Unit 1: The particle nature of matter

Question 1

Demonstrate understanding of the terms atom,
molecule and ion

Answer 1

Atoms: The basic units of matter that have chemical elements. An atom is the smallest part of an element that displays the characteristics of that particular element.

Molecules: A group of two or more atoms covalently bonded together.

Ions: A particle that has an unequal number of protons and electrons due to electron loss or gain. It is a charged particle.
Cation - A positively charged ion due to electron loss
Anion - A negatively charged ion due to electron gain

Question 2

Define a physical change and give examples

Answer 2

A change which does not alter the chemical makeup of a substance or what the substance is.
e.g. Ice melting into water (or any change of state in general)

Physical changes can be reversed. e.g. Steam can be condensed back into water.

Question 3

Understand that some chemical reactions can be
reversed by changing the reaction conditions
(Limited to the effects of heat and water on
hydrated and anhydrous copper(II) sulfate and
cobalt(II) chloride.) (Concept of equilibrium is
not required.)

Answer 3

Some chemical reactions are reversible. You use the symbol ⇌ to represent a reversible reaction.

The heating of hydrated copper(II) sulfate and cobalt(II) chloride are examples of reversible reactions.

1st reaction equation:
CuSO 4 .5H 2 O(s) (pale blue solid) ⇌ CuSO 4 (s) (white solid) + 5H 2 O(l)

hydrated copper(II) sulfate ⇌ anhydrous copper(II) sulfate

Explanation: When heated, the water is driven off, producing anhydrous copper sulfate which is a white solid. The reaction is reversible, which means that as soon as any water is around, anhydrous copper sulfate will be converted back into the blue hydrated form.

2nd reaction equation: CoCl 2 .6H 2 O(s) (pink solid) ⇌ CoCl 2 (s) (blue solid) + 6H 2 O(l)

hydrated cobalt(II) chloride ⇌ hydrated cobalt(II) chloride

https://www.savemyexams.co.uk/igcse/chemistry/cie/23/revision-notes/6-chemical-reactions/6-2-reversible-reactions–equilibrium/6-2-1-reversible-reactions/

Question 4

Describe the differences between elements,
mixtures and compounds

Answer 4

Element: Substances that cannot be chemically broken down into simpler substances. contains only one type of atom.

Compound: Pure substances made from two or more elements chemically bonded in a fixed ratio. All compounds are molecules.
- the composition of the new compound is always the same
- The properties of the new compounds are very different from those of the elements in it
- The compound cannot easily be separated into its elements

Mixtures: 2 or more different types of atoms which are combined together - they are not chemically bonded however and can be separated. The substances in the mixture have to be in the same state. If it has 2 substances in different states - this is known as a suspension.
- The compositions of the mixture can be varied
- The properties of the substances present remain the same
- The substances in the mixture can be separated by physical methods such as filtration, distillation, or magnetic attraction.
- An example of a mixture is air

Question 5

Define the terms solvent, solute, solution and
concentration

Answer 5

Solvent: This is ususally a liquid or gas. It is a substance which dissolves another substance.

Solute: This can be a solid, liquid, or gas. It is a substance which is dissolved in a solvent.

Solution: A mixture in which a solute has dissolved in a solvent.
Common solutions:
- Sea water: Various salts (the solutes) e.g. sodium chloride, are dissolved in water (the solvent)
- Fizzy drinks: CO2 (the solute) is dissolved in water (the solvent)
- Removing nail polish: Acetone dissolves the nail polish

Concentration: A measure of how much solute is dissolved in a solvent/the amount of solute per unit of the solution. The SI convention is either mol/dm^3 (moles/decimeter cubed) or g/dm^3 (grams per decimeter cubed). To figure out concentration always change the mass to g and the volume to dm^3. Remember that to convert centimeter cubed to decimeter cubed you must divide by 1000.

Question 6

Describe the structure of an atom

Answer 6

• Made up of 3 subatomic particles: Protons, Nuetrons, and Electrons
• The protons and nuetrons are a part of the central nucleus and can be referred to as nucleons
• Electrons orbit the nucleus in a series of shells
• Electrons are held in place by a force of attraction from the nucleus’ positive charge. The number of electrons in an atom is always equal to the number of protons found in the nucleus. This means an atom has no overall charge: the number of positive charges inside the nucleus is matched by an equal number of negative charges surrounding it.

Question 7

Describe the build-up of electrons in ‘shells’
and understand the significance of the noble
gas electronic structures and of the outer-shell
electrons. (The ideas of the distribution of electrons in s and p orbitals and in d-block elements are
not required.)

Answer 7

They are unreactive because they have a full outer shell and so they don’t need to react
They exist on their own because they have a full outer shell
All gaseous at room temperature
Melting and boiling point increase as you go down the group
Density goes up as you go down the group
Argon is the most abundant noble gas in the atmosphere. This is due to its very stable nucleus and inert properties. It is used to provide inert atmospheres in various reactions which are carried out in laboratories and as well as other uses. Therefore, the most abundant noble gas in the atmosphere is argon.
Helium→ Keeps satellite instruments cool→ fill up balloons
Neon→ High voltage driving equipment
Argon→ Gas shield for arc welding→ fill up lamps
Krypton→ Combined with gasses to make luminous signs
Xenon→ Produces ultraviolet light
Radon→ Used to treat tumours

All noble gases are colorless and odorless.
All gases are very unreactive and monoatomic due to having a full valence shell.

Question 8

State the charges and approximate relative
masses of protons, neutrons and electrons

Answer 8

• Protons have a relative mass of one and are positively charged
• Nuetrons have a relative mass of one and have no charge
• Electrons have a negligible mass and have a negative charge

Question 9

Define and use proton number

Answer 9

The proton number (atomic number) is the number of protons in the nucleus of an
atom

Question 10

Define and use nucleon number

Answer 10

The nucleon number (mass number) is the total number of protons and neutrons in the nucleus of an atom

Question 11

Use proton number and the simple structure of
atoms to explain the basis of the Periodic Table,
with special reference to the elements of proton
numbers 1 to 20

Answer 11

Within the first 20 elements (hydrogen to calcium), the arrangement of electrons gives us some significant clues about:

which group each element will be found in
the chemical behaviour of the different elements.

Question 12

Define isotopes

Answer 12

Atoms of the same element which have the same proton number but a different nucleon number

Question 13

Do isotopes have the same properties as the normal atom? why or why not?

Answer 13

Isotopes have the same properties because they have the same number of electrons in their outer shell - valence electrons determine most of the elements properties e.g. reactivity

Question 14

Can you?
- Use the symbols of the elements and write the
formulae of simple compounds
- Deduce the formula of a simple compound from
the relative numbers of atoms present
- Deduce the formula of a simple compound from
a model or a diagrammatic representation
- Construct and use word equations
- Interpret and balance simple symbol equations
- Construct and use symbol equations, with state
symbols, including ionic equations
- Deduce the balanced equation for a chemical
reaction, given relevant information

Question 15

Determine the formula of an ionic compound
from the charges on the ions present

Answer 15

Use the cross method - the charge on one becomes the subscript of the other in the ionic compound.

Question 16

Define relative atomic mass, Ar

Answer 16

the average mass of naturally occurring atoms of an element on a scale where the 12C atom has a mass of exactly 12 units

Question 17

Define relative molecular mass, Mr

Answer 17

the sum of the relative atomic masses (relative formula mass or Mr will be used for ionic compounds)

Question 18

Describe the Periodic Table

Answer 18

a method of classifying elements and its use to predict properties of elements

Question 19

The change from metallic to nonmetallic character across a _______

Answer 19

period

Question 20

Describe the relationship between group number,
number of outer-shell electrons and metallic/
non-metallic character

Answer 20

Non-metallic character relates to the tendency to accept electrons during chemical reactions. Metallic character refers to the tendency to lose electrons during chemical reactions.
1. Metallic tendency increases going down a group.
2. Non-metallic tendency increases going from left to right across the periodic table.

1. Because more electron shells means that the valence electrons are further away from the positive nucleus -> meaning that the electrostatic attraction is weaker and making it easier for them to be donated (thus making metals further down the group more reactive).
2. BecausetThe tendency to gain electrons increases on moving across a period due to an increase in the nuclear charge and decrease in the atomic size. Hence, the non-metallic character increases across a period.

Question 21

Describe lithium, sodium and potassium

Answer 21

in Group I as a collection of relatively soft metals
showing a trend in melting point, density and
reaction with water

Question 22

Describe the halogens, chlorine, bromine and
iodine

Answer 22

in Group VII, they are a collection of diatomic
non-metals showing a trend in colour and
physical state

Question 23

Predict the properties of other elements in
Group I (Group 1: alkalis metals), given data, where appropriate

Answer 23

Alkali metals:
- Melting point decreases as you go down the group
- All Group I metals react vigorously with water to produce a metal hydroxide and hydrogen gas. e.g. with lithium and water as hydrogen gas is given off by the reaction, effervescence can be seen.
- As you go down the group the reactivity increases.

Lithium - Period 2
Sodium - Period 3
Potassium - Period 4
Rubidium - Period 5
Caesium - Period 6

Properties:
Very reactive
Soft
Malleable
Ductile
Conducts Heat
Conducts Electricity
Low Density
Low Melting Points
Dull Outside, Shiny Inside

Question 24

State the reaction of chlorine, bromine and
iodine with other halide ions

Answer 24

Halogen displacement reactions are redox reactions because the halogens gain electrons and the halide ions lose electrons. When we consider one of the displacement reactions, we can see which element is being oxidised and which is being reduced.

Question 25

Predict the properties of other elements in
Group VII (Group 7: Halogens), given data where appropriate

Answer 25

Flouride (F2), At room temp: gas, yellow (colourless in aqueous solutions.

Chlorine (Cl2), at room temp: gas, Green/Yellow (Colourless in aqueous solution)

Bromine (Br2), at room temp: liquid, Orange/Red

Iodine (I2), At room temp: Solid, Purple (brown when liquid). Iodine forms a purple vapour when it is warmed.

Astatine (At2), At room temp: solid, Black

The colour becomes darker as you move down the halogen group. Melting and boiling point increases as you go down the group 7. Reactivity goes down as you go down the group.

Question 26

Identify trends in other groups, given data about
the elements concerned

Answer 26

In transition metals:
Transition elements, and their compounds, are often used as catalysts (see subtopic C7.1):

vanadium(V) oxide is used in the production of sulfuric acid (see section C12.1.1)
iron is used in the manufacture of ammonia (see subtopic C11.4)
nickel is used in the manufacture of margarine.

Question 27

Describe the transition elements

Answer 27

a collection of metals having high densities, high melting points and forming coloured compounds, and which, as elements and compounds, often act as catalysts

Question 28

Describe the noble gases

Answer 28

in Group VIII or 0, as being unreactive, monoatomic gases and explain this in terms of electronic structure. They are also colourless gasses.

Question 29

State the uses of the noble gases

Answer 29

providing an
inert atmosphere, i.e. argon in lamps, helium for
filling balloons

Question 30

Define what a chemical change is and give examples of them

Answer 30

When a chemical reaction changes what a substance is, the reactants are different from the products. Observations such as colour change, temperature change (because of energy being taken in or given out, effervescence (a gas formed in a liquid, bubbles may form) and changes in odour can all be indicators of a chemical change. Also precipitation and formation of bubbles can be indicators of a chemical change.

Chemical changes are often irreversible - or are at least very hard to reverse.

example of chemical reaction: aluminium powder reacts with Iodine, Clouds of purple iodine vapour are formed due to the heat being given out. The mixture catches fire producing white smoke and leaving a glowing residue of aluminium iodide.

Question 31

Describe the difference between metals and non-metals:

Answer 31

Metals:
- Metals found on the left hand side of the periodic table
- Large atomic radius
- Conduct heat and electricity
- Have a range of melting point values
- Malleable and ductile
- Shiny

Non-metals:
- Non-metals found on the right hand side of the periodic table
- Smaller atomic radius
- Do not conduct heat or electricity (with the exception of graphite which is a non metal that conducts electricity)
- Generally have low melting points
- Brittle
- Dull

Question 32

Define a period and a group on a periodic table

Answer 32

• The period is the same as the number of electron shells. These are the rows.
• The group is the same as the number of electrons in the outer shell. These are the columns.

Question 33

State the electron configurations:

Answer 33

1st Shell - 2 Electrons
2nd Shell - 8 Electrons
3rd Shell - 8 Electrons (up to 18)
4th Shell - 18 Electrons (up to 32)

Question 34

What are all the symbols of the state of a reactant/product in a chemical equation?

Answer 34

(s) - Solid
(l) - Liquid
(g) - Gas
(aq) - aqueous or a substance dissolved in a solvent

Question 35

What are some of the naming conventions for compounds

Answer 35

• usually ends in ‘ide’
• if oxygen is present in it then it would most probably end in ‘ate’