If you have some formulas of actual compounds, you can predict the formulas of similar compounds using the Periodic Table.
Elements in the same chemical family have similar chemical properties.
•Remember: columns in the Periodic Table are familes (or groups) of similar elements
•That means they will often form compounds with similar chemical formulas (same atom ratio)
Example 1:
Given: AlF3 is an actual compound.
•The 1:3 ratio in this formula is caused by the chemical properties of aluminum and fluorine.
•Similar compounds will also have this 1:3 ratio.
Question: Predict the formulas for the element combinations below, given that AlF3 is an actual compound.
| Elements | Formula (Answer) |
Comments |
| Al + Cl | AlCl3 | Cl is in the same family as F, so Al and Cl have a 1:3 ratio like AlF3. |
| Al + Br | AlBr3 | Br is in the same family as F, so Al and Br have a 1:3 ratio like AlF3. |
| B + F | BF3 | B is in the same family as Al, so B and F have a 1:3 ratio like AlF3. |
| B + Cl | BCl3 | B is in the same family as Al, and Cl is in the same family as F. |
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