In this video, we will focus on dot and cross drawing of sodium chloride ionic compound, NaCl.

Before we even start, let’s go back to the basics.

Why do atoms of elements form bonds?

Atoms of elements (except the noble gases) form chemical bond to achieve stable noble gas electronic configuration. If the atom has only 1 shell, the maximum number of electrons it can have is 2. This, we call it the duplet configuration. If it has more than 1 shell, the maximum number of electrons it can have is 8. This, we call it the octet configuration. When discussing the octet rule, we do not consider d or f electrons. Only the s and p electrons are involved in the octet rule. Do note, spdf orbital will not be discussed at secondary level.

Periodic Table

We can determine the number of electrons each atom has from the periodic table. In the periodic table, the number at the top tells us the number of proton an atom has. Since number of protons and electrons are the same in an atom, this number also tells us how many electrons each atom has. The number at the bottom tells us the number of protons and neutrons each atom has.

Drawing Sodium chloride

Let’s focus on sodium now. Sodium has 11 electrons. The first shell holds 2 electrons, the second shell holds 8 electrons. The last electron is in the third shell. Now, sodium atom would love to donate this electron to a non-metal atom so that it can achieve an octet configuration.

Now the non-metal in this compound is chlorine. Chlorine has 17 electrons. The first shell holds 2, second shell holds 8. It has 7 in the third shell. Chlorine has only 7 electrons in its outermost shell. It needs 1 more electron to achieve the octet configuration. Hence, it will take in 1 electron from sodium so that it can have 8 electrons in its outermost shell.

So, sodium atom will donate 1 electron to chlorine atom, to form sodium ion and chloride ion. Let’s work out the charges of the ions.

Sodium atom has 11 protons, which gives it a charge of +11, while 11 electrons, which gives it a charge of -11. Hence, the overall charge of this atom is 0. When sodium gives away its electron to the non-metal, the number of protons remained unchanged. Hence, the positive charge is still +11. However, there are only 10 electrons left. Hence, the negative charge is -10. Overall charge in this ion is +1. We will need to represent this charge in the dot and cross diagram. Put the bracket, and the charge.

For chlorine, the atom has 17 protons, which gives it a charge of +17, while 17 electrons, which gives it a charge of -17. The overall charge of this atom is 0. When chlorine takes in electron from sodium, the number of protons remained unchanged. Hence, the positive charge is still +17. However, there are 18 electrons now. Hence, the negative charge is -18. Overall charge in chloride ion is -1. Put the bracket and the charge in the dot and cross diagram.

Sometimes, in the examination questions, they will ask you to draw only the outermost electrons. Hence, we can omit the inner shells, and this is what you should draw.

In a nutshell, a metal loses its outermost electons to form positive ion while a non-metal gains the electrons to form negative ion. The oppositely charged ions are held together by strong electrostatic forces of attraction, which we call the ionic bond.

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