PRESENTED BY- ABHINAB BORUAH

R.NO-16 CLASS-10(A)

ATOMS

Father of Modern Chemistry: Antoine L. Lavoisier

Antoine-Laurent de Lavoisier (26 August 1743 – 8 May1794)was a French nobleman and chemist central to the 18th- century Chemical Revolution and a large influence on both the histories of chemistry and biology. Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.

Laws of Chemical CombinationsThere are two laws of chemical combination.: * Law of Conservation of Mass. * Law of Constant Proportions.

Law of Conservation of Mass

 * Antoine L. Lavoisier, a French scientist, established the theory of Law of Conservation of Mass. * The law of conservation of mass states, “Mass can neither be created nor destroyed in a chemical reaction”.

Law of Constant Proportions * Law of Constant Proportion states that a chemical compound always contains exactly the same proportion of elements by mass. * This law is also known as Law of definite proportions. Joseph Louis Proust gave this law hence, this law is also known as Proust’s Law.

John DaltonJohn Dalton (6 September

1766 – 27 July 1844) was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness.

Main points of Dalton's atomic theory

* Elements are made of extremely small particles called atoms. *Atoms of a given element are identical in size, mass, and other properties; * Atoms of different elements differ in size, mass, and other properties. * Atoms cannot be subdivided, created, or destroyed. Atoms of different elements combine in simple whole- number ratios to form chemical compounds. * In chemical reactions, atoms are combined, separated, or rearranged.

What is an Atom?* Atom can be defined as the smallest particle of matter that takes part in a chemical reaction.

How big are Atoms? Atoms are very small, they are smaller than anything that we can imagine or compare with.

Characters of atoms:* Atom is the smallest particle of matter. *All elements are made of tiny particles called atom. *Atoms are very small in size and cannot be seen through naked eyes. * Atom does not exist in free-state in nature. But atom takes part in a chemical reaction.*The properties of a matter depend upon the characteristics of atoms. *Atoms are the building block of an element similar to a brick which combine together to make a building. *The size of atoms is indicated by its radius. * In ancient time atoms was considered indivisible.

Symbols of Atoms of Different ElementsSymbols of some elements are formed from the first letter of the name and a letter, appearing later in the name. E.g.: (i) chlorine: Cl(ii) zinc: Zn etc. Some have been taken from the names of elements in Latin, German or Greek. E.g.: Iron is Fe from ferrum, Sodium is Na from natrium, Potassium is K from kalium

Atomic Mass*Mass of atom is called atomic mass. Since, atoms are very small consequently actual mass of an atom is very small. For example the actual mass of one atom of hydrogen is equal to 1.673 x 10-24 g. This is equal to 0.000000000000000000000001673 gram. To deal with such small number is very difficult. Thus for convenience relative atomic mass is used.

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