Ionic Bonds
The Bonds Between Metals & Non-Metals
The simplest compounds which form Ionic Bonds are those that
result from an exchange of electrons between Metals (Groups IA, IIA and
IB through VIIIB of the Periodic Table) and the Halogens
(Group VIIA).
The Metals need to give up electrons to attain a full outer shell (the
most stable state for an element) and the Halogens need to accept
electrons to attain a full outer shell.
To understand the fundamental properties of Metals and Halogens that
lead to Ionic Bonds we refer you to our section on Atomic
Structure.
The best way to understand Ionic Bonds is to illustrate how some common
Metals and Halogens form ions through the exchange of electrons. We
begin with one of the simplest compounds forming Ionic Bonds - Sodium
Chloride - common table salt.
As we learned in our section on Atomic Structure elements can be
represented by concentric circles representing the shells containing
electrons in their orbitals as shown in the picture above.
There is another much more convenient "short hand" representation of the
atomic structure of an element called the Lewis Atomic Structure. In
this representation only the "reactive electrons" in the Outer Shell are
shown. The Lewis Structure of the element Sodium (Na) is shown in the
picture above.
Sodium has only one electron in its Outer Shell and so can achieve the
stable state of a full shell by loosing the outermost electron. When
Sodium looses this electron it becomes the positively charged Sodium
Ion. The Lewis Structure for the Sodium Ion is also shown in the
picture above.
The next step in understanding the Ionic Bonds of Sodium Chloride is
to explain the formation of the Chloride Ion.
As seen in the above picture the Halogen element Chlorine (Cl)can be
represented by its full shell diagram containing all electrons. Being a
Halogen (Group VII) Chlorine has seven electrons in its Outer Shell and
thus can attain the full-shell stability by gaining one electron. When
this electron is gained the negatively charged Chloride Ion is formed.
The picture above shows the Lewis Structures of Chlorine and the
Chloride Ion.
Now that we have constructed the Lewis Structures of the Sodium Ion
and the Chloride Ion we are ready to understand how the Ionic Bonded
Sodium Chloride is formed.
In the above picture we show the Lewis Structures of both the Sodium Ion
which has a +1 charge and is called a mono-valent cation and the Chloride Ion which
has a -1 charge and is called a mono-valent anion.
We know from our own experiences with static electricity (rubbing a
balloon on your head and sticking it to the wall) that positive and
negative charges attract each other.
This attraction of unlike charges is called electrostatic attraction,
and is the force that holds the Sodium Ion and the Chloride Ion together as shown in the Lewis Structure of Sodium Chloride in
the picture above.
We continue our explanation of Ionic Bonds with another simple
compound - Magnesium Chloride. As before we start with the atomic
structures of first Magnesium and then Chloride.
The full shell atomic structure of Magnesium showing all the shells and electrons, along with the
Lewis Structures of Magnesium and the Magnesium Ion which show only the
"reactive electrons" in the Outer Shell are shown in the above picture.
Magnesium has two electrons in its Outer Shell and so can achieve the
stable state of a full shell by loosing both of these outermost
electron. When Magnesium looses these two electrons it becomes the
double positively charged Magnesium Ion. The Lewis Structure for the
Magnesium Ion is shown in the picture above.
The picture above shows the Halogen Chlorine and is the same as we
demonstrated previously. It is included here for completeness. As
before the Halogen element Chlorine (Cl)can be represented by its full
shell diagram containing all electrons. Being a Halogen (Group VII)
Chlorine has seven electrons in its Outer Shell and thus can attain the
full-shell stability by gaining one electron. When this electron is
gained the negatively charged Chloride Ion is formed. The picture above
shows the Lewis Structures of Chlorine and the Chloride Ion.
Now that we have constructed the Lewis Structures of the Magnesium Ion
and the Chloride Ion we are ready to understand how the Ionic Bonded
Magnesium Chloride is formed.
In the above picture we show the Lewis Structures of both the Magnesium
Ion which has a +2 charge and is called a di-valent cation and the
Chloride Ion which has a -1 charge and is called a mono-valent anion.
The +2 charge of the Magnesium Ion attracts two Chloride Ions to
form Magnesium Chloride (MgCl2).
We know from our own experiences with static electricity (rubbing a
balloon on your head and sticking it to the wall) that positive and
negative charges attract each other.
This attraction of unlike charges is called electrostatic attraction,
which is the force that holds the Magnesium Ion and two Chloride Ions
together as shown in the Lewis Structure of Magnesium Chloride in the
picture above.
From the above discussion it should be clear that the secret to
understanding Ionic Bonds is to understand the atomic structure of the
participating elements.
This same process of starting with the full shell atomic structure
representation of each element involved in an Ionic Bond and then
proceeding to the Lewis Structure of the cations and anions formed to
give the most stable state, can be used for any Ionic
compound.
Click here for a tutorial on the Periodic Table
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