Chapter 5 - Electrons, Bonding and Structure

Question 1

Solubility of ionic compounds

Answer 1

• most Ionic, compounds dissolve in polar solvent eg. Water.
• Polar molecules break the ionic lattice and surround the ions in solution
• Solubility decreases as ionic charge increases

Question 2

Instances where ionic compounds may not be soluble

Answer 2

• in ionic, compounds containing molecules with large ionic charge the attraction may be too strong for polar molecules to break the lattice

Question 3

What is a dative covalent bond?

Answer 3

A covalent bond in which the shared pair of electrons has been supplied by one of the bonded atoms only

Question 4

Things to remember about dative covalent bonds

Answer 4

• Same, average bond, enthalpy as a normal covalent bond
• only bond with an electron deficient atom
• Represented as an arrow in the display formula

Question 5

Explain electron pair repulsion

Answer 5

Lone pairs of electrons repel more than bonded pairs as they are more electronegative

(Each lone pair roughly reduces the bond angle by 2.5°)

Question 6

What is the most electronegative atom?

Answer 6

Fluorine

Question 7

What are the three types of intermolecular force?

Answer 7

• Permanent dipole – dipole interactions
• Induced dipole – dipole interactions
• Hydrogen bonds

Question 8

What molecules do induced dipole – dipole interactions exist between?

Answer 8

All molecules, whether polar or non– polar (only temporary)

Question 9

How do induced dipole – dipole interactions occur?

Answer 9

• movement of electrons, produces a changing dipole in molecules
• Any incident and instantaneous dipole will exist with a constantly shifting position
• inducing a dipole on neighbouring molecules
• causing them to attract each other

Question 10

What determines the strength of induced dipole – dipole interactions?

Answer 10

• larger numbers of electrons mean larger induced dipoles
• Therefore boiling point increases as there are stronger attractive forces between molecules

Question 11

What is a permanent dipole – dipole interaction?

Answer 11

Forces of attraction between the permanent dipoles in polar molecules

Question 12

Why is the density of water greater than that of ice?

Answer 12

• Hydrogen bonds in water hold water molecules apart in an open lattice structure
• The water molecules in ice are further apart than in water
• Therefore, solid ice is less dense than water and floats

Question 13

Why does water have a relatively high melting and boiling point?

Answer 13

• hydrogen bonds are extra forces over induced dipole – dipole interactions, and stronger
• A greater quantity of energy is required to break the hydrogen bonds in water
• when ice melts, the rigid arrangement of hydrogen bonds is broken
• When water evaporates the hydrogen bonds break completely

Question 14

What do simple molecules form in solid-state?

Answer 14

A simple, molecular lattice

Question 15

What is a simple molecular lattice?

Answer 15

• Covalently bonded molecules held in place by weak intermolecular forces

Question 16

Example of simple, molecular lattices

Answer 16

• ice
• I2

Question 17

Why does simple molecular substances have low, melting and boiling points?

Answer 17

• Weak, intermolecular forces between molecules can be broken by low energy

Question 18

Electrical conductivity of simple, molecular substances

Answer 18

No mobile charge particles so there is nothing to complete an electric circuit. Therefore they do not conduct electricity.

Question 19

Describe the solubility of nonpolar, simple, molecular substances

Answer 19

• soluble in nonpolar solvents as intermolecular forces form between molecules and the solvent weakening the intermolecular forces in the simple, molecular lattice, causing them to break and the compound dissolves
• Insoluble in polar solvents, as there is little interaction between molecules in the lattice and solvent molecules, the intermolecular forces in the polar solvent or too strong to be broken

Question 20

Describe the solubility of polar simple, molecular substances

Answer 20

• Tend to be soluble in polar solvents as the solute, molecules and solvent molecules attract each other. The solubility depends on the strength of the dipole.