B. Li (lithium) is the least reactive in group 1A elements
Further explanation
The periodic system of elements is an arrangement of elements classified based on similar properties and their atomic number order.
The periodic system is divided into groups (vertical order) and periods (horizontal order)
If we look at the atomic number of the elements in group 1A:
- H: 1
- Li: 3
- Na: 11
- K: 19
- Rb: 37
- Cs: 55
- and Fr: 87
Shows that ,the element is getting down, the shell electron is increasing, so that in one group, from top to bottom, the radius of the atom tends to get bigger, according to the electron shell increase.
Ionization energy is the energy that an atom needs in the gas phase to release its electrons
In one group, from top to bottom, the first ionization energy tends to get smaller, because the addition of electron shells makes the attraction of the atomic nucleus to the outer electrons (valence electron) weaker, so that it is easily released, forming cations +
Group 1A elements from top to bottom, the easier the elements release electrons, and the more reactive
For this reason, IA elements (also called alkali metal elements) are highly reactive metals.
This reactivity causes a very large reaction to water and air
From the properties above shows that the metal that is less reactive from group 1A is Lithium
Learn more
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Keywords: element, group 1A, ionisation energy, valence electron
