John Dalton -1807

Symbol : A short form of an element.

1814 – Berzelius:

Representation of the elements by the letters of their names. ( either English or Latin)

First letter is always capital and second is small.Berzelius

NONO NAMENAME SYMBOLSYMBOL NONO NAMENAME SYMBOLSYMBOL

11 HydrogenHydrogen HH 88 SilverSilver AgAg

22 MercuryMercury HgHg 99 PotassiumPotassium KK

33 FluorineFluorine FF 1010 IronIron(Ferrum)(Ferrum) FeFe

44 SodiumSodium NaNa 1111 TinTin SnSn

55 PhosphorusPhosphorus PP 1212 MercuryMercury HgHg

66 CopperCopper CuCu 1313 LeadLead PbPb

77 ZincZinc ZnZn 1414 GoldGold AuAu

Valency :Valency :

It is the number of electrons It is the number of electrons gained, lost or shared by an atom gained, lost or shared by an atom during the formation of a chemical during the formation of a chemical compound.compound.

OROR

The number of hydrogen atoms The number of hydrogen atoms which can combine with or which can combine with or displace one atom of element or displace one atom of element or radical so as to form a compound.radical so as to form a compound.

Na = +1

Cl = -1

O = 2 Cl = 1

FORMATION OF IONSFORMATION OF IONS

  Sodium has 1 electron in its outer shell. It will loseits outer electron to complete its octet and acquire stable electronic configuration.

Chlorine has 1 electron in its outer shell. It will gain 1 electron to complete its octet and acquire stable electronic configuration.

FORMATION OF IONSFORMATION OF IONS

  Magnesium has 2 electrons in its outer shell. It will loseits 2 outer electrons to complete its octet and acquire stable electronic configuration.

Oxygen has 6 electrons in its outer shell. It will gain 2 electrons to complete its octet and acquire stable electronic configuration.

METALSMETALS VALENCYVALENCY NON METALSNON METALS VALENCYVALENCY

+ 1+ 1 -1-1

+ 2+ 2 -2-2

+3+3 -3-3

-1e

Al

Na +Na

Mg

Cl

S

N

-2e

-3e

+1e

+2e

+3e

Cl -

S --

N ---

Mg ++

Al+++

Atoms of elements like iron, copper sometimes lose more electrons than are present in its outermost shell ( valence shell) i.e loss from penultimate shell and exhibit more than one valency called variable valency.

Eg. Fe 2+ and Fe 3+ ; Cu 1+ and Cu 2+.

RADICALS:RADICALS:A radical is an atom or group of atoms with valency and charge.

RADICALS

POSITIVE NEGATIVE

UNIVALENT

BIVALENT

TRIVALENT

UNIVALENT

BIVALENT

TRIVALENT

Nitride N 3-

Representation of a molecule of an Representation of a molecule of an element or a compound by symbols is element or a compound by symbols is known as chemical formula.known as chemical formula.

Eg. The chemical formula for:Eg. The chemical formula for:

1] Oxygen is O1] Oxygen is O22

    2] copper sulphate is CuSO2] copper sulphate is CuSO44

3] potassium permanganate is KMnO3] potassium permanganate is KMnO44

WRITING FORMULA OF A COMPOUNDWRITING FORMULA OF A COMPOUND

Step 1 - Write the positive ion on the left side and the negative ion on the right side. Step 2 - Write their valencies. Step 3 – Interchange the valency and shift to lower right sides.Step 4 - Write the completed formulae with those same numbers at the bottom.Step 5 – Reduce to the simplest ratio if possible.

CHEMICALCHEMICAL EQUATIONSEQUATIONS

CHEMICAL EQUATIONS :CHEMICAL EQUATIONS :

Chemical equation is a shorthand for a chemical reaction.Chemical equation is a shorthand for a chemical reaction.

Eg. Eg.

NHNH44OH OH + HCl + HCl NHNH44Cl Cl + + HH22OO

Reactants

[left side]

Products

[right side]

INFORMATION PROVIDED BY EQn.

• Reactants

• Products

• Direction [rev or irrev]

• States of matter

LIMITATIONS OF EQUATION

• The concentration

• The speed of reaction

• Change in colour

• Completion of reaction

• Evolution of sound or light

EXAMPLES OF CHEMICAL EQUATIONS:EXAMPLES OF CHEMICAL EQUATIONS:

One reactant and two or three products.One reactant and two or three products.

2Pb(NO2Pb(NO33))22 2PbO + O 2PbO + O22 + 4NO + 4NO22 Two reactants and one product.Two reactants and one product.

NHNH3 3 + H + H22O NHO NH44OHOH

Two reactants and two products.Two reactants and two products.

Mg + 2HCl MgClMg + 2HCl MgCl22 + H + H22

Two reactants and three or four products.Two reactants and three or four products. KK22CrCr22OO7 7 + 14HCl 2KCl + 2CrCl+ 14HCl 2KCl + 2CrCl33 + 7 + 7 HH22OO + 3Cl + 3Cl22

BALANCED CHEMICAL EQUATIONS:BALANCED CHEMICAL EQUATIONS:

A equation is balanced if…A equation is balanced if…

No of atoms of No of atoms of

each element [ L.H.S.] each element [ R.H.S.] =

Rules for Balancing EquationsRules for Balancing Equations

1. Write the correct formulas for all the reactants and 1. Write the correct formulas for all the reactants and products in the reaction.products in the reaction. 2. Count the number of atoms of each element in the2. Count the number of atoms of each element in the reactants and products. reactants and products. 3. Balance the elements one at a time by using coefficients. 3. Balance the elements one at a time by using coefficients. 4. It is best to begin with an element other than 4. It is best to begin with an element other than hydrogen or oxygen. hydrogen or oxygen. 5. Check each atom to be sure that the equation is5. Check each atom to be sure that the equation is balanced.balanced. 6. Finally, make sure that all the coefficients are in the6. Finally, make sure that all the coefficients are in the lowest possible ratio.lowest possible ratio.

Note! Subscripts should never be changed when trying to Note! Subscripts should never be changed when trying to balance a chemical equation. balance a chemical equation.

Balancing of a chemical equations-An exampleBalancing of a chemical equations-An example

KK22CrCr22OO7 7 + HCl KCl + CrCl+ HCl KCl + CrCl33 + H + H22O + ClO + Cl22

Balance the potassium and Chromium atoms. ( generally metals first)

KK22CrCr22OO7 7 + HCl + HCl 2 2 KCl + KCl + 2 2 CrClCrCl33 + H + H22O + ClO + Cl22

Balance the oxygen atoms.

KK22CrCr22OO7 7 + HCl + HCl 2 2 KCl + KCl + 2 2 CrClCrCl33 + + 77 H H22O + ClO + Cl22

Balance the hydrogen atoms.

KK22CrCr22OO7 7 + + 14 14 HCl HCl 2 2 KCl + KCl + 2 2 CrClCrCl33 + + 77 H H22O + ClO + Cl22

Balance the chlorine atoms.

KK22CrCr22OO7 7 + + 14 14 HCl HCl 2 2 KCl + KCl + 2 2 CrClCrCl33 + + 77 H H22O + O + 3 3 ClCl22

THANK YOU