Chapter U1.13, Problem 5E

Interpretation Introduction

(a)

Interpretation:

Approximate mass of an isotope of iron is to be calculated.

Concept introduction:

An atom consists of subatomic particles like protons, neutrons and electrons. Mass number denotes the sum of number of protons and neutrons in an atom. This also gives the mass of an atom.

Answer to Problem 5E

An isotope of iron with 26 protons and 32 neutrons will have a mass of 58 amu.

Explanation of Solution

It is given that

Number of protons = 26

Number of neutrons = 32

Mass number = number of protons + number of neutrons

= 26 + 32

= 58

Mass of an atom is the approximate mass of nucleus of the atom. Since nucleus contains protons and neutrons, mass of atom is almost same as mass number expressed in atomic mass unit (amu).

Therefore, mass of an isotope of iron is 58 amu.

(b)

Interpretation Introduction

Interpretation:

Symbol for given isotope of iron is to be written.

Concept introduction:

An atom consists of subatomic particles like protons, neutrons and electrons. Atomic number denotes the number of protons or electrons in an atom. Mass number denotes the sum of number of protons and neutrons in an atom. Isotopes of an element can be denoted by a symbol.

Answer to Problem 5E

Symbol for the isotope of iron is as follows:

${}_{26}^{58}\text{Fe}$

Explanation of Solution

• To write the symbol of the isotope, first one write the symbol of element. Here it is iron so symbol is Fe.
• Next write the superscript number. The mass number of each isotope is shown as the superscript number on top. This is a whole number calculated as the sum of number of protons and neutrons in the atom. Here mass number of iron is 58 (26 + 32).
• The subscript number is the atomic number of the element which is the number of protons. Since number of protons is also equal to the number of electrons, it also denotes number of electrons in the atom. Here the subscript will be 26.
• Symbol for the isotope of iron can be written as:

${}_{26}^{58}\text{Fe}$