Question

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

Short answer

The predicted charges for the ions of the given elements are: (a) \(Ga^{3+}\) (b) \(Sr^{2+}\) (c) \(As^{3-}\) (d) \(Br^{-}\) (e) \(Se^{2-}\)

Step-by-step solution

Locate the elements in the Periodic Table

For each element, find its position in the Periodic Table. The group number indicates the number of valence electrons of the element. (a) Ga (Gallium) is in Group 13 (b) Sr (Strontium) is in Group 2 (c) As (Arsenic) is in Group 15 (d) Br (Bromine) is in Group 17 (e) Se (Selenium) is in Group 16 Step 2: Predict the charge of the ions

Determine the charge of the ions

The tendency of an element to lose or gain electrons and form ions depends on its group and valence electrons. Elements from Groups 1 to 14 tend to lose electrons, while elements from Groups 15 to 18 tend to gain electrons. (a) Ga (Group 13; 3 valence electrons) \(\Rightarrow\) Ga will lose 3 electrons to achieve a stable electron configuration, so the charge will be \(+3\). (b) Sr (Group 2; 2 valence electrons) \(\Rightarrow\) Sr will lose 2 electrons to achieve a stable electron configuration, so the charge will be \(+2\). (c) As (Group 15; 5 valence electrons) \(\Rightarrow\) As will gain 3 electrons to achieve a stable electron configuration, so the charge will be \(-3\). (d) Br (Group 17; 7 valence electrons) \(\Rightarrow\) Br will gain 1 electron to achieve a stable electron configuration, so the charge will be \(-1\). (e) Se (Group 16; 6 valence electrons) \(\Rightarrow\) Se will gain 2 electrons to achieve a stable electron configuration, so the charge will be \(-2\). So, the predicted charges for the ions of the given elements are: (a) \(Ga^{3+}\) (b) \(Sr^{2+}\) (c) \(As^{3-}\) (d) \(Br^{-}\) (e) \(Se^{2-}\)

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom. They play a key role in chemical bonding and reactions. These electrons are furthest from the nucleus, meaning they can be lost, gained, or shared in interactions with other atoms.
By knowing the number of valence electrons an element has, we can predict its reactivity and the kind of ions it will form.
For example, elements in Group 1 of the periodic table have 1 valence electron and tend to lose it, forming a +1 charge. On the other hand, elements in Group 17 have 7 valence electrons and tend to gain one electron to complete their outer shell, resulting in a −1 charge.

Periodic Table

The periodic table is a systematic way of arranging elements based on their atomic number, electron configurations, and recurring chemical properties.
It is divided into groups (columns) and periods (rows), helping us quickly identify an element's valence electrons and predict its ion formation based on its position.
For instance, elements on the left side, such as metals, usually lose electrons while those on the right, particularly nonmetals, tend to gain electrons.
This organization allows us to easily predict the charge of ions formed by elements just by locating them on the table.

Element Groups

Element groups are the vertical columns in the periodic table. Each group contains elements with the same number of valence electrons in their outer shell. These shared characteristics lead to similar chemical behavior within a group.
For example, Group 1 elements (alkali metals) always have 1 valence electron and tend to form +1 ions by losing this electron.

• Group 13 elements have 3 valence electrons and commonly form +3 ions.
• Group 17 elements typically form -1 ions by gaining an electron to complete their valence shell.

Understanding element groups helps in determining how atoms of different elements will interact with each other.

Stable Electron Configuration

Stable electron configuration refers to a state where an atom's outer electron shell is complete, similar to the electron configuration of noble gases. Atoms and ions achieve stability by having a full valence shell, which usually means 8 valence electrons, also known as the octet rule.
During chemical reactions, atoms will lose, gain, or share electrons to reach this stable state.
Elements strive for a stable electron configuration because it is energetically favorable and leads to less reactive and more stable compounds.

• Metals tend to lose electrons to reach stability, resulting in positively charged ions.
• Nonmetals tend to gain or share electrons to fill their valence shells, forming negatively charged ions or covalent bonds.

This drive for stability is the fundamental reason why chemical reactions occur and how compounds are formed.