Nature of Matter
You are already familiar with the term matter from your earlier classes. Anything which had mass and occupies space is called matter.
Everything ground us, for example, Book, pen, pencil, water, air, all living beings etc. are composed of matter. You know that they have mass and they occupy space.
You are also aware that matter can exist in three physical states viz. solid, liquid and gas. The constituent particles of matter in these three states can be represented as shown in Fig (Upper) In solids, these particles are held very close to each other in an orderly fashion and there is not much freedom of movement. In liquids, the particles are close to each other but they can move around.
However, in gases, the particles are far apart as compared to those present in solid or liquid states and their movement is easy and fast. Because of such arrangement of particles, different states of matter exhibit the following characteristics :
- Solids have definite volume and definite shape.
- liquids have definite volume but not the definite shape. They take the shape of the container in which they are placed.
- Gases have neither definite volume nor definite shape. They completely occupy the container in which they are placed.
These three states of matter are interconvertible by changing the conditions of temperature and pressure.
On heating a solid usually changes to a liquid and the liquid on further heating Changes to the gaseous (or vapour) state. In the reverse process, a gas on cooling liquifies to the liquid and the liquid on further cooling freezes to the solid.
At the macroscopic or bulk level, matter can be classified as mixtures or pure Substances. These can be further sub-divided as shown in Following Fig.
Many of the substances present around you are mixtures. For example,sugar solution in water, air, tea etc. are all mixtures. A mixture contains two or more substances present in it (in any ratio) which are called its components A mixture may be homogeneous or heterogeneous. In a homogeneous mixture, the components completely mix with each other and its composition is uniform throughout Sugar solution, and air are thus, the examples of homogeneous mixtures. In contrast to this, in heterogeneous mixtures, the composition is not uniform throughout and sometimes the different components can be observed.
For example, the mixtures of salt and sugar, gains and pulses along with some dirt (often stone) pieces, are heterogeneous mixtures, You can think of many more examples of mixtures which you come across in the daily life. It is worthwhile to mention here that the components of a mixture can be separated by using physical methods such as simple hand picking, filtration, crystallisation, distillation etc.
Pure substances have characteristics different from the mixtures. They have fixed composition, whereas mixtures may contain Components in any ratio and their composition is variable. Copper, silver, gold, water, glucose are some examples of pure substances. Glucose contains carbon, hydrogen and oxygen in a fixed ratio and thus, like all other pure substances has a fixed composition. Also, the constituents of pure substances cannot be separated by simple physical methods
Pure substances can be further classified into elements and compounds An element consists of only one type of particles These particles may be atoms or molecules. You may be familiar with atoms and molecules from the previous classes however, you will be studying about them in detail in Future Posts. Sodium, copper, silver, hydrogen, oxygen etc. are some examples of elements.
They all contain atoms of one type. However, the atoms of different elements are different in nature Some elements such as sodium or copper, contain single atoms held together as their constituent particles whereas in some others, two or more atoms combine to give molecules of the element Thus, hydrogen, nitrogen and oxygen gases consist of molecules in which two atom combine to give their respective molecules. This is illustrated an Fig (Above).
when two or more atoms of different elements combine, the molecule of a compound is obtained. The examples of some compounds are water, ammonia, carbon, dioxide, sugar etc. The molecules of water and carbon dioxide are represented in above Fig…
|A depiction of molecules of water and carbon dioxide|
You have seen above that a water molecule comprises two hydrogen atoms and one oxygen atom. Similarly, a molecule of carbon dioxide contains two oxygen atoms combined with one carbon atom. Thus, the atoms of different elements are present in a compound in a fixed and definite ratio and this ratio is characteristic of a particular compound. Also, the properties of a compound are different from those of its constituent elements.
For example, hydrogen and oxygen are gases whereas the compound formed by their combination i.e., water is a liquid. It is interesting to note that hydrogen burns with a pop sound and oxygen is a supporter of combustion, but water is used as a fire extinguisher.
Moreover, the constituents of a compound cannot be separated into simpler substances by physical methods. They can be separated by chemical methods.
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