Chapter 9, Problem 124A

(a)

Interpretation Introduction

Interpretation: To find the number of valence electrons in the given elements.

Concept Introduction: The total number of electrons present in the outermost shell of an atom is called the valence electrons. The chemical properties and reactivity of an element depend greatly on the number and nature of these valence electrons.

Answer to Problem 124A

Lithium atom has only one valence electron.

Explanation of Solution

The electronic configuration of lithium with atomic number 3, is: ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{1}}$ . So, it has only one electron in the outermost shell. Thus, lithium has only one valence electron.

(b)

Interpretation Introduction

Interpretation: To find the number of valence electrons in the given element.

Concept Introduction: The total number of electrons present in the outermost shell of an atom is called the valence electrons. The chemical properties and reactivity of an element depend greatly on the number and nature of these valence electrons.

Answer to Problem 124A

Sulfur belongs to the oxygen family and the number of valence electrons on a sulfur atom is six.

Explanation of Solution

The atomic number of sulfur is 16 and its electronic configuration is: ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^{\text{4}}$ . The outermost shell of the sulfur atom is the N-Shell (3^rd shell) and it contains a total of six electrons, two in the s-sub shell and four in the p-subshell. Thus there are six valence electrons on sulfur atoms.

(c)

Interpretation Introduction

Interpretation: To find the number of valence electrons in the given elements.

Concept Introduction: The total number of electrons present in the outermost shell of an atom is called the valence electrons. The chemical properties and reactivity of an element depend greatly on the number and nature of these valence electrons.

Answer to Problem 124A

The noble gas neon has eight electrons in its valence shell. It has its octet completed.

Explanation of Solution

Neon is a noble gas with atomic number 10 with a filled octet. Its electronic configuration is: ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}$ . Its outermost shell is filled with eight electrons, two electrons in the s-sub shell and six electrons in the p-subshell.

(d)

Interpretation Introduction

Interpretation: To find the number of valence electrons in the given elements.

Concept Introduction: The total number of electrons present in the outermost shell of an atom is called the valence electrons. The chemical properties and reactivity of an element depend greatly on the number and nature of these valence electrons.

Answer to Problem 124A

Calcium is an alkaline earth metal with atomic number 20. It contains two valence electrons.

Explanation of Solution

The electronic configuration of calcium is: ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^{\text{6}}{\text{4s}}^{\text{2}}$ . Its outermost shell is the one with the principal quantum number, $\text{n}\text{=}\text{4}$ . It contains only two electrons. Hence calcium has two valence electrons.

(e)

Interpretation Introduction

Interpretation: To find the number of valence electrons in the given elements.

Concept Introduction: The total number of electrons present in the outermost shell of an atom is called the valence electrons. The chemical properties and reactivity of an element depend greatly on the number and nature of these valence electrons.

Answer to Problem 124A

Bromine belongs to the halogen family and it contains 7 valence electrons.

Explanation of Solution

The atomic number of bromine is 35 and its electronic configuration is: ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^{\text{6}}{\text{4s}}^{\text{2}}{\text{3d}}^{\text{10}}{\text{4p}}^{\text{5}}$ . Its outermost shell (n = 4) contains 7 electrons, two in the s-sub shell and five electrons in the p-subshell. Thus the number of valence electrons in the bromine atom is 7.

(f)

Interpretation Introduction

Interpretation: To find the number of valence electrons in the given elements.

Concept Introduction: The total number of electrons present in the outermost shell of an atom is called the valence electrons. The chemical properties and reactivity of an element depend greatly on the number and nature of these valence electrons.

Answer to Problem 124A

The phosphorus atom has five valence electrons in its outermost shell.

Explanation of Solution

The electronic configuration of phosphorous with atomic number 15 is: ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^3$ . It has two electrons in its 3s- subshell and three electrons in its 3p-subshell.