Structure of Matter

Question 1

Elements

Answer 1

Exist as atoms or molecules
Molecules of an element comprises of 2 or more of the same atoms that are chemically combined

Cannot be broken down into simpler substances through any chemical or physical processes

Question 2

Compounds

Answer 2

A substance containing two or more elements that are chemically combined fixed ratio, consist of either molecules or ions

Can only be broken down through chemical processes

The physical and chemical properties are different from its constituting elements

Question 3

Mixtures

Answer 3

Contains two or more substances that are mixed together in a variable ratio, consist of elements, compounds or both

Can be separated through physical methods

The physical and chemical properties are the same as its constituting components

Question 4

Ionic Compound

Answer 4

Ionic compounds have a giant ionic lattice structure consisting of oppositely charged anions and cations. Strong electrostatic forces of attraction exist between the oppositely charged cations and anions.

Ionic compounds have high mp and bp as lots of energy is required to overcome the strong electrostatic forces of attraction holding the ions in the lattice together

mp and bp are influenced by the strength of electrostatic forces of attraction
E.g. MgO has higher mp than NaCl as ions in MgO have +2, -2 charge compared to NaCl ions, +1, -1

Ionic compounds conduct electricity when dissolved in water or in molten state, but not in solid state
In aqueous and molten states, ions are free to move and hence can conduct electricity

Question 5

Simple Molecular Structure

Answer 5

Covalent substances consisting of small discrete molecules that are held together by weak IMF of attraction (a.k.a van der Waal’s force of attraction)

Have low mp and bp as small amounts of energy is required to overcome the weak IMF

The strength of IMF is dependent on molecular size
molecular size increases, strength of IMF increases
hence larger simple molecules have higher mp and bp

Substances do not conduct electricity as they do not have any freely-moving charge carriers

Question 6

Giant molecular structure

Answer 6

Covalent substances with giant molecular structures consist of an extensive network of atoms held together by covalent bonds

Have high mp and bp as a lot of energy is required to overcome the strong covalent bonds
Apart from graphite, giant molecular substances do not conduct electricity

Question 7

Diamond and Graphite

Answer 7

Both are allotropes of carbon which have giant molecular structures
Carbon atoms arranged in different manners hence different properties

In diamond, each atom is covalently bonded to four other atoms
All valence electrons in each carbon atom are used for covalent bonding, hence diamond cannot conduct electricity