2. Atoms, Elements & Compounds

Question 1

Describe the differences between elements, compounds and mixtures

Answer 1

Elements
1. Pure substance
2. Atoms contain the same number of Protons
3.Cannot be split into something simpler
Compounds
1. A pure substances made of 2 or more elements chemically combined
2. Cannot be split physically
Mixtures
1. A combinations of 2 or more substances that aren’t chemically combined
2. Can be separated physically

Question 2

Describe the structure of the atom

Answer 2

A central nucleus containing neutrons and protons surrounded by electrons in shells

Question 3

State the relative charges and relative masses of a proton, a neutron and an electron

Answer 3

Charges: 1+ (p), 1- (e), 0 neutral (n)
Relative mass: 1 (p), 1 (n), 1/1840 (e)

Question 4

Define proton number/atomic number

Answer 4

The number of protons in the nucleus of an atom (shares the same number as electrons)

Question 5

Define mass number/nucleon number

Answer 5

The total number of protons and neutrons in the nucleus of an atom
So, neutrons = mass number - proton number

Question 6

State the electronic configuration and its details

Answer 6

• Numbers of electrons in each shells
• Rule: 2.8.8
• Determine the number of electrons in the outer shell: Group
• Determine the number of shells: Period

Question 7

State what makes Group VIII (noble gases) special

Answer 7

• Full/complete electrons in the outer shell
• Unreactive

Question 8

Define isotopes

Answer 8

Different atoms of the same
element that have the same number of protons but different numbers of neutrons

Question 9

Why do isotopes of the same element have the same chemical properties?

Answer 9

Because they have the same number of electrons and therefore the same electronic configuration
- The change of mass however affects the physical properties

Question 10

State the formula for the relative atomic mass of an element from the percentage abundance of its isotopes

Answer 10

From percentage abundance = (% isotope A x mass of isotope A) + (% isotope B x mass of isotope B) ÷ 100

Question 11

State the formula for the relative atomic mass of an element from the relative abundance of its isotopes

Answer 11

From relative abundance = total of relative abundance ÷ total number of isotopes

Question 12

Describe the formation of anions and cations

Answer 12

• The purpose of an ion is to have a complete outermost shell. So they need to lose or gain electrons resulting to its charge,
  i. Ions with a +ve charge are Cations as they lose electrons
  ii. And Ions with -ve charge are Anions as they gain electrons

Question 13

State ionic bond

Answer 13

Ionic bond: A strong electrostatic attraction between oppositely charged ions in all directions
(Happens b/w metals & non-metals)

Question 14

Describe the giant lattice structure of ionic compounds

Answer 14

• Where the atoms are arranged in an ordered and repeating fashion
  -The lattice structure consist of a regular arrangement of alternating positive and negative ions

Question 15

Describe and explain the properties of ionic compounds

Answer 15

1. High melting points and boiling points: A lot of energy is needed to overcome the electrostatic forces
2. Good electrical conductivity when aqueous or molten and poor when solid
   - When dissolved in water, the ions are able to move
   - However at solid, the ions are fixed in a lattice structure
3. Solid at room temperature

Question 16

State how covalent bond is formed

Answer 16

Covalent bond: Formed when a pair of electrons is shared between two atoms leading to noble gas electronic configurations
(Occurs between non-metals only)

Question 17

Describe and explain the properties of simple molecular compounds

Answer 17

1. Low melting point and boiling point: Weak intermolecular forces
2. Poor conductor of electricity: No free electrons or ions

Question 18

Describe the giant covalent structures of graphite

Answer 18

1. Lattice
2. 1 carbon atom attached to 3 others
3. Weak intermolecular forces

Question 19

Describe the giant covalent structures of diamond

Answer 19

1. Tetrahedron
2. 1 carbon atom attached to 4 others
3. No intermolecular forces

Question 20

Relate the structures and bonding of graphite to their uses and state its properties

Answer 20

Properties: High M.P & B.P, conducts electricity, slippery
Uses: Lubricant and pencil lead - Layers can slide over e/o

Question 21

Relate the structures and bonding of diamond to their uses and state its properties

Answer 21

Properties: Very high M.P & B.P, doesn’t conduct electricity, extremely hard & dense
Uses: Cutting tools - Strong covalent bonds so very hard & dense

Question 22

Describe the giant covalent structure of silicon(IV) oxide (8 points)

Answer 22

1. Structure: Tetrahedron (similar to diamond)
2. 1 oxygen atom bonded to 2 silicon atoms bonded to 4 oxygen atoms
3. No intermolecular forces
4. Hard
5. Doesn’t conduct electricity
6. High M.P & B.P
7. Insoluble in water
8. Used to make sandpaper and line the inside of furnaces
   (3-8 similar to diamond)

Question 23

Describe metallic bonding

Answer 23

Metallic bonding: The electrostatic attraction between the positive ions in a giant metallic lattice and a ‘sea’ of delocalised electrons

Question 24

Explain in terms of structure and bonding the properties of metals

Answer 24

1. High M.P and B.P: A lot of energy is needed to overcome the strong electrostatic forces
2. Conductors of heat and electricity: Consists a sea of free (delocalised) electrons
3. Most are malleable (bent into shape) and ductile: Layers are arranged in a way that it slides over each other when force is applied