Question

Write the ionic charge for each of the following ions as predicted from the group number in the periodic table: (a) \(\mathrm{Cs}\) ion (b) Ga ion (c) Oion (d) I ion

Short answer

(a) +1, (b) +3, (c) -2, (d) -1.

Step-by-step solution

Understanding Group Numbers and Ionic Charge

To predict the ionic charge of an element, we need to determine its group number on the periodic table. Group numbers are typically used to identify the number of valence electrons an atom has, which in turn affects whether the atom will lose or gain electrons to become an ion. For main-group elements, the ionic charge is often determined by how many electrons are needed to achieve a full outer shell, typically resembling the nearest noble gas configuration.

Determine the Ionic Charge of Cs

Cesium (Cs) is located in group 1 of the periodic table. Elements in group 1 typically have one valence electron, which they tend to lose in order to achieve the stable electron configuration of the closest noble gas, resulting in an ion with a +1 charge.

Determine the Ionic Charge of Ga

Gallium (Ga) is located in group 13 of the periodic table. Elements in group 13 typically lose three valence electrons to achieve a stable electron configuration, resembling the nearest noble gas. Therefore, the gallium ion typically carries a +3 charge.

Determine the Ionic Charge of O

Oxygen (O) is located in group 16 of the periodic table. Elements in group 16 typically gain two electrons to complete their valence shell, achieving a stable electron configuration like the nearest noble gas. Therefore, the oxygen ion, also called an oxide ion, usually has a -2 charge.

Determine the Ionic Charge of I

Iodine (I) is located in group 17 of the periodic table. Elements in this group typically gain one electron to complete their valence shell, mimicking the electron configuration of the nearest noble gas. As a result, the iodine ion usually has a -1 charge.

Key concepts

Periodic Table Groups

The periodic table is arranged in vertical columns called groups. Each group contains elements that exhibit similar chemical properties. This similarity arises because the atoms of these elements have the same number of valence electrons in their outermost shell. For example, group 1 elements, also known as alkali metals, all have one valence electron. This makes them prone to losing one electron to form a +1 ionic charge. As we move to group 2, the alkaline earth metals typically have two valence electrons. This results in them commonly forming ions with a +2 charge. The group numbers can be helpful predictors of the charges of ions that elements typically form.

• Group 13 elements generally form ions with a +3 charge because they lose three valence electrons.
• Group 16 elements, like oxygen, usually gain two electrons to form -2 charged ions.
• Group 17, known as the halogens, typically gain one electron resulting in a -1 charge.

Understanding these group trends is vital in predicting the ionic charges of elements based on their position in the periodic table.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They play a key role because they determine how an element will react chemically with other substances. The drive to achieve a stable electron configuration generally guides their participation in chemical reactions. Elements within the same group in the periodic table have an identical number of valence electrons. This number dictates their typical ionic charges. For example:

• Group 1 elements like cesium have one valence electron. They tend to lose it easily to form a +1 ion.
• In Group 13, elements including gallium have three valence electrons, hence often form +3 ions by losing these electrons.
• Group 16 elements such as oxygen generally have six valence electrons. They gain two to complete their shell, forming a -2 ion.

Valence electrons are so crucial because the closer an element's total valence electrons are to a full set, the more predictable the ionic charge becomes.

Noble Gas Configuration

Noble gases, found in Group 18 of the periodic table, have a full set of valence electrons, which makes them extremely stable. Other elements strive to attain a similar electron configuration, which often directs their chemical behavior. For instance, elements will either lose or gain electrons to mimic the electron arrangement of the nearest noble gas. By doing this, they achieve what is called the 'noble gas configuration'.

• Alkali metals, such as cesium from Group 1, will lose one valence electron to match the configuration of the previous noble gas.
• Elements like gallium from Group 13 lose three electrons to resemble the electron setup of a noble gas.
• Halogens, such as iodine, will gain one electron to complete their valence shell, echoing the configuration of a noble gas.

Achieving the noble gas configuration allows an element to attain a more stable, energy-efficient form, often affecting the charges of the ions they form. Therefore, understanding noble gas configurations is fundamental for predicting ionic charges and reactions.