Question

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

1. What is meant by “atomic number of an element”? What do you understand by an ‘atom’
2. Write down the electronic configuration of the chlorine atom.
3. State the number of protons, electrons, and neutrons in the following isotopes: ³⁵Cl₁₇, ³⁷Cl₁₇
4. Explain why the two atoms in (iii) above have the same chemical reactions.
5. If molten magnesium chloride is electrolyzed suggest a suitable electrode [anode].

Answer 1

1. Atomic number is the number of protons in an atom.
   Atom: The basic unit of matter is the smallest particle of an element that can take part in a chemical reaction.
2. The number of electrons in a chlorine atom is 17 [2, 8, 7], and their distribution in various shells is K = 2, L = 8, and M = 7.
3. Two isotopes of chlorine are
   \[\ce{^37_17Cl}\] number of protons = 17 and
   number neutrons = 35 – 17 = 18
   Number of electrons = 17
   \[\ce{^37_17Cl}\] number of protons = 17
   electrons = 17
   neutrons = 20 i.e., (37 – 17)
4. Two isotopes of chlorine have the same chemical reactions as their atomic number, i.e., the number of electrons, i.e., electronic configuration, is the same (17).
5. When molten magnesium chloride is electrolysed, the suitable anode used is carbon.