Chapter 5: Structure and Properties of Materials

Question 1

What is the structure of ionic compounds?

Answer 1

Giant crystal lattice structure

Question 2

What are the physical properties of ionic substances?

Answer 2

High melting point and boiling point, do not conduct electricity in solid state but conducts in molten and aqueous states, usually soluble in water but insoluble in organic solvents.

Question 3

Why do ionic substances have high melting and boiling points?

Answer 3

A lot of energy is required to overcome the strong electrostatic forces of attraction between oppositely charged negative and positive ions

Question 4

Why do ionic substances not conduct electricity in solid state?

Answer 4

Its ions are being held together in a fixed position

Question 5

Why do ionic substances conduct electricity in molten and aqueous states?

Answer 5

Its ions are mobile and free to move around to conduct electricity

Question 6

What is the structure of simple covalent compounds?

Answer 6

Simple molecular structure/simple discrete molecules

Question 7

What are the physical properties of covalent compounds?

Answer 7

Low melting point and boiling point, cannot conduct electricity in any state, usually insoluble in water but soluble in organic solvents.

Question 8

Why do covalent compounds have low melting and boiling points?

Answer 8

Little energy is needed to break the weak intermolecular forces of attraction between the molecules.

Question 9

Why are covalent compouds not able to conduct electricity in any state?

Answer 9

They do not contain any ions or free moving electrons that can conduct electricity.

Question 10

What are physical properties of metals?

Answer 10

High melting point and boiling point (except group 1), high densities (except group 1), good conductors of heat and electricity, malleble and ductile, strong and shiny.

Additional:
Solid at room temperature (except mercury)

Question 11

Why do metals have high melting and boiling points?

Answer 11

Due to their strong metallic bonds. A large amount of energy is needed to break the strong electrostatic forces of attraction between the positive metal ions and the ‘sea’ of delocalised electrons.

Question 12

Why are metals malleable and ductile?

Answer 12

The atoms in a pure metallic element are in fixed and orderly arrangement. The layers of atoms slide over each other easily without disrupting the metallic bonds.

Question 13

Why do metals have high density?

Answer 13

The atoms are packed closely together in a given volume (density = mass/volume)

Question 14

Why are metals good conductors of heat and electricity?

Answer 14

The ‘sea’ of delocalised electrons can move about freely to conduct electricity or to transfer heat from one point to another uickly.

Question 15

What are the physical properties of group 1 metals that differ from the usual metals?

Answer 15

Low melting and boiling points, low density and soft.

Question 16

Why do group 1 metals have low melting and boiling points?

Answer 16

They only have 1 valence electron that is delocalised from their valence shells, hence the summative quantity of negatively charged delocalised electrons and the single positively charged ions are less than the other metals. Thus, the electrostatic forces of attraction are less compared to metals from other groups. (This explains the weaker metallic bonds in group 1 metals.) Hence, less energy is required to break the electrostatic forces of attraction.

Question 17

Why do group 1 metals have low density?

Answer 17

(Observation: they float on the surface of water when they react violently with it)

Among all the metals, alkali metals have the lowest relative atomic masses.

Question 18

Why are group 1 metals soft?

Answer 18

They are malleable and ductile but not strong. They can be cut with knife due to the weaker metallic bonds

Question 19

What is an alloy and what is its purpose?

Answer 19

It is a mixture of metal with other elements and its purpose is to make pure metals stronger and harder (as pure metals are usually soft due to their structures) and to add in other elements to make pure metals more resistant to corrosion.

Question 20

What is the structure of an alloy?

Answer 20

A mixture of different metals and elements of different atomic sizes. The different size atoms disrupt the orderly arrangement of the pure metal, making it difficult for the layers to slide past each other. Thus, alloys are stronger and harder than pure metals.

Question 21

What are the constituent elements in brass?

Answer 21

copper, zinc

Question 22

What are the constituent elements in bronze?

Answer 22

copper, tin

Question 23

What are the constituent elements in mild steel?

Answer 23

iron, carbon

Question 24

What are the constituent elements in stainless steel?

Answer 24

iron, chromium, nickel, carbon