Question

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

Are these elements metals or non-metals?

Answer 1

Identification of metals and non-metals-

• 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 5, 6 or 7 electrons in their outermost shell gain electrons to form negative ions i.e., anions, and are non-metals.
• To know whether these elements are metals or non-metals we need to know the number of valence electrons of these elements.
• 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.

Hence, P, Q, and R are metals.