The atomic number of an element is 8. How many electrons will it gain to form a compound with sodium ?

Options

A. one
B. Two
C. Three
D. Four

Explanation

To determine how many electrons an element with atomic number 8 will gain to form a compound with sodium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Element**:
The atomic number of the element is 8. Referring to the periodic table, the element with atomic number 8 is oxygen (O).

**Hint**: Look up the periodic table to find the element corresponding to the atomic number given.

2. **Determine the Electron Configuration**:
Oxygen has an electron configuration of 2, 6. This means it has 2 electrons in its first shell and 6 electrons in its second shell.

**Hint**: Remember that the first shell can hold a maximum of 2 electrons, while the second shell can hold up to 8.

3. **Calculate the Valency of Oxygen**:
The valency of an element is determined by the number of electrons it needs to gain or lose to achieve a full outer shell. Since oxygen has 6 electrons in its outer shell, it needs 2 more electrons to complete the octet (8 electrons in the outer shell).

**Hint**: For elements with more than 4 electrons in the valence shell, subtract the number of valence electrons from 8 to find how many electrons are needed to complete the shell.

4. **Determine the Valency of Sodium**:
Sodium (Na) has an atomic number of 11, with an electron configuration of 2, 8, 1. Sodium has 1 electron in its outer shell and tends to lose that electron to achieve a stable configuration, resulting in a +1 charge.

**Hint**: Look at the group number of sodium in the periodic table to determine its typical charge when forming compounds.

5. **Forming a Compound**:
To form a neutral compound with oxygen, which has a valency of -2, we need to balance the charges. Since each sodium atom contributes a +1 charge, we need 2 sodium atoms to balance the -2 charge from one oxygen atom.

**Hint**: The total positive charge from sodium must equal the total negative charge from oxygen for the compound to be neutral.

6. **Conclusion**:
Therefore, oxygen will gain 2 electrons to form a compound with sodium, resulting in the compound Na2O.

**Final Answer**: Oxygen gains 2 electrons to form a compound with sodium.