electrons.

Question 29

Factors that increase the metallic bonding.

Answer 29

1. Greater number of protons = greater nuclear charge hence stronger bond
2. Number of delocalized electrons per atom (greater number, stronger bond)
3. The size of the ion (smaller ion, stronger bond)

Question 30

Why is Mercury a liquid at room temperature?

Answer 30

Because some of the electrons of mercury are more tightly bound to the nucleus which weakens the metallic bonding between atoms.

Question 31

Why can metals conduct electricity?

Answer 31

Because of the movement of delocalized electrons.

Question 32

Factors responsible for heat conduction in metals.

Answer 32

It is partially due to the movement of delocalized electrons but mainly due to the vibrations passed on from one metal ion to the next.

Question 33

In hydrogen bonding, what does hydrogen bonds with?

Answer 33

A hydrogen atom bonds to a highly electronegative atom.

Question 34

How does electronegativity differ in groups and periods?

Answer 34

Down the group, decreases.
Across the period, increases.

Question 35

How to use the differences in electronegativity to deduce whether it is a covalent or ionic compound?

Answer 35

1. Covalent: the difference is 1.0 or less
2. Ionic: the difference is 2.0 or more
3. If the difference is zero, covalent bond.
4. Cases where it has both covalent and ionic characteristic, difference is intermediate eg. 1.0