The question asks about the trend of atomic and ionic radii of alkali metals (Group 1 elements) as we move down the group from lithium to caesium. This trend is determined by the number of electron shells and the effective nuclear charge.
Correct Option: B) Increase steadily
As we descend Group 1, a new electron shell is added to each successive element. This addition of electron shells increases the distance of the outermost electrons from the nucleus, leading to a steady increase in both atomic and ionic radii.
The question asks to identify the alkali metal with the smallest atomic radius. To answer this, we need to recall the trend of atomic radius in the periodic table, specifically for elements within the same group (alkali metals).
C) Lithium (Li) — Lithium is the first element in Group 1 (alkali metals) after hydrogen. As atomic radius increases down a group, Lithium, being at the top among the given options, has the smallest atomic radius.
The question asks about the trend of ionization enthalpy for alkali metals as we move down Group 1 of the periodic table. We need to recall the definition of ionization enthalpy and how atomic properties change down a group.
B) Decreases — As explained above, due to increasing atomic size and shielding effect, the outermost electron is less tightly held, and thus less energy is required to remove it.
The question asks to identify the alkali metal with the highest first ionization enthalpy. Ionization enthalpy is the energy required to remove the outermost electron from a gaseous atom. We need to recall the trend of ionization enthalpy down a group in the periodic table.
Therefore, Lithium has the highest first ionization enthalpy among the given alkali metals.
C) Lithium (Li) — Lithium is the first element in the alkali metal group. Due to its smallest atomic size and least shielding effect among the alkali metals, its outermost electron is held most strongly by the nucleus, requiring the most energy to remove it.
The question asks about the trend of hydration enthalpy of alkali metal ions down the group. Hydration enthalpy is the energy released when one mole of gaseous ions dissolves in water to form hydrated ions. It is primarily dependent on the charge density of the ion.
A) Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺ — This order correctly reflects the decreasing hydration enthalpy down the group, which is due to the decreasing charge density of the ions as their size increases.
The question asks why alkali metals are soft and can be cut with a knife. This property is related to the type and strength of bonding present in these metals. We need to evaluate each option based on the characteristic properties of alkali metals and their metallic bonding.
B) Weak metallic bonding — Alkali metals have only one valence electron per atom, which contributes to a relatively weak metallic bond. This weak bonding results in their characteristic softness and low melting points, allowing them to be easily cut with a knife.