States Of Matter

• States Of Matter

Matter exists in three physical states: gas, liquid and solid.

The three states of matter : gas, liquid and solid.

Let us now discuss the three states of matter in detail.

A gas which is also known as vapor has no fixed volume or shape. Rather, it takes up the volume and shape of its container. The particles in a gas are far apart and are moving at high speeds colliding repeatedly with each other and with the walls of the container.

A liquid has a definite volume independent of its container, but has no definite shape. It takes up the shape of the portion of the container that it occupies. The particles in a liquid are packed more closely together than in a gas, however, they move rapidly sliding over each other.

A solid has both a distinct volume and a shape. In a solid, the particles are packed tightly together to give a definite arrangement in which the particles move about a mean position.

• Classification of matter

Most forms of matter that we encounter are not chemically pure and can be separated into different substance. A pure substance can be either an element or a compound that have distinct properties and a composition that does not vary from sample to sample. Mixtures, however , are composed of different substance with varying composition. Therefore, matter can be classified according to its composition as an element, compound or mixture.

Elements

An element is a substance that consists of only one kind of atom. For example, magnesium is and element made up of magnesium atoms only. At present over one hundred elements vary widely in their abundance. For example, only five elements (Oxygen, silicon, aluminium, iron and calcium) account for over 90% Earth's crust. To refresh your memory look at table 1 that gives some common elements with their chemical symbols.

                                                                          

Element	Symbol
Carbon	C
Oxygen	O
Aluminium	Al
Calcium	Ca
Nickel	Ni
Copper	Cu
Antimony	Sb
Mercury	Hg
Bismuth	Bi
Plutonium	Pu

                                                                             

Compounds

When two or more different element are combined chemically, a compound is formed. In a compound, the atoms of the constituent elements are in a definite characteristic ratio. There are only over one hundred elements, but millions of compounds are known to date. The symbol for a compound is called its chemical formula. As you already know, it is made up from chemical symbols of the elements and numbers indicate the number of atoms present in each element for a particular compound.

For example, consider water. It is a compound made two elements, hydrogen and oxygen in a fixed ratio of 2 : 1 and the chemical formula is given as H₂O.

Similarly the formula for carbon dioxide is give as CO₂ where elements, carbon and oxygen are combined in a 1 : 2 ratio.

Mixtures

Most of the matter we encounter are mixtures of different substance. In a mixture, the substances are not chemically joined. The substances making up a mixture are called components of that mixture. For example, consider a cup of coffee. It is a mixture of the following composition: water , coffee, milk and sugar. Some mixtures have the same composition, properties and appearance throughout and are called homogeneous mixtures. For example, a solution of copper sulfate is a homogeneous mixture. Mixtures which are not universal throughout are called is a homogeneous mixtures. Soil is a good example of a heterogeneous mixture. 

The classification of matter in to elements, compounds and mixtures that we discussed in this section is summarized in  image.

• Properties of matter

Every substances a unique set of properties and these properties can be categorized as physical or chemical. Physical properties can be measured without changing the identity and composition of the substance. For example color, odor, melting point, boiling point and hardness are physical properties. Chemical properties describe how substances undergo change or react to form other substances. For example, flammability, the ability of a substance to burn in the presence of oxygen is a chemical property.

The changes that substance undergo can also be categorized as either physical or chemical. During a physical change, a substance changes its physical its physical appearance but not its composition. A good example of a physical change is the evaporation of water. When water evaporates, it changes from the liquid state to the gas state but it is still composed of water  molecules. In a chemical change, a substance is transformed into a chemically different substance. Consider burning of hydrogen in air to form water. In this case, hydrogen undergoes a chemical change, as it has combined with oxygen to form water.