Atoms And Molecules

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compound

Back 1

is composed of two or more elements chemically combined in definite proportions

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law of conservation of mass

Back 2

during chemical changes, the sum of masses of all the reactants remains equal to the mass of products

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law of definite proportions

Back 3

in a compound , the elements are always present in definite proportion of mass

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daltons atomic theory

Back 4

all matter whether element or compound is composed of small particles called atoms and molecules

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atom

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is the smallest particle of an element and retains its identity throughout all physical or chemical changes

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molecule

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is a group of two or more atoms that are chemically bonded together and forms the smallest part if an element or compound

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ion

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is a charged particle and can be positively or negatively charged

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molecules of element

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The molecules of an element are constituted by the same
type of atoms.

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molecules of compound

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Atoms of different elements join together in definite
proportions to form molecules of compounds.(hetero atomic molecules)

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atomicity

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The number of atoms contained in a molecule of a substance (element or
compound) is called its atomicity.

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monoatomic molecules

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Noble gases helium, neon and argon exist as He Ne and Ar
respectively.

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diaatomic molecules

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H2 , O2, N2,Cl2, CO , HCl .

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symbols

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The abbreviation used to represent an element is generally the first letter in
capital of the English name of element.

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polyatomic ion

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Polyatomic Ion : A group of atoms carrying a charge is as polyatomic ion.
eg: NH4
+
- Ammonium Ion ; CO3
2-
- Carbonate ion

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valency

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Valency : The number of electrons which an atom can lose , gain or share to form a bond.
OR
It is the combining capacity of an atom of the element.

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chemical formula

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Chemical Formula: A chemical formula is a short method of representing chemical
elements and compounds.

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mole concept

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The mole (mol) is the amount of a substance that contains as many elementary entities as
there are atoms in exactly 12.00 grams of 12C

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gram molecular mass

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Gram molecular mass is the mass in grams of one mole of a molecular substance.
Ex: The molecular mass of N2 is 28, so the gram molecular mass of N2 is 28 g.

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atomic mass unit

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An atomic mass unit or amu is one twelfth of the mass of an unbound atom of carbon-12. It
is a unit of mass used to express atomic masses and molecular masses.
Also Known As: Unified Atomic Mass Unit (u).

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molecular mass

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A number equal to the sum of the atomic masses of the atoms in a
molecule.