atomsandmolecules-140218075841-phpapp02

8/10/2019 atomsandmolecules-140218075841-phpapp02

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ATOMS AND

MOLECULES


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History of Atoms The idea of divisibility of matter was considered

long back in India, around 500 BC An Indian!hiloso!her Maharishi Kanad, !ostulated that ifwe go on dividing matter "!adarth#, we shall getsmaller and smaller !articles


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Pakudha Kaccayana, elaborated

this doctrineand said that these !articles normallye$ist in a combined form which givesus various forms of matter

Democritus and Leucippus suggestedthat if we go on dividing matter, a stagewill come when !articles obtained cannotbe divided further %emocritus calledthese indivisible !articles atoms

"meaning indivisible#

Democritus

Leucippu


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Father of Modern Chemistry:Antoine L. Laoiser

Antoine!Laurent deLaoisier"'( August )*+ -. /ay)*+#was a 1renchnobleman and chemist central to the ).th2century Chemical3evolution and a largein4uence on boththe histories of chemistryand biology Antoine

avoiser laid the foundationof chemical sciences byestablishing two im!ortantlaws of chemicalcombination


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Da#ton$s Atomic Theory

6ohn %alton, a British Chemistsand scientists gave the Atomic

Theory in ).0. This theory is

!o!ularly known as %alton9sAtomic Theory in the honor of

6ohn %alton He gave the theory

on the basis of aws of ChemicalCombination and e$!lains them!ro!erly In his theory he e$!lainsabout atom


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:hat is an Atom;

Atom can be de


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Characteristics of atoms=

Atom is the smallest !article of matterAll elements are made of tiny !articles called atom

Atoms are very small in si>e and cannot be seenthrough naked eyes

Atom does not e$ist in free2state in nature Butatom takes !art in a chemical reaction

The !ro!erties of a matter de!end u!on thecharacteristics of atoms

Atoms are the building block of an element similar

to a brick which combine together to make abuilding

The si>e of atoms is indicated by its radius

In ancient time atoms was considered indivisible


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7ymbols of Atoms of %i?erent8lements

7ymbols of some elements are formed

from the inc= @n etc

7ome have been taken from the

names of elements in atin, erman orreek

8g= s Iron is 1e from ferum,7odium is a from natrium,

otassium is D from kalium


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Atomic Mass

/ass of atom is called atomic mass 7ince, atomsare very small conseEuently actual mass of anatom is very small 1or e$am!le the actual massof one atom of hydrogen is eEual to )(* $ )02'+g This is eEual to000000000000000000000000)(* gram To dealwith such small number is very diFcult Thus forconvenience relative atomic mass is used


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E%istence of Atoms

Atoms of most of the elements e$ist in theform of molecule or ion, since they aremost reactive 1or e$am!le, hydrogen,o$ygen, chlorine, etc However, atoms of

some elements, which are non2reactive,e$ist in free2state in nature 1or e$am!lehelium, neon, argon, etc

Gsually atoms are e$ist in following two

forms 2) In the form of molecules

' In the form of ions


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/olecule

A molecule is a grou! of two or moreatoms that are chemically bondedtogether, that is, tightly heldtogether by attractive forces


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Atomicity

Mono!atomic::hen molecule is formed by singleatom only, it is called mono2atomic moleculeenerally noble gases form mono2atomicmolecules 1or e$am!le= Helium "He#, eon "e#,

Di!atomic::hen molecule is formed by thecombination of two atoms of it is called diatomicmolecule 1or e$am!le= Hydrogen "H'#, $ygen

"'#, itrogen "'#, Chlorine "Cl'#, etc

Tri!atomic::hen molecule is formed by thecombination of three atoms it is called tri2atomicmolecule 1or e$am!le= molecule of o>one "#


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/olecules of 8lements

The molecules of an element areconstituted by the same ty!e of atoms

eg= J ' "$ygen as# Kdi2atomic9

J ">one# Ktri2atomic9

+J +"hos!horous# Ktetra2atomic9

.7J 7."7ul!hur# K!oly2atomic9


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