The sum of number of valence electrons and valency of an element with atomic number 15 is_____.

Options

A. 8
B. 6
C. 5
D. 10

Explanation

To solve the problem, we need to find the sum of the number of valence electrons and the valency of the element with atomic number 15, which is phosphorus (P). Here's a step-by-step solution:

### Step 1: Identify the Element
The element with atomic number 15 is phosphorus (P).

### Step 2: Write the Electronic Configuration
Phosphorus has 15 electrons. The electronic configuration can be written as:
- 1s² 2s² 2p⁶ 3s² 3p³

### Step 3: Determine the Number of Valence Electrons
The valence electrons are the electrons in the outermost shell. For phosphorus, the outermost shell is the third shell (n=3), which contains:
- 3s² (2 electrons)
- 3p³ (3 electrons)

Adding these together gives:
- Total valence electrons = 2 (from 3s) + 3 (from 3p) = 5 valence electrons.

### Step 4: Determine the Valency
Valency is the combining capacity of an element. For phosphorus, we look at the number of unpaired electrons in the valence shell:
- In the 3p orbital, there are 3 unpaired electrons.

Phosphorus can form three bonds by using these unpaired electrons, so its valency is 3.

### Step 5: Calculate the Sum
Now we need to find the sum of the number of valence electrons and the valency:
- Sum = Number of valence electrons + Valency
- Sum = 5 (valence electrons) + 3 (valency) = 8.

### Final Answer
The sum of the number of valence electrons and valency of the element with atomic number 15 is **8**.

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