Hydration Energy Order of Alkali Metals

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In summary, the conversation discusses the hydration of ions under the subheading "Properties of Alkali Metals" on a cheatsheet for s-block elements in chemistry. The third definition states that the smaller the size of the cation, the larger the extent of hydration, and the order of hydration energy is Cs+ > Rb+ > K+ > Na+ > Li+. However, according to the table, Cs+ has the greatest radius and therefore should have the least hydration energy, contradicting the given order. The expert summarizer notes that technically the order is correct in terms of negative hydration enthalpies, but it is likely that the list should be reversed.
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https://www.toppr.com/iit-jee/chemistry/s-block-elements/cheatsheet/
in this under sub heading properties of alkali metals third definition hydration of ions
it is written as Smaller size of cation, larger is the extent of hydration and hydration energy order is-
Cs+>Rb+>K+>Na+>Li+
but according to the table cs cation has greatest radius so hydration energy should be least but the order shows different story.
 
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gracy said:
Smaller size of cation, larger is the extent of hydration and hydration energy order is-
Cs+>Rb+>K+>Na+>Li+

Technically it is correct - hydration enthalpies are always negative, and -264 kJ/mol (for Cs+) > -520 kJ/mol (for Li+) :wink:

But I doubt that's what they meant, you are right, the list should be reversed.
 
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FAQ: Hydration Energy Order of Alkali Metals

What is the "hydration energy order" of alkali metals?

The hydration energy order of alkali metals refers to the trend in which these metals become more hydrated (or surrounded by water molecules) as you move down the periodic table. This means that the hydration energy decreases as you move down the group, with the largest hydration energy belonging to the topmost alkali metal, lithium, and the smallest belonging to the bottommost alkali metal, francium.

How is the hydration energy order of alkali metals determined?

The hydration energy order is determined by measuring the enthalpy change when an alkali metal is added to water. This enthalpy change is a measure of the strength of the bond between the metal ion and the water molecules. A larger, more negative enthalpy change indicates a stronger bond and thus a higher hydration energy.

What factors influence the hydration energy order of alkali metals?

The main factor that influences the hydration energy order of alkali metals is the size of the metal ion. As you move down the group, the metal ions become larger, making it easier for them to be surrounded by a larger number of water molecules. Additionally, the charge of the metal ion can also play a role, with higher charged ions having a stronger attraction to water molecules.

Why does the hydration energy decrease as you move down the group?

The decrease in hydration energy as you move down the group is due to the increasing size of the metal ions. As the ions become larger, they are less able to attract and bind with water molecules, resulting in a weaker hydration energy. Additionally, the increasing number of electrons in the outermost energy level also leads to a decrease in the effective nuclear charge, further weakening the attraction to water molecules.

What is the significance of the hydration energy order of alkali metals?

The hydration energy order of alkali metals is important in various chemical and biological processes. For example, it can affect the solubility of alkali metal salts in water and their ability to react with other substances. In biological systems, the hydration energy order can impact the transport and distribution of alkali metals in the body. Additionally, it can also be used to predict the reactivity of alkali metals in different chemical reactions.

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