Which of the elements show least values of ionisation within their periods ?

Options

A. Alkaline earth metals
B. Alkali metals
C. Noble gases
D. Chalcogens

Answer

To determine which elements show the least values of ionization energy within their periods, we can follow these steps:

### Step 1: Understand Ionization Energy
Ionization energy is the energy required to remove an electron from an atom in its gaseous state. Generally, it increases across a period from left to right due to the increase in nuclear charge and decrease in atomic size.

**Hint:** Remember that ionization energy is influenced by atomic size and nuclear charge.

### Step 2: Analyze Periodic Trends
As we move from left to right across a period in the periodic table, the atomic size decreases. This is because the number of protons increases, pulling the electrons closer to the nucleus. A smaller atomic size means that electrons are held more tightly, which increases ionization energy.

**Hint:** Consider how atomic size changes across a period and its effect on ionization energy.

### Step 3: Identify Groups of Elements
In the periodic table, elements are grouped into families or groups. The alkali metals (Group 1) have the lowest ionization energies in their respective periods because they have a single electron in their outermost shell, which they can lose easily.

**Hint:** Look for the group that has the least tightly held outer electrons.

### Step 4: Compare Elements in a Period
For example, in the second period, we have:
- Lithium (Li)
- Beryllium (Be)
- Boron (B)
- Carbon (C)
- Nitrogen (N)
- Oxygen (O)
- Fluorine (F)
- Neon (Ne)

Among these, lithium (Li) being an alkali metal has the least ionization energy compared to beryllium and the other elements in the period.

**Hint:** Identify the element in the first group of a period to find the one with the least ionization energy.

### Step 5: Conclusion
Therefore, the element that shows the least value of ionization energy within their periods is the alkali metal, specifically the first element in the period, which is lithium (Li) in the second period or sodium (Na) in the third period.

**Final Answer:** The alkali metals show the least values of ionization energy within their periods.