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Created: 19 Jan, 2010; Last Modified: 14 Oct, 2016

Matter - 01

Nature of Matter

Anything that we see around us is made up of matter. Matter is anything which has mass and occupies space.

Properties

A property is any characteristic of matter which can be detected or measured, and can be used to identify or describe the matter. Properties can be of two types – physical properties and chemical properties.

A substance is matter which can be identified by a fixed set of properties.

A physical property of matter can be determined without carrying out any chemical reaction on it. Thus, for example, properties like colour of gold or the boiling point of water are physical properties.

A chemical property of matter is determined only when the matter reacts with another kind of matter and converts to a third kind. Thus, a new shiny iron nail reacts with oxygen in air over time to form a layer of brown rust covering the nail. This reaction of iron with oxygen is one of its chemical properties.

Properties can also be classified as being qualitative or quantitative. Qualitative properties are those which can only be described and cannot be measured and expressed numerically, such as the colour of gold. Quantitative properties can be measured and expressed numerically, such as the boiling point of water, which is 100°C.

Yet another classification of properties is into extensive properties and intensive properties. Extensive properties depend on the amount of matter present, such as the mass or the volume of a sample. Intensive properties do not depend upon the amount of matter, such as density and freezing point. Incidentally, all chemical properties are intensive properties.

Each substance has its own unique set of properties which differentiate it from other substances.

Particles

All matter is made up of very small particles, so small that they cannot be seen with the naked eye. These particles are separated from each other by emptiness. A lot of the properties of matter becomes clear by understanding how these particles behave.

Today we refer to these particles as atoms and molecules. Atoms are the smallest particles of interest to chemistry, while molecules are collection of atoms which behave as a single unit. For some kinds of matter, atoms are the smallest units, while for others, molecules are.

Classification of Matter

Two major categories of classification of matter are physical classification and chemical classification. Fig. depicts the classification of matter into the two major categories, and the sub-classifications therein.

classification-of-matter.png
Fig 1: Classification of Matter

Physical Classification

This classification divides matter into three categories – solids, liquids, and gases – known as the three states (or phases) of matter. (Fig. )

States of Matter

Solid
crystalline-sodium-chloride-lattice.png
Fig 2: A conceptual view of particles of crystalline common salt (sodium chloride). The lines between the particles are drawn to illustrate the structure—they do not exist in reality.

Solids are matter having fixed shape, fixed volume and are almost impossible to compress. Of course, solids can be crushed into powder form (in which case the fixed shape is destroyed), but in essence the powder still remains a solid.

Solids are composed of particles which are very near to each other because of mutual forces of attraction, and thus in some kind of order. The particles' movement is limited to vibrating in the positions they are in. If energy is added to the solid in the form of heat, the particles become more energetic in their vibrations.

Solids can occur in two forms. Crystalline solids are made up of crystalsA crystal is a small unit of matter consisting of particles arranged into a fixed geometrical shape..

Amorphous solids have no such small units and hence their internal structure is shapeless.

Common salt (sodium chloride) is crystalline with cubic crystals (Fig. ). Glass, on the other hand, is an amorphous solid as it has no such internal structure with definite shape.

Liquid

Liquids are matter having a fixed volume but no fixed shape – they take the shape of the container. Liquids are very difficult to compress.

Liquids are composed of higher energy particles which overcome their mutual forces of attraction and move independently. This is the reason why liquids do not have a fixed shape. The particles move in straight lines until they collide with other particles and rebound. Since the particles are a little more spread apart when compared to solids, liquids can be compressed a little.

For a liquid in a container, its top free surface consists of moving particles which are attracted by the particles below, and do not have energy enough to overcome the attraction. As a result, they remain within the boundary of the top surface and cannot escape, giving the liquid the fixed volume.

Gas

Gases are matter having neither a fixed shape nor a fixed volume. They are very easy to compress.

Gases consist of high energy particles which are so far from each other that the forces of attraction between them become negligible. The particles can spread out to occupy whatever space is available. Thus, gases have neither fixed shape nor fixed volume.

Change of State

change-of-state.png
Fig 3: Change of State

Matter can undergo changes between these three physical states through changes in physical properties, but without involving any change in chemical properties. Such changes are called physical changes. Energy is either absorbed or released during a physical change.

The change of state from solid to liquid is called melting or fusion, while the reverse process is called freezing or solidification.

The melting point is the temperature at which a substance changes from solid to liquid. Conversely, freezing point is the temperature at which a substance changes from a liquid to solid. These two temperatures are essentially the same – which one is used depends upon whether the substance is being heated or being cooled.

The change of state from liquid to gas is called vaporisation or boiling, while the reverse process is called condensation. The boiling point is the temperature at which a substance changes from liquid to gas. Conversely, condensing point is the temperature at which a substance changes from a gas to liquid.

When liquids gradually turn into gases at temperatures less than their boiling point, the process is called evaporation.

Some substances, like iodine and solid carbon dioxide, can go directly from solid to gaseous state without melting – this is known as sublimation. The reverse process of sublimation is called deposition.

Chemical Classification

A chemical change involves a chemical reaction resulting in change in chemical properties of the substance.

In any chemical change, (1) one or more substances are used up (at least partially), (2) one or more new substances are formed, and (3) energy is absorbed or released. The chemical properties of substances are revealed as they undergo chemical changes.

The chemical classification scheme broadly divides matter into two categories – pure substances and mixtures.

Pure Substances

A pure substance (or simply substance) is matter which can be identified by a fixed set of properties, which distinguishes it from other substances. A substance cannot be further broken down into simpler substances by physical means (i.e. through physical changes), although some substances can be broken down through chemical means (through chemical changes).

A sample of pure water has a fixed freezing point of 273K (0°C), a boiling point of 373K (100°C) and a density of 1000kg/m3, irrespective of where the sample is derived from. Such properties identify water as a unique substance, with no other substance matching these characteristics.

Elements
Table 1: Names & Symbols of some common elements.
Element Symbol
aluminium Al
argon Ar
barium Ba
boron B
bromine Br
calcium Ca
carbon C
chlorine Cl
fluorine F
helium He
hydrogen H
iodine I
lithium Li
magnesium Mg
manganese Mn
nitrogen N
oxygen O
phosphorus P
silicon Si
sulphur S
zinc Zn
copper (cuprum) Cu
iron (ferrum) Fe
lead (plumbum) Pb
mercury (hydrargyrum) Hg
potassium (kalium) K
silver (argentum) Ag
sodium (natrium) Na

An element is a pure substance which cannot be further split up by chemical reactions into simpler substances. They are the fundamental substances of which all matter is composed. The smallest particle of an element of importance to chemistry is the atom.

There are 115 known elements presently, out of which only 91 occur naturally. The remaining elements have been produced artificially by nuclear scientists in the laboratory using particle accelerators.

To simplify the representation of elements in chemical reactions, they are represented by symbols. Basically, the symbol of an element refers to one atom of the element. Some symbols are derived from the latin name of the particular elements. The names and symbols of some common elements are listed in Table .

Elements may be solids, liquids or gases. At room temperatures, only mercury, bromine and francium are liquids. Hydrogen, nitrogen, oxygen, fluorine, chlorine and the noble gases (helium, neon, argon, xenon, krypton and radon) are gases. The rest of the elements are solids. The Periodic Table is a chart of elements presenting details about all of them.

Elements are further classified as metals, non-metals & metalloids. About 80% of elements are metals.

Metals are elements which have “metallic” lustres, are malleableA malleable substance can be hammered into thin sheets. and ductileA ductile substance can be drawn out as thin wires., are of high relative density, and are good conductors of heat and electricity. All metals are solid except mercury, which is the only liquid metal at room temperature.

Non-metals do not possess any of the properties of metals. They do not have a lustre, are not malleable or ductile, and do not have high relative density. Non-metals are solids or gases except bromine, which is the only non-metal which is liquid at room temperature.

Metalloids (or semi-metals) are those elements which exhibit both the properties of metals and non-metals to some extent, such as boron and silicon.

Compounds

A compound is a pure substance which is formed by chemical combination of two or more elements in a fixed ratio by mass. Compounds are the substances which can be decomposed by chemical methods into their constituent elements.

The smallest unit of a compound, known as a molecule, or a formula unit, is composed of atoms of the constituent elements. A compound is represented by a chemical formula which indicates one molecule (formula unit) of the compound containing atoms of its elements.

The number of possible compounds is almost infinite. A chemical compound always contains the same elements chemically combined together in a fixed proportion by weight. A compound has properties which are very much different from its constituent elements.

Those compounds which are composed of carbon and hydrogen, along with other elements, are called organic compounds, as these compounds form the basis of all life on earth. All other compounds are categorised under the name of inorganic compounds.

(a) Water, chemically known as hydrogen monoxide, is a compound which contains hydrogen and oxygen combined in the ratio of 1:8 by weight. Its chemical formula is H2O. It is a liquid which cannot catch fire, though it is made up of hydrogen, a gas which is combustible, and oxygen, another gas which supports combustion. Thus, the properties of water are very much different from its constituent elements. Water can be decomposed into hydrogen and oxygen by the passage of electric current through it.

(b) Common salt, or sodium chloride, is a compound of sodium, a soft silvery highly reactive metal, and chlorine, a greenish poisonous gas. But common salt is non-poisonous and essential part of our diet.

Mixtures

A mixture is a sample of matter containing two or more pure substances physically mixed together, without any chemical interaction, in any ratio by weight.

Since the mixture is formed by physical combination of substances, the substances making up the mixture do not lose their individual properties. Also, as the components of the mixture can be present in any ratio by weight, it is possible to have mixtures in varying concentrations.

Mixtures are categorised into homogeneous and heterogeneous mixtures.

A homogeneous mixture (or a uniform mixture) is one in which the composition is the same throughout. A homogeneous mixture is also called a solution, and consists of a substance designated as a solventA solvent is a substance, usually a liquid, having the power of dissolving other substances in it. (the substance present in largest amount) and other substances (one or more) as solutesA solute is a substance that is dissolved in a solvent to form a solution.. Generally, a solvent is a liquid, while solutes can be solid, liquid or gaseous.

A solution with water as the solvent is termed an aqueous solution.

An alloy is a solution of two or more metals, and generally stands for a solid solution of the metals. An alloy of mercury with a metal is called an amalgam.

Liquids that mix together completely are called miscible liquids. The final solution looks like a single liquid. In contrast, liquids which do not mix completely and tend to settle down as different layers are said to be immiscible.

Soda water is an example of a homogeneous mixture or solution, in which water (a liquid) is the solvent and carbon dioxide (a gas) is the solute. Brass is another example (a solid solution) in which copper is the solvent and zinc the solute.

A heterogeneous mixture (or a non-uniform mixture) is one in which the composition varies throughout.

A rock can be classified as a heterogeneous mixture. It generally consists of a number of mineral components distributed non-uniformly.

In any mixture, (a) the composition can be varied and (b) each component of the mixture retains its own properties. Mixtures can be separated into component substances by physical means because each component retains its properties.

Table 2: Examples of different types of mixtures.
Type of Mixture Homogeneous Heterogeneous
Solid in solid alloys like
- bronze
- brass
- coins
- sugar and salt
- gunpowder (charcoal, sulphur and potassium nitrate)
- iron and sulphur
Solid in liquid - brine (salt in water)
- sugar solution
- fresh precipitates in test tubes
- muddy water
Solid in gas iodine vapour in air smoke (carbon particles in air)
Liquid in solid amalgams (mercury in metals like copper, zinc etc.) bromine absorbed in charcoal
Liquid in liquid All miscible liquids like:
- water + alcohol
- alcohol + benzene
All immiscible liquids like
- oil + water
- benzene + water
- chloroform + water
- carbon tetrachloride + water
Liquid in gas Moist air, any gas collected over water Air near rivers, lakes and seas
Gas in solid hydrogen in palladium chlorine in charcoal
Gas in liquid - Aerated water
- carbon dioxide in water
River or lake water at different depths
Gas in gas Air (oxygen + nitrogen + other gases)

 

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Bibliography

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