In this lesson, we will learn about what ions are, and how they are formed.
Knowledge Core
When an atom gains or loses electrons, they develop a charge.
Recall that electrons are negatively charged, so the gain or loss of electrons will create
a charge.
These charged particles are called ions.
When an atom loses electrons, they become positively charged.
Positively charged ions are called cations.
An easy way to remember this is to recall that cats have paws.
When an atom gains electrons, they become negatively charged.
Negatively charged ions are called anions.
Let's look at Na as an example.
Its electronic structure is 2, 8, 1.
It has one electron in its valence, or outermost shell.
When Na loses this valence electron, it becomes a positively charged Na
This charge is written as a superscript when writing the formula.
When drawing the electronic structure, enclose it in square brackets, and write the charge
on the top right hand corner.
Now, let's look at O as another example.
Its electronic structure is 2, 6.
Therefore, there are six electrons in its valence shell.
Oxygen gains two electrons to form a negatively charged O2-
Remember to include the charge when writing the formula and when drawing the electronic
structure.
If we look at the electronic structures of these two ions, we will see that they have
a complete outer shell.
We will also see that they have the same electronic structure as that of a noble gas.
How are you feeling about ions?
Are you ready to form ions on your own?
Let's try.
Please pause the lesson and draw the electronic structure of a Ca
The electronic structure of Ca is 2, 8, 8, 2.
It loses its two valence electrons to form a Ca
The electronic structure of Cl is 2, 8, 7.
It gains an electron to form a Cl
Both ions also have the same electronic structure as a Ar atom.
Did you get the structures right?
Did you remember to specify the charges?
What do Na and Mg have in common?
They are both metals, and metals lose their valence electrons to form cations.
Group 1 metals, such as Na, have one valence electron, and they lose this electron to form
ions with a +1 charge.
Group 2 metals, such as Mg, have two valence electrons, and they lose these electrons to
form ions with a +2 charge.
O and F are both non-metals -- non-metals tend to gain electrons to form anions.
ion have the same electronic structure as a Ne atom.
O is in Group 6, and has six valence electrons.
It gains two electrons to form an ion with a -2 charge.
F is in Group 7, and has seven valence electrons.
It gains one electron to form an ion with a -1 charge.
Group 3 elements, such as aluminium, lose three electrons to form ions with a +3 charge.
Group 5 elements, such as nitrogen, gain three electrons to form ions with -3 charge.
Group 4 elements, such as carbon, tend form covalent compounds -- stay tuned!
In conclusion, an ion is a charged particle formed from either the gain or loss of electrons.
A positively charged ion is known as a cation, and a negatively charged ion is known as an
anion.
The ions formed have the same electronic structure as their nearest noble gas.