Calculate the number of cations anions, and formula units per cell unit of the following : rock-salt structure, and flourite....I have no idea how to do the second one but for the first one I got 13, 14, and 13.5 respectively. Also, what are the coordination numbers of the ions in flourite?
To calculate the number of cations, anions, and formula units per cell unit of the rock-salt structure, you are correct. The rock-salt structure consists of one cation (usually a metal ion) and one anion (usually a halide ion) per unit cell.
In a rock-salt structure, there is one cation and one anion, so the numbers are as follows:
- Number of cations = 1
- Number of anions = 1
- Number of formula units per cell unit = 1
For the fluorite structure, the coordination numbers of the ions are different. The fluorite structure consists of cations (usually metal ions) surrounded by eight anions (usually fluoride ions) and vice versa.
In the fluorite structure, the coordination number of the cations is 8, as each cation is surrounded by eight anions. The coordination number of the anions is also 8, as each anion is surrounded by eight cations.
Let me know if you have any more questions!
To calculate the number of cations, anions, and formula units per unit cell in different crystal structures, you need to understand the arrangement of ions in these structures.
1. Rock-Salt Structure (NaCl):
In a rock-salt structure, each ion is surrounded by six ions of opposite charge. This is called a coordination number of 6.
- Cations (Na+ ions): In NaCl, there is one Na+ ion per unit cell. Therefore, the number of cations per cell unit is 1.
- Anions (Cl- ions): Similarly, there is also one Cl- ion per unit cell. Thus, the number of anions per cell unit is 1.
- Formula Units per Cell Unit: Since the ratio of Na+ to Cl- ions is 1:1, the number of formula units per cell unit is 1.
So, for the rock-salt structure (NaCl), the number of cations, anions, and formula units per cell unit is 1, 1, and 1 respectively.
2. Fluorite (CaF2):
In a fluorite structure, each cation (Ca2+) is surrounded by eight anions (F-) and each anion is surrounded by four cations. This results in a coordination number of 8 for Ca2+ ions and a coordination number of 4 for F- ions.
- Cations (Ca2+ ions): In CaF2, there is one Ca2+ ion per unit cell. Hence, the number of cations per cell unit is 1.
- Anions (F- ions): Since each Ca2+ ion is surrounded by 8 F- ions, and there are four F- ions in each unit cell, we need to divide by 8 to obtain the number of anions per Ca2+ ion. So, the number of anions per cell unit is 4/8 = 0.5.
- Formula Units per Cell Unit: As in the rock-salt structure, the ratio of Ca2+ to F- ions is 1:2. So, in this case, the number of formula units per cell unit is 1.
Therefore, for the fluorite structure (CaF2), the number of cations, anions, and formula units per cell unit is 1, 0.5, and 1 respectively.
Additionally, to determine the coordination numbers in fluorite, the coordination number for Ca2+ ions is 8, and the coordination number for F- ions is 4.