chapter 4: elements, mixtures and compounds

Question 1

what is an element?

Answer 1

an element is a pure substance that cannot be broken down into two or more substances by chemical or physical processes

Question 2

how are elements classified?

Answer 2

• metallic and non-metallic properties
  > metals, non metals, metalloids
  -physical states ( at room temp and pressure)
  > gases, liquids and solids

Question 3

what are atoms?

Answer 3

• the smallest particles of an element that have the chemical properties of that element
• each element only contains one type of atom
  > monatomic elements
• have the same number of protons and electrons

Question 4

what are molecules?

Answer 4

a group of two or more atoms chemically combined
> diatomic molecules
> polyatomic molecules

Question 5

what are polyatomic molecules and what is one example?

Answer 5

• contains three or more atoms
  > ozone is created when three atoms of oxygen are chemically combined
  >triatomic

Question 6

what are compounds?

Answer 6

• a pure substance containing two or more elements chemically combined in a fixed ratio

Question 7

does a compound have the same properties as the elements that form it? give an example

Answer 7

• a compound has different properties from its constituent elements
  eg. magnesium burns in oxygen > magnesium oxide
  but magnesium oxide does not have the same properties as magnesium or oxygen

Question 8

how can we decompose compounds?

Answer 8

• thermal decomposition and electrolysis

> breaks down compounds into elements or simpler compounds

Question 9

what is a mixture and what can they be made up of?

Answer 9

• two or more substances that are not chemically combined
  > can be made up of elements or compounds
• components of a mixture are not fixed, can be present in any ratio

Question 10

what is the formation, separation, properties, energy change and composition of a mixture?
( use the elements: sulfur and iron)

Answer 10

formation: can be formed by adding sulfur power to iron fillings
separation: can be done by physical processes such as magnetic separation, filtration or distillation
properties: chemical properties of a mixture is the same as its components

energy change: no chemical reaction takes place when its formed, little or no energy change

composition: components can be mixed in any proportion

Question 11

what is the formation, separation, properties, energy change and composition of a compound?
( use the elements: sulfur and iron)

Answer 11

formation: compound of iron and sulfur
- when mixture is heater, it glows and a black solid, iron (II)sulfide is formed

separation: can only be broke down into simpler substances by chemical methods
> thermal decomposition & electrolysis

properties: physical and chemical properties different from its constituent element

energy change: chemical reaction takes place when compound formed
> reactants get hot or cold

composition: elements of a compound are always combined in a fixed proportion

Question 12

what are alloys?

Answer 12

a mixture of metals with other elements