1.4 Bonding

Question 1

What is an ionic bond?

Answer 1

A bond between a positive and negative ion. The ions are held together by strong electrostatic attraction.

Question 2

Draw a dot-and-cross diagram for the ionic compound NaCl

Answer 2

The sodium atom has lost one electron to form a sodium ion,
Na⁺

The chlorine atom has gained this electron to form a chloride ion, Cl⁻.

Question 3

What is an ionic crystal?

Answer 3

A giant lattice of ions, held together by the electrostatic attraction of oppositely charged ions.

Question 4

Why do ionic compounds have high melting points?

Answer 4

lonic compounds have strong electrostatic attraction between the oppositely charged ions which requires a lot of energy to break and is required to melt the compound. Therefore, ionic compounds have high melting points.

Question 5

What is a covalent bond?

Answer 5

A bond formed that involves the sharing of electron pairs between atoms.
It forms due to the electrostatic attraction between the positive nuclei of the bonded atoms and the negative electrons which are between the two nuclei.

Question 6

What is a coordinate (dative) covalent bond?

Answer 6

A type of covalent bond whereby both electrons in the shared pair are donated by one of the bonding atoms only. It is indicated using an arrow from the lone electron pair.

Question 7

Define electronegativity

Answer 7

The power of an atom to attract negative charge towards itself within a covalent bond.

Question 8

Define bond polarity

Answer 8

Bond polarity refers to the separation of electric charge along a bond. Polar bonds arise when the electrons in the bond are not shared equally.

Question 9

Explain what is meant by a temporary dipole

Answer 9

Electrons are constantly moving around the nucleus.
At any one time there will be an uneven distribution of electrons, making one half of the molecule more negatively charged than the other. This creates a temporary dipole.

Question 10

Explain what is meant by a permanent dipole

Answer 10

If two atoms that are covalently bonded have different electronegativities, a polar bond forms. The more electronegative atom draws more of the negative charge towards itself and away from other atom, producing a ∂- region and a ∂+ region. This is a permanent dipole.

Question 11

Explain what is meant by an induced dipole

Answer 11

An induced dipole is created when electron distribution around a molecule is influenced by a charged particle.

Question 12

Compare the bond character in a covalent bond, intermediate bond and ionic bond.

Answer 12

Covalent bond - electrons shared equally between atoms, leading to no overall charge.

Intermediate bond - electrons shared unequally so there are partial charges on the atoms.

lonic bond - complete transfer of electrons between atoms to produce ions with full charges.

Question 13

What types of intermolecular forces are there?

Answer 13

• Temporary dipole interactions
• Permanent dipole interactions
• Hydrogen bonding

Question 14

How do temporary dipole interactions occur between molecules?

Answer 14

There is an uneven distribution of electrons around the molecule. This creates an uneven distribution of charge, which creates a temporary dipole in the molecule. The temporary dipoles induce dipoles in neighbouring molecules.

Question 15

What is a permanent dipole-dipole interaction?

Answer 15

The electrostatic attraction between oppositely charged permanent dipoles of neighbouring molecules.

Question 16

What are hydrogen bonds?

Answer 16

Hydrogen bonds are the electrostatic attraction between electron deficient hydrogens and a highly electronegative atom - commonly nitrogen, fluorine or oxygen.

Question 17

Why does water have a high melting and boiling point?

Answer 17

Hydrogen bonds form between water molecules due to the electronegative oxygen and the slightly positive hydrogen atom. Hydrogen bonds require a lot of energy to break.

Question 18

Why are alcohols soluble in water?

Answer 18

Alcohols form hydrogen bonds with the water molecules due to the electronegative oxygen being bonded to a hydrogen in the -OH group. This makes them soluble in water.

Question 19

How can the electron pair repulsion theory be used to predict the shapes of simple molecules and ions?

Answer 19

The shape of a molecule is determined by the arrangement of electron pairs around the central atom. The electron pairs repel which lead to specific shapes depending on how many electron pairs are present. There is greater repulsion between lone pairs compared with bonding pairs.

Relative repulsion:
Lone pair-lone pair> lone pair-bonding pair> bonding pair-bonding pair

Question 20

Name the shape of BeCl₂. What is the bond angle?

Answer 20

Linear
Angle = 180°

Question 21

Name the shape of BCl₃. What is the bond angle?

Answer 21

Trigonal planar
Angle = 120°

Question 22

Name the shape of CH₄. What is the bond angle?

Answer 22

Tetrahedral
Angle = 109.5°

Question 23

Name the shape of NH₃. What is the bond angle?

Answer 23

Trigonal pyramidal
Bond angle = 107°

Question 24

Name the shape of NH₄⁺. What is the bond angle?

Answer 24

Tetrahedral
Bond angle = 109.5°

Question 25

Name the shape of H₂O. What is the bond angle?

Answer 25

Bent
Bond angle = 104.5°

Question 26

Name the shape of SF₆. What is the bond angle?

Answer 26

Octahedral
Bond angle = 90°

Question 27

State the VSEPR principle and its use in predicting the shapes of simple molecules and ions.

Answer 27

This is the valence shell electron pair repulsion principle.

Any lone pairs present around the central atom provide additional repulsive forces, which changes the bond angle and the shape of the molecule.

For every lone pair present, the bond angle between covalent bonds is reduced by 2.5°.

Question 28

What does the ‘power’ in every atom depend on?

Answer 28

the power is different for every atom depending on its size and nuclear charge.

Question 29

Electronegativity _______ along a period, as atomic radius decreases and _______ down a group, as shielding _________

Answer 29

increases
decreases
increases

Question 30

What can the differing bond characteristics affect?

Answer 30

boiling point
greater attraction between molecules, so more energy is required to break down intermolecular forces of attraction.
solubility
more polar molecules are more soluble as partial charged attraction to opposite partial charges.