Chapter 3, Problem 37P

Interpretation Introduction

(a)

Interpretation:

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

Concept Introduction:

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

When drawing or understanding an electron-dot symbol of an element, one should consider below facts;

• 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 more than 4 electrons, the dots are paired.

Valence electrons are the most loosely bound electrons of an element. They are in the outermost shell, which is also called "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 to obtain the electronic configuration of the noble gas closest to it in the periodic table to form ions.

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.

For example, Sodium (Na) atom has 11 electrons ( $1s^{2}2s^{2}2p^{6}3s^1$ ) and the valence shell ( $3s^1$ ) is not fully filled. In order to achieve the stable electronic configuration of the nearest noble gas, Na must lose one electron and become Na⁺ cation. Now, the electronic configuration of Na⁺ cation is similar to Ne, which is $1s^{2}2s^{2}2p^6$.

Interpretation Introduction

(c)

Interpretation:

The formula of an ionic compound formed from Q and fluorine 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.

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

Interpretation Introduction

(d)

Interpretation:

The formula of an ionic compound formed from Q and oxygen 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.

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