Ionic Bonding

Intro to Physics and Chemistry Index

General Chemistry Index

Where are we going with this? This page will give the ability to use laboratory observations and data to compare and contrast ionic, covalent, network, metallic, polar, and non-polar substances with respect to constituent particles, strength of bonds, melting and boiling points, and conductivity; provide examples of each type.

Ionic Bonding
When ions bond… 

Ionic bonding occurs when two ions are attracted to each other after one atom has transferred its electron(s) to another. This is usually between a metal and a non-metal.

So, some of the elements (many of the metals) three or less electrons in the valence set of orbitals. Then, there are some elements missing only a few electrons to completely fill their valence set.

Compounds formed between many metals and nonmetals create ionic bonds. In ionic bonding, the electrons of the metal can be considered to be transferred to the nonmetal.

Story (sort of) time…

So, for instance, sodium (Na) meets up with chlorine (Cl). Sodium has that one electron stuck out there by itself in the last set of orbitals (in the 3s orbital) and chlorine is missing one electron in it's last set of orbitals (in the 3p set). 

Sodium transfers its electron to chlorine, allowing both of the atoms to have complete sets of orbitals, BUT, since the after-transfer number of protons and electrons are different, both of the atoms are not in balance regarding charge. (Thus, they are considered ions.) They have opposite charges, in fact. Since opposite charges attract, the two ions stick to each other (think of static cling!)

This is ionic bonding…

When electronegativity differences are high (such as between metals and nonmetals), the atom with the positive valence transfers its electron(s) to the atom with the negative valence, thus creating ions that are oppositely charged which cling to each other.

A little more… 

Depending on the charge, ions get names…

Cation: the positively charged ion

Anion: the negatively charged ion

How ionic compound molecules form…

The ultimate result of ionic bonding is that the valence charges of the ions sums to zero. 

Once the final molecule has a zero charge, the net charge will be zero.

It is very easy to predict ionic compounds.

Example:

Mg has a valance charge of +2.

S has a valence charge of -2. 

Thus, one atom of Mg will combine with 1 atom of S and the net charge will be:

+2 -2 = 0

Li has a valence charge of +1.

S still has a valence charge of -2.

Therefore, it will take 2 Li to combine with 1 S to get a balanced charge of 0:

+1 +1 -2 = 0

Writing them out…

EXAMPLES:

If you had:

H+1

O-2

You get H2O

_____________

If you have polyatomic ions, you can think of them as chunks. Then, apply the process to the whole chunk.

If you had:

Zn+2

PO4-3

You get  Zn3(PO4)2

NOTE: If the subscript of a polyatomic ion is 1, do NOT use parenthesis.

Using the "criss cross" method:

• the absolute value of the charge of the positive ion becomes the subscript for the negative ion
• the absolute value of the charge of the negative ion becomes the subscript for the positive ion

NOTE: reduce the subscripts to lowest terms. For example, if you end up with

Mg2S2 

you should write

MgS