Question

Which of the following statement is false? (1) Hydrogen can be placed in the halogen group because it forms hydrides like chlorides. (2) The best explanation for not placing hydrogen with the group of alkali metals or halogens is that the IP of \(\mathrm{H}_{2}\) is too higher than alkali metal but too low than halogens. (3) The tendency of hydrogen to gain one electron to acquire He configuration resembles halogens. (4) Hydrogen molecules are diatomic and form \(\mathrm{H}\) ions similar to halogens.

Short answer

Statement 4 is false.

Step-by-step solution

- Understand the statements

Read each statement carefully to understand what it implies about the placement of hydrogen in the periodic table.

- Evaluate Statement 1

Hydrogen can be placed in the halogen group because it forms hydrides like chlorides. This statement is true because hydrogen does form hydrides (e.g., HCl, HF), similar to how halogens form halides.

- Evaluate Statement 2

The best explanation for not placing hydrogen with the group of alkali metals or halogens is that the ionization potential (IP) of \(\text{H}_2\) is too high compared to alkali metals but too low compared to halogens. This statement is true as hydrogen has unique ionization properties that differ from both groups.

- Evaluate Statement 3

The tendency of hydrogen to gain one electron to achieve the He configuration resembles halogens. This is true because like halogens, hydrogen can gain an electron to achieve a noble gas configuration (He).

- Evaluate Statement 4

Hydrogen molecules are diatomic and form \(\text{H}^+\) ions similar to halogens. This statement is false. Halogens typically form \(\text{X}^-\) anions, not cations like \(\text{H}^+\). Hydrogen forming \(\text{H}^+\) ions does not resemble the behavior of halogens.

Key concepts

Periodic Table Placement

Hydrogen's placement in the periodic table is unique and often a topic of debate. It is usually found at the top of Group 1 with alkali metals, but it shares properties with both Group 1 elements and Group 17 elements (halogens).
While alkali metals have one electron in their outer shell, just like hydrogen, they are all metals and have lower ionization energies. On the other hand, halogens also require one electron to achieve a noble gas configuration, which is somewhat similar to hydrogen's behavior.
However, hydrogen's unique characteristics, such as its high ionization energy relative to alkali metals and its formation of different kinds of chemical bonds, justify a separate and distinct placement in the periodic table.

Hydrides

Hydrides are compounds that hydrogen forms with other elements. Hydrogen can form several types of hydrides:

• Ionic hydrides: Formed with alkali and alkaline earth metals, such as sodium hydride (NaH).
• Covalent hydrides: Formed with nonmetals, like methane (CH₄) and ammonia (NH₃).
• Metallic hydrides: Formed with transition metals, such as palladium hydride (PdH).

This ability to form hydrides makes hydrogen similar to halogens, which form halides by gaining one electron. Examples include HCl and HF, which resemble halogen compounds like NaCl and KF.

Ionization Potential

Ionization potential (IP) refers to the energy required to remove an electron from an atom or molecule. For hydrogen, the first ionization energy is quite high compared to alkali metals, yet lower than halogens.
This difference in ionization potential plays a critical role in determining hydrogen's chemical properties. It has a first ionization energy of 13.6 eV, which is much higher than sodium (5.14 eV) but lower than chlorine (12.97 eV).
This unique ionization energy places hydrogen in between these two groups, thus making it difficult to categorize it strictly as either an alkali metal or a halogen.

Noble Gas Configuration

One of the key similarities between hydrogen and halogens is that both aim to achieve the stable electronic configuration of noble gases. For hydrogen, gaining one electron results in a configuration similar to helium (He), which is wholly stable.
This tendency underlies many of the chemical reactions of hydrogen, where it aims to gain an electron to achieve this noble gas configuration. Examples can be seen in the formation of hydrides like HCl, where hydrogen bonds with a halogen to attain a He-like electron configuration.
Despite these similarities, hydrogen has unique properties that distinguish it from true halogens, but the noble gas configuration serves as a critical point of comparison.