C1 - Elements, Compounds, and Mixtures

What is an element?

A substance in which all the atoms are the same.

How many different elements are there?

Around 100.

Where are elements shown?

On the periodic table.

What does each symbol on the periodic table represent?

A different element.

Give the symbol for magnesium.

Mg (capital M, lowercase g).

Give the symbol for sulfur.

S (capital S).

What do all atoms in an element have in common?

They are all the same type.

What is a compound?

A substance made from two or more different elements chemically combined in fixed proportions.

What does 'chemically combined' mean?

The elements are bonded together and cannot be easily separated.

What is meant by 'fixed proportions' in a compound?

The ratio of each type of atom is always the same in that compound.

Give an example of a compound.

Magnesium sulfide (MgS).

What elements make up magnesium sulfide?

Magnesium and sulfur.

How do the properties of a compound compare to the properties of the elements it is made from?

Compounds usually have completely different properties from their elements.

What is required to separate a compound into its elements?

A chemical reaction.

Is it easy to separate a compound into its elements?

No, it's often difficult.

What is a mixture?

A combination of different elements or compounds that are not chemically combined.

Can the substances in a mixture be separated?

Yes, by physical separation techniques.

List four physical methods used to separate mixtures.

Filtration, distillation, crystallization, chromatography.

What is the difference between a mixture and a compound?

Mixtures are not chemically combined; compounds are.

What is a molecule?

Two or more atoms chemically combined, which can be the same or different elements.

Are all molecules compounds?

No, only molecules with different elements are compounds.

Are all compounds molecules?

Yes, because compounds consist of atoms chemically bonded.

Give an example of a molecule that is also a compound.

Water (H₂O), methane (CH₄), ammonia (NH₃).

Give an example of a molecule that is not a compound.

Oxygen (O₂) or chlorine (Cl₂).

Why is O₂ a molecule but not a compound?

It is made of two atoms of the same element chemically combined.

Why is CH₄ (methane) a compound?

It is made from different elements (carbon and hydrogen) chemically combined.

What is the difference between an atom and a molecule?

An atom is a single particle of an element; a molecule is two or more atoms bonded together.

Can elements exist as molecules?

Yes, if two or more atoms of the same element are bonded (e.g. O₂, Cl₂).

What type of bond holds atoms together in molecules?

Chemical bonds.

What type of separation is used for mixtures?

Physical methods.

What type of separation is used for compounds?

Chemical reactions.

Why is the periodic table important for elements?

It shows all known elements and their symbols.

How do you recognise a chemical symbol?

It starts with a capital letter and may have a second lowercase letter.

What does 'chemically combined' mean in compounds and molecules?

The atoms are bonded together and cannot be separated by physical methods.

What is a pure substance in chemistry?

A single element or compound, not mixed with anything else.

How can you identify a compound from its chemical formula?

It contains symbols of more than one element.

How is a mixture different from a pure substance?

A mixture contains two or more substances not chemically joined.

How do you separate salt from water in a solution?

By evaporation or distillation.

What technique would you use to separate sand from water?

Filtration.

What technique would you use to separate dyes in ink?

Chromatography.

What does chromatography separate based on?

The different solubilities of the substances in a solvent.