What would the formular be for the molecule made from calcium and oxygen?

Question

i really need some help on what the symbol is for these to elements mixed together. The symbol for calcium is ca and the symbol for oxygen is O but how do i put those negative and positive things that have something to do with the electrons and ions? remember i want to join the two together and get the symbol. Please show reasoning?

sorry for the muddles details but i don't know how else to explain it :(

Answer 1

Firstly the symbol for calcium is Ca

When you look at a periodic table you will notice that Ca is in what we call group 2. (Second column in the table). All group 2 elements have 2 electrons in their outer electron shell. They will all lose 2 electron when forming an ion to give a +ve ion (cation) with a charge of +2

Ca(2+)    the 2+ is shown as a superscript

Oxygen is in group 6. All elements here have 6 electrons in their outer electron shell. They want to have 8 electrons in their outer shell and so will gain 2 electrons to form a negative ion (anion) with a charge of -2

O(2-)

The overall aim of forming an ionic compound is to form a neutral molecule. So ions will combine in ratios that cancel out their +ve and -ve charges. In this case

Ca(2+) and O(2-) are equal but opposite. They will form

CaO

If you were using sodium (Na) instead of calcium it would be a bit different. Sodium is in group 1. It has 1 electron in its outer shell and so will lose 1 electron to form

Na(+) with a single +ve charge.

Combining this with O(2-) you can see you will need two Na(+) to cancel out The 2-ve charge of the O(2-)

thus Na2O       (the 2 is shown as a subscript.)

This works for the elements in group 1, 2, 6 and 7 (elements in group 7 gain 1 electron to form anions with a -1 charge). They will nearly alway behave in this fashion when forming ionic compounds.

To work out formulas involving polyatomic ions (ions that contain more than one atom covalently bound together) you actually just really need to memorise the charge on the most common. Once you can remember their charges they combine as described above. In a ratio that leaves a neutral ionic compound.

A couple of one you may need are

hydroxide ion OH(-)

sulfate ion SO4(2-)

ammonium ion NH4(+)

for example Ca(2+) + 2(OH)(-) --------> Ca(OH)2

and Ca(2+) + SO4(2-) -------------> CaSO4

Some of the metals in the middle of the periodic table are also a bit tricky as they are capable of forming cations with different charges.