Science

Chemistry

Chemistry Other

Chapter 4- Elements, Compounds and Mixtures

Atom: the smallest particle of an element that has the same chemical properties as that element/monoatomic element, e.g. xenon, argon.
Molecule: group of two or more atoms that are chemically combined together, e.g. iodine, ozone.
Element: a pure substance made of atoms that cannot be broken down into simpler substances by chemical processes, e.g. carbon, sodium.
Compound: a pure substance made of two or more elements chemically combined in a fixed ratio, e.g. water, ammonia.
Mixtures: two or more substances that are not chemically combined and are in an unfixed ratio, e.g. air, blood.

ELEMENTS:

Chemical symbols are used to represent elements. The periodic table consists of all elements arranged in order of increasing proton number.
Elements may be monoatomic, e.g. Ne, C, K, diatomic, e.g. H2, N2, Cl2, or polyatomic, e.g. O3, P4, S8
Elements are characterised as either metallic or non-metallic.

Metals	Non-metals
Lusturous	Dull appearance
Usually solids at rtp	Liquids, gases or solids with low boiling points at rtp.
Malleable, ductile, and sonorous	Brittle
Typically high melting and boiling points.	Typically low melting and boiling points.
Good conductors of heat and electricity	Poor conductors of heat and electricity

NAMING COMPOUNDS

The name of the metal element is always written first.
A compound made up of two elements has a name that ends with -ide, e.g. Sodium Chloride.
A compound with hydroxide ions is named a hydroxide, e.g. Sodium hydroxide.
A compound with a polyatomic anion containing oxygen ends with -oate, e.g. Sodium nitrate.

STEPS FOR WRITING CHEMICAL FORMULAE

For compounds containing metallic and non-metallic elements, write the symbol of the metallic element first.
Number of atoms of each element is written as a subscript to the right of each element. 1 is not written.
Oxygen atom is written at the end of the formula.
Some chemical formulae contain brackets if the number of atoms is common and the compound contains more than two elements.

DIFFERENCES BETWEEN COMPOUNDS AND MIXTURES

Compounds	Mixtures
Physical and chemical properties are different from its components.	Chemical properties are the same as its components.
Chemical reactions take place when a compound is formed and there is energy change.	No chemical reactions take place when a mixture is formed and there is little or no energy change.
The components have to be mixed in a fixed ratio.	The components can be mixed in any ratio.
Only separated by chemical reactions (e.g. decomposition) or by electrolysis.	Separated by physical processes such as filtration and crystallisation.
Examples include ammonia, water and salt.	Examples include alloys, blood and air.

Chapter 4- Elements, Compounds and Mixtures

Atom: the smallest particle of an element that has the same chemical properties as that element/monoatomic element, e.g. xenon, argon.
Molecule: group of two or more atoms that are chemically combined together, e.g. iodine, ozone.
Element: a pure substance made of atoms that cannot be broken down into simpler substances by chemical processes, e.g. carbon, sodium.
Compound: a pure substance made of two or more elements chemically combined in a fixed ratio, e.g. water, ammonia.
Mixtures: two or more substances that are not chemically combined and are in an unfixed ratio, e.g. air, blood.

ELEMENTS:

Chemical symbols are used to represent elements. The periodic table consists of all elements arranged in order of increasing proton number.
Elements may be monoatomic, e.g. Ne, C, K, diatomic, e.g. H2, N2, Cl2, or polyatomic, e.g. O3, P4, S8
Elements are characterised as either metallic or non-metallic.

Metals	Non-metals
Lusturous	Dull appearance
Usually solids at rtp	Liquids, gases or solids with low boiling points at rtp.
Malleable, ductile, and sonorous	Brittle
Typically high melting and boiling points.	Typically low melting and boiling points.
Good conductors of heat and electricity	Poor conductors of heat and electricity

NAMING COMPOUNDS

The name of the metal element is always written first.
A compound made up of two elements has a name that ends with -ide, e.g. Sodium Chloride.
A compound with hydroxide ions is named a hydroxide, e.g. Sodium hydroxide.
A compound with a polyatomic anion containing oxygen ends with -oate, e.g. Sodium nitrate.

STEPS FOR WRITING CHEMICAL FORMULAE

For compounds containing metallic and non-metallic elements, write the symbol of the metallic element first.
Number of atoms of each element is written as a subscript to the right of each element. 1 is not written.
Oxygen atom is written at the end of the formula.
Some chemical formulae contain brackets if the number of atoms is common and the compound contains more than two elements.

DIFFERENCES BETWEEN COMPOUNDS AND MIXTURES

Compounds	Mixtures
Physical and chemical properties are different from its components.	Chemical properties are the same as its components.
Chemical reactions take place when a compound is formed and there is energy change.	No chemical reactions take place when a mixture is formed and there is little or no energy change.
The components have to be mixed in a fixed ratio.	The components can be mixed in any ratio.
Only separated by chemical reactions (e.g. decomposition) or by electrolysis.	Separated by physical processes such as filtration and crystallisation.
Examples include ammonia, water and salt.	Examples include alloys, blood and air.