How many protons, electrons and neutrons are there in the following atoms? N 7 14 , C 6 12 , C 6 14 , O 8 14 , O 8 16 , K 19 40 , Ar 18 40

The relationship between atomic number Z , mass number A and the number of neutrons in an atom is: Mass number A = No. of protons p or atomic number Z + No. of neutrons n Hence, A = Z + n So, n = A - Z Z = p = e (the number of electrons), for a neutral atom. By using the above relationship, the number of protons, electrons and neutrons in the given atoms can be calculated as follows: Symbols protons p electrons e neutrons n = A - Z N 7 14 7 7 7 C 6 12 6 6 6 C 6 14 6 6 8 O 8 14 8 8 6 O 8 16 8 8 8 K 19 40 19 19 21 Ar 18 40 18 18 22

Which of these are isotopes? N 7 14 , C 6 12 , C 6 14 , O 8 14 , O 8 16 , K 19 40 , Ar 18 40

The atoms of the same element having the same atomic number, but different mass numbers are called isotopes of the element. They have the same number of protons but different numbers of neutrons. Among the given elements there are two pairs of isotopes. They are: (i) C 6 12 , C 6 14 (Here, C atoms have the same atomic number 6 , but different mass numbers 12 and 14 ) (ii) O 8 14 , O 8 16 (Here, O atoms have the same atomic number 8 , but different mass numbers 14 and 16 ).

Which of these are isobars? N 7 14 , C 6 12 , C 6 14 , O 8 14 , O 8 16 , K 19 40 , Ar 18 40

Atoms of different elements having different atomic numbers but with the same mass number are called isobars. They have the same number of nucleons but different numbers of protons. Among the given elements isobars are: (i) N 7 14 , C 6 14 , O 8 14 (Here, the atoms N , C , O have the same mass number 14 , but different atomic numbers) (ii) K 19 40 , Ar 18 40 ( Here, the atoms K and Ar have same mass number 40 , but different atomic numbers).