Hydrogen has one electron like alkali metals yet forms diatomic nonmetallic gas, so it sits uniquely at the top.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
Hydrogen has one valence electron, like the alkali metals, yet it forms a diatomic nonmetallic gas, and it can gain an electron to form a hydride ion. Its ionisation energy is high, so it does not form H+ freely in most chemistry. It is therefore placed above group 1 in some tables and above group 17 in others, reflecting its unique character. Hydrogen is a special case and is not a true alkali metal. It is the lightest and most abundant element in the universe.
Key ideas: Hydrogen (1s1) fits group 1 by its valence electron and +1 state, group 17 by needing one electron (hydride H-) and diatomic H2, and group 14 by half-filled, similar electronegativity (2.1) and IE. It is usually placed at the top of group 1 but is a nonmetal gas. It has three isotopes: protium, deuterium, tritium.
Common mistakes and connections: Students claim hydrogen is an alkali metal; it is not, since its IE (1312 kJ per mol) is far higher and it forms covalent bonds. Under extreme pressure (about 400 GPa) it is predicted to be metallic. It is unique because it has no inner core, and links to acid-base chemistry (H+ as proton) and hydrides.
Hydrogen forms diatomic H2 like a halogen, yet has one valence electron like the alkali metals, so no single group fits it perfectly. The interactive lesson shows this as a live animation or chart.
Hydrogen gas can reduce metal oxides, yet the hydride ion H- behaves much like a halide in forming salts such as NaH.
Hydrogen has one electron like alkali metals yet forms diatomic nonmetallic gas, so it sits uniquely at the top.
Hydrogen Position is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Lanthanide Contraction, Periodic Trends in Oxidation State, Periodic Trends in Oxides.
The next topics in Atomic Structure & Periodicity are Quark Structure of Nucleons and Nuclear Binding Energy.
Yes. The interactive lesson includes a self-check question on Hydrogen Position, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Hydrogen Position is topic 99 of 115 in Atomic Structure & Periodicity.