Question

For the following ions, indicate whether electrons must be gained or lost from the parent neutral atom, and how many electrons must be gained or lost. a. \(\mathrm{O}^{2-}\) b. \(\mathrm{P}^{3-}\) c. \(\mathrm{Cr}^{3+}\) d. \(\mathrm{Sn}^{2+}\) e. \(\mathrm{Rb}^{+}\) f. \(\mathrm{Pb}^{2+}\)

Short answer

a. \(\mathrm{O}^{2-}\) gains 2 electrons. b. \(\mathrm{P}^{3-}\) gains 3 electrons. c. \(\mathrm{Cr}^{3+}\) loses 3 electrons. d. \(\mathrm{Sn}^{2+}\) loses 2 electrons. e. \(\mathrm{Rb}^{+}\) loses 1 electron. f. \(\mathrm{Pb}^{2+}\) loses 2 electrons.

Step-by-step solution

a. Determine the electron change for \(\mathrm{O}^{2-}\)

To do this, we need to look at the periodic table and locate the element oxygen (O). Oxygen is in group 16 (or 6A), which means it has 6 valence electrons. When it forms an ion, it will gain 2 electrons to have a full outer shell of 8 electrons, becoming more stable. Therefore, \(\mathrm{O}^{2-}\) gains 2 electrons from its neutral form.

b. Determine the electron change for \(\mathrm{P}^{3-}\)

Phosphorus (P) is located in group 15 (or 5A) of the periodic table and has 5 valence electrons. To become more stable, it will gain 3 electrons to fill its outer shell with 8 electrons. Hence, \(\mathrm{P}^{3-}\) gains 3 electrons from its parent neutral atom.

c. Determine the electron change for \(\mathrm{Cr}^{3+}\)

Chromium (Cr) is a transition metal and can form multiple oxidation states. In this case, it has lost 3 electrons and has a charge of \(+3\). So, \(\mathrm{Cr}^{3+}\) loses 3 electrons from its neutral form.

d. Determine the electron change for \(\mathrm{Sn}^{2+}\)

Tin (Sn) is in group 14 (or 4A) and has 4 valence electrons. To become more stable, it loses 2 electrons, resulting in a charge of \(+2\). Thus, \(\mathrm{Sn}^{2+}\) loses 2 electrons from its parent neutral atom.

e. Determine the electron change for \(\mathrm{Rb}^{+}\)

Rubidium (Rb) is an alkali metal in group 1 (or 1A), having 1 valence electron. To become more stable, it loses 1 electron, resulting in a charge of \(+1\). Therefore, \(\mathrm{Rb}^{+}\) loses 1 electron from its neutral form.

f. Determine the electron change for \(\mathrm{Pb}^{2+}\)

Lead (Pb) is in group 14 (or 4A) and has 4 valence electrons. To become more stable, it loses 2 electrons, resulting in a charge of \(+2\). Therefore, \(\mathrm{Pb}^{2+}\) loses 2 electrons from its parent neutral atom.

Key concepts

Electron Gain and Loss

When atoms form ions, they either gain or lose electrons to achieve a more stable electron arrangement, often matching that of the nearest noble gas. This process involves either adding electrons (gain) to create negatively charged ions or removing electrons (loss) to create positively charged ions. Understanding which process occurs depends on the type of element and its position in the periodic table.
- **Negative ions** (anions) are formed when atoms gain electrons. For example, oxygen, which is initially neutral, gains two electrons to become O^{2-} . This gives it a full set of valence electrons similar to neon, thus making it more stable. - **Positive ions** (cations) result when atoms lose electrons. For instance, rubidium (Rb^+) loses one electron from its neutral state to achieve a full outer shell like krypton, which stabilizes the ion.
Gaining or losing electrons alters the electron count but not the number of protons. The change in electron count leads to a net charge, defining the ion's positive or negative status.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how an atom interacts chemically with other elements. These electrons are responsible for the formation of chemical bonds, and understanding them is key to understanding ion formation.
- **Count of Valence Electrons**: The number of valence electrons can be determined from the group's number in the periodic table where the element resides. For instance, oxygen is in group 16, indicating it has 6 valence electrons. To stabilize, it needs to gain 2 electrons to complete its outer shell with 8 electrons. - **Chemical Stability**: Atoms tend to undergo reactions to achieve a full valence shell. This often means having either 2 or 8 valence electrons becomes the focus. Elements like phosphorus, which has 5 valence electrons, gain 3 more electrons during ion formation to achieve stability akin to argon.
Having filled valence electron shells is often called a 'stable electron configuration,' reminiscent of noble gases which are inert and do not readily form bonds.

Periodic Table Groups

The periodic table is organized in a way that elements with similar properties are aligned in vertical columns known as groups or families. These groups help predict the behavior of elements, particularly how they gain or lose electrons.
- **Group Characteristics**: Each group contains elements that have the same number of valence electrons and thus similar chemical behaviors. For instance, all the elements in group 1 have 1 valence electron and tend to lose it to form a +1 ion. - **Electron Configuration**: Moving across a period from left to right in the periodic table increases the number of valence electrons among elements. Group 2 elements, like beryllium and magnesium, have 2 valence electrons and will typically lose these to form +2 ions. - **Predictive Power**: The location of an element in the periodic table indicates its tendencies in ion formation. For example, elements in group 17 are highly reactive non-metals that tend to gain 1 electron to reach the stable configuration of a noble gas, leading to a -1 charge.
Understanding these periodic trends allows for predictions about which ions will form under different circumstances, aiding in the study of chemistry.