Alkali Metals (S-Block Elements)

This set of vocabulary flashcards covers the introduction, physical properties, periodic trends, and flame tests of Group 1 Alkali Metals as described in the lecture notes.

s-block elements

The elements in which the last electron enters the outermost s-sublevel.

Alkali metals

Elements including $Li$, $Na$, $K$, $Rb$, $Cs$, and $Fr$ that form hydroxides on reaction with water which are strongly alkaline in nature.

Francium ($^{223}Fr$)

A radioactive isotope of the alkali metal group with a half-life of $21\,\text{minutes}$.

Atomic and Ionic radii order

The trend for both atoms and monovalent ions ($M^+$) follows the order: $Li < Na < K < Rb < Cs$.

Ionization Enthalpy (IP) order

The order of ionization potential for alkali metals is $Li > Na > K > Rb > Cs$.

Hydration Enthalpy order

The order of enthalpy released upon hydration is $Li^+ > Na^+ > K^+ > Rb^+ > Cs^+$.

Ionic mobility and conductance

In aqueous solution, the order of mobility is $Cs^+ > Rb^+ > K^+ > Na^+ > Li^+$.

Degree of hydration (Lithium)

$Li^+$ has the maximum degree of hydration, resulting in mostly hydrated salts such as $\text{LiCl} \cdot 2H_2O$.

Density order

Generally increases down the group, but Potassium ($K$) is lighter than Sodium ($Na$) due to vacant 'd' shells; the specific order is $Cs > Rb > Na > K > Li$.

Melting and Boiling points order

The order for these physical properties is $Li > Na > K > Rb > Cs$.

Crimson red

The specific flame color detected during a flame test for Lithium ($Li$).

Yellow

The specific flame color detected during a flame test for Sodium ($Na$).

Violet

The specific flame color detected during a flame test for Potassium ($K$).

Red violet

The specific flame color detected during a flame test for Rubidium ($Rb$).

Blue

The specific flame color detected during a flame test for Caesium ($Cs$).

Photoelectric effect

A property where light energy absorbed is sufficient to make an atom lose electrons, making Caesium and Potassium useful as electrodes in photoelectric cells.

Reactivity with air

The order of reactivity is $Li < Na < K < Rb < Cs$, where metals tarnish in dry air via the formation of oxides (e.g., $4Li + O_2 \rightarrow 2Li_2O$).