CLASSIFICATION OF MATTER

Matter can be identified by its characteristic inertial and gravitational mass and the space that it occupies. Two principal ways of classifying matter are according to its physical state (as a gas, liquid, or solid) and according to its composition (as an atom, molekul, compound, or mixture).

A. PHYSICAL STATE

            A sample of matter can be a gas, a liquid, or a solid. These three forms of matter are called the states of matter. The states of matter differ in some of their simple observable properties

1. A gas (also known as vapor) has no fixed volume or shape; rather, it conforms to the volume and       shape of its container. A gas can be compressed to occupy a smaller volume, or it can expand to         occupy a larger one.

2. A liquid has a distinct volume independent of its container but has no specific shape: It assumes         the shape of the portion of the container that it occupies.

3. A solid has both a definite shape and a definite volume: It is rigid. Neither liquids nor solids can be     compressed to any appreciable extent.

In a gas the molecules are far apart and are moving at high speeds, colliding repeatedly with each other and with the walls of the container. In a liquid the molecules are packed more closely together, but still move rapidly, allowing them to slide over each other; thus, liquids pour easily. In a solid the molecules are held tightly together, usually in definite arrangements, in which the molecules can wiggle only slightly in their otherwise fixed positions. Thus, solids have rigid shapes.

The three physical states of water are water vapor, liquid water, and ice. In this photo we see both the liquid and solid states of water. We cannot see water vapor. What we see when we look at steam or clouds is tiny droplets of liquid water dispersed in the atmosphere. The molecular views show that the molecules in the solid are arranged in a more orderly way than in the liquid. The molecules in the gas are much farther apart than those in the liquid or the solid.

B. PURE SUBSTANCE

            A pure substance (usually referred to simply as a substance) is matter that has distinct properties and a composition that doesn't vary from sample to sample. Water and ordinary table salt (sodium chloride), the primary components of seawater, are examples of pure substances.

1. Atoms are the basic units of matter and the defining structure of elements. Atoms are made up of       three particles: protons, neutrons and electrons.

2. Elements cannot be decomposed into simpler substances. On the molecular level, each element is       composed of only one kind of atom

3. Compounds are substances composed of two or more elements, so they contain two or more kinds     of atoms. Water, for example, is a compound composed of two elements, hydrogen and oxygen.

4. Mixtures are combinations of two or more substances  in which each substance retains its own           chemical identity.

Atom    

Smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry. Most of the atom is empty space. The rest consists of a positively charged nucleus   of protons and neutrons surrounded by a cloud of negatively charged electrons. The nucleus is small and dense compared with the electrons, which are the lightest charged particles in nature. Electrons are attracted to any positive charge by their electric force; in an atom, electric forces bind the electrons to the nucleus.

Elements

At the present time 114 elements are known. These elements vary widely in their abundance. For example, only five elements account for over 90% of the Earth's crust: oxygen, silicon, aluminum, iron, and calcium. In contrast, just three elements (oxygen, carbon, and hydrogen) account for over 90% of the mass of the human body. All the known elements and their symbols are listed on the front inside cover of this text. The table in which the symbol for each element is enclosed in a box is called the periodic table

Compounds

Most elements can interact with other elements to form compounds. Hydrogen gas, for example, burns in oxygen gas to form water. Conversely, water can be decomposed into its component elements by passing an electrical current through it. Pure water, regardless of its source, consists of 11% hydrogen and 89% oxygen by mass. This macroscopic composition corresponds to the molecular composition, which consists of two hydrogen atoms combined with one oxygen atom. The properties of water bear no resemblance to the properties of its component elements. Hydrogen, oxygen, and water are each unique substances.

Mixtures

Most of the matter we encounter consists of mixtures of different substances. Each substance in a mixture retains its own chemical identity and hence its own properties. Whereas pure substances have fixed compositions, the compositions of mixtures can vary. A cup of sweetened coffee, for example, can contain either a little sugar or a lot. The substances making up a mixture (such as sugar and water) are called components of the mixture. 

Some mixtures, such as sand, rocks, and wood, do not have the same composition, properties, and appearance throughout the mixture. Such mixtures are heterogeneous. Mixtures that are uniform throughout are homogeneous. Air is a homogeneous mixture of the gaseous substances nitrogen, oxygen, and smaller amounts of other substances. The nitrogen in air has all the properties that pure nitrogen does because both the pure substance and the mixture contain the same nitrogen molecules. Salt, sugar, and many other substances dissolve in water to form homogeneous mixtures. Homogeneous mixtures are also called solutions.

REFERENCE

https://www.britannica.com/science/atom

http://www.dictionary.com/browse/atom

http://www.eschooltoday.com/science/elements-mixtures-compounds/introduction-to-elements-compounds-and-mixtures.html

http://wps.prenhall.com/wps/media/objects/165/169061/blb9ch0102.html