End Of Year Exams

Question 1

How did Dmitri Mendeleev create his periodic table?

Answer 1

• Mendeleev arranged the elements in order of increasing relative atomic mass.
• Then, he arranged the elements by putting those with similar properties below each other into groups
• He left gaps for yet to be discovered elements

Question 2

How was the modern periodic table created?

Answer 2

• After the discovery of protons, scientists realised that the atomic number of an element is the same as the number of protons in its nucleus.
• In the modern periodic table, the elements are arranged according to their atomic number - not their relative atomic mass.
• Rows, called periods, in order of increasing atomic number
• Vertical columns, called groups, where the elements have similar properties

Question 3

How does the electronic configuration of an element relate to its position on the periodic table?

Answer 3

• The number of shells in the electronic configuration of an element is represented in the periodic table as the period number that element is situated in
• The number of electrons in the outermost shell of an element is represented in the periodic table as the group number that element is situated in
• The number of electrons in all shells of an element is represented in the periodic table as the element’s atomic number

Question 4

What does the electronic configuration of sodium (2.8.1) show?

Answer 4

It is in:
- Period 3
- Group 1
- Has the atomic number of 11

Question 5

What is the link between the electronic configuration of an element and its properties?

Answer 5

When atoms collide and react, it is the outer electrons that meet and interact. So, elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.

Question 6

Describe Dalton’s model’s features

Answer 6

• atoms cannot be broken down into anything simpler
• the atoms of a given element are identical to each other
• the atoms of different elements are different from one another
• during chemical reactions atoms rearrange to make different substances

Question 7

How does today’s model of atomic structure differ from Dalton’s model

Answer 7

• atoms can be broken down into three smaller particles: protons, neutrons and electrons
• atoms of an element have identical numbers of protons and electrons, but can have different numbers of neutrons
• atoms of different elements have different numbers of protons and electrons

Question 8

Describe atomic structure

Answer 8

An atom has a central nucleus surrounded by electrons arranged in areas called shells.

Question 9

What are the relative charges of protons, electrons and neutrons

Answer 9

Proton: +1
Electron: -1
Neutron: 0

Question 10

What are the relative masses of protons, electrons and neutrons

Answer 10

Proton: 1
Electron: 1/1835
Neutron: 1

Question 11

What is an isotope?

Answer 11

Atoms of an element that have the same number of protons and electrons, but different numbers of neutrons in their nuclei are called isotopes.

Question 12

What is an ion

Answer 12

An ion is an atom or group of atoms with a positive or negative charge. Ions form when atoms lose or gain electrons to obtain a full outer shell.

Question 13

How is an ion made

Answer 13

• Metal atoms lose electrons, so they have more protons than electrons to become positively charged ions (cations)
• Non-metal atoms gain electrons, so they have more electrons than protons to become negatively charged (anions)

Question 14

What is a covalent bond

Answer 14

When atoms share electrons on their outer shell in order to gain a full outer shell
This occurs between non metals

Question 15

What is a metallic bond

Answer 15

This occurs between metals
Metallic bonding is the attraction between the positive ions in a regular lattice and the delocalised electrons. Delocalised electrons are free to move throughout the whole structure.

Question 16

What phases does chromatography rely on

Answer 16

Chromatography relies on two different ‘phases’:
- the stationary phase, which in paper chromatography is very uniform, absorbent paper
- the mobile phase is the solvent that moves through the paper, carrying different substances with it

Question 17

Why do some substances move faster through chromatography paper

Answer 17

The different dissolved substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper.

Question 18

Why is a chromatogram used

Answer 18

Separation by chromatography produces a chromatogram. A paper chromatogram can be used to distinguish between pure and impure substances:
- a pure substance produces one spot on the chromatogram
- an impure substance, or mixture, produces two or more spots

A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if:
- they produce the same number of spots, and these match in colour
- the spots travel the same distance up the paper

Question 19

What are the structures of each chemical bond?

Answer 19

Ionic: Giant ionic lattice
Covalent: Simple covalent, giant covalent
Metallic: Giant metallic lattice

Question 20

Describe the structure of a giant ionic lattice

Answer 20

An ionic compound is a giant structure of ions. The ions have a regular, repeating arrangement called an ionic lattice.

The lattice is formed because the ions attract each other and form a regular pattern with oppositely charged ions next to each other.

An ionic lattice is held together by strong electrostatic forces of attraction between the oppositely charged ions. The forces act in all directions in the lattice.

Question 21

What are the properties of an ionic compound?

Answer 21

• Crystalline solids
• Can be dissolved or molten
• Hard and brittle
• Can only conduct electricity when dissolved or molten
• High melting and boiling points

Question 22

Why are ionic compounds crystalline?

Answer 22

Because of the strong electrostatic interaction between these oppositely charged ions, ionic compounds form rigid crystals.

Question 23

Why do ionic compounds have high melting and boiling points?

Answer 23

The ionic compounds are usually hard because the ions are held by strong force of attraction as the positive and negative ions are strongly attracted to each other and difficult to separate.

Question 24

Why can ionic compounds only conduct electricity when molten or dissolved?

Answer 24

Ionic compounds conduct electricity when molten, because their ions are free to move from place to place.

Ionic compounds cannot conduct electricity when solid, as their ions are held in fixed positions and cannot move.

Question 25

What is the difference between giant covalent and simple covalent compounds?

Answer 25

The key difference is that simple covalent molecules have a small and fixed number of atoms, while giant structures have large and variable numbers of atoms.

Question 26

Describe the structure of simple covalent bond

Answer 26

There are strong covalent bonds between atoms that form molecules together. However, there are weak intermolecular forces between the molecules.

Question 27

What are the properties of a simple covalent substance

Answer 27

• Cannot conduct electricity
• Low melting and boiling points
• Don’t dissolve in water

Question 28

Why can’t simple molecules conduct electricity?

Answer 28

The molecules have a neutral charge so they can’t conduct electricity and there are no electrons that are free to move

Question 29

Why do simple molecules have low melting and boiling points?

Answer 29

They have relatively low melting points and low boiling points because the molecules are held together by weak intermolecular forces that break down easily.

Question 30

What are the properties of giant covalent structures?

Answer 30

• High melting and boiling points
• Most compounds don’t conduct electricity however some do.

Question 31

What is an allotrope?

Answer 31

Allotropes are different forms of the same element, in the same state.

Question 32

Describe the structure of diamond

Answer 32

• Giant covalent structure
• Each carbon atom is bonded to 4 other carbon atoms
• Has a tetrahedral 3D structure

Question 33

What are the properties of diamond and what are its uses

Answer 33

• High melting and boiling points
• Doesn’t conduct electricity
• Hard
• Used to cut through metals, rocks and glass

Question 34

Describe the structure of graphite

Answer 34

• Each carbon atom forms three covalent bonds with 3 other atoms
• Forms layers of hexagonal rings
• Weak forces of attraction between layers
• There is one delocalised electron for each atom

Question 35

What are the properties of graphite and its uses

Answer 35

• High melting and boiling points
• Good electrical conductivity
• Soft
• Lubricant
• Pencils

Question 36

What are the properties of graphene

Answer 36

• High melting and boiling points
• Good electrical conductivity
• Very strong

Question 37

What is the structure of a giant metallic lattice?

Answer 37

Metals are giant lattices of positive ions arranged in regular layers, with delocalised electrons free to move throughout the structure.

Question 38

What are the properties of giant metallic structures?

Answer 38

• High melting and boiling points
• Good electrical conductivity
• Malleable and ductile

Question 39

Why do giant metallic substances have high melting and boiling points?

Answer 39

High temperatures are required to break strong metallic bonds.

Question 40

Why do giant metallic substances have good electrical conductivity?

Answer 40

Metal’s delocalised electrons can move and carry charge.

Question 41

Why are giant metallic substances malleable and ductile?

Answer 41

Metal’s layers of ions can slide over each other, but are still held together by the delocalised electrons. This means metal is malleable (it can be hammered into shape) and ductile (it can be drawn out into wires)