Question

Which of the following is correct? (1) Hydrogen has same ionisation potential as sodium. (2) Hydrogen has the same electronegativity as halogens. (3) Hydrogen will not be liberated at anode. (4) Hydrogen has an oxidation state of \(+1\) and \(-1\)

Short answer

Statements 3 and 4 are correct.

Step-by-step solution

Analyze Statement 1

Check if hydrogen has the same ionisation potential as sodium. Hydrogen has a much higher ionisation potential compared to sodium due to its small size and stable electron configuration. Therefore, statement 1 is incorrect.

Analyze Statement 2

Verify if hydrogen has the same electronegativity as halogens. Hydrogen's electronegativity is around 2.1, while halogens have higher electronegativities (e.g., fluorine is 4.0). Hence, statement 2 is incorrect.

Analyze Statement 3

Determine if hydrogen will not be liberated at the anode. Hydrogen, being less electronegative than oxygen, gets liberated at the cathode as positive ions are attracted to the cathode during electrolysis. So, statement 3 is correct.

Analyze Statement 4

Check if hydrogen has oxidation states of +1 and -1. Hydrogen can indeed have an oxidation state of +1 (as in water) and -1 (as in hydrides). Therefore, statement 4 is correct.

Conclusion

Compare the correctness of all statements. Statements 3 and 4 are correct.

Key concepts

Ionisation potential

Ionisation potential is the energy required to remove an electron from an atom or ion. It's an important property in understanding the reactivity of elements.

For hydrogen, this energy is relatively high at 13.6 eV because it only has one electron held closely to the nucleus. On the other hand, sodium has a much lower ionisation potential, around 5.1 eV.

This is because sodium's outermost electron is further away from the nucleus and experiences less electrostatic pull. This critical difference in ionisation potentials explains why the first statement in the exercise is incorrect.

Electronegativity

Electronegativity measures an atom's ability to attract electrons in a chemical bond.

Hydrogen's electronegativity is approximately 2.1. Though this is moderately high, it's still significantly lower compared to halogens, which are known for their high electronegativities (e.g., fluorine has an electronegativity of 4.0).

Because electronegativity varies greatly among elements, it plays a crucial role in determining the nature of bonds—whether they’ll be more ionic or covalent. This difference in electronegativity between hydrogen and halogens makes the second statement in the exercise incorrect.

Oxidation states

Oxidation states indicate the degree of oxidation (loss of electrons) of an atom in a chemical compound.

Hydrogen is unique in that it can have multiple oxidation states. In most compounds, hydrogen has an oxidation state of +1, as in water (H₂O). This is because hydrogen typically loses its single electron during bond formation.

However, hydrogen can also have an oxidation state of -1, as seen in hydrides like sodium hydride (NaH), where it gains an electron. This versatility is why the fourth statement in the exercise is correct.

Electrolysis

Electrolysis is a process that uses electrical energy to drive non-spontaneous chemical reactions.

In the context of electrolysis, hydrogen is often involved in reactions where it can be liberated at the cathode, not the anode. This is because positively charged hydrogen ions (H⁺) are attracted to the cathode, where they gain electrons and form hydrogen gas.

For instance, during water electrolysis, hydrogen gas is generated at the cathode, and oxygen gas forms at the anode. This fundamental aspect of electrolysis explains why the third statement in the exercise is correct.