1. Valence Electrons:
- Aluminum (Al) belongs to Group 13 (or IIIA) of the periodic table and has an atomic number of 13.
- Chlorine (Cl) belongs to Group 17 (or VIIA) of the periodic table and has an atomic number of 17.
- Aluminum has three valence electrons in its outermost energy level (3 valence electrons), while Chlorine has seven valence electrons (7 valence electrons).
2. Ionic Bonding:
- Ionic bonding occurs when one or more electrons are transferred from one atom to another, resulting in the formation of positively charged ions (cations) and negatively charged ions (anions).
- In the case of AlCl3, Aluminum (Al) loses its three valence electrons to Chlorine (Cl), resulting in the formation of positively charged Aluminum ions (Al3+) and negatively charged Chloride ions (Cl-).
3. Formula Determination:
- To determine the correct formula, we need to balance the charges of the ions. Since Aluminum loses three electrons and each Chlorine gains one electron, we need three Chloride ions (3Cl-) to balance the charge of one Aluminum ion (Al3+).
- Therefore, the formula becomes AlCl3, where the subscript "3" indicates that there are three Chlorine atoms for every one Aluminum atom in the compound.
It's important to note that the formula AlCl3 represents the simplest whole-number ratio of ions that satisfies the valence requirements and charge balance. This is why the formula AlCl3 is correct, rather than other possible formulas like AlCl2 or Al2Cl6, which would not balance the charges correctly.
