Question

Predict the chemical properties of francium, the last member of Group \(1 \mathrm{~A}\)

Short answer

Francium is predicted to be highly reactive, soft, and form +1 ions, similar to other alkali metals.

Step-by-step solution

Understanding Group 1A Elements

Group 1A, also known as the alkali metals, includes elements like lithium, sodium, potassium, rubidium, cesium, and francium. These elements have one electron in their outermost shell which makes them highly reactive, especially with water.

Alkali Metal Trends

As you move down Group 1A from lithium to francium, the elements increase in atomic size and decrease in ionization energy. This means the outer electron is more easily lost, making the elements more reactive as you go down the group.

Predicting Reactivity of Francium

Given the trends in Group 1A, francium, being the heaviest alkali metal, would be expected to be the most reactive. Its large atomic size and low ionization energy make it very eager to lose its outer electron.

Other Properties of Francium

Francium would likely have properties similar to other alkali metals like a soft texture, low melting point, and the formation of +1 oxidation state in compounds. However, due to its radioactivity and scarcity, it's challenging to confirm these properties experimentally.

Key concepts

Group 1A elements

Group 1A elements, also known as alkali metals, are found in the first column of the periodic table. This group includes lithium, sodium, potassium, rubidium, cesium, and francium. Each of these elements has a single electron in their outermost energy level or electron shell. This single electron significantly influences their chemical behavior, making them highly reactive.

These elements are important in various applications, from lithium batteries to sodium lamps. However, their reactivity means they must be handled with care.

• Alkali metals are shiny and soft; they can often be cut with a knife.
• They have low melting points compared to most other metals.
• In nature, they are always found in compounds, never in their metallic form, due to their reactivity.

Alkali metals

Alkali metals exhibit distinct properties that differentiate them from other periodic table groups. Their notable ability to lose a single electron easily leads to their high reactivity, especially toward water and halogens.

When reacting with water, alkali metals form hydroxides and release hydrogen gas, often producing heat and sometimes even flames. Here's what happens:

• The metal donates its single outer electron to form a positive ion.
• This electron loss makes the metal reactive, allowing it to bond readily with other elements, such as oxygen or halogens.

Unlike many other groups, each subsequent member of the alkali metals demonstrates stronger reactions due to decreasing ionization energy as atomic size increases. This trend underscores their unique position in elemental chemistry.

Reactivity trends

Reactivity trends in alkali metals are an intriguing aspect of their chemistry. As we move down the group from lithium to francium, chemical reactivity increases. This heightened reactivity is tied to decreases in ionization energy — the energy required to remove the outermost electron.

Here's why this trend occurs:

• Increased distance from the nucleus: The outer electron is further from the nucleus in larger atoms, weakening the nuclear attraction.
• Increased shielding effect: Additional inner electrons block the outer electron from the positive pull of the nucleus, making it easier to lose.
• Resulting in a greater tendency to react as the ability to lose an electron becomes easier.

Francium, being at the bottom of this group, is predicted to be the most reactive, but its scarcity and radioactivity make studying it challenging.

Electron configuration

Understanding electron configuration is critical in predicting the reactivity of alkali metals. These configurations determine how electrons are arranged in an atom, influencing chemical properties.

For alkali metals like francium, the electron configuration ends in a single electron in the outermost shell: \(ns^1\).

• This outer electron is easily lost, as shown by its placement in the s orbital with a principal quantum number corresponding to the period it is in.
• In the case of francium, the electron configuration is \([Rn]7s^1\), meaning it has one electron on the seventh outer level ready to be donated or shared in reactions.

This easily lost electron is the key to its high reactivity, particularly in reactions where it seeks a stable noble gas electron configuration by forming positive ions.