Basic chemistry concepts – Matter, Element, Atom, Molecule, Compound and Mixture.

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What is chemistry?

The branch of science which deals with the study of composition, structure, properties and change of matter is called chemistry.

Every material in existence is made up of matter - even our own bodies. Chemistry is involved in everything we do, from growing and cooking food to cleaning our homes and bodies to launching a space shuttle. Chemistry is one of the physical sciences that help us to describe and explain our world.
Many people think of chemists as being white-coated scientists mixing strange liquids in a laboratory, but the truth is we are all chemists. Understanding basic chemistry concepts is important for almost every profession. Chemistry is part of everything in our lives. 

Matter and it’s classification

Anything that occupies space and has weight and can be felt (by any one or more of our senses) is called matter.

Everything that is around us including the pen, book, pencil, air, all living beings are composed of matter. They all have mass and occupy space.

Classification of matter can be done by two ways – physical and chemical classification.

classification of matter

States of matter :

There are four states of matter in the universe: solid, liquid, gas and plasma. But, matter on earth exists mostly in three states: solid, liquid and gas.

Differences between solid, liquid and gas :

solid, liquid and gas conversion

Generally, on heating – solid changes to liquid and liquid changes to gas. On the other hand, on cooling – gas changes to liquid and liquid changes to solid. Eg.

ice water and steam

What is Plasma ?

At very high temperature(of stars), atoms lose their electrons. The mixture of electrons and nuclei forms plasma state of matter.

Like gases, plasma have not fixed shape and volume, and are less dense than solids or liquids. But unlike ordinary gases( which are neutral), plasmas are made up of electrically charged particles(ions and electrons). Plasma makes up the sun and other stars, and it is the most common state of matter in the universe as a whole.

plasma in chemistry

Changes of Phase : freezing, melting, condensation, vaporization, sublimation and deposition

A phase is a distinctive form of a substance, and matter can change among the phases. It may take extreme temperature, pressure or energy, but all matter can be changed.

There are six distinct changes of phase which happens to different substances at different temperatures. The six changes are:

  • Freezing – the substance changes from a liquid to a solid.
  • Melting – the substance changes back from the solid to the liquid.
  • Condensation – the substance changes from a gas to a liquid.
  • Vaporization – the substance changes from a liquid to a gas.
  • Sublimation – the substance changes directly from a solid to a gas without going through the liquid phase.
  • Deposition: the substance changes directly from a gas to a solid without going through the liquid phase.
  • Ionization – Ions are formed by gain or loss of electrons from an atom or molecule.

Elements

An element is a simplest form of a pure substance that can neither be decomposed into nor built up from simpler substances by ordinary physical or chemical process.

An element is a substance that is made entirely from one type of atom. For example, the element hydrogen is made from atoms containing a single proton and a single electron. If you change the number of protons an atom has, you change the type of element it is.

There are total 118 elements with their atomic number from 1 to 118. Out of which 92 ( approximation) occur naturally while the rest are prepared artificially in the laboratories.

Elements are further classified as metals, non- metals and metalloids. Out of the 118 elements of the periodic table, 84 are metals, 7 are metalloids and rests of them are non-metals.

metals, non metals and metalloids in periodic table

1. Metals : Metals are generally solids (except mercury, which is the only metal which exists in liquid state in room temperature). They are good conductors of heat and electricity, and are malleable (they can be hammered into sheets) and ductile (they can be drawn into wire). Iron, Aluminum, Copper, Silver and Gold are common example of metal

2. Non-metals : Non-metals are generally found in gaseous state but iodine is found in solid state and bromine is the found in liquid state. They are usually poor conductor of heat and electricity and are not malleable and ductile. Examples of non-metal are carbon, hydrogen, oxygen, nitrogen, sulphur, etc.

3. Metalloids : The elements which possess both the characteristics of metals as well as non-metals are called metalloids. In their physical properties, they are more like the nonmetals, but under certain circumstances, several of them can be made to conduct electricity. Some examples of metalloid are Silicon, Arsenic, Bismuth, Antimony, etc.

Compound

A compound is a pure substance formed by the chemical union of two or more elements in a fixed proportional by weight. For example:- water is a compound of hydrogen and oxygen combined together in a fixed proportional 1:8 by weight.

The properties of compound are entirely different from it’s constituents. For example, hydrogen burns, oxygen supports burning but water(containing hydrogen and oxygen) neither burns nor supports the burning.

Mixture

Anything obtained by mixing two or more substances (elements or compounds) in any proportion so that their components do not lose their identity is called mixture. Mixture can be separated by different method depending upon the nature of mixing components. Some of the methods are filtration, sublimation, evaporation, distillation, crystallization, etc.

Mixture is of two types:-

homogeneous and heterogeneous mixture

1. Homogenous mixture:-

The mixture in which the components mixed are uniformly distributed throughout the mixture is called homogeneous mixture. The mixing components cannot be seen. Homogeneous mixtures are also called as solutions

Example: – alcohol in water, air, petrol, sugar solution, etc.

2. Heterogeneous mixture:-

The mixture in which the components mixed are not uniformly distributed in the mixture is called heterogeneous mixture. The mixing components can be seen through our naked. Examples:- Mixture of oil and water, sand and water, iron and wood dust, etc.

Differences between compound and mixture :
Compound Mixture
  • A compound is a pure substance formed by the chemical union of two or more elements in a fixed proportional by weight.
  • The constituents of a compound are always present in fixed ration by weight.
  • Compounds are always homogenous in nature.
  • The constituents of compound cannot be easily separated by simple mechanical methods.
  • The properties of compound are entirely different from it’s constituents.
  • They have sharp melting and boiling point.
  • Examples:- Water, HCl, NaCl, etc.
  • Anything obtained by mixing two or more substances (elements or compounds) in any proportion so that its component does not lose their identity is called mixture.
  • The constituents of a mixture may be present in any ratio.
  • Mixture may be homogenous or heterogeneous.
  • The constituents of mixture can be easily separated by simple mechanical methods.
  • The properties of mixture are in between those of it’s constituents.
  • They don’t have sharp melting and boiling point.
  • Examples:- Air, salt solution, etc.

Atoms and Molecules

Atom :

An atom is the smallest particle of an element which can take part in chemical reaction. Atom consists of three fundamental particles like proton, neutron and electron. Atoms of same elements are similar in properties whereas atoms of different elements are different in properties. Example:- ‘H’ represent the atom of hydrogen.

nucleon in an atom

Atoms may or may not have independent existence. Atoms of inert gases like helium, neon, argon, etc. have independent existence whereas atoms of oxygen, nitrogen, etc. do not have independent existence. Atoms combine with each other to form stable molecules (like O2).

Molecules :

Molecule is the smallest unit of an element or a compound which can exist in free state in nature and possess all the properties of the element or compound.

→ Molecules containing atoms of same element are called homoatomic molecules. Eg. H2, N2, P4, O2, O3, S8, etc.

→ Molecules containing atoms of different elements are called heteroatomic molecules. Eg. HCl, CO2, NH3, CH4, PCl5, etc.

Depending on the number of atoms presenet, a molecule is called monoatomic, diatomic and polyatomic molecule. Eg.

  • Monoatomic molecule – He, Ne, Ar, Kr, Xe and Rn.
  • Diatomic molecule – H2, NaCl, O2, HCl, etc.
  • Polyatomic molecule – P4, NH3, H2SO4, etc.
Difference between compound and molecule :
  • A compound is a substance that is composed from two or more different elements. Eg. Water (H2O), table salt (NaCl), carbon dioxide (CO2), methane (CH4), etc .
  • A molecule is a group of two or more atoms held together by chemical bonds. Eg. H2 , NaCl, N2, etc.
  • All compounds are molecules but all molecules are not compound. Things like nitrogen gas (N2), oxygen(O2), etc.are molecules but not compounds since they only contain one kind of element.

examples of atom, ion, molecule and compound

Objective questions

Q 1) Air is an example of :

a. compound.

b. homogeneous mixture.

c. heterogeneous mixture.

d. molecule.

Q 2) On heating, solid camphor directly changes to gas, this process is called :

a. evaporation

b. melting

c. deposition

d. sublimation.

Q 3) Proton and neutron is combinely called :

a. electron.

b. atom.

c. nucleon

d. element.

Q 4) Plasma is formed by :

a. ionization of gas.

b. condensation of gas.

c. melting of solid.

d. deposition of gas.

Q 5) ‘He’ indicates :

a. An atom of helium

b. A molecule of helium

c. both a and b

d. An ion of helium.

Q6) Which one of the following is not a pure substance?

a. Diamond

b. Gold

c. Air

d. Ammonia

Q7) The chemical symbol for tungsten is

a. Tg

b. W

c. Tu

d. Hg

8)  Which of the following elements show the characteristics of both metals and non-metals?

a. Si

b. Br

c. Ti

d. K

9) HCl is an example of

a. Diatomic molecule.

b. Heteroatomic molecule

c. Homoatomic molecule

d. Both ‘a’ and ‘b’

10) The most common state of matter in the universe is

a. Solid

b. Liquid

c. Gas

d. Plasma

Answer 

1- b, 2-d, 3-c, 4-a, 5-c, 6-c, 7-b, 8-a, 9-d, 10-d

References