elements-compounds-and-mixtures

Elements, Compounds and Mixtures (IGCSE)

Core
•Describe the differences between elements, mixtures and compounds, and between metals and non-metals

Element is the simplest subtance that cannot be broken down by any chemical methods. Compound is made of two or more elements chemically combined together. Mixture is made from two or more substances physically combined together.

Example of elements: copper, carbon and all found in the Periodic table.
Examples of compounds: water, carbon dioxide, ethanol
Examples of mixtures: seawater, air, petroleum

Differences between Element and Compound

Element	Compound
Simplest form of matter	Consists of two or more different elements chemically combined together
Consist of only 1 type of atom	2 or more types of atoms
Cannot be decomposed into simpler substance by chemical methods	Can be decomposed into simpler substance by chemical methods

Differences between mixture and compound

Compound	Mixture
Elements are joined chemically in fixed proportions by mass	Constituents present in variable proportions
Formed by chemical reaction. Heat change is involved.	No chemical reaction involved. Usually no heat change is involved
Have properties different from properties of constituent elements	Have same properties same as constituents
Elements in compounds can be separated by chemical means	Constituents are separated by physical means
Fixed melting and boiling point	Melts and boils over a range of temperatures

Differences between mixture and compound

General properties of metals	General properties of non-metals
good conductors of electricity and heat	Poor conductor of electricity or heat
high melting and boiling points, usually they are solids at room temperature	lower melting and boiling points –usually they are liquids or gases at room temperature
Usually hard, strong. They are malleable and ductile.	Usually brittle
look shiny when they are polished	look dull, in the solid state
sonorous	Non-sonorous
have high density	have low density
form positive ions when they react.	often form negative ions when they react.
Usually forms basic oxides	Usually forms acidic oxides

•Describe an alloy, such as brass, as a mixture of a metal with other elements

Alloy is harder than pure metal. Atoms of pure metals are of same size and arranged in orderly and regular rows. The layers of atoms can easily slide over each other with a small amount of force or energy, making pure metal soft. In alloy, atoms of different sizes of different elements disrupt the regular arrangement of pure metals, much more energy is needed for the layers of atoms to slide over each other.

Example: Brass is an alloy made from copper and zinc. Steel is an alloy made from iron and carbon.