We are all aware of our Modern Periodic table. But it took chemists years and many attempts to arrive at our current periodic table. And one main point of contention in the previous attempts was the position of hydrogen in the periodic table. Let us take a look at the unique position of hydrogen in the periodic table.
Position of Hydrogen in the Periodic Table
So if you glance at the periodic table, you will see hydrogen is the first element in the table. It is the smallest element on the table. It has atomic number one, which means it has only one electron orbiting it its shell. In fact, Hydrogen has only one shell. It is also the lightest element on the periodic table.
Now we know that the position of elements on the periodic table largely depends on their electronic configuration. Hydrogen has the electronic configuration of 1. It can get rid of one electron to attain noble gas configuration. This characteristic of hydrogen matches those of alkali metals. But they hydrogen atoms can also gain one electron similar to halogens. Let us see how this plays out.
Similarities to Metals
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
- Electronic Configuration: Like all the elements of the group, Hydrogen also has one electron in its last shell, the valence shell. Let us take a look at the composition of valence shells of a few of these alkali metals.
H (z=1) : K1
Li (z=3) : K2, L1
Na (z=11) : K2, L8, M1
- 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
Video on Hydrogen
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 Kcal per mole, The maximum ionization potential for metals is 147 Kcal 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.
- Electronegativity: They also share the same electronegative nature. Hydrogen also gains one electron (not looses) 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.
Learn more about the Different type of Hydrides.
Solved Question for You
Q: Hydrogen is mainly found in the combined state like in water and not the free state. True or False?
Ans: This statement is True. The earth’s crust contains nearly 1% of hydrogen by weight. In free state, hydrogen occurs only in traces in the atmosphere. It is mainly found in combined state and not the free state. Its main sources are water, acids, organic matter etc.