The elements

In our world today, there are millions of substances in everyday use - liquids ranging from our drinking water to the fuel used in our cars, solids ranging from the sugar that we have on our breakfast cereal, and gases ranging from the air that we breathe to the gas we use to cook our food.

All of these substances are made from just over 100 different elements (103 to be precise). Of these elements, approximately 90 are naturally occurring and can be found in the earth's crust, the ocean and in our atmosphere.
The remaining elements are not naturally occurring and are classed as man made.

Elements are the building blocks of substances - they cannot be broken down into anything simpler.

 
Chemical names and symbols

Each chemical element is uniquely identified by it's chemical name and symbol.

• The element Oxygen has the symbol - O
• The element Sodium has the symbol - Na
• The element Americium has the symbol - Am

Element symbols either have one or two letters only. The first is always an uppercase (capital) letter and the second is always a lowercase letter.

You can quickly test your knowledge of the above information.

 
Classifying elements

Elements can be classified in several different ways e.g. as metal / non-metal, solid / liquid / gas, naturally occurring / man-made, radioactive / non-radioactive.

Elements are arranged into the Periodic Table.

The periodic table below shows the metals and the non-metals in the periodic table.

Metals are found to the left of the diagonal zig-zag line and non-metals are found to the right. A simple test to determine whether an element is a metal or non-metal is electrical conductivity.

• All metals conduct electricity at room temperature.
• Non-metals do not conduct electricity at room temperature.
• An exception to this rule is that the element carbon in the form of graphite conducts electricity at room temperature.

You can test the electrical conductivity of some elements in the Virtual Lab.

 
The Periodic table below shows the physical state of the elements at 20°C.

To help you decide whether an element will be a solid, liquid or gas at room temperature (20°C) look at the Periodic table (in the Data book) which shows melting and boiling points.

• If the melting point and boiling point are both < 20°C then the element will be a GAS
• If the melting point < 20°C and boiling point > 20°C then the element will be a LIQUID
• If the melting point and boiling point are both > 20°C then the element will be a SOLID

Elements/substances that are solids are often given the suffix (s) - e.g. Ca (s) or Calcium (s)
Elements/substances that are liquids are often given the suffix (l) - e.g. Hg (l) or Mercury (l)
Elements/substances that are gases are often given the suffix (g) - e.g. Ar (g) or Argon (g)

 
This Periodic table tells you the symbols of some of the naturally occurring and man-made elements.

• Some naturally occuring elements are radioactive (e.g. radium).
• Many of the man-made elements are radioactive and those above element number 92 are made inside nuclear reactors.

A horizontal row of elements in the Periodic Table is called a PERIOD.
The vertical columns in the Periodic table are called GROUPS, and are shown below.

The groups run from Group 1 to Group 7, followed by Group 0.

• Elements in the same group of the Periodic table have similar chemical properties.
• The Alkali metals (Group 1) all react quickly with water to make an alkali and hydrogen - they are stored under oil.
• The Halogens (Group 7) are all reactive non-metals which react with metals to make salts.
• The Noble gases (Group 0) are all very unreactive elements.
• The Transition metals (between Groups 2 and 3) are reactive metals. These metals are often used as catalysts.

You can quickly test your knowledge of the above information.

 
Chemical reactions.

Elements can undergo Chemical reactions. When elements react together a new substance is always formed. The substances formed when elements join together in a chemical reaction are called Compounds.
Compounds can also undergo chemical reactions, and again a new substance is always formed.

We can usually tell that a chemical reaction has taken place if :

1. There is a change in appearance.

This can often be seen if the substance changes colour, or if a gas is given off during the reaction, or a precipitate is formed.

2. There is a change in energy

The simplest way to detect an energy change in a reaction is to measure the change in temperature. A change in energy can also be shown by light being produced or a noise, e.g. an explosion.

Reactions that give energy out are called EXOTHERMIC reactions.
Reactions that take energy in are called ENDOTHERMIC reactions.

 
Naming compounds.

When elements react together, they form a new compound. The name of this new compound is derived from the elements that form it.

1. The elements in the compound are usually placed according to their position in the periodic table. Elements that are further to the left of the periodic table are written before elements that are further to the right of the periodic table.
2. If there are only two elements in the compound, the second part of name of the compound will end in -IDE.
3. If the compound contains 'lots' of oxygen as well as two other elements, then the ending of the second part of the compound name will be -ATE.
4. If the compound contains 'a smaller' amount of oxygen (less than for in the corresponding -ATE compound) as well as two other elements, then the ending of the second part of the compound name will be -ITE.

You can quickly test your knowledge of the above information.

 
Word equations.

The reactions between elements (or compounds) can be shown by use of a word equation. This is used to show the REACTANTS and the PRODUCTS.

REACTANTS PRODUCTS

1. Reactants are the substances that have undergo a chemical reaction together and are shown on the left of the word equation.
2. Products are the substances that are formed as a result of a chemical reaction and are shown on the right of the word equation.
3. When writing a word equation, we use the symbol (meaning 'reacts to give') and not the = sign.
   The reason is that if we used an equal sign, we are saying that the products are the same as the reactants. This is not the case, as all chemical reactions produce a new substance.

For example, the reaction between sodium metal and chlorine gas would be :

sodium + chlorine sodium chloride

 
Mixtures

When elements or compounds come together but do not react, a MIXTURE is formed.

The air that we breathe is a mixture of the elements oxygen (21%), nitrogen (78%), and various other gases (1%) that have not reacted together.

The test for oxygen is that it relights a glowing splint. However, there is not a high enough percentage of oxygen in the air to test this.

Substances that exist in a mixture can be separated by physical methods (e.g. filtration, distillation, chromatography, etc.).

Chromatography - can be used to separate small quantities of similar substances e.g. dyes in coloured ink.

You can quickly test your knowledge of the above information.

 
Solutions.

Solutions are formed when a substance dissolves in another substance.

The substance that is dissolved is called the SOLUTE and the substance that it dissolves in is called the SOLVENT.

• If the solute dissolves in the solvent, it is said to be SOLUBLE.
• If the solute does not dissolve in the solvent, it is said to be INSOLUBLE.

When a solution is made with very little solute present (or a large amount of solvent), it is said to be a DILUTE SOLUTION.
When a solution is made with a lot of solute present (or a small amount of solvent), it is said to be a CONCENTRATED SOLUTION.
When a solution is made with the maximum amount of solute that will dissolve, it is said to be a SATURATED SOLUTION.

Substances that are in solution are often given the suffix (aq) - e.g. NaCl (aq) or Sodium chloride (aq)

The term aq refers to the solute being dissolved in the solvent water - i.e. it is an AQUEOUS SOLUTION.

• To dilute a concentrated or saturated solution, more solvent should be added.
• To make a dilute solution a concentrated one, solvent should be removed (usually done by boiling the solution), or more solute should be added.
• To make a solution a saturated one, more solute should be added until no more can dissolve, or solvent should be removed until the solute begins to come out of the solution.

You can quickly test your knowledge of the above information.

New words and their meanings

SUBSTANCE - a general name for a chemical.

ELEMENT - the simplest type of chemical substance.

NATURALLY OCCURRING ELEMENTS - elements that can be found in nature (in the earth's crust, oceans or air).

MAN-MADE ELEMENTS - elements that do not occur in nature and are synthesised in the laboratory.

PERIODIC TABLE - a table of all the known elements sorted into vertical groups and horizontal periods.

ELECTRICAL CONDUCTIVITY - the ability of a substance to allow electricity to flow through it. All metals are conductors of electricity, and non-metals do not conduct electricity (except carbon in the form graphite).

ALKALI METALS - the elements in group 1 of the periodic table. They are reactive metals.

HALOGENS - the elements in group 7 of the periodic table. They are reactive non-metals.

NOBLE GASES - the elements in group 0 of the periodic table. They are very unreactive gases.

TRANSITION METALS - the elements found between group 2 and 3 of the periodic table. They are reactive metals often used as catalysts.

COMPOUND - formed when two or more elements react together.

EXOTHERMIC - a chemical reaction that gives out energy (usually heat) to its surroundings. This usually means the reaction heats up.

ENDOTHERMIC - a chemical reaction that takes in energy (usually heat) from its surroundings. This usually means the reaction cools down.

MIXTURE - formed when substances a placed together but do not react with one another.

SOLUTION - formed when a SOLUTE dissolves in a SOLVENT.