Question

Three elements P, Q and R have atomic numbers 4,12 and 20 respectively.

Are these elements going to have similar or different chemical properties?

Answer 1

• Chemical properties of an element are determined by the number of valence electrons.
• Valence electrons- The electrons present in the valence shell i.e., the outermost shell of an atom are known as valence electrons.
• Valence electrons take part in the chemical reaction.
• These electrons decide the chemical properties of an atom.
• To know the number of valence electrons in P, Q, and R we first need to write the electronic configuration of these elements.
• 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 P-

• The atomic number of element P is 4.
• 2 electrons will fill the first shell i.e., the K shell.
• 2 electrons will fill the second shell i.e., the L shell.
• Hence, the electronic configuration of element P can be written as 2,2.

Element Q-

• The atomic number of element Q 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, the electronic configuration of element Q can be written as 2,8,2.

Element R-

• The atomic number of element R is 20.
• 2 electrons will fill the first shell i.e., the K shell.
• 8 electrons will fill the second shell i.e., the L shell.
• 8 electrons will enter the third shell i.e., the M shell.
• 2 electrons will enter the fourth shell i.e., the N shell.
• Hence, the electronic configuration of element R can be written as 2,8,8,2.

Here, elements P, Q, and R have 2 valence electrons that are present in the valence shell.

Since the number of valence electrons is the same in elements P, Q, and R, they will exhibit the same chemical properties.