Question

How to determine valency of element with example

Answer 1

The valency of an element is defined as the combining capacity of an atom, traditionally measured by the number of hydrogen atoms it can combine with or displace in forming compounds. Valency is often related to the number of valence electrons in an atom, which are the electrons in the outermost shell.

### Steps to Determine Valency:

1. **Identify the number of valence electrons:**
- The valence electrons are the electrons in the outermost shell of an atom. For main group elements, the number of valence electrons can be identified from their group number in the periodic table.

2. **Determine the maximum number of electrons the atom can gain or lose:**
- For metals (found on the left side of the periodic table), valency usually corresponds to the number of electrons lost to achieve a stable electron configuration (usually, this is a full outer shell, resembling the electron configuration of noble gases).
- For nonmetals (found on the right), valency often corresponds to the number of electrons gained to complete their valence shell.

3. **Count the electrons needed for the atom to achieve a stable electron configuration:**
- This helps you to infer whether the element is more likely to donate or accept electrons.

### Example: Valency of Oxygen

1. **Identify the number of valence electrons:**
- Oxygen (O) is in Group 16 of the periodic table. It has 6 valence electrons.

2. **Determine the maximum number of electrons it can gain or lose:**
- Oxygen needs 2 more electrons to complete its outer electron shell (which could hold 8 electrons total). Therefore, oxygen can gain 2 electrons.

3. **Conclusion:**
- The valency of oxygen is 2, as it can form bonds by gaining 2 electrons.

### Example: Valency of Sodium

1. **Identify the number of valence electrons:**
- Sodium (Na) is in Group 1 of the periodic table. It has 1 valence electron.

2. **Determine the maximum number of electrons it can gain or lose:**
- Sodium prefers to lose its one valence electron to achieve a stable configuration like neon, which has a full outer shell.

3. **Conclusion:**
- The valency of sodium is 1, as it can form bonds by losing 1 electron.

### Summary
- Oxygen has a valency of 2.
- Sodium has a valency of 1.

Valency helps in predicting how elements will bond with one another to form compounds.