Chapter 3, Problem 38P

Interpretation Introduction

(a)

Interpretation:

The group number of the given electron-dot symbol should be stated.

Concept Introduction:

In an electron-dot symbol, dots represent the valence electrons around the elemental symbol.

When understanding an electron-dot symbol of an element, below facts should be considered;

• Each dot represents 1 electron.
• The dots are placed on the four sides of the elemental symbol.
• For 1 to 4 valence electrons, single dots are used.
• For > 4 electrons, the dots are paired.

Valence electrons are the most loosely bound electrons of an element. They are in the outermost shell, or the valence shell. Chemical properties of an element and its place in the periodic table depend on the number of valence electrons of that element: For main group elements, the group number is also the number of valence electrons of the element.

Interpretation Introduction

(b)

Interpretation:

The charge of the ion formed by the given element should be determined.

Concept Introduction:

An atom of a main group element loses or gains electrons forming ions to obtain the electronic configuration of the noble gas closest to it in the periodic table.

Cations are formed by losing electrons; thus they have fewer electrons than protons and are positively charged.

Anions are formed by gaining electrons;thus they have more electrons than protons and are negatively charged.

E.g. Oxygen (O) atom has 8 electrons ( $1s^{2}2s^{2}2p^4$ ) and the valence shell ( $2s^{2}2p^4$ ) is not fully filled. In order to achieve the stable electronic configuration of the nearest noble gas (Octet rule), O must gain two electrons and become O^2-anion. Now, the electronic configuration of O^2- anion is similar to Ne, which is $1s^{2}2s^{2}2p^6$.

Interpretation Introduction

(c)

Interpretation:

The formula of an ionic compound formed byZ and sodium should be determined.

Concept Introduction:

Ionic compounds are composed of cations and anions, which are tightly attracted to each other.

The sum of the charges in an ionic compound must be zero.

The formula for an ionic compound shows the ratio of ions that combine to give zero charge.

When cations and anions have different charges, the number of cations and anions differ so that the overall charge of the ionic compound be zero.

As an example, see the formulae of NaCl and MgCl₂.

  $\begin{array}{l}{\text{Na}}^{\text{+}}{\text{ + Cl}}^{-}\to \text{ NaCl}\\ {\text{Mg}}^{\text{2+}}{\text{ + Cl}}^{-}{\text{+ Cl}}^{-}\to {\text{ MgCl}}_2\end{array}$

Interpretation Introduction

(d)

Interpretation:

The formula of an ionic compound formed byZ and magnesium should be determined.

Concept Introduction:

Ionic compounds are composed of cations and anions, which are tightly attracted to each other.

The sum of the charges in an ionic compound must always be zero.

The formula for an ionic compound shows the ratio of ions that combine to give zero charge.

When cations and anions have different charges, the number of cations and anions differ so that the overall charge of the ionic compound be zero.

As an example, see the formulae of NaCl and MgCl₂.

  $\begin{array}{l}{\text{Na}}^{\text{+}}{\text{ + Cl}}^{-}\to \text{ NaCl}\\ {\text{Mg}}^{\text{2+}}{\text{ + Cl}}^{-}{\text{+ Cl}}^{-}\to {\text{ MgCl}}_2\end{array}$