Aluminum bromide hexahydrate
How would you know its AlBr3 * 6H2O instead of just AlBr * 6H2O?
Al has a charge of 3, and Br has a charge of 1. it takes 3 Br for every Al.
Ahh Okay. So its one of those things i have to memorize?
yes.
Actually, you memorize some of it but not all of it. And if you will look at the periodic table you need not memorize any of it. Look at Al in the periodic table. It is in group 13 so the valence is 3 just as elements in group 14 are 4 etc. Get it? 3 from 13 and 4 from 14. For group 15, 16, 17, the valence is -(8-5) = -3, -(8-6)=-2 or -(8-7)=-1. So you can see Al has a valence of +3, Br has a valence of -1, compounds are zero charge; therefore, aluminum bromide is AlBr3. (The general rule is that 1, 2, 13, 14 have valences of +1, +2, +3, +4 and groups 15, 16, 17, have the difference from 8 with a negative sign added.
It occurred to me that I omitted groups 3,4,5,6,7,8,9,10,11,12 but those (between 2 ann 13) are done differently.
Ahh, now i remember my teacher telling me about it.
To determine whether the compound is Aluminum Bromide Hexahydrate (AlBr3 * 6H2O) or Aluminum Bromide Monohydrate (AlBr * 6H2O), we need to understand the valence charges of Aluminum (Al) and Bromide (Br) ions.
1. Identify the valence charges of Aluminum and Bromide ions:
- Aluminum (Al) is a Group 13 element, and it typically forms a +3 charge.
- Bromide (Br) is a halogen element, and it forms a -1 charge when it accepts one electron.
2. Determine the overall charge of the compound:
- Here, we have a hydrate compound, denoted by the presence of H2O. Water (H2O) is neutral, so it does not contribute to the compound's overall charge.
- Since there is no indication of any positive or negative ions other than Aluminum and Bromide, the overall charge of the compound should be zero.
3. Calculate the number of bromine ions based on the overall charge:
- Aluminum has a +3 charge, so to balance the overall charge to zero, there should be three bromine ions, each with a -1 charge (3 x -1 = -3).
4. Determine the number of water molecules required to balance the charge:
- Since each water molecule is neutral, we need to have six water molecules to balance the charge from the three bromine ions (6 x 0 = 0).
Hence, based on the valence charges and the overall charge, the compound is Aluminum Bromide Hexahydrate (AlBr3 * 6H2O) rather than Aluminum Bromide Monohydrate (AlBr * 6H2O).