Quick Notes Ionic Bonding
- Ionic bonding describes the electrostatic attraction that holds oppositely charged ions together.
- The greater the charge of the ions involved, the stronger the ionic bonding between them due to the increased attraction.
- To get a full outer shell, atoms lose or gain electrons.
- Metals lose electrons to get a full outer shell and become positively charged ions.
- Non-metals (usually) gain electrons to get a full outer shell and become negatively charged ions.
Full Notes Ionic Bonding
The most stable configuration for most atoms is to have eight electrons in their outermost shell (octet rule). Note, transition metals are an exception to this, (see Transition Metals). The reactivity of an element can often be linked to how easily an atom can ‘get’ to having eight electrons in its outermost shell. This explains why the noble gases (group 8 in the periodic table) are so unreactive, as they do not want to change their electron number.
To get a ‘full outer shell’ electrons can lose or gain electrons and become charged ions.
Electrons are negatively charged (e-). So, if an atom loses an electron, it becomes a positively charged ion; if an atom gains an electron, it becomes a negative ion. Oppositely charged ions attract each other and form ionic compounds (compounds made of ions).
A common example is the reaction between sodium and chlorine.
Sodium has one electron in its outer shell and chlorine has seven electrons in its outer shell. In order for both sodium and chlorine to have full outer shells, sodium ‘gives’ an electron to chlorine.
In the process, sodium becomes a positively charged ion (because it has lost a negatively charged electron); chlorine becomes a negatively charged ion (because it has gained a negatively charged electron).
Positively charged and negatively charged ions are attracted to each other (electrostatic attraction). With the above example, the positive sodium ion is attracted to the negative chloride ion. The ions move towards each other because of this attraction, forming the compound ‘NaCl’.
The bonding between the oppositely charged ions is called ‘ionic bonding’.
The stronger the ionic charge (the charge on the ion), the stronger the ionic bonding.
The group number (one to eight) in the periodic table tells us how many electrons an atom needs to lose or gain to get to a full outer shell, so it can be used to predict the charge of the ion formed. See above.
A large number of oppositely charged ions will arrange themselves to maximise attraction between the opposite charges and minimise the repulsion between the same charges. This leads to the formation of regular, repeating structures called ionic lattices.
For example, with sodium chloride, the positive sodium ions want to be as far away from each other as possible and the negative chloride ions also want to be as far away from each other as possible. To achieve this, the ions arrange themselves in a regular pattern.
Lattice structures are three dimensional, meaning each ion is attraction to several other ions in the structure, making the ionic lattice very strong and hard to break. This is why ionic compounds usually have very high melting and boiling points.