Language of chemistry class 7

1.CHEMICAL SYMBOL

• A chemical symbol is a unique, one or two letter abbreviation used to represent the name of a chemical element.
• Chemical symbols provide a concise way to refer to elements, making it easier to write and understand chemical formulae and equations.
• Chemical symbols are the building blocks of chemical formulae, which indicate the composition of molecules and compounds.
• Chemical symbols are universally accepted which helps to facilitate communication and understanding in the field of chemistry.
• Chemical symbols are derived from the name of elements in English, Greek, Latin etc.
• The first letter of the symbol is written in capital and second one is written in small,
• Some elements and their symbols are-
  
  

  S.N.	Elements(English name)	symbols
  1.	Hydrogen	H
  2.	Helium	He
  3.	Lithium	Li
  4.	Berylium	Be
  5.	Boron	B
  6.	Carbon	C
  7.	Nitrogen	N
  8.	Oxygen	O
  9.	Fluorine	F
  10.	Neon	Ne
  11.	Sodium	Na
  12.	Magnesium	Mg
  13.	Aluminium	Al
  14.	Silicon	Si
  15.	Phosphorus	P
  16.	Sulphur	S
  17.	Chlorine	Cl
  18.	Argon	Ar
  19.	Potassium	K
  20.	Calcium	Ca
  21.	Iron	Fe
  22.	Copper	Cu
  23.	Silver	Ag
  24.	Gold	Au
  25.	Zinc	Zn
  26.	Iodine	I
  27.	Bromine	Br
  28.	Manganese	Mn
  29.	Nickel	Ni
  30.	Tin	Sn
  31.	Lead	Pb
  32.	Mercury	Hg




• Elements which symbols have been derived from their latin name:-
  
  

  S.N.	Elements(English name)	Latin name	symbols
  1.	Sodium	Natrium	Na
  2.	Potassium	Kalium	K
  3.	iron	Ferrum	Fe
  4.	Copper	Cuprum	Cu
  5.	Silver	Argentum	Ag
  6.	Tin	Stannum	Sn
  7.	Gold	Aurum	Au
  8.	Lead	Plumbum	Pb
  9.	Mercury	Hydrargyrum	Hg




• Inert (noble) gases and their symbols:-
  
  
  

  S.N.	Inert gases	symbols
  1.	Helium	He
  2.	Neon	Ne
  3.	Argon	Ar
  4.	Krypton	Kr
  5.	Xenon	Xe
  6.	Redon	Rn



• What does a chemical symbol represent?:-
A chemical symbol represents -
(i) a specific chemical element :- For example, H represents hydrogen element, O reprsents oxygen element, Na represents sodium element.
(ii)individual atom of an element in chemical formula and chemical equations:-
For example - Chemical formula of water is H₂O. Here, H represents one atom of hydrogen, O represents one atom of oxygen.

2.ATOMS, MOLECULES AND IONS

• ATOM:- It is the basic building block of matter, the smallest unit of an element that retains the chemical properties of that element.Except inert gases ,generally, an atom does not exist in free state in nature.
• MOLECULE:- A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds.A molecule can exist in free state in nature.
• ION:- A chemical species(atom or molecule) that holds a positive or negative charge of some magnitude is called an ion.Two types of ions are-
  (i)Cation :- It is with positive charge.Example - Na⁺ (sodium ion), Mg²⁺ (Magnesium ion), Al³⁺ Aluminium ion)
  (ii)Anion :- It is with negative charge.Example - Cl^- (Chloride ion), O^2- (oxide ion), N^3- (Nitride ion)
  

3.VALENCY OF AN ELEMENT

• The combining capacity of an element with other elements to form a molecule is known as its valency.
• In the case of an ion, the charge present on it, is equal to its valency.
• The chemical species of valencies 1,2,3,4 are called monovalent,divalent,trivalent and tetravalent respectively.
• Valencies of some chemical species :-
  

  S.No.	Monovalent	Name
  1.	H+	Hydrogen
  2.	Na+	Sodium
  3.	K+	Potassium
  4.	Ag+	Silver
  5.	NH4+	Ammonium
  6.	H-	Hydride
  7.	Cl-	Chloride
  8.	F-	Fluoride
  9.	Br-	Bromide
  10.	I-	Iodide
  11.	NO3-	Nitrate
  12.	NO2-	Nitrite
  13.	CH3COO-	Acetate
  14.	OH-	Hydroxide
  15.	HCO3-	Hydrogencarbonate, Bicarbonate
  16.	HSO4-	Hydrogencsulphate, Bisulphate
  17.	HSO3-	Hydrogensulphite, Bisulphite

  
  

  S.No.	Divalent	Name
  1.	Mg2+	Magnesium
  2.	Ca2+	Calcium
  3.	Zn2+	Zinc
  4.	Fe2+	Ferrous
  5.	CO32-	Carbonate
  6.	SO42-	Sulphate
  7.	SO32-	Sulphite
  8.	O2-	Oxide

4.CHEMICAL EQUATIONS

1. Chemical Equation :-The equation in which a chemical change is represented by using symbols and chemical formulas of substances,is called a chemical equation.
2. Reactants :-The substances that react among themselves are called reactants.
3. Products:-The substances that are formed after a chemical reaction, are called products.
4. Balanced chemical equation :-The chemical equation in which the number of atoms of each element on the reactant side is the same as that on the product side , is called a balanced chemical equation.

Examples :-
(i) 2C + O₂ → 2CO
Reactants - Carbon , Oxygen
Product - CO ,Carbon monoxide
(ii) H₂ + Cl₂ → 2HCl
Reactants -
Product -
(iii) 2H₂ + O₂ → 2H₂O
Reactants -
Product -
(iv) 2Mg + O₂ → 2MgO
Reactants -
Product -
(v) C + O₂ → CO₂
Reactants -
Product -

Q. Balance the following chemical equations.
(i) H₂ + Br₂ → HBr
(ii) H₂ + I₂ → HI
(iii) Ca + O₂ → CaO
(iv) C + H₂ → CH₄
(v) N₂ + H₂ → NH₃
Q.Complete the following :-

Q. Choose the correct option.

Q. Match the column A and column B.

Q. Write the formula of each of the following compounds.

Q. True or false .