AQA GCSE Chemistry - Topic 1: Atomic Structure and the Period Table - Flashcards (copy)

What is an element?

An element is a substance of only one type of atom.

Elements can be classified into two groups based on their properties; what are these groups?

Metals and non-metals

Elements may combine through chemical reactions to form new products; what are these new substances called?

Compounds

What is a compound?

Two or more elements combined chemically in fixed proportions which can be represented by formulae.

Do compounds have the same properties as their constituent elements?

No, they have different properties.

What is a mixture? Does it have the same chemical properties as its constituent materials?

A mixture consists of two or more elements or compounds not chemically combined together; it does have the same chemical properties.

What are the methods through which mixtures can be separated? Do these involve chemical reactions?

• Filtration

• Crystallisation

• Simple distillation

• Fractional distillation

• Chromatography

They do not involve chemical reactions

Describe and explain simple distillation.

Simple distillation is used to separate liquid from a solution - the liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we can get to keep the liquid.

Describe and explain crystallisation/evaporation.

Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent. The solution is heated until all the solvent evaporates; the solid stays in the vessel.

Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution. Then, we cool down the solution. As we do it, the solid starts to crystallise as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration.