Question

How do the isotopes hydrogen-1 and hydrogen-2 differ?

Answer 1

Hydrogen-2 has one neutron; hydrogen-1 has none

Answer 2

Answer: They differ by the number of neutrons

Explanation:

Isotopes are defined as the chemical species which have same number of protons but differ in the number of neutrons.

The general isotopic representation is $_{Z}^A\textrm{X}$

where,

Z = Atomic number of the atom

A = Mass number of the atom

X = Symbol of the atom

Atomic number is defined as the number of protons or electrons that are present in a neutral atom.

Atomic number = number of protons = number of electrons

Mass number is defined as the sum of number of protons and number of neutrons present in an atom.

Mass number = Number of neutrons + Number of protons.

We are given two isotopes:

$_1^1\textrm{H}\text{ and }_1^2\textrm{H}$

• For $_1^1\textrm{H}$ isotope:

Number of protons = 1

Mass number = 1

Number of neutrons = 1 - 1 = 0

• For $_1^2\textrm{H}$ isotope:

Number of protons = 1

Mass number = 2

Number of neutrons = 2 - 1 = 1

Hence, they differ by the number of neutrons