An element, X is represented as 4020X.

 An element, X is represented as 4020X. 

(i) How many electrons and how many neutrons are present in the atom of X?

(ii) Write the electronic configuration of the atom.

(b) Chlorine, whose atomic number is 17, reacts with the elements. 4020X to form a compound.

(i) What type of bond is formed between X and chlorine?

(ii) Explain how the bond between X and chlorine is formed.

(iii) Write the formula of the compound formed and state three properties of the compound.

(c) Chlorine has two isotopes of mass numbers 35 and 37 respectively. Suggest the possible relative molar masses of a chlorine molecule.

(d) Calculate the mass of one atom of carbon, given that one mass of carbon weighs 12.0g. (L=6.02*10^23)

SOLUTIONS:

(a)(i) 20 electrons and 20 neutrons.

(ii) 1S2 2S2 2P6 3S2 3P6 4S2.

(b)(i) Ionic bond

(ii) Element X has valency electrons of 2 which is lost completely to two chlorine atoms with valency electrons of 7. When this takes place each of the atoms involved in the bond completes its outermost octet electronic structure as the noble gases.

(iii) XCl2. The properties of the compound are:

(1) It is soluble in water.

(2) It is not decomposed by heat.

(3) It conducts electricity i.e. (an electrolyte).

(4) It has high boiling point.

(5) It reacts with hot concentrated H2SO4 acid to produce HCl.

CaCl2+H2SO4 --> CaSO4+2HCl.

(c) The relative molar mass of chlorine is 35.5

(d) No moles= No of atoms/6.02*10^23

Solving for No of atoms

No of atoms= No of moles*6.02*10^23

                =Mass/molar mass*6.02*10^23

                =12/12*6.02*10^23

                =6.02*10^23 atoms

QUESTION SOURCE: WAEC 1988 THEORY QUESTION 14(a)(i)(ii)(b)(i)(ii)(iii)(c)(d)