CHEMISTRY [2 Mark Question Answer]

1. Symbols increase scientific communication across the world.
2. Symbols help to make equations and data shorter and concise.
3. Symbols are helpful for Scientists as it would take time and paper to do their job.
They had to write out the full name of every element instead of its symbol

Importance of symbols and Formulae:
Symbols and formulae of substance gives a lot of information like.
1. Types of elements present in the compound. E.g. (H20 is made of two elements hydrogen and oxygen).
2. Number of each kind of atoms in one molecule. E.g. (water has 2 atoms of hydrogen combined with 1 atom of oxygen.)
3. Mass of one molecule of the compound. E.g. [H2O has mass (1 × 2) + 16 = 18 g].

Atom: An atom is the smallest indivisible unit of an element which exhibits all the properties of that element and may or may not have an independent existence. An atom is the smallest indivisible unit of an element which exhibits all the properties of that element and may or may not have an independent existence.

Four Important Characteristics of Compounds are as follows:
1. When the compound is formed energy like heat, light, or electricity is either needed or produced.
2. A compound has properties entirely different from the properties of its constituents.
3. Change in weight takes place.
4. It cannot be separated into its constituents by simple physical means.

Sodium is a metal that is stored in kerosene oil as it reacts very fast with air and water. Chlorine is a reactive greenish-yellow gas which is poisonous. When these two elements combine chemically they form common salt sodium chloride which is a non-poisonous colourless solid substance that we use in our food to add taste and to obtain some nutrition.

Metals:
1. Metals are ductile i.e. can be drawn into wires.
2. Metals are malleable i.e. can be beaten to form sheets.
3. They are sonorous.

Non-metals:
1. Non-metals are mostly soft solids that cannot be drawn into wires.
2. They are mostly gases and are not malleable.
3. They do not produce sound when struck.

The elements which form water are Hydrogen and oxygen.
Justification: Water has entirely different properties (i.e. is a liquid, extinguishes fire) from the elements it is made up of i.e. Hydrogen a gas catches fire oxygen a gas supporter of combustion.

1. Energy is needed to form water on combining O2 with H2.
2. We can not separate the constituents of water by simple physical means.

Compounds: Compounds are pure substances composed of two or more elements in definite proportion by mass and has a definite set of properties. The compound is made up of only one kind of molecules

Elements: An element is defined as a pure substance made up of only one kind of atoms that cannot be converted into anything simpler than itself by any physical or chemical process.

Pure substances: “A substance of a definite composition which has consistent properties throughout, is called a pure substance” Types of pure substances: Pure substances are of two types
(i) Elements
(ii) Compounds

Symbols: The short form or abbreviated name of the element (or radicals) The reason for representing the following element by their symbol is as follow:

Copper by ‘Cu’ – Deriving symbols from their Latin names

Symbols: The short form or abbreviated name of the element (or radicals) The reason for representing the following element by their symbol is as follow:

Helium by He – First two letters of the name of Noble gases.

Symbols: The short form or abbreviated name of the element (or radicals). The reason for representing the following element by its symbol is as follow:

Hydrogen by ‘H’ – First letter of the name of the element

The arrow indicates the direction of the reaction

(a) K — Valency-1 (C)
(b) Zn — Valency-2 (B)
(c) Al — Valency-3 (A)
(d) Na — Valency-1 (C)
(e) Ca — Valency-2 (B)

Sodium Chloride

Elements	Symbols
(Sodium)	Na
[Chlorine(Chloride)]	Cl

No. of atoms of this element present

1 atom of - Na, 1 atom of - Cl

For arranging all the elements in a systematic and simple manner. The arrangement of elements was done in the form of a table called Periodic Table in which elements are arranged in increasing order of their atomic numbers. Elements in the Periodic Table are arranged in Horizontal rows called Periods and vertical columns called groups. Metallic elements are placed on the left non-metallic on the right and noble gases on the extreme right of the Periodic table.