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### Calculating Number of Valence Electrons

Posted: Fri Oct 25, 2019 10:07 am
How do you calculate the number of valence electrons just from the problem giving you the name of the element?

### Re: Calculating Number of Valence Electrons

Posted: Fri Oct 25, 2019 10:23 am
One way you could calculate the number of valence electrons:
1. Use a periodic table to find atomic number, which is the # of electrons the element has.
2. Write out the electronic configuration.
3. Count how many electrons are in the last shell.

Ex:
1. Chlorine - 17 electrons.
2. Electronic configuration - 1s^2 2s^2 2p^6 3s^2 3p^5
3. - in n=3, chlorine has 7 electrons = 7 valence electrons.

### Re: Calculating Number of Valence Electrons

Posted: Fri Oct 25, 2019 11:05 am
You can just count from left to right to find the number of valence electrons in the ground state for an atom (e.g.Titanium is the fourth element from the left, so it has 4 valence electrons)

### Re: Calculating Number of Valence Electrons

Posted: Fri Oct 25, 2019 11:11 am
The number of valence electrons is equal to the main-group number. Hydrogen is in group 1 and has one valence electron. Oxygen is in group 6 and has 6 valence electrons.

### Re: Calculating Number of Valence Electrons

Posted: Fri Oct 25, 2019 11:24 am
The number of valence electrons is obtained by knowing its group number which you can identify by looking at the periodic table ad counting the rows that run down vertical. However if you want to know the general number of total electrons in all shells you look at the atomic number of the element.

### Re: Calculating Number of Valence Electrons

Posted: Fri Oct 25, 2019 12:04 pm
The number of valence electrons is the group number, which you can count from left to right on the periodic table.

### Re: Calculating Number of Valence Electrons

Posted: Fri Oct 25, 2019 4:12 pm
A simple trick is to look at the group number above each column on the periodic table. For groups 1 and 2 there are simply 1 and 2 valence electrons respectively. For groups 13-18 you only look at the last digit which is the number of valence electrons; so, group 13 would have 3 valence electrons, group 14 would have 4, and so on...

### Re: Calculating Number of Valence Electrons

Posted: Sat Oct 26, 2019 5:39 pm
When dealing with elements in the s and p blocks, just count the elements from left to right, SKIPPING the d block, until you get to your desired element.

For example, for Oxygen, the elements in that row are
Li, Be, B, C, N, O, F, Ne.

In that order, Oxygen is the 6th element. Thus, Oxygen has 6 valence electrons.