Hydrogen Position in Periodic Table - NEET Notes, Formula & Common Mistakes
Hydrogen·2 min read·NEET 2026
What NEET Asks
NEET questions frequently test hydrogen's unique dual nature: its similarities and differences with both alkali metals and halogens.
Expect conceptual MCQs regarding its anomalous position and the properties justifying it.
This topic occasionally appears, carrying 4 marks, so a clear understanding is crucial for NEET success.
Key Points
Hydrogen (atomic number 1) has electron configuration 1s¹. This forms the basis of its unique chemistry.
Resembles Group 1 (Alkali Metals): Can lose 1 electron to form H⁺ (like M⁺). Forms oxides, halides, sulfides.
Resembles Group 17 (Halogens): Can gain 1 electron to form H⁻ (like X⁻). Exists as a diatomic molecule (H₂), high ionization enthalpy, non-metallic.
Differences from Group 1: High ionization enthalpy, non-metallic, gaseous, forms covalent compounds.
Differences from Group 17: No non-bonding electrons, forms H⁺ readily, oxide (H₂O) is neutral.
Due to this distinctive mix of properties, hydrogen is placed anomalously, usually above Group 1.
Must-Know Formula / Reaction
Electron Configuration: H (Z=1) = 1s¹
Explanation: Governs its tendency to lose or gain electrons for stability.
Common Mistakes
Students often confuse forming H⁺ with true metallic character; hydrogen is non-metallic.
Don't strictly assign hydrogen to either Group 1 or 17; its anomalous nature is key.
Forgetting hydrogen forms both H⁺ (proton) and H⁻ (hydride), showcasing its dual behavior.
Rapid Revision
Hydrogen's 1s¹ configuration allows it to mimic Group 1 (H⁺ formation) and Group 17 (H⁻ formation). High ionization energy, non-metallic, and gaseous state distinguish it from alkali metals. Diatomic nature and hydride formation distinguish it from halogens. Its position is thus anomalous.
Frequently Asked Questions
Why is the position of hydrogen in the periodic table considered anomalous?▾
Hydrogen's position is anomalous because it shares properties with both alkali metals (Group 1) and halogens (Group 17). It can lose an electron to form H⁺ like alkali metals, and gain an electron to form H⁻ like halogens, making its definitive placement difficult.
In what ways does hydrogen resemble Group 1 (alkali metals)?▾
Hydrogen resembles alkali metals in that it has one electron in its outermost shell (1s¹) and can lose it to form a unipositive ion (H⁺). It also forms oxides, halides, and sulfides, similar to alkali metals.
How does hydrogen show similarity with Group 17 (halogens)?▾
Hydrogen resembles halogens by requiring only one electron to complete its duplet, forming a uninegative ion (H⁻). It also exists as a diatomic molecule (H₂) and forms covalent compounds, similar to halogens.
Practice NEET Chemistry with AI
Get AI-powered doubt solving, personalized revision plans, and unlimited MCQ practice tailored to your weak areas.