what is the diference between Mg and Mg ions?

Question

what and how can i know the charge sign and number for these ions?
Mg, K, S, Al, Cl, O, B, P?

can i know them from the periodic table???

Answer 1

Yes , you can in most cases

In order to make stable ions , the outer shell of electrons must be either empty or full.

The elements which are in the periodic table in the left column (usually called first) have one electron on the outer shell. the trend to give that electron to make a positive ion with charge s+1. Ex : K (potassium) gives its electron to make the ion K+)

The elements which are bear that column (second from the left) give 2 electrons and form bivalent positive ion with charge +2 . Ex (Mg forming ion Mg++).

The elements on the third column from the left form trivalent positive ions ex (Al giving Al+++)

We go no to the Right side. Completely at the right, you find gazes with shell full. In general these elements have no chemical properties as the outer shell is full

Near that column, you find elements beginning with F. These elements tends to gain one electron to fill their outer shell. They give rise to ions with charge -1. Ex = Cl which yields ion Cl-)

Near that column you find a column beginning with oxygen. These elements need to electrons to fill the outer shell and form bivalent negative ions as O-- or S--

going one column further at the left you have elements beginning with B which form elements with 3 negative charges such as B--- or P--- gaining 3 electrons

Answer 2

Magnesium has an atomic number of 12, which means it has 12 protons and 12 electrons in its elemental form. When an atom has the same number of protons and electrons it is considered to be electrically neutral, having no positive or negative charge. Magnesium however does not exist in nature in its elemental form, because it likes to get rid of its two valence electrons in the 2s shell. When it gives up those two electrons, it becomes positively charged, forming it's ion Mg 2+. An ion is simply an electrically charged species. I say species because an ion can be an atom, or a molecule.

You can tell what the most likely charge on an atom will be by looking at the periodic table. Atoms prefer to have a 8 total valence electrons "the octet rule". So they will either gain electrons to get to 8 or lose electrons. Remember that the periodic table is organized in rows and columns. The atoms in column 1A all have one electron in the s valence shell. The atoms in 2A have 2 electrons in their valence s shell. The atoms in 3A have 3 electrons in the valence shell, 2 in s and 1 in p. And so on.

The atoms of the first column (also called group), will lose that electron in the s shell to become positively charged. So, Na for example, in its elemental form has an atomic number of 11, it has 11 protons and 11 electrons. It will lose the s shell electron, because if it loses that electron it will have 8 total valence electrons (its prefered state) so it then becomes Na+.
You may find it helpful to go through the motions of writing out the electrons, according to the electron configurations to help you figure it out. Wikipedia has a good review of electron configurations here http://en.wikipedia.org/wiki/Electron_configuration

Hope this helped.