Classification of Matter

Matter 

can be identified by its characteristic inertial and gravitational mass and the space that it occupies. Matter is typically commonly found in three different states: solid, liquid  and gas

Introduction

A substance is a sample of matter whose physical and chemical properties are the same throughout the sample because the matter has a constant composition. It is common to see substances changing from one state of matter to another. To differentiate the states of matter at least at a particle level, we look at the behavior of the particles within the substance. When substances change state, it is because the spacing between the particles of the substances is changing due to a gain or loss of energy. For example, we all have probably observed that water can exist in three forms with different characteristic ways of behaving: the solid state (ice), liquid state (water), and gaseous state (water vapor and steam). Due to water's prevalence, we use it to exemplify and describe the three different states of matter. As ice is heated and the particles of matter that make up water gain energy, eventually the ice melts in to water that eventually boils and turns into steam.  

Before we examine the states of matter,  we will consider some ways samples of matter have been classified by those who have studied how matter behaves.

States of Matter

Everything that is familiar to us in our daily lives - from the land we walk on, to the water we drink and the air we breathe - is based upon the states of matter called gases, liquids, and solids.    

Solids

When the temperature of a liquid is lowered to the freezing point of the substance (for water the freezing point is 0^oC), the movement of the particles slows with the spacing between the particles changing until the attractions between the particles lock the particles into a solid form. At the freezing point, the particles are closely packed together and tend to block the motions of each other. The attractions between the particles hold the particles tightly together so that the entire ensemble of particles takes on a fixed shape. The volume of the solid is constant and the shape of a solid is constant unless deformed by a sufficiently strong external force.  (Solids are thus unlike liquids whose particles are slightly less attracted to one another because the particles of a liquid are a bit further apart than those in the corresponding solid form of the same substance.)  In a solid the particles remain in a relatively fixed positions but continue to vibrate.  The vibrating particles in a solid do not completely stop moving and can slowly move into any voids that exist within the solid.

Liquids

When the temperature of a sample increases above the melting point of a solid, that sample can be found in the liquid state of matter. The particles in the liquid state are much closer together than those in the gaseous state, and still have a quite an attraction for each other as is apparent when droplets of liquid form. In this state, the weak attractive forces within the liquid are unable to hold the particles into a mass with a definite shape. Thus a liquid's shape takes on the shape of any particular container that holds it.  A liquid has a definite volume but not a definite shape. Compared to to the gaseous state there is less freedom of particle movement in the liquid state since the moving particles frequently are colliding with one another, and slip and slide over one another as a result of the attractive forces that still exist between the particles, and hold the particles of the liquid loosely together.  At a given temperature the volume of the liquid is constant and its volume typically only varies slightly with changes in temperature.

Gases

In the gas phase, matter does not have a fixed volume or shape. This occurs because the molecules are widely separated with the spaces between the particles typically around ten times further apart in all three spatial directions, making the gas around 1000 times less dense than the corresponding liquid phase at the same temperature. (A phase is a uniform portion of mater.) As the temperature of a gas is increased, the particles to separate further from each other and move at faster speeds.  The particles in a gas move in a rather random and independent fashion, bouncing off each other and the walls of the container.  Being so far apart from one another, the particles of a real gas only weakly attract each other such that the gas has no ability to have a shape of its own. The extremely weak forces acting between the particles in a gas and the greater amount of space for the particles to move in results in almost independent motion of the moving, colliding particles. The particles freely range within any container in which they are put, filling its entire volume with the net result that the sides of the container determine the shape and volume of gas. If the container has an opening, the particles heading in the direction of the opening will escape with the result that the gas as a whole slowly flows out of the container.

Other States of Matter

Besides of the three classical states of matter, there are many other states of matter that share characteristics of one more of the classical states of matter. Most of these states of matter can be put into three categories according to the degrees in varying temperature. At room temperature, the states of matters include liquid crystal, amorphous solid, and magnetically ordered states. At low temperatures the states of matter include superconductors, superfluids, and Bose-Einstein condensate state of matter. At high temperatures the states of matter include, plasma and Quark-gluon plasma. These other states of matter are not typically studied in general chemistry.  

Atom

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

Protons and neutrons are heavier than electrons and reside in the center of the atom, which is called the nucleus. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus. The electron cloud has a radius 10,000 times greater than the nucleus.

Protons and neutrons have approximately the same mass. However, one proton weighs more than 1,800 electrons. Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well. Adding a proton to an atom makes a new element, while adding a neutron makes an isotope, or heavier version, of that atom.

Element

An element is a substance consisting of atoms which all have the same number of protons - i.e. the same atomic number.

Elements are chemically the simplest substances and hence cannot be broken down using chemical methods. Elements can only be changed into other elements using nuclear methods. there are currently 115 elements and three elements claimed, but not accepted (113, 115, 118)

Compound

A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition.

The ratio of each element is usually expressed by chemical formula.

For example, water (H2O) is a compound consisting of two hydrogen atoms bonded to an oxygen atom.

The atoms within a compound can be held together by a variety of interactions, ranging from covalent bonds to electrostatic forces in ionic bonds.

A continuum of bond polarities exist between the purely covalent bond (as in H2) and ionic bonds.

For example H2O is held together by polar covalent bonds.

Sodium chloride is an example of an ionic compound

Mixture

Microscopic view of a gaseous mixture containing two elements (argon and nitrogen) and a compound (water).

Note that a mixture:

• consists of two or more different elements and/or compounds physically intermingled,
• can be separated into its components by physical means, and
• often retains many of the properties of its components.

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