Question

The monatomic ions of Groups \(1 \mathrm{~A}(1)\) and \(7 \mathrm{~A}(17)\) are all singly charged. In what major way do they differ? Why?

Short answer

Group 1A ions are positively charged due to electron loss, while Group 7A ions are negatively charged due to electron gain.

Step-by-step solution

- Identify the groups

First, understand that Group 1A (1) contains alkali metals like lithium (Li), sodium (Na), and potassium (K), while Group 7A (17) contains halogens like fluorine (F), chlorine (Cl), and bromine (Br).

- Determine the charge of ions

Next, recognize that alkali metals in Group 1A form ions with a +1 charge, while the halogens in Group 7A form ions with a -1 charge.

- Compare the nature of the charges

Compare the charges: Group 1A ions have a positive charge because they lose one electron, while Group 7A ions have a negative charge because they gain one electron.

- Explain why the charges differ

Discuss why these charges differ. Alkali metals (Group 1A) have one valence electron that is easily lost to achieve a stable electron configuration. On the other hand, halogens (Group 7A) need one more electron to complete their valence shell, so they tend to gain an electron to become stable.

Key concepts

Group 1A Alkali Metals

Group 1A elements are known as alkali metals. This group includes elements like lithium (Li), sodium (Na), and potassium (K). These metals share some common characteristics:

• They all have one valence electron in their outermost shell.
• They are very reactive, especially with water.
• They are silver-colored and soft enough to be cut with a knife.

Alkali metals have a significant tendency to lose that one valence electron. By losing it, they achieve a stable electron configuration similar to the noble gases. Therefore, they form +1 ions. For example:

• Lithium (Li) loses one electron to form Li⁺
• Sodium (Na) loses one electron to form Na⁺
• Potassium (K) loses one electron to form K⁺

This loss makes the ions positively charged, or cations. The reactivity of alkali metals increases as you move down the group. This means potassium (K) is more reactive than sodium (Na), which is more reactive than lithium (Li).

Group 7A Halogens

Group 7A elements, also known as halogens, include fluorine (F), chlorine (Cl), and bromine (Br). Halogens have their own unique properties:

• They have seven valence electrons in their outermost shell.
• They are highly reactive, particularly with alkali metals and alkaline earth metals.
• They exist in different states: fluorine and chlorine as gases, bromine as a liquid, and iodine as a solid.

Halogens need one more electron to complete their valence shell to become stable. When they gain an electron, they form -1 ions. For example:

• Fluorine (F) gains one electron to form F⁻
• Chlorine (Cl) gains one electron to form Cl⁻
• Bromine (Br) gains one electron to form Br⁻

These gained electrons make the ions negatively charged, or anions. The reactivity of halogens decreases as you move down the group. This means fluorine (F) is more reactive than chlorine (Cl), which is more reactive than bromine (Br).

Ionic Charges

Ionic charges refer to the difference in the number of electrons and protons in an atom. When atoms gain or lose electrons, they become ions and obtain a charge:

• Cations: These are positively charged ions formed by losing electrons. For instance, Group 1A alkali metals form +1 cations because they lose one electron.
• Anions: These are negatively charged ions formed by gaining electrons. For example, Group 7A halogens form -1 anions by gaining one electron.

The formation of ions is driven by the atoms' desire to have a stable electron configuration, usually similar to the nearest noble gas. For alkali metals:

• When a sodium atom (Na) loses one electron, it becomes Na⁺.

For halogens:

• When a chlorine atom (Cl) gains one electron, it becomes Cl⁻.

The positive (+1) and negative (-1) charges indicate how many electrons have been lost or gained, respectively. This behavior explains why alkali metals tend to form cations while halogens form anions. Understanding these concepts is crucial when studying chemical reactions and bonding.