Question

In the periodic table the position of the element still uncertain is of :

• A. Lithium
• B. Hydrogen
• C. Helium
• D. Carbon

Hint:

Hydrogen is unique because:
It has 1 valence electron, like Group 1 (Alkali Metals).
It needs 1 electron to complete its valence shell (K-shell), like Group 17 (Halogens) need 1 for their p-octet.
It's a non-metal gas, unlike alkali metals. It forms diatomic molecules (H\(_2\)), like halogens. Because it shares properties with multiple groups but doesn't fit perfectly into any single one, its position is sometimes debated or shown separated. This makes its position "still uncertain" in a conceptual sense.

Answer 1

The Correct Option is B

Concept: The periodic table organizes elements based on their atomic number and recurring chemical properties. While most elements have a clearly defined position, the placement of Hydrogen has been a subject of discussion due to its unique properties. Step 1: Properties of Hydrogen Hydrogen (H) has atomic number 1, with an electronic configuration of 1s\(^1\). It exhibits properties that allow it to resemble:
Alkali Metals (Group 1):
Like alkali metals, it has one valence electron (ns\(^1\)).
It can lose this electron to form a positive ion (H\(^+\), a proton).
It forms similar types of oxides, halides, and sulfides.
Halogens (Group 17):
Like halogens, it is one electron short of a complete valence shell (for hydrogen, the K-shell which is full with 2 electrons). Halogens are one electron short of a p-subshell octet.
It can gain an electron to form a negative ion (H\(^-\), hydride ion), similar to halogens forming halide ions (e.g., F\(^-\), Cl\(^-\)).
It exists as a diatomic molecule (H\(_2\)), similar to halogens (F\(_2\), Cl\(_2\), Br\(_2\), I\(_2\)).
It is a non-metal, like halogens.
Group 14 (Carbon group - less common placement): Some arguments place it here due to having a half-filled valence shell and similar electronegativity to carbon, but this is not a widely accepted placement. Step 2: Common Placement and Uncertainty
Most commonly, Hydrogen is placed at the top of Group 1 (Alkali Metals) because of its 1s\(^1\) electron configuration.
However, it differs significantly from alkali metals: it's a gas, a non-metal, and forms covalent bonds much more readily.
Sometimes it is placed separately in the periodic table, or even occasionally above Group 17 (Halogens), to reflect its unique dual nature. This dual resemblance means its position is not as straightforward as other elements and is sometimes considered "uncertain" or anomalous. Step 3: Analyzing the options
(1) Lithium (Li): Atomic number 3 (1s\(^2\)2s\(^1\)). Clearly an alkali metal (Group 1). Its position is certain.
(2) Hydrogen (H): As discussed, its position is unique and debated due to its properties resembling both Group 1 and Group 17.
(3) Helium (He): Atomic number 2 (1s\(^2\)). It has a completely filled K-shell, making it very unreactive. It is placed in Group 18 (Noble Gases) due to its chemical inertness, even though its valence shell configuration (1s\(^2\)) technically fits Group 2 (Alkaline Earth Metals) based on s-block filling. However, its properties align with noble gases, so its position in Group 18 is well-established.
(4) Carbon (C): Atomic number 6 (1s\(^2\)2s\(^2\)2p\(^2\)). Clearly in Group 14. Its position is certain. Of the options, Hydrogen is the element whose position in the periodic table has historically been and continues to be the most discussed and sometimes considered "uncertain" or unique.