Question

Atomic number of element with lowest first ionisation enthalpy is:

• A. 32
• B. 19
• C. 35
• D. 87

Hint:

Alkali metals at the bottom of their group, such as Francium, have the lowest ionization energies because the outermost electron is in a higher energy level and is less tightly bound to the nucleus.

Answer 1

The Correct Option is D

Step 1: Understand ionization energy trends.
Ionization energy is the energy required to remove an electron from a gaseous atom.
First ionization energy decreases down a group due to increasing atomic size, facilitating electron removal.
Conversely, ionization energy increases across a period left-to-right as nuclear charge rises, hindering electron removal.
Step 2: Identify the correct group of elements.
The query seeks the element with the lowest first ionization enthalpy.
Alkali metals (Group 1) generally possess the lowest ionization energies due to having one valence electron, which is readily lost.
Step 3: Consider the position of the elements in the periodic table.
Element with atomic number 19 is Potassium (K), an alkali metal.
Element with atomic number 32 is Germanium (Ge), a metalloid.
Element with atomic number 35 is Bromine (Br), a halogen.
Element with atomic number 87 is Francium (Fr), an alkali metal and the heaviest alkali metal.
Step 4: Compare the ionization energies.
Francium (atomic number 87) exhibits the lowest ionization energy, being at the bottom of the alkali metal group. Its outermost electron is most distant from the nucleus, making it easiest to remove.