CS - Stage 7 - Unit 2: Matter

The particles in a solid are very close together.

This makes it difficult for the volume of a solid

to be made smaller. Solids have a fixed shape

because attractive forces hold the particles together.

These forces stop the particles from moving around.

The particles can only vibrate. This means that a

solid cannot flow.

Solids

The volume of a liquid cannot be changed. The

particles are very close together and cannot be

compressed. The particles touch each other but

they can move past each other. The attractive forces

between the particles are weak enough to allow

them to move but strong enough to hold them

together.

Liquids

Particles in a gas are a long way apart so they can

move quickly in all directions. The particles can

move easily because there are no attractive forces

between them. This means that gas has no fixed

shape or volume.

When you compress a gas, the particles move closer

together and the gas takes up less space.

Gases

Heat is energy
When the particles receive energy they vibrate more / move faster and further apart.
- In solids: when they vibrate fast enough, the attractive force could not hold the particles together -> they start to slide past each other -> become a liquid
- In liquids: the attractive force is less than in solids, when the particles get enough energy to break free -> they become free and can move freely -> become a gas

When they lose energy they move less and stay closer together, reverse of the above process.

Changes of state

Use a measuring cylinder.

The liquid forms a curve at the top (meniscus)
To read the correct volume:
- Your eye is level with the meniscus
- Read the measurement at the bottom of the meniscus

The thermometer uses the effect of heat on a liquid to read the temperature from the scale when the liquid expands

Measuring volume of a liquid

​Using particles theory to explain the changes of state

The water on Earth is being constantly recycled.

1. Water moves into the atmosphere
Evaporation: Directly from the open water
Transpiration: evaporate from plants
2. Water in the atmosphere cools down
Condensation: Water vapour cools and changes to droplets of water, forming clouds
3. Water falls from clouds
Precipitation: the water droplets become heavy enough
4. Water falls on the surface of the Earth
Open water: precipitation collects in rives, lakes and oceans
5. Water in the ground
Groundwater: soak into the soil and rocks. Some moves to the streams and rivers. Some can move to the ground
Surface run-off: when groundwater move to the ground. When there is a lot -> soil can be carried off the land into rivers, can cause silted up and blocked.

​

The water cycle

Atom means "cannot be divided"

​- Nowadays we can see some of large kinds of atom with scanning tunnelling microscopes.
- There are many different types of atom (94 natural + 24 lab-made)
- Each type has different properties


Element is a substance made of just one kind of atom

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Atoms, elements and the Periodic Table

Periodical Table is a useful way to arrange the elements.

​- They are arranged by mass of the atom and the number of electrons at the outer-most layer
- Elements with similar number of electrons outer layer are put into same groups (columns)
- Each row is called a period. Left side tends to give electron (Metals)
Symbol is useful shorthand way to refer to the elements. Usually made by 2 characters, first is always in UPPERCASE, latter is in LOWERCASE

​

Atoms, elements and the Periodic Table

When the particles of a substance is made by different types of atom joined (bonded) together.

Compounds

​​Formula (singular)
Formulae (plural)
Particle diagrams

Compound is a substance forms of one type of particle (molecules - can be bonded from different types of atoms)

Mixture is a substance forms of different types of particles/molecules in one place

Mixture vs Compound

Poll

Describe ways in which the Sodium Chlorine (NaCl) is different from Sodium (Na)?

• NaCl does not have shiny surface like Sodium (metal)

• NaCl is white, while Na has a silver-like color

• NaCl is formed of small salt crystals instead of a solid cube

• NaCl is edible (can be eaten), Sodium is not

Open Ended

Describe differences between Sodium Chlorine (NaCl) and Chlorine (Cl2)?

Multiple Select

Which two elements are combined in Sodium Chlorine?

• Na

• Fe

• Cl

• O

• Ca

Multiple Select

Which two elements are combined in Hydrogen Sulfide?

• He

• H

• S

• O

• Ca

Multiple Select

Which two elements are combined in Magnesium Oxide?

• Cl

• Mg

• S

• O

• Ma

Open Ended

A student wrote this name for a compound made of Calcium and Sulfur:

Sulfur Calcium

What is wrong here?

Give a name of your choice!