In conclusion to my previous question, HOW Did you get the answer of O -2 so that I could then work it out?

Answer 1

In the Periodic Table, the elements on the far left (hydrogen, lithium, sodium, potassium etc) like to lose one electron to become +1 ions. The next row, beryllium, magnesium, calcium, like to lose two and become 2+ ions. Next row lose three, next don't gain or lose but share four of their electrons to make four covalent bonds. Next row, nitrogen etc. like to gain three electrons to become 3- ions. Oxygen and sulphur prefer to gain two (2-) and fluorine, chlorine etc. gain one to become F-, Cl- etc. The elements on the far right side are called inert because they don't like to react at all, being happy with their complete electron shells.

This is a very simplistic explanation and you need to read some good in-depth stuff to understand better, not keep asking questions here. Try Wikipedia or look up "valency", "ion" or "electron shell" on the net.

Answer 2

OK the GCSE level answer, which is still works (for non transistion metal elements) even if it is a highly simplified version is:

Atoms are most stable when they have a full outer shell of electrons. The first shell can contain 2 electrons the second and 3rd both 8. Oxygen has the atomic number 8, so the first shell has 2 electrons and the 2nd 6 electrons, leaving 2 free spaces for more electrons to be donated by other atoms. Thus it has a valency of -2. So Carbon which is element 6 has 2 electrons in the first shell and 4 in the second so can get a full outer shell either by losing 4 electrons or by gaining them.

Hope this makes sense.

Answer 3

Oxygen=-2 because on/in the periodic table oxygen has an atomic no. of 6 meaning it needs 2 electrons to make a complete octet structure in the outer electron shell, thus the -2, if it were potassium which in group 1, it will give it's electron to make a complete octet structure thus the +1. Hope this helps

Answer 4

The Roman numerals denote the number of valence electrons. A compound is formed and stable when it has 8 valence electrons.
The first row (H,Li,Na,etc) have one. They can combine with atoms that have 6 or 7 to form stable compounds. Column VI are minus 2 (2 short of stable, -2) column VII atoms are one short (-1).

Hence, NaCl, H20, CaCl2, CaO.
The atoms in column VIII are non-reactive under standard conditions since they are "happy" (have 8 valence electrons)

Answer 5

What was the original question?