Answer
The valency of fluorine in CaF₂ is 1.
Detailed Explanation
The chemical formula is:
CaF₂
Here:
- Ca = Calcium
- F = Fluorine
- The subscript 2 means that there are two fluorine atoms.
Calcium has a valency of 2, while fluorine has a valency of 1.
To make the compound electrically neutral:
Ca²⁺ + 2F⁻ → CaF₂
Therefore, each fluorine atom has a charge of −1, and its valency is 1.
Easy Trick
Think:
Calcium = 2
Fluorine = 1
So:
Ca²⁺ + F⁻ + F⁻ → CaF₂
The two fluorine atoms are needed to balance the +2 charge of calcium.
Related Questions and Answers
1. What is the valency of calcium in CaF₂?
Answer: The valency of calcium is 2.
Explanation: Calcium loses two electrons to form Ca²⁺.
2. What is the valency of fluorine?
Answer: The valency of fluorine is 1.
Explanation: Fluorine needs one electron to complete its outermost shell, so it generally forms F⁻.
3. What is the chemical name of CaF₂?
Answer: Calcium fluoride.
Explanation: The compound contains calcium and fluorine, so it is named calcium fluoride.
4. Why is the formula of calcium fluoride CaF₂?
Answer: Because calcium has valency 2 and fluorine has valency 1.
To balance the valencies:
Ca = 2
F = 1
Therefore, two fluorine atoms are required for one calcium atom:
CaF₂
5. What ions are present in CaF₂?
Answer: CaF₂ contains:
- Ca²⁺ — calcium ion
- F⁻ — fluoride ion
There are two fluoride ions for every calcium ion.
Ca²⁺ + 2F⁻ → CaF₂
6. What is the charge on a fluoride ion?
Answer: The charge on a fluoride ion is −1.
Explanation: A fluorine atom gains one electron and becomes:
F + e⁻ → F⁻
7. Is fluorine a metal or non-metal?
Answer: Fluorine is a non-metal.
Explanation: Fluorine belongs to Group 17 of the periodic table and is a halogen.
8. What happens to fluorine when it forms fluoride ion?
Answer: Fluorine gains one electron and forms the fluoride ion, F⁻.
F + e⁻ → F⁻
This gives fluorine a stable outer electron configuration.
9. What is the difference between valency and ionic charge?
Answer: Valency indicates the combining capacity of an atom, while ionic charge indicates the electrical charge carried by an ion.
For fluoride:
- Valency = 1
- Ionic charge = −1
For calcium:
- Valency = 2
- Ionic charge = +2
10. How can we find the valency of an element from its compound?
Answer: Look at how many atoms of each element are required to form a neutral compound.
For CaF₂:
- One calcium atom combines with two fluorine atoms.
- Calcium has valency 2.
- Fluorine has valency 1.
Therefore:
Ca = 2, F = 1
11. What is the valency of oxygen in MgO?
Answer: The valency of oxygen is 2.
Magnesium also has valency 2, so the formula is:
MgO
12. What is the valency of chlorine in NaCl?
Answer: The valency of chlorine is 1.
Sodium has valency 1 and chlorine has valency 1, so:
NaCl
13. What is the valency of oxygen in CaO?
Answer: The valency of oxygen is 2.
Calcium has valency 2, so one calcium atom combines with one oxygen atom:
CaO
14. What is the valency of nitrogen in Mg₃N₂?
Answer: The valency of nitrogen is 3.
Magnesium has valency 2 and nitrogen has valency 3. Their valencies are balanced using three magnesium atoms and two nitrogen atoms:
Mg₃N₂
15. What is the valency of aluminium in Al₂O₃?
Answer: The valency of aluminium is 3.
Oxygen has valency 2. The valencies balance as:
Al = 3
O = 2
Therefore, the formula is:
Al₂O₃
Quick Revision Table
| Compound | Element | Valency |
|---|---|---|
| CaF₂ | Calcium | 2 |
| CaF₂ | Fluorine | 1 |
| NaCl | Sodium | 1 |
| NaCl | Chlorine | 1 |
| MgO | Magnesium | 2 |
| MgO | Oxygen | 2 |
| Al₂O₃ | Aluminium | 3 |
| Al₂O₃ | Oxygen | 2 |
| Mg₃N₂ | Magnesium | 2 |
| Mg₃N₂ | Nitrogen | 3 |
⭐ Most Important Point
In CaF₂, fluorine has valency 1 and exists as F⁻, while calcium has valency 2 and exists as Ca²⁺.
Ca²⁺ + 2F⁻ → CaF₂