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- Describe the formation of ions by electron loss or gain.
In the last topic, I mentioned that elements gain or lose or share electrons when undergoing reactions with other elements. Here, I’ll explain how it works.
We know that atoms are neutrally charged (no. of positive charges (protons)= no. of negative charges (electrons)). When it loses or gains electrons the charge balance is tipped. An ion is an atom that is electrically charged. It will be positively charged if it loses electrons (because there are more protons than electrons now) and negatively charged when it gains more electrons (more electrons than protons present now).
We saw that elements in the last group (column) of the periodic table – the noble gases- have full electron shells- they are stable. They cannot lose or gain electrons. The other elements in the periodic table don’t have a full outer shells and so reacts with other elements- they can gain or lose electrons.
After any reaction, the atoms of an element has to have full outer shells- that is, they must become stable. They can do this by gaining or losing electrons from and to the other element’s atoms respectively. You’ll understand this with the example below.
- Describe the formation of ionic bonds between metals and non-metals as exemplified by elements from Groups I and VII.
(Note that the columns in the periodic table are called groups. The block of elements in the yellow colour above are not considered part of any groups here).
The elements in group 1 and 2 are metals and the elements in group 7 are non-metals. Let’s take the electronic configurations of metal ‘Na’ Sodium and the non-metal ‘Cl’ Chlorine.
Sodium has a configuration of 2,8,1
Chlorine has a configuration of 2,8,7
Both elements are not stable. In order to make them both stable, sodium needs to lose 1 electron and Chlorine needs to gain 1 electron. So sodium will have to lose it’s outer electron to chlorine.
Now the configuration of Sodium will be 2,8 and the configuration of Chlorine will be 2,8,8. Both have full outer shells and so have become stable.
Since sodium lost a negatively charged particle, it’s overall charge becomes positive, making it a positive (+1) sodium ion. Chlorine gained one electron, so it gained an extra negative charge, making it a negative (-1) Chlorine ion. (The new compound formed is sodium chloride).
- Explain the formation of ionic bonds between metallic and non-metallic elements.
The above is an example of an ionic bond, where, oppositely charged ions are attracted. In the chemical bond created between metals and non-metals are always ionic because the metal (Sodium) becomes a positive ion and the non-metal (Chlorine) becomes a negative ion.
Another example of ionic bonding bonding is the one between the metal Magnesium and the non-metal Oxygen. Magnesium has configuration 2,8,2 and oxygen has configuration 2,6.
In order to be stable magnesium either needs to lose the 2 electrons or get 6 electrons. Oxygen needs to gain two electrons or give out 6 electrons. The quicker reaction is magnesium giving out the two electrons to oxygen. Now the configuration of magnesium is 2,8 and that of oxygen is 2,8. Magnesium lost two electrons, so has a +2 charge and oxygen gained two electrons so has -2 charge.
- Describe the lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions, exemplified by the sodium chloride structure
In ionic compounds (compounds formed through ionic bonding), the strong attractive forces between the positive and negative ions result in the formation of a giant ionic structure. This ions are regularly arranged in what is known as a lattice. The attractive forces are very strong in every direction that it takes a lot of energy to break them apart. This is also why ionic compounds have every high melting and boiling points.
Notes submitted by Lintha
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