Density of Alkali Metals

The elements in Group 1 of the periodic table are arranged in a vertical column, mainly on the left side. Group 1 elements are referred to as alkali metals. Each alkali metal atom’s outermost surface contains a single electron with a significantly weaker bond to the nucleus than electrons in the inner shells. Additionally, alkali metals have low densities, causing the first three elements (lithium, sodium, and potassium) to float over water.

Alkali Metals

“Alkali” derives from the Arabic word for “saltwort ashes.” In chemistry, it states a base that can be dissolved in water. Group 1 of the periodic table, excluding hydrogen, contains alkali metals. It leads to poor metallic bonding since they all have a single electron on their outer shells. However, the properties and trends of these metals are very similar.

Alkali metals have existed for a long time. Sir Humphry Davy accomplished the isolation of sodium and potassium metals in 1807.

The density of alkali metals

The density of alkali metals is the total differential between the mass and volume (size) of the elements that gives the effect of the increased row number on density.

To figure out how the row number changes density, you look at the total density-  d=m/v.

Alkali metals have relatively low densities in comparison to other metals. For example, Li, Na, and K are significantly lighter than water. The density of alkali metals increases as you progress from Li to Cs.

Alkali metals have less densely packed atoms due to their relatively large size. Both atomic size and mass grow as one moves down the group, but the rise in atomic mass balances for the larger atomic size. As a result, alkali metals’ densities increase from Li towards Cs. On the other hand, potassium is considerably lighter than sodium, which is most likely the result of an unusual rise in the atomic radius of potassium.

The alkali metals were considered superior to others because they were smarter and had lower density than water.

Trends in Density

Lithium, sodium, and potassium are all relatively light metals with densities lower than water (less than 1 g cm-3). It is challenging to come up with a straightforward explanation for this trend since the density of alkali metals is dependent on two parameters, both of which fluctuate as the group progresses downward. The atoms are arranged in the same manner. The only variables that must be considered are the number of atoms that can pack into a given volume and the mass of the atoms. The amount packed relies on the atom’s volume, which depends on the atom’s radius.

As the atomic radius decreases, the atomic volume increases. So, sodium atoms can be filled into a specific volume more densely than lithium atoms. However, as particles grow in size, their masses increase as well. Therefore, a given quantity of sodium atoms weighs more than an equal quantity of lithium atoms. Thus, a cubic centimetre (1 cm3) of sodium has fewer atoms than a cubic centimetre (1 cm3) of lithium, and each atom is heavier. It is necessary to perform mathematical calculations to determine the densities.

Key Activities in Density of Alkali Metals

As you move down Group 1 elements, the density of alkali metals increases (except at potassium).

The density of alkali metals changes due to a combination of two elements that change as you proceed.

There is only one consideration for these metals: how many atoms can be packed into a given volume and how much mass is associated with each atom. How many you can put depends on their mass – which depends on their atomic size.

As one moves down Group 1, the atomic radius rises with its atomic volume. It means that sodium atoms cannot be packed into the same volume as lithium atoms.

However, as one descends the group, the atoms’ mass increases. For example, an equal number of sodium and lithium atoms will have a different mass.

Thus, a cubic centimetre of sodium has fewer atoms than a cubic centimetre of lithium, but each weighs heavier.

Alkali Metal Density Calculation

Density = Mass / Volume

1) If mass increases but the volume decreases, density (mass/volume) increases.

2) If mass decreases but volume increases, the density (mass/volume) decreases.

3) When both mass and volume increase, we must determine which one increases at a faster rate (as these 2 are contradictory variables)

• If the mass increases faster than volume, the density increases too.
• Density decreases if volume increases faster than mass (i.e. the denominator in mass/volume increases, resulting in a smaller overall percentage).

4) When mass and volume decrease simultaneously, you can use the same logic.

In general, the rate of mass increase is greater than the volume increase in alkali metals.  Hence, the density of alkali metals increases as one moves down the group.

Conclusion

The alkali metals are the elements found in the first group of the periodic table. Alkali metals have a high degree of reactivity, and the lower the ionisation energy count, the more reactive they become. Alkali metals have the lowest ionisation energy of all the Group 1 elements, which describes their low density. However, they should be kept completely isolated from oxygen to avoid reactivity. Additionally, it is lightweight and easy to cut due to its low cohesive energy. The more cohesive energy there is, the softer it becomes.