Q59 of 181 Page 306

Consider the following elements:
₂₀Ca, ₈O, ₁₈Ar, ₁₆S, ₄Be, ₂He

Which of the above elements would you expect to be:

(i) Very stable?

(ii) In group 2 of the periodic table?

(iii) In group 16 of the periodic table?

(i) Argon and Hellium are the most stable among these all.

(ii) Calcium and Beryllium have 2 valence electrons so they belong to 2^nd group.

(iii) Oxygen and Sulphar have 6 valence electrons so the belong to 16 group.

The atomic numbers of the three elements X, Y and Z are 2, 6 and 10 respectively.

(i) Which two elements belong to the same group?

(ii) Which two elements belongs to the same period?

Give reasons for your choice.

An atom has the electron structure of 2, 7.

(a) What is the atomic number of this atoms?

(b) To which of the following would it be chemically similar?

₇N, ₁₅P, ₁₇Cl, ₁₈Ar

In each of the following pairs, choose the atom having the bigger size:

(a) Mg (At. No. 12) or Cl( At. No. 17)

(b) Na (At. N0. 11) or K (At. No. 19)

The atomic numbers of three elements A, B and C are given below:

(i) Which element belongs to group 18?

(ii) Which element belongs to group 15?

(iii) Which element belongs to group 13?

(iv) To which period/periods do these elements belongs?

Consider the following elements:20Ca, 8O, 18Ar, 16S, 4Be, 2HeWhich of the above elements would you expect to be:(i) Very stable?(ii) In group 2 of the periodic table?(iii) In group 16 of the periodic table?