Question

Elements X,Y,Z have atomic numbers 6,9 and 12 respectively.

Which one forms anions - negative ions;

Answer 1

• Let us first write the electronic configuration of elements X,Y and Z.
• The electronic configuration of an element describes how electrons are distributed in its atomic orbitals.
• The electrons are filled in the increasing number of shells viz. K,L,M,N,etc.
• Number of electrons in a shell is given by 2n² where n is the number of shells.
• Putting n=1,2,3 and 4, we get the number of electrons 2,8,18,32 that can be filled in each shell respectively.

Element X-

• The atomic number of Element X is 6.
• 2 electrons will fill the first shell i.e., the K shell.
• 4 electrons will fill the second shell i.e., the L shell.
• Hence, its configuration will be 2,4.

Element Y-

• The atomic number of Element Y is 9.
• 2 electrons will fill the first shell i.e., the K shell.
• 7 electrons will fill the second shell i.e., the L shell.
• Hence, its configuration will be 2,7.

Element Z-

• The atomic number of Element Y is 12.
• 2 electrons will fill the first shell i.e., the K shell.
• 8 electrons will fill the second shell i.e., the L shell.
• 2 electrons will enter the third shell i.e., the M shell.
• Hence, its configuration will be 2,8,2.

Identification-

• Elements that have 1,2 or 3 electrons in their outermost shell lose electrons to form positive ions i.e., cation and are metals.
• Elements that have 4,5,6 or 7 electrons in their outermost shell gain electrons to form negative ions i.e., anions, and are non-metals.
• It could gain four electrons forming C^4– anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.
• Here, element Y has 7 electrons in its outermost shell.
• It will gain an electron to get 8 electrons in its outermost shell acquiring a negative charge due to an excess electron than the proton.

Hence, element Y will form an anion-negative ion.