Question

The electronic configuration of an element T is 2,8, 7.

(a) What is the group number of T?

(b) What is the period number of T?

(c) How many valence electrons are there in an atom of T?

(d) What is the valency of T?

(e) Is it a metal or nonmetal?

Answer 1

(a)

• Electronic configuration of any atom is the arrangement of electrons in various shells of that atom. First shell can accommodate a maximum of two electrons, the second shell can accommodate a maximum of eight electrons and the third shell can accommodate a maximum of eighteen electrons.
• In order to calculate the number of electrons in any element, add the electrons present in various shells of that atom. Add the electrons present in the first, second, and third shell of element T to calculate the number of electrons in T.

$\begin{array}{rcl}\mathrm{Number}\mathrm{of}\mathrm{electrons}& =& 2+8+7\\ & =& 17\end{array}$

• In the case of a neutral atom, the atomic number is defined as the number or count of protons or electrons present in that atom.
• Therefore, the atomic number of the element T is 17.
• According to the periodic table, the element with atomic number 17 is Chlorine (Cl). Chlorine (Cl) lies in Group 17 of the periodic table.

(b)

• The period number of an element can be determined by the number of shells filled. The electronic configuration of chlorine is 2, 8, 7.
• According to the electronic configuration, there are three filled shells. Hence, Chlorine (Cl) lies in the third Period of the periodic table.

(c)

• Valence electrons of any element are defined as the number of electrons present in the outermost shell of that element.
• In the case of Group 13 to 18, the formula to calculate the number of valence electrons is:

$\mathrm{Number}\mathrm{of}\mathrm{valence}\mathrm{electrons}=\mathrm{Group}\mathrm{number}-10$

Substitute 17 for Group number to calculate the number of valence electrons in atom T.

$\begin{array}{rcl}\mathrm{Number}\mathrm{of}\mathrm{valence}\mathrm{electrons}& =& 17-10\\ & =& 7\end{array}$

(d)

• Valency of any element is the tendency of any element to accept or lose electrons to form a molecule with other elements.
• Valency of elements with valence electrons 5, 6, 7 can be calculated by subtracting valence electrons from 8.
• Valency of T is calculated as:

$\begin{array}{rcl}\mathrm{Valency}\mathrm{of}\mathrm{T}& =& 8-7\\ & =& 1\end{array}$

(e)

• In a period, the metallic character decreases from going left to right due to the increase in the nuclear charge.
• Due to the increase in the nuclear charge, the valence electrons are pulled in more strongly by the nucleus and it becomes more difficult for the atoms to lose electrons.
• Since Chlorine (Cl) lies on the right side of the periodic table, it is classified as non-metal.