Free help with homework

Why join Brainly?

  • ask questions about your assignment
  • get answers with explanations
  • find similar questions


The no. of atoms donated or accepted by the atom of an element so as to have 8 electrons in its outermost shell is called VALENCY.
It is predicted by:
 number of valence electrons = main group number
                    (neutral atoms)

0 0 0
kindly mark as the best if it was helpful to you
The formulas for chemical compounds have an overall charge of zero. This sum of zero results from adding up all the positive and negative charges in the formula. 
Suppose atom A has a charge or oxidation number sometimes called valence of plus 3 
and A combines with atom B with a charge of minus one. 
The only way for the compound consistling of atoms of A and B to come out with an overall charge of zero is to combine one atom of A with three atoms of B. AB3 
Lets say atom C has a charge of plus 2 and atom D a charge of minus 3 
You can come out with a total charge of zero by combining three atoms of C with a total charge of plus 6 with two atoms of D with a total charge of minus 6 
So we have put together formulas based on oxidation numbers of combining atoms. 
Based on valence electrons. 
If an atom has 7 valence electrons, it will gain one more electron to make a stable octet of 8 electrons. Thus its charge will be minus one We will call this an atom of Fluorine 
Another atom has three valence electrons and by losing all three in a chemical reaction it will leave an octet of electrons exposed which was just below the outer energy level. Lets say this was an atom of Aluminum. It now has a charge of plus 3 because it lost three negative electrons. 
When plus 3 Al combines with minus one charged F, the result is AlF3 With only two valence electrons, Ca will lose two electrons, leaving a stable octet below and take on a charge of plus 2. Phosphorous has 5 valence electrons, only 3 electrons away from an octet if it could gain three more electrons. By gaining 3 electrons from Ca, phosphorous atoms would have a charge of minus 3 
So how would plus 2 Ca go with a minus 3 P. Total charge must come out zero, so with three Ca and two P the overall charge is zero, formula Ca3P2 
Any atom with one valence electron will lose it taking on a charge of plus 1. 

Three valence electrons on an atom are usually donated leaving an octet below and a plus 3 charge on the resulting ion. Six valence electrons, close to an octet by gaining 2 electrons, the atom will take on a charge of minus 2. This would be like Al2S3 Any atom with 6 valence electrons, (close to an octet) will usually gain 2 electrons taking on a charge of minus 2. This would be something like Na2S
0 0 0
The Brain
  • The Brain
  • Helper
Not sure about the answer?
Learn more with Brainly!
Having trouble with your homework?
Get free help!
  • 80% of questions are answered in under 10 minutes
  • Answers come with explanations, so that you can learn
  • Answer quality is ensured by our experts