Shastri ji for neet
Matter and Its Nature
Matter is anything which occupies space and has mass. All the things around
us e.g., water, air, book, table etc., are matter.
There are five states of matter namely solid, liquid, gases, plasma and
Bose-Einstein condensate. Out of these, three states i.e., solid, liquid and gas
are general states and taught in our schools. These three states provide a basis
for the physical classification of matter.
Solids have a definite volume and shape; liquids have a definite volume but not
definite shape; gases have neither a definite volume nor a definite shape.
These three states of matter are the result of competition between
intermolecular interactions (attractive force between molecules) and thermal
energy (responsible for repulsion between molecules).
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.
Plasma is seen as a state containing gaseous ions and free electrons and exists
when gaseous state is taken to very high temperatures (say 1000 to
1,000,000,000°C). Here, it is necessary that the entire gas as a whole have no
charge and is not of too much density. So, in short we can say plasmas as low
density ionised gases at very high temperatures. Plasmas can be seen in
northern lights or ball lightenings, flames, lightenings, neon lights, stars in
particular sun, clouds of gas and dust around stars.
BE condensate was predicted in 1924 by Satyendra Nath Bose and Albert
Einstein but due to lack of equipments, it was only created in 1935 by Cornell,
Ketterle and Weimann. Its concept and existence is totally opposite to
plasmas. The state is conceptualised at supercold conditions.
The supercold above means only a few billionth of a
degree above absolute zero. Cornell and Weimann
developed BEC at such temperature with rubidium.
The supercold above means only a few billionth of a
degree above absolute zero. Cornell and Weimann
developed BEC at such temperature with rubidium.
Dalton’s Atomic Theory
J. Dalton in 1803, proposed the atomic theory of matter on
the basis of laws of chemical combinations. (which are
given later in this chapter)
According to which
(i) matter is made up of indivisible and indestructible
particles, called atoms.
(ii) all atoms of an element have identical mass and
similar chemical properties. (Atoms of different
elements have different masses and different
chemical properties).
(iii) when atoms combine, they do so in the ratio of small
whole numbers to form compound atoms or simply
compounds or molecules. Compounds formed by
such combinations are alike in every respect.
(iv) chemical reactions involve only combination,
separation or rearrangement of atoms.
(v) atoms are neither created nor destroyed in the course
of an ordinary chemical reaction.
J. Dalton in 1803, proposed the atomic theory of matter on
the basis of laws of chemical combinations. (which are
given later in this chapter)
According to which
(i) matter is made up of indivisible and indestructible
particles, called atoms.
(ii) all atoms of an element have identical mass and
similar chemical properties. (Atoms of different
elements have different masses and different
chemical properties).
(iii) when atoms combine, they do so in the ratio of small
whole numbers to form compound atoms or simply
compounds or molecules. Compounds formed by
such combinations are alike in every respect.
(iv) chemical reactions involve only combination,
separation or rearrangement of atoms.
(v) atoms are neither created nor destroyed in the course
of an ordinary chemical reaction.
Limitations of Dalton’s Atomic Theory
(i) It failed to explain how atoms of different elements
differ from each other.
(ii) It failed to explain how and why atoms of elements
combine with each other to form compound atoms or
molecules.
(iii) It failed to explain the nature of forces that bind
together different atoms in a molecule.
(iv) It did not make any distinction between ultimate
particle of an element that takes part in reaction
(atoms) and the ultimate particle that has independent
existence (molecules).
The hypothesis of Dalton is even accepted today by the
scientific community with two modifications only.
1. Atom is divisible and destructible.
2. All atoms of an element are not identical in mass.
Atoms and Molecules
An atom is defined as “the smallest particle of matter which
may or may not exist independently but can take part in a
chemical reaction.’’
A molecule is defined as “the smallest particle of matter which
can exist independently but cannot take part in a chemical
reaction.’’
Both atoms and molecules are basic constituents of matter
with the condition that atoms combine to form the
molecules.
The molecules may be
(i) monoatomic, i.e., contain 1 atom only, e.g., Na, K etc.
(ii) diatomic, i.e., contain 2 atoms, e.g.,N , O2 2 etc.
(iii) triatomic, i.e., contain 3 atoms, e.g.,O3
etc.
(iv) polyatomic, i.e., contain more than 3 atoms e.g., P4 , S 8 etc.
