Chapter U1.13, Problem 6E

Interpretation Introduction

(a)

Interpretation:

Average atomic mass of phosphorus should be written.

Concept introduction:

Mass of an atom is concentrated in the nucleus of an atom. The atomic mass is calculated by considering number of protons and neutrons. Each isotope of an element has a different mass. So the average mass of all isotopes of the element is calculated to give average atomic mass.

Answer to Problem 6E

According to the periodic table, phosphorus has an average atomic mass of 30.97

Explanation of Solution

Average atomic mass is calculated by taking the average of the masses of the isotopes of an element. This is often expressed as a decimal number on the periodic table. Masses and abundance of isotopes are used in calculation. Phosphorus occurs in many isotopic forms. The average atomic mass of phosphorus is calculated by considering the relative abundance of each isotope in nature. This value comes out to be 30.97.

(b)

Interpretation Introduction

Interpretation:

Atomic number of phosphorus should 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. All isotopes of an element have same atomic number.

Answer to Problem 6E

According to the periodic table, phosphorus has an atomic number of 15.

Explanation of Solution

Atomic number is the number of protons in the nucleus of an atom. Elements differ from each other in the number of protons they contain. Isotopes of an element are similar in the number of protons. Hence, all isotopes of an element have same atomic number. Phosphorus has 15 protons so atomic number of phosphorus is 15.

(c)

Interpretation Introduction

Interpretation:

The isotope of phosphorus that occurs in abundance is to be predicted.

Concept introduction:

The percentage of each isotope of an element that occurs in nature is called natural abundance of the isotope. The average atomic mass is the average of the masses of all the isotopes of an element in a large sample of the element.

Answer to Problem 6E

Phosphorus - 31 will be found in greatest abundance in nature.

Explanation of Solution

From the periodic table, one can see that atomic number of phosphorus is 15

Number of protons = number of electrons = atomic number = 15

Phosphorus has average atomic mass of 30.97

Mass number = average atomic mass rounded off to nearest whole number = 31

Therefore, most of the phosphorus atoms found in nature will have a mass of 31 amu and mass number 31. So this isotope of phosphorus can be written as:

${}_{15}^{31}P$

Phosphorus - 31 will be most abundantly found isotope of phosphorus in nature.