[2 Mark Question Answer]

Question 12 Marks

Name the particles which revolves around the nucleus of an atom and state its mass and charge.

Answer

The electrons revolve around the nucleus of an atom in fixed paths which are called orbits. The mass of an electron is 1/1837 times the mass of one proton. Therefore, the mass of an electron is considered negligible. The charge on an electron is taken as a unit negative charge. Mass of electron is $9.1093837015 \times 10-31\text {kg}$
Hence, the particle which revolves around the nucleus of an atom is called an electron.

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Question 22 Marks

Name two particles found inside the nucleus of an atom and state their mass and charge. What is the collective name of these particles?

Answer

Nucleus: The small region situated in the center of an atom is called the nucleus. The two particles found inside the nucleus of an atom are the following:
Protons: Proton is a positively charged particle present inside the nucleus of an atom. Its charge is taken as a unit positive charge and its mass is 1.67262192 $\times$ 10^-27 kilograms.
Neutrons: A neutron is a neutral particle present inside the nucleus of an atom. It has no electrical charge and its mass is almost equal to the mass of the proton. 1.67493 $\times$ 10^-27 kilograms.
Protons and neutrons are the two particles found inside the nucleus. They are collectively called nucleons.

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Question 32 Marks

Give three examples of elements having variable valency.

Answer

Valency: The combining capacity of an atom is known as its valency. The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.
Variable valency:
$\rightarrow$ Some metals can lose different numbers of electrons to form ions with different charges, this is called variable valency.
$\rightarrow$ In some cases, the metals can lose electrons from the inner shell of the atom.
$\rightarrow$ If an element exhibit two different electropositive valences, then for lower valency, the suffix -onus is used.
$\rightarrow$ For higher valency, the suffix - ic is used at the end of the metal name.
$\rightarrow$ Copper can show two valency Cu+2andCu+1.
$\rightarrow$ Cu+2 is called Cupric ion and Cu+1 is called Cuprous ion.
$\rightarrow$ Iron(Fe) can also show +2and+3 oxidation states.
$\rightarrow$ Mercury (Hg) can show +1 and +2 oxidation states.
Hence the transition elements have variable valences. For example, Copper, Iron, and Mercury.

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Question 42 Marks

What is variable valency?

Answer

Normally, the metals donate electrons from their valence shell, so as to form positively charged ions. However, some metals lose electrons from the shell next to the valence shell. In such a situation the element exhibits more than one electropositive valency Such elements are said to have variable valency.

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