Na & Ne - Cl & Ar and Ionic bond 

We know that the sodium atom has 11 electrons. Thus the first two shells fill up completely with two and eight electrons respectively and the eleventh electron comes into the third shell. So the electronic structure or configuration of a sodium atom becomes (2,8,1). Now lets take the chlorine atom. A chlorine Atom has a total of 17 electrons. These fill up in the first, second and third shell in the electronic configuration 2,8,7. In this way, we get one electron in the outermost shell of sodium and seven electrons in the outermost shell of chlorine.

                                                                  

If, in some way, sodium and chlorine get 8 electrons in the last shell, they will both become inert/non-reactive and chemically stable like the noble gases.

That is what happens - all elements in the Periodic Table want to get an electronic structure like the Nobel gases and become chemically stable.

For that to happen they require eight electrons in their outermost  shell.

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Now, the number of electrons cannot be changed so easily. After all, nature does not work like our App!

So generally : in nature elements are ready and willing to combine with those elements with whom they can either share or give or take a specific number of electrons in such a way that in every outer orbit there are eight electrons.

Apparently, this is also the reason for their chemical reactivity.

So when sodium and chlorine are brought together, the sodium atom immediately gives its outermost electron to the chlorine atom. This way the sodium atom is now left with an extra +1 charge and its electronic configuration becomes (2,8) which is like the structure of the inert gas, Neon, which is closest to it. Now instead of calling it a sodium atom, we will call it a sodium ion. Its chemical nature is very different from that of a sodium atom. In the same way, after accepting an electron from sodium, chlorine has one extra (-1) charge and its electronic configuration becomes (2,8,8) which is the like the electronic structure, (2,8,8) of the inert gas, Argon, closest to it. Now we will call it the chlorine negative ion instead of the chlorine atom. Its chemical nature is very different from the chemical nature of the chlorine atom.

In the end, the sodium positive ion and the chlorine negative ion get attracted by the electronic force and form Sodium Chloride (NaCl) or Salt which is a compound.

So the bond that is formed between the Sodium ion and the Chlorine ion to form NaCl compound, is called an Ionic Bond.

Sometimes, electrons in the outermost shell of an atom are shown by big dots and sometimes by crosses. Whenever we make a new molecule, we should be clear about which electron is from which atom and how many electrons are shared by which atoms. What matters for you is the number of electrons.

As we have seen in the earlier paragraph how the atoms of Na and Cl have a tendency to change their electronic configuration to that of the atoms of the inert gas closest to them. This tendency respectively converts them to Na+ and Cl- ions and finally the electronic (or electrostatic)? Interaction between these positive and negative ions results into a molecule of NaCl.

As a result of this entire process we can see that the atoms of Na and Cl elements combine with one another and form a new particle of a new substance, NaCl. This new particle which is made by the combining of two or more atoms is called a molecule. In this example of NaCl given above, we will call the kind of bond formed between Na and Cl as Ionic Bond.
 

There are other common examples of substances being formed as a result of this Ionic Bond; Sodium Flouride (NaF), Potassium Chloride (KCl), Calcium Chloride (CaCl2)

Just like NaCl, can you draw the process of making the above mentioned substances from their basic elements, in your copy?