Ionic bonding 

​​In a nutshell

​An ionic bond is formed when metal atoms donate electrons to non-metal atoms. This movement of electrons can be represented by dot and cross diagrams.

Ionic bonding 

An ionic bond forms when a metal atom donates electrons to a non-metal atom. The metal atom will form a positive ion and the non-metal atom will form a negative ion. The opposite charges between ions form electrostatic forces.

Dot and cross diagrams

​These diagrams are used to show the electrons of the metal and non-metal atom in an ionic bond. They are also used to show the movement of electrons from the metal to the non-metal atom. ​

Example 

The sodium atom (metal atom) will donate its one outer shell electron. A single positively charged ion is formed, $$Na^+$$. The chlorine atom (non-metal atom) accepts the single electron from the sodium atom, forming a single negatively charged ion, $$Cl^-$$.​

Factors affecting ionic bonding  

Ionic charge

The higher the charge on an ion, the stronger the ionic bond. This leads to a higher melting and boiling point, where more energy is needed to break the stronger ionic bonds. 

Ionic radii 

The smaller the ion, the stronger the ionic bond. Smaller sized ions can pack closer together, increasing the electrostatic attraction between ions and therefore the ionic strength. This leads to a higher melting and boiling point, where more energy is needed to break the stronger ionic bonds. 

Lattice structure

Ionic compounds will form giant lattice structures made up of the oppositely charged ions that are bonded together electrostatically. 

Example 

The repeated lattice structure of oppositely charged $$Na^+$$ and $$Cl^-$$ ions in the ionic compound, sodium chloride. 

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Ionic radii trends 

Down the group 

The ionic radius of a charged ion will increase down the group due to an extra electron shell being added continually for each element down the group.

Isoelectronic ions 

Isoelectronic ions are ions of different atoms with the same number of electrons.

Example

$$O^{2-}$$ and $$F^-$$ are examples of two isoelectronic ions. 

The number of protons increases as the amount of positive charge increases amongst the isoelectronic ions. The attraction of the negatively charged electrons in an ionic bond will increase towards the positive charge of the nucleus. This increased attraction causes the ionic radius to decrease. 

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Ions and the periodic table 

Ions are formed when atoms either gain or lose electrons. 

There are two types of ions:

• Cations - Positively charged ions formed from the loss of electrons.
  
• Anions - Negatively charged ions formed form the gain of electrons.

An atom will lose/gain electrons to form a stable full outer shell of electrons, so the group number in the periodic table (the number of outer shell electrons) will determine the type of ion that is formed. Positive ions will form when electrons are lost and negative ions when electrons are gained. 

Example 

A magnesium atom is located in Group $$2$$​. The atom will contain two outer electrons, so will lose two from its outer shell to form a full outer shell. As two electrons are lost, the ion formed will have a charge of $$2+$$​.

Ions formed by Group 1 and 2 metals

• Lose electrons to form cations​
• Group $$1$$​ elements lose one electron to form $$1+$$​ charged ions 
• Group $$2$$​ elements lose two electrons to form $$2+$$​ charged ions

Ions formed by Group 6 and 7 non-metals

• Gain electrons to form anions 
  
• Group $$7$$​ elements gain one electron to form $$1-$$​ charged ions
  
• Group $$6$$ elements gain two electrons to form $$2-$$​ charged ions 

The charge of the ion can be worked out by using the periodic table and looking up the group number of an atom.

Metals lose electrons to form positive ions and they are located on the left-hand side of the periodic table. Non-metals gain electrons to form negative ions and they are located on the right-hand side of the periodic table.  

Properties of ionic compounds

The table below describes some of the properties of ionic compounds.