Should hydrogen be placed in the group 17 of halogens or group 1 of alkali metals in the Modern Periodic table? Explain the answer
Answers
Hydrogen does not belong to either the Alkali Metals or the Halogens on the periodic table. However, if it had to be placed in one, it would be the Alkali Metals and not the Halogens, as it shares similarities with the Alkali Metals as it doesn’t whatsoever with the Halogens.
Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Its monoatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% by mass.
It is the smallest element in the periodic table. Also anciently called as building block for other elements.
Hydrogen shares many similarities with alkali metals, i.e. elements in group I-A. This is one of the factors that dictates the position of hydrogen in the table. Let us take a look at the similarities
Similarities with Metals
• Electronic Configuration: Like all the elements of the group, Hydrogen also has one electron in its last shell, the valence shell.
• Noble Gas Configuration: Like alkali metals, it needs to lose one electron in its valence shell to achieve stable configuration as that of the next noble gas, which in this case is helium. It hence forms the H+ ion.
• Good Reducing Agent: Hydrogen is a strong reducing agent like all the other alkali metals.
Fe2O3 + 4 H2 → 3Fe + 4H2O
B2O3 + 6 K → 2B + 3 K2O
• Forms Halides : Also just like alkali metals, hydrogen combines with electronegative elements to form halides
2Na + Cl2 → 2NaCl
H2 + Cl2 → 2HCl
Differences with Metals
• Non-metal: Hydrogen is essentially not a metal like all alkali metals, but a non-metal
• Loss of Electron: Although it has only one electron in its outer shell, hydrogen cannot easily lose this electron to gain electropositivity. All other alkali metals can do this with ease.
• State: At room temperatures where all alkali metals exist is the solid state, hydrogen is a gas.
• Size of Atom: The H+ ion of hydrogen is much smaller than ions of alkali metals.
• Ionization Potential: The ionization potential of hydrogen is over 300 Kilocalories per mole, The maximum ionization potential for metals is 147 Kilocalories per mole.
Similarities to Halogens
• Noble Gas Configuration: Hydrogen can gain one electron to complete its valence shells. Halogens also have seven electrons in their last shell and can gain one electron to gain noble gas configuration.
• Electro negativity: They also share the same electronegative nature. Hydrogen also gains one electron (not loses) to become stable and so do halogens.
H + e‾ → H‾
Cl + e‾ → Cl‾
• Diatomic Molecules: Both hydrogen and halogens form diatomic molecules. Hydrogen forms H2 and, halogens are Cl2, F2 etc.
• Reaction with Metals: Hydrogen combines with metals to form metallic hydrides. Similarly, halogens also combine with metals to form metal halides.
2Na + H2 → 2NaH
Ca + H2 → CaH2
• Covalent Bonding: Halogens and hydrogen both also combine with non-metals to form molecules with covalent bonding.
Differences with Halogens
• Structure of Atom: Hydrogen has only one electron in its outer shell. All halogens have seven electrons in their last shell
• Size of Atom: The size of the H- ion is much larger than those of the ions of Halogens. This is because hydrogen has only one electron and proton and the pull of the nucleus is less.
• Reaction with Water: Also unlike halogens, the hydrogen ion H- is unstable in water.
Now since H atom shows similar as well as dissimilar properties with both IA and VII A group elements it is placed above the periodic table currently (But in previous system it was placed in IA group.)
Hope it helps....
