Ionic bonding

When a metal like sodium reacts with a non-metal like chlorine, they form an ionic bond.

Sodium has the atomic number 11, meaning that it has 11 protons and 11 electrons.

Due to details of its atomic structure, a sodium atom tends to lose one of its electrons, causing it to go down to 10 electrons.

When this happens, the particle will still have 11 protons in its nucleus.

So 11 protons minus 10 electrons gives us an overall “one plus” charge.

We refer to charged particles as ions.

A positively charged ion is called a cation. Metals tend to lose electrons to form cations.

Chlorine, on the other hand, is a non-metal.

Non-metals tend to gain electrons to form negatively charged ions called anions.

A chlorine atom has an atomic number of 17, so it has 17 protons and 17 electrons.

When the neutral chlorine atom gains an electron it ends up with 18 electrons, but it still has 17 protons in its nucleus, so overall there’s a net charge of one minus.

Now we have a positively charged sodium cation, and a negatively charged chloride anion.

Opposite charges attract, so that creates an ionic bond.

Compounds that contain ionic bonds are called ionic compounds.

Now, in sodium chloride, it extends beyond just two ions.

A chloride ion sits next to a sodium ion, which sits next to another chloride ion, and another sodium ion, and on it goes.

And this entire crystal structure is held together by electrostatic attractions.

These tasty little crystals form what we call table salt.

On the periodic table, elements like sodium appear in the first column on the far left of the table.

These “group 1A” elements tend to lose one electron and form a “one plus” charged cation.

In contrast, elements like chlorine are in “group 7A” on the other side of the periodic table.

These atoms tend to gain one electron and form a “one minus” charged anion.

So both group 1A elements like sodium, and group 7A elements like chlorine, try to have the same number of electrons as the closest noble gas on the periodic table.

Sodium loses one electron, leaving it with eight electrons in its outer shell, just like the noble gas neon.

Chlorine gains one electron, leaving it with eight electrons in its outer shell, just like the noble gas argon.

The pattern extends to other groups on the periodic table.

Magnesium is in group 2A, and so it needs to lose 2 electrons to have the same number of electrons as the noble gas neon.

So Magnesium forms a two plus cation.

Oxygen is in group 6A, and it needs to gain 2 electrons to have the same number of electrons as the noble gas neon.

So oxygen forms a two minus anion.

Nitrogen is in group 5A, and it needs to gain 3 electrons to have the same number of electrons as neon.

So nitrogen forms a three minus anion.

Ionic compounds are electrically neutral with no overall charge.

This helps us predict how ionic compounds are likely to form.

For example, potassium is in group 1A, so it forms a “one plus” cation, and bromine is in group 7A, so it forms a “one minus” anion.

So potassium and bromine would come together to form Potassium bromide , or KBr, an ionic compound with an overall charge of zero.

Now, let’s look at a different example.