Group I Elements: Properties and Predictions

This section explores the properties of Group I elements (alkali metals) and provides guidance on predicting the properties of other elements within the group.

Properties of Group I Elements

Group I elements (Li, Na, K, Rb, Cs, Fr) exhibit characteristic properties due to their electronic configuration. They all have one electron in their outermost shell, which is readily lost to form a +1 ion.

Reactivity

Reactivity increases down the group. This is because the outermost electron is further from the nucleus and less strongly attracted, making it easier to remove.

Explanation: As you go down the group, the atomic radius increases. The shielding effect of inner electrons also increases. This leads to a weaker effective nuclear charge experienced by the valence electron, making it easier to lose.

Metallic Properties

Group I elements are highly metallic. They are:

• Good conductors of heat and electricity
• Malleable and ductile (can be hammered into sheets and drawn into wires)
• Have low melting and boiling points compared to non-metals
• Lustrous (shiny)

Reaction with Water

Group I elements react vigorously with water. The reactivity increases down the group.

Equation: $2M(s) + 2H_2O(l) \rightarrow 2MOH(aq) + H_2(g)$

Explanation: The reaction produces hydrogen gas and a metal hydroxide. The heat produced can be enough to ignite the hydrogen gas, leading to a flame.

Reaction with Halogens

Group I elements react readily with halogens (Group VII) to form ionic compounds.

Equation: $2M(s) + X_2(g) \rightarrow 2MX(s)$ (where X = F, Cl, Br, I)

Explanation: The alkali metal loses an electron to form a +1 ion, and the halogen gains an electron to form a -1 ion, resulting in an ionic bond.

Predicting Properties of Other Group I Elements

Based on the known properties of one or two Group I elements, you can predict the properties of others in the group. Remember that reactivity increases down the group.

Reactivity Prediction

If you know the reactivity of Li, you can predict the reactivity of Na, K, Rb, Cs, and Fr. For example, K will be more reactive than Na, and Cs will be more reactive than K.

Reaction with Water Prediction

If you know that Na reacts with water, you can predict that K, Rb, Cs, and Fr will also react with water, and their reactions will be more vigorous than that of Na.

Reaction with Halogens Prediction

If you know that Li reacts with chlorine, you can predict that Na, K, Rb, Cs, and Fr will also react with chlorine, and their reactions will be more vigorous than that of Li.

Table Summarizing Group I Properties

Element	Atomic Mass (amu)	Reactivity with Water	Reaction with Chlorine	Metallic Properties
Lithium (Li)	6.94	Reacts, but less vigorously	Reacts	Malleable, ductile, lustrous, good conductor
Sodium (Na)	22.99	Reacts vigorously, produces a flame	Reacts	Malleable, ductile, lustrous, good conductor
Potassium (K)	39.10	Reacts very vigorously, produces a bright flame	Reacts	Malleable, ductile, lustrous, good conductor
Rubidium (Rb)	85.47	Reacts very vigorously, produces a bright flame	Reacts	Malleable, ductile, lustrous, good conductor
Cesium (Cs)	132.91	Reacts very vigorously, produces a bright flame	Reacts	Malleable, ductile, lustrous, good conductor
Francium (Fr)	223	Highly reactive, likely very vigorous reaction	Reacts	Likely metallic, but properties not well known due to radioactivity