Chemistry End of Year 9 Exam Revision

Atoms

The smallest thing everything is made of

Molecules

Two or more atoms joined together. They can be the same or different atoms.

Elements

A substance made of only one type of atom

Compounds

Two or more different elements that are chemically joined together

What do you call the inside of an atom and what does it have?

The nucleus and it has the protons and neutrons

Where are the electrons in an atom

Orbiting around the nucleus in the electron shells

Protons relative atomic mass

1

Neutrons relative atomic mass

1

Electrons relative mass

1/2000

Protons relative charge

+1

Neutrons relative charge

0

Electrons relative charge

-1

Atomic number

Number of protons

Mass number

Total number of protons and neutrons

Isotopes

Atoms of the same element with the same number of protons but different number of neutrons

How to calculate the mean relative atomic mass of an atom of an element

mass of -element- atoms x number of -element- atoms/total number of -element- aoms.

If not given the number of -element- atoms you will be given a percentage - e.g: 26% and 84% - so just assume 100 atoms

How are elements in the periodic table organised into periods

Periods are the horizontal rows on the periodic table, and each element in each period has the same number of electron shells

How are elements in the periodic table organised into groups

Groups are the vertical rows on the periodic table, and each element in each group has the same number of electrons in their outer - shell

How to figure out an electron configuration of an atom of an element just by looking at it on the periodic table

Find the atomic number (the number below the element) and then as electron configurations:

• 1st shell → 2 max

• 2nd shell → 8 max

• 3rd shell → 8 max (for first 20 elements)

Metals vs Non-metals (conductivity + oxides)

• Metals = conduct + basic

• Non-metals = don’t conduct + acidic

Where are the non-metals on the periodic table

On the right, Starting with carbon and then going in a zig-zag pattern downwards to end with radon

How to figure out the electron configuration of an element simply from its period and group

Example:

Magnesium:

• Group 2 → 2 outer electrons

• Period 3 → 3 shells

👉 2,8,2

Why does elements in the same group have similar properties

Because they have the same number of electrons in their outer shell, so when they react and become an ion they all lose or gain the same amount, causing similar reactions

Why don’t Noble gases readily react?

👉 Group 0 (or 18)

👉 They have full outer shells

• He = 2

• Others = 8

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💡 Why no reaction?

👉 Atoms want a full outer shell

👉 Noble gases ALREADY have it
👉 so they don’t need to gain/lose electrons

What are Ions

charged particles

How are ions formed

when two or more atoms react together they need to make full outer shells, so they gain or lose electrons, making them charged positively (if they lost electrons) and negatively (if they gained electrons) by a certain number

Charges I need to know: Group 1, 2, 3, 5, 6, 7, hydrogen, hydroxide, ammonium, carbonate, nitrate, and sulfate

Metals:

• Group 1 → +1

• Group 2 → +2

• Group 3 → +3

Non-metals:

• Group 7 → -1

• Group 6 → -2

• Group 5 → -3

Compound Ions:

• Hydrogen → H⁺

• Hydroxide → OH⁻

• Ammonium → NH₄⁺

• Carbonate → CO₃²⁻

• Nitrate → NO₃⁻

• Sulfate → SO₄²⁻

Writing formulas:

Example 1: Na⁺ and Cl⁻

Example 2: Mg²⁺ and Cl⁻

Example:

Na⁺ and Cl⁻

👉 +1 and -1 → balance

= NaCl

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Example:

Mg²⁺ and Cl⁻

👉 need 2 Cl⁻ to balance +2

= MgCl₂

What are dot and cross diagrams for and what does a dot and cross mean?

They are used to show when atoms have reacted together and become ions, by drawing a normal atoms structure but then doing Dot = one atom’s electrons, Cross = the other atom’s electrons

What are the three states of matter?

Solid, liquid, and gas

What does the state depend on

The force of attraction between particles in the material

What's the force of attraction like in solids?

Strong

What's the force of attraction like in liquids?

Weak

What's the force of attraction like in gases?

Very weak

What is the structure of a solid like?

The particles are held in fixed positions, regularly arranged and touching, the solid will have a defined shape and volume, and the particles will vibrate around in fixed positions - If heated more of the particles will vibrate - Solid has the lowest amount of energy

What is the solid version of water?

Ice

What is the structure of a liquid like?

The particles are randomly arranged and touching - some may not touch - slowly moving and free to move past each other, the liquid will have a defined volume but no fixed shape - shape of the base of container, and the particles are constantly moving around their positions - If heated the particles will move faster

What is the state of water?

Liquid

What is the structure of a gas like?

The particles are randomly arranged and far apart, free to move far away from each other , the gas will have no defined volume and no fixed shape - shape of container, filling the container, and the particles are constantly fast moving, freely and randomly - If heated the particles will move faster - Gas has the highest amount of energy

What is the gaseous version of water

Steam

Substances can or cannot change from one state to another?

Can

Why can substances change state?

Because an increase in temperature increases kinetic energy and when there is enough kinetic energy bonds can be broken

What is the term for a solid turning into a liquid?

Melting

What is the term for a liquid turning into a gas?

Boiling or evaporating

What is the term for a gas turning into a solid

Deposition

What is the term for a solid turning into a gas?

Sublimation

What is the term for a liquid turning into a solid?

Freezing

What is the term for a gas turning into a liquid?

Condensing

What is a solvent?

A liquid in which a solute dissolves

What is a solute?

The substance being dissolved

What is a solution?

The mixture formed when a solute dissolves in a solvent.

What is a saturated solution?

A solution that contains the maximum amount of dissolved solute it can hold at a specific temperature - different solvents have different saturation points

What does solubility mean?

A measure of how much of a solute can dissolve in a solvent

What is diffusion?

The movement of particles from an area of high concentration to an area of lower concentration

What is dilution?

The process of making a solution weaker by adding more of a solvent

What does soluble mean?

A substance that can dissolve in a liquid

What does insoluble mean?

A substance that can't dissolve in a liquid

How is the solubility of a solid affected?

Temperature - as the temperature increases solids become more soluble

How is the solubility of a gas affected?

Temperature and pressure - as the temperature increases gases become less soluble, and as the pressure increases gases become more soluble

What is solubility measured in?

Grams of solute per 100 grams of solvent (g/100g)

What is a solubility curve?

A graph of solubility against temperature, used to find the solubility of a substance at a specific temperature

What is a heating curve?

A graph of temperature against the amount of heat added or removed

What is concentration?

The number of particles in a given volume of a substance

Melting point of pure water vs impure water

For a pure substance the temperature is fixed when it melts or boils. Mixtures will melt and boil over a range of temperatures

Test for pure water:

Heat liquid and then measure its boiling point and check it boils at 100 degrees Celsius

Filtration

Used to separate an insoluble solid from a liquid.

Simple distillation

Used to separate a liquid from a solution. The liquid (solvent) evaporates and then condenses in the condenser. The salt(solute) remains in the flask.

Fractional distillation

Used to separate liquids with similar boiling points.

Crystallisation

Obtaining a solute from a solution

Paper chromotography

Separating mixtures of soluble substances

Filtration example

Sand and water

Simple distillation example

Sugar and water

Fractional distillation example

Ethanol and water

Crystallisation example

Sodium chloride from a sodium chloride solution

Paper chromatography example

Food colourings, inks and dyes

How does a condenser work?

Gas is cooled and condenses (gas to liquid)

Filtration diagram

Simple distillation diagram

Fractional distillation diagram

Paper Chromatography diagram

How does simple distillation work?

The liquid (solvent) evaporates and then condenses in the condenser. The salt(solute) remains in the flask.

What does Rf value measure?

How far a substance travels during a chromatography experiment.

Equation for Rf value

Rf = Distance moved by dye from baseline/Distance moved by solvent from baseline

Atoms

The smallest thing everything is made of

Molecules

Two or more atoms joined together. They can be the same or different atoms.

Elements

A substance made of only one type of atom

Compounds

Two or more different elements that are chemically joined together

Mixtures

Two or more substances that are together but not chemically joined.

In the periodic table which elements exist as diatomic molecules and what’s a good way of remembering?

I have no bright or clever friends. Iodine, Hydrogen, Nitrogen, Bromine, Oxygen, Chlorine, Fluorine

Chemical formulae ending meanings

When 2 elements are chemically combined the ending of the second element changes to -ide, and when there are 3 elements and 1 is oxygen the ending changes to -ate.

What do you call the inside of an atom and what does it have?

The nucleus and it has the protons and neutrons

Where are the electrons in an atom

Orbiting around the nucleus in the electron shells

Symbol for protons

p or p^+

Symbol for neutrons

n or n^0

Symbol for electrons

e or e^-

Protons relative mass

1

Neutrons relative mass

1

Electrons relative mass

1/2000

Protons relative charge

+1

Neutrons relative charge

0