Properties and Structure of Materials - Ionic Compounds

Question 1

What are ionic compounds?

Answer 1

Compounds formed with a metal and a non-metal.

Question 2

How are ionic compounds made?

Answer 2

Made by the combination of atoms or groups of atoms where electrons are transferred from one to another.

Question 3

List the properties of ionic compounds.

Answer 3

• Have high melting and boiling points and are all solids at room temperature.
• Are hard but brittle.
• Not malleable or ductile.
• Do not conduct electricity as solids.
• Good conductors of electricity as liquids/dissolved in water.
• Vary from soluble to insoluble in water.

Question 4

If ionic compounds have a high melting point, what does this tell us about the structure?

Answer 4

Forces between the particles are strong.

Question 5

If ionic compounds have hard, brittle crystals, what does this tell us about the structure?

Answer 5

Forces between the particles are strong.

Question 6

If ionic compounds do not conduct electricity in the solid state, what does this tell us about the structure?

Answer 6

No free-moving charged particles are present.

Question 7

If ionic compounds conduct electricity in the molten state, what does this tell us about the structure?

Answer 7

Free-moving charged particles are present in molten forms.

Question 8

What does the ionic bonding model tell us?

Answer 8

• One set of atoms, generally metal atoms, lose electrons and so become cations.
• These lost electrons are transferred to another set of atoms.
• The other set of atoms (generally non-metal), become anions.
• Large numbers of cations and anions combine to form a three-dimensional
  lattice (or crystal lattice).
• The lattice is held together strongly by electrostatic forces of attraction between the oppositely charged ions. The electrostatic force of attraction holding the ions together is called ionic bonding.

Question 9

How are sodium chlorides forces of attraction maximised?

Answer 9

In the case of sodium chloride, in order to maximise the forces of attraction, each sodium ion (Na+) is surrounded by six chloride ions (Cl−) and each chloride ion is surrounded by six sodium ions.

Question 10

How can we use the ionic bonding model to prove that ionic compounds have high melting/boiling points?

Answer 10

Ionic compounds are hard and have high melting and boiling points. This is because of the large amount of energy required to overcome the strong forces of attraction between the positively and negatively charged ions in the ionic lattice.

Question 11

How can we use the ionic bonding model to prove that ionic compounds are hard and brittle?

Answer 11

• There are strong electrostatic forces of attraction between ions in an ionic compound, so a strong force is needed to disrupt the crystal lattice.Therefore, one of the properties of ionic compounds is that they are hard.
• When an ionic compound is hit, the ions move within the lattice so that like-charged ions line up opposite each other and then repel, causing the lattice to be disrupted. This makes ionic compounds brittle.

Question 12

How can we use the ionic bonding model to prove that ionic compounds do not conduct electricity in the solid state?

Answer 12

Ionic compounds do not conduct electricity in the solid state. Although the solid ionic lattice contains charged particles, the particles are not free to move.

Question 13

How can we use the ionic bonding model to prove that ionic compounds conduct electricity in the molten/dissolved in water state?

Answer 13

When ionic compounds are dissolved in water or are in molten form, the charged particles are free to move, which means they can conduct electricity.

Question 14

Are ionic compound soluble or insoluble in water?

Answer 14

In water, ionic compounds vary from very soluble to insoluble. The solubility depends on whether the forces between the water molecules and the ions in the lattice are strong enough to pull the ions out of the lattice.

Question 15

How are ions formed?

Answer 15

• Metal atoms lose electrons to form cations.
• Non-metal atoms gain electrons to become anions.
• Ions have stable electron configurations.
• When an ionic compound is formed from positively charged metal ions and negatively charged non-metal ions, the ions combine to produce an overall zero charge.

Question 16

What is the octet rule?

Answer 16

Most importantly, the ions that are formed usually have a full valence shell—a stable electron configuration. Most of the main group elements can accommodate eight electrons in their valence shell. So in the process of forming ions, both positive and negative, the tendency is for ions to end up with eight electrons in their outer shell (valence shell).This is known as the octet rule.

Question 17

What do electron transfer diagrams show?

Answer 17

Used to show how electrons are transferred from metallic atoms to non-metallic atoms to form an ionic compound.

Question 18

What are rules for writing chemical formula for ions?

Answer 18

• Write the symbol for the positively charged ion first.
• Use subscripts to indicate the number of each ion in the formula. Write the
  subscripts after the ion they refer to.
• If there is just one ion present in the formula, omit the subscript ‘1’.
• Do not include the charges on the ions in the balanced formula.

Question 19

What are the rules for writing chemical formula for complex ionic compounds?

Answer 19

• If different elements are present, then they are combined in a fixed ratio.
• The group of atoms behaves as a single unit with a specific charge.
• Subscripts are used to indicate the number of each kind of atom in the ion.
• Need to be written within brackets if there is more than one present in an ionic formula (e.g. Mg(NO3)2).

Question 20

What do subscripts indicate?

Answer 20

The ratio of ions in a crystal lattice.

Question 21

What is an empirical formula?

Answer 21

A formula that is expressed in terms of the simplest whole number ratio of particles.

Question 22

What are the rules for naming ionic compounds?

Answer 22

• The name of a positively charged ion remains unchanged.
• For simple non-metal ions (anions), the name of the ion is similar to that of the atom but ends in ‘-ide’.
• For polyatomic anions containing oxygen, the name of the ion will usually end in ‘-ite’ or ‘-ate’.

Question 23

What is a polyatomic ion?

Answer 23

Group of atoms that have a charge.

Question 24

What are some uses of ionic compounds?

Answer 24

• Magnesium oxide and other ionic compounds are used to line furnaces.
• Calcium phosphate is a constituent of bone tissue that gives it strength.

Question 25

Which of the formulas below is incorrect?
(a) Ba2F
(b) CaS
(c) Na3P
(d) AlCl3

Answer 25

A

Question 26

Ionic substances are brittle because:
(a) electrons have been transferred between species.
(b) electrons are shared between species.
(c) they are solids at room temperature.
(d) the charged species are arranged in a rigid lattice.

Answer 26

D

Question 27

Which of the following substances is not able to conduct electricity?
(a) NaCl(aq)
(b) Au(s)
(c) KF(s)
(d) Hg(l)

Answer 27

C

Question 28

15. Which statement regarding ions is correct?
    (a) Cations have a negative charge.
    (b) Negative ions have lost protons.
    (c) Positive ions have lost electrons.
    (d) An example of an anion is NH4+.

Answer 28

C

Question 29

How are giant ionic lattices formed?

Answer 29

Cations and anions combine to form a three-dimensional lattice. This lattice is held together by electrostatic forces of attraction between the oppositely charged ions.

Question 30

Why can ionic solids dissolved in water or in their molten form conduct electricity but ionic solids cannot?

Answer 30

In an ionic solid the ions are not free to move, for a substance to conduct electricity, it need charged particles that are free to move, therefore, ionic solids cannot conduct electricity. However, when an ionic solid is melted the ions become free to move, enabling the cations and anions to conduct electricity in the molten compound. This is similar to when ionic solids are dissolved in water, the ions bonds are broken, so the ions can move freely.

Question 31

Why is a high temperature required to melt an ionic solid?

Answer 31

To melt an ionic solid, energy is required to allow the ions to break free and move. Large amounts of energy are required to overcome the electrostatic attraction between the oppositely charged ions and allow them to move freely. This means the ionic bonds between the positive and negative ions must be strong, meaning a high temperature is required to overcome these bonds and melt an ionic solid.