Chlorine is an element of atomic number 17. It is a mixture of two isotopes having mass number of 35 and 37.

(i) What is meant by 'atomic number of an element' ? What do you understand by an 'atom'.

(ii) Write down the electronic configuration of the chlorine atom.

(iii) State the number of protons, electrons and neutrons in the following isotopes: $^{35}\text{Cl}${17}, $^{37}\text{Cl}{17}$

(iv) Explain why the two atoms in (iii) above have the same chemical reactions.

(v) If molten magnesium chloride is electrolyzed suggest a suitable electrode [anode].

(i) Atomic number [Z] of an element is the number of :

• Protons - in the nucleus of an atom
• Electrons - in the complete atom
• Positive charges - in the nucleus of it's atom

An atom is the smallest particle of an element which can take part in a chemical reaction and is considered the basic unit of matter. e.g. O,Cl are atoms.

(ii) Atomic number of Chlorine is 17 so it has 17 electrons. Hence, its electronic configuration = 2, 8, 7

(iii) $^{35}\text{Cl}_{17}$ —

• No. of protons = 17
• No. of electrons = 17
• No. of neutrons = A - Z = 35 - 17 = 18

$^{37}\text{Cl}_{17}$ —

• No. of protons = 17
• No. of electrons = 17
• No. of neutrons = A - Z = 37 - 17 = 20

(iv) As the two atoms in (iii) above are isotopes and hence have same electronic configuration. Therefore, they have similar chemical properties because chemical properties are dependent on electronic configuration of an element.

(v) Carbon anode is used when molten magnesium chloride is electrolyzed.