How do you find the number of valence electrons in a molecule? Do I need to use the Lewis structure diagram to find out? Please help! I need to the total number of valence electrons for SiH4, H2SO4, CCl4, BF3 and I don't know how!
I have never used the term "valence electrons" for anything other than for atoms. Never for molecules; however, I suspect you are to count the electrons in the Lewis dot structure. Here is a site that explains how to draw Lewis structures. Post again with specific questions if you still need help.
http://misterguch.brinkster.net/lewisstructures.html
To determine the number of valence electrons in a molecule, you generally have two options: using the Lewis structure diagram or referring to the periodic table.
Method 1: Using the Lewis structure diagram
1. Write the Lewis structure for the molecule. This involves determining the central atom(s) and the surrounding atoms (ligands), and connecting them with bonds.
2. Count the number of electrons that each atom brings to the molecule. Hydrogen (H) brings 1 valence electron, while elements from Group 14 to Group 17 (like carbon, nitrogen, oxygen, sulfur, and halogens) bring the respective number of valence electrons (4, 5, 6, 6, and 7).
3. Add up the valence electrons for all the atoms in the molecule.
Method 2: Using the periodic table
1. Identify the group number of each atom in the molecule by referring to the periodic table. Group number represents the number of valence electrons an element has.
2. Determine the number of valence electrons each atom contributes, considering their group numbers.
- For Group 1 elements (e.g., hydrogen, H), there is 1 valence electron.
- For Group 2 elements (e.g., beryllium, Be) and Group 13 elements (e.g., boron, B), there are 2 valence electrons.
- For elements in Groups 14 to 17 (e.g., carbon, C; oxygen, O), the number of valence electrons corresponds to the group number.
3. Sum up the valence electrons contributed by all the atoms in the molecule.
Now, let's apply these methods to find the number of valence electrons for the given molecules:
1. SiH4 (Silane)
Method 1 (using Lewis structure):
- Silicon (Si) brings 4 valence electrons.
- Hydrogen (H) brings 1 valence electron each.
Total: 4 + (4 × 1) = 8 valence electrons.
Method 2 (using periodic table):
- Silicon (Si) is in Group 14, so it has 4 valence electrons.
- Hydrogen (H) is in Group 1, contributing 1 valence electron each.
Total: 4 + (4 × 1) = 8 valence electrons.
2. H2SO4 (Sulfuric acid)
Method 1:
- Hydrogen (H) brings 1 valence electron each.
- Sulfur (S) brings 6 valence electrons.
- Oxygen (O) brings 6 valence electrons each.
Total: (2 × 1) + 6 + (4 × 6) = 32 valence electrons.
Method 2:
- Hydrogen (H) is in Group 1, contributing 1 valence electron each.
- Sulfur (S) is in Group 16, bringing 6 valence electrons.
- Oxygen (O) is in Group 16, contributing 6 valence electrons each.
Total: (2 × 1) + 6 + (4 × 6) = 32 valence electrons.
3. CCl4 (Carbon tetrachloride)
Method 1:
- Carbon (C) brings 4 valence electrons.
- Chlorine (Cl) brings 7 valence electrons each.
Total: 4 + (4 × 7) = 32 valence electrons.
Method 2:
- Carbon (C) is in Group 14, so it has 4 valence electrons.
- Chlorine (Cl) is in Group 17, contributing 7 valence electrons each.
Total: 4 + (4 × 7) = 32 valence electrons.
4. BF3 (Boron trifluoride)
Method 1:
- Boron (B) brings 3 valence electrons.
- Fluorine (F) brings 7 valence electrons each.
Total: 3 + (3 × 7) = 24 valence electrons.
Method 2:
- Boron (B) is in Group 13, so it has 3 valence electrons.
- Fluorine (F) is in Group 17, contributing 7 valence electrons each.
Total: 3 + (3 × 7) = 24 valence electrons.
In summary, you can use either the Lewis structure diagram or the periodic table to determine the number of valence electrons in a molecule. Both methods should give you the same results, as demonstrated with the examples provided.