Question

Using the periodic table, predict the charges of the ions of the following elements: (a) Ga, (b) \(\mathrm{Sr},(\mathrm{c}) \mathrm{As}\) (d) \(\mathrm{Br}\) (e) Se.

Short answer

The charges of the ions for the given elements are: (a) Gallium (Ga): Ga³⁺, (b) Strontium (Sr): Sr²⁺, (c) Arsenic (As): As³⁻, (d) Bromine (Br): Br⁻, and (e) Selenium (Se): Se²⁻.

Step-by-step solution

(a) Gallium (Ga)

To predict the charge of Ga ion, we first find its position in the periodic table. Gallium is located in Group 13 (or IIIA) of the periodic table. Elements in this group usually have three valence electrons. In order to reach a stable electron configuration, elements in Group 13 tend to lose three electrons to form ions with a +3 charge. Therefore, the most common ion of gallium is Ga³⁺.

(b) Strontium (Sr)

Strontium is located in Group 2 (or IIA) of the periodic table. Elements in this group have two valence electrons. In order to achieve a stable electron configuration, elements in Group 2 tend to lose two electrons to form ions with a +2 charge. Therefore, the most common ion of strontium is Sr²⁺.

(c) Arsenic (As)

Arsenic is located in Group 15 (or VA) of the periodic table. Elements in this group have five valence electrons. In order to achieve a stable electron configuration, elements in Group 15 tend to gain three electrons to form ions with a -3 charge. Therefore, the most common ion of arsenic is As³⁻.

(d) Bromine (Br)

Bromine is located in Group 17 (or VIIA) of the periodic table. Elements in this group are known as halogens, and they have seven valence electrons. In order to achieve a stable electron configuration, halogens tend to gain one electron to form ions with a -1 charge. Therefore, the most common ion of bromine is Br⁻.

(e) Selenium (Se)

Selenium is located in Group 16 (or VIA) of the periodic table. Elements in this group have six valence electrons. In order to achieve a stable electron configuration, elements in Group 16 tend to gain two electrons to form ions with a -2 charge. Therefore, the most common ion of selenium is Se²⁻.

Key concepts

Ion Charge Prediction

Predicting the charge of an ion from the periodic table is like solving a puzzle. You need to know where the element is located in the table and understand the typical charge tendencies of that group.

Each element's charge is determined by its need to either lose or gain electrons to achieve a stable electron configuration. For example, elements in Group 1 typically form +1 ions by losing one of their extra electrons. Likewise, Group 17 elements, known as halogens, form -1 ions by gaining one electron.

Let's take a closer look at gallium (Ga), strontium (Sr), arsenic (As), bromine (Br), and selenium (Se) to see how their typical ion charges are predicted:

• Gallium: Loses 3 electrons, forming Ga³⁺.
• Strontium: Loses 2 electrons, forming Sr²⁺.
• Arsenic: Gains 3 electrons, forming As³⁻.
• Bromine: Gains 1 electron, forming Br⁻.
• Selenium: Gains 2 electrons, forming Se²⁻.

Each prediction leverages the group's common tendencies, resulting in predictable ion charges.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They play a crucial role in determining how an element will react chemically and the type of ions it will form.

The periodical placement of an element offers vital clues about its valence electrons. Elements in the same group share the same number of valence electrons, which often leads to similar chemical behavior.

For example:

• Elements in Group 1 have one valence electron.
• Elements in Group 2 have two valence electrons.
• Elements in Group 13 have three valence electrons, like gallium.
• Elements in Group 15 have five valence electrons, like arsenic.
• Elements in Group 17, the halogens, have seven valence electrons, like bromine.
• Elements in Group 16 have six valence electrons, like selenium.

Understanding both the number and arrangement of valence electrons provides insights into the reactivity and potential ion formation of each element.

Stable Electron Configuration

The concept of a stable electron configuration is essential to understanding why elements form ions. Atoms are most stable when their outer electron shell is full. They will either lose, gain, or share electrons to reach this stable state.

For most elements, having eight electrons in their outer shell is ideal, referred to as the "octet rule."

This rule guides many chemical reactions and bonding processes:

• Elements like those in Group 1 achieve stability by losing one electron, filling the previous shell.
• Group 15 elements like arsenic achieve a full shell by gaining three electrons, completing their valence shell to eight.
• Halogens need to gain only one electron to complete their outer shell.

Elements that achieve a stable electron configuration become more energetically favorable and less reactive.

Group Properties

The periodic table is organized in a way that groups elements with similar properties together. This organization helps predict the chemical behavior of elements and their ions.

Each group, or column, in the periodic table shares distinct properties due to having the same number of valence electrons:

• Group 1 (alkali metals) are highly reactive and form +1 ions.
• Group 2 (alkaline earth metals) form +2 ions by losing two electrons.
• Group 13 elements are typically trivalent, like gallium forming +3 ions.
• Group 15 elements, such as arsenic, commonly form -3 ions.
• Group 17, the halogens, are known for forming -1 ions.
• Group 16 elements, like selenium, tend to gain two electrons to form -2 ions.

Understanding the properties of these groups is key to predicting element behavior, reactivity, and ion formation across the periodic table.