Page 20 - Chemistry ICSE Class IX

8 ICSE Chemistry – 9

ASSIGNMENT 1

Atomic symbols, Valence electrons, Valency, Radicals

ϭ͘ tŚĂƚ ŝƐ ŵĞĂŶƚ ďLJ ĂƚŽŵŝĐ ƐLJŵďŽů͍
Ϯ͘ tƌŝƚĞ ƚŚĞ ĂƚŽŵŝĐ ƐLJŵďŽůƐ ŽĨ ƚŚĞ ĨŽůůŽǁŝŶŐ ĞůĞŵĞŶƚƐ͗
;ĂͿ /ŽĚŝŶĞ ;ďͿ ^ŝůŝĐŽŶ ;ĐͿ DĂŐŶĞƐŝƵŵ ;ĚͿ 'ŽůĚ
ϯ͘ tŚĂƚ ŝƐ ƚŚĞ ƋƵĂůŝƚĂƟǀĞ ƐŝŐŶŝĮĐĂŶĐĞ ŽĨ ƚŚĞ ĂƚŽŵŝĐ ƐLJŵďŽů͍
ϰ͘ ,Žǁ ŵĂŶLJ ǀĂůĞŶĐĞ ĞůĞĐƚƌŽŶƐ ĂƌĞ ƚŚĞƌĞ ŝŶ ĂŶ ĂƚŽŵ ŽĨ ĐĂƌďŽŶ ;ĂƚŽŵŝĐ ŶƵŵďĞƌ ϲͿ͍
ϱ͘ ;ĂͿ ĞĮŶĞ ǀĂůĞŶĐLJ͘
;ďͿ ĂůĐƵůĂƚĞ ƚŚĞ ǀĂůĞŶĐLJ ŽĨ ĂůƵŵŝŶŝƵŵ ; ůͿ ŝŶ ĂůƵŵŝŶŝƵŵ ŽdžŝĚĞ ; ů O Ϳ͘
Ϯ ϯ
ϲ͘ EĂŵĞ ƚǁŽ ĞůĞŵĞŶƚƐ ƚŚĂƚ ƐŚŽǁ ǀĂƌŝĂďůĞ ǀĂůĞŶĐŝĞƐ͘
ϳ͘ tƌŝƚĞ ƚŚĞ ŶĂŵĞƐ ĂŶĚ ĨŽƌŵƵůĂĞ ŽĨ ƚǁŽ ĞĂĐŚ ŽĨ ƚŚĞ ĂĐŝĚ ĂŶĚ ďĂƐŝĐ ƌĂĚŝĐĂůƐ͘
ϴ͘ DĂƌŬ ƚŚĞ ĐŽƌƌĞĐƚ ĂŶƐǁĞƌ͘ dŚĞ ǀĂůĞŶĐLJ ŽĨ ŶŝƚƌŽŐĞŶ ŝŶ ŶŝƚƌŽŐĞŶ ĚŝŽdžŝĚĞ ;EK Ϳ ŝƐ
Ϯ
;ĂͿ ŽŶĞ ;ďͿ ƚǁŽ ;ĐͿ ƚŚƌĞĞ ;ĚͿ ĨŽƵƌ

Molecule and Molecular Formula

What is a molecule
A molecule is the smallest particle of an element or of a compound which
dŚĞ ĐŽŶĐĞƉƚ ŽĨ ŵŽůĞĐƵůĂƌ ĨŽƌŵƵůĂ can exist independently under ordinary conditions and shows all the
ŝƐ ĂƉƉůŝĐĂďůĞ ƚŽ ŽŶůLJ ŵŽůĞĐƵůĂƌ properties of that substance (element or compound).
ĐŽŵƉŽƵŶĚƐ͕ ŝŶ ǁŚŝĐŚ ĚŝƐĐƌĞƚĞ A molecule may contain atoms of the same or different elements. Each
ŵŽůĞĐƵůĞƐ ĞdžŝƐƚ͘ molecule is described by its formula called molecular formula.
ͻ
/Ŷ ŝŽŶŝĐ ĐŽŵƉŽƵŶĚƐ ĂŶĚ ŝŶ ĞůĞŵĞŶƚƐ What is a molecular formula
ǁŚŝĐŚ ĨŽƌŵ ŐŝĂŶƚ Žƌ ŶĞƚǁŽƌŬ
ŵŽůĞĐƵůĞƐ͕ ƚŚĞ ĐŽŶĐĞƉƚ ŽĨ ĚŝƐĐƌĞƚĞ A molecular formula contains two or more chemically bonded atoms of the
ŵŽůĞĐƵůĞ ĨĂŝůƐ͕ ďĞĐĂƵƐĞ ŶŽ ĚŝƐĐƌĞƚĞ same or different type. Therefore, a molecule can be represented in terms
ŵŽůĞĐƵůĞ ĞdžŝƐƚƐ ŝŶ ƐƵĐŚ ƐƵďƐƚĂŶĐĞƐ͘ of symbols and number of atoms of each element present in it.
&Žƌ ƐƵĐŚ ĐĂƐĞƐ͕ ŝƚ ŝƐ ĂƉƉƌŽƉƌŝĂƚĞ ƚŽ ƵƐĞ Molecular formula may be de ned as follows:
ƚŚĞ ƚĞƌŵ ĐŚĞŵŝĐĂů ĨŽƌŵƵůĂ͘
A shorthand notation of a molecule in terms of symbols and number
of the atoms of various elements present in it is called its molecular
formula.
The molecular formula of a substance may also be de ned as follows:
The symbolic representation of a molecule of any substance
describing the actual number of various atoms present in it, is called its
molecular formula.
For example, the molecular formula of water is H O. Thus, one
2
molecule of water contains two atoms of hydrogen and one atom of oxygen.
The molecular formula of carbon dioxide is CO . Thus, one molecule
2
of CO contains one atom of carbon and two atoms of oxygen.
2
What is meant by the atomicity of a molecule
Molecules are generally classi ed in terms of number of atoms present in
it. For example,
ƒ The molecules of noble gases contain only one atom. So, noble gases
are monatomic, K G , noble gases exist in the atomic form.
ƒ The molecules of gases like hydrogen, oxygen, nitrogen, etc. contain
two atoms. Therefore, the molecules of hydrogen (H ), oxygen (O )
2
2