Here we’ll have a look at what atoms and ions are, and how atoms change into ions. We’ll start off by looking at how metal atoms form ions.

Atoms and Ions

Part 1Ions of Metals

n

n n

nn

n

In the center of all atoms there is a nucleus

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

n

n n

nn

n

A nucleus is made up of protons and neutrons.

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

protons and

neutrons

n

n n

nn

n

The nucleus we’ve shown here is the nucleus of a magnesium atom. The box for magnesium on the periodic table is shown on the left.

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

n

n n

nn

n

The atomic number is located on top of the element’s symbol on the periodic table. For magnesium, the atomic number is 12

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

n

n n

nn

n

The atomic number tells us the number of protons in the nucleus of an element’s atom.

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

n

n n

nn

n

So a nucleus of magnesium has 12 protons.

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

n

n n

nn

n

12 protons are drawn in this model here

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

n

n n

nn

n

The nuclei of most magnesium atoms have 12 neutrons. Just be aware that number of neutrons in a nucleus is not always equal to the number of protons.

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

n

n n

nn

n

Neutrons have no charge, so the number of neutrons an atom contains, has no effect on the charge of ions that form. Only protons and electrons determine ion charges.

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

p

The nucleus of a magnesium atom12 protons12 neutrons

Neutrons have no charge so they have

no effect on the charge of an ion

n

n n

nn

n

All protons have a positive charge

n

np

pn

nn

np

pp

p

p

pn

n

p

pn

np

pn

n

p

p

p

p

n

np

pn

n p

pn

n

p

pp

pProtons have a

positive (+) charge

n

n n

nn

n

So we’ll change the p’s in our diagram to positive charges.

n

n+

+n

nn

n+

++

+

+

+n

n

+

+n

n+

+n

n

+

+

+

+

n

n+

+n

n +

+n

n

+

++

+Protons have a

positive (+) charge

n

n n

nn

n

Because neutrons have no charge, we’ll just leave these with the letter “n”.

n

n+

+n

nn

n+

++

+

+

+n

n

+

+n

n+

+n

n

+

+

+

+

n

n+

+n

n +

+n

n

+

++

+Neutrons have no

charge, or a charge of 0

n

n n

nn

n

There are 12 positively charged protons in the a magnesium nucleus, so the nucleus of a magnesium atom

n

n+

+n

nn

n+

++

+

+

+n

n

+

+n

n+

+n

n

+

+

+

+

n

n+

+n

n +

+n

n

+

++

+

The nucleus of a

magnesium atom has a total charge

of +12

n

n n

nn

n

has a total charge of positive 12. (hold before clicking)

n

n+

+n

nn

n+

++

+

+

+n

n

+

+n

n+

+n

n

+

+

+

+

n

n+

+n

n +

+n

n

+

++

+

The nucleus of a

magnesium atom has a total charge

of +12

+12

n

n n

nn

n

Electrons have a negative charge. So a neutral atom of magnesium must have 12 electrons to balance the positive 12 charge on the nucleus

n

n+

+n

nn

n+

++

+

+

+n

n

+

+n

n+

+n

n

+

+

+

+

n

n+

+n

n +

+n

n

+

++

+

A neutral atom of magnesium has 12

electrons

+12

The nucleus of a

magnesium atom has a total charge

of +12

Here, we’ll use the Bohr Model of the atom, where the electrons occupy shells around the nucleus.

electrons in shells

2, 8, 2

A neutral atom of magnesium

has 12 electrons

The first shell has two electrons, the maximum number it can hold.

–

–

electrons in shells

2, 8, 2

A neutral atom of magnesium

has 12 electrons

The second shell has 8 electrons, the maximum number it can hold. That’s 2 plus 8, which is a total of 10 so far. And magnesium has 12 electrons..

–

–

– –

– –

–

–

–

–

electrons in shells

2, 8, 2

A neutral atom of magnesium

has 12 electrons

So the 3rd shell of a magnesium atom has 2 electrons

–

–

–

– –

– –

–

–

–

––

electrons in shells

2, 8, 2

A neutral atom of magnesium

has 12 electrons

So this accounts for 2 + 8 + 2 which equals all 12 electrons in a magnesium atom.

–

–

–

– –

– –

–

–

–

––

electrons in shells

2, 8, 2

A neutral atom of magnesium

has 12 electrons

The nucleus has 12 protons and 12 neutrons. Instead of a picture, this is usually simplified by showing a circle (click) with 12 p and 12 n

–

–

–

– –

– –

–

–

–

––

12 p 12 n

So this is how we represent a neutral magnesium atom.

–

–

–

– –

– –

–

–

–

––

12 p 12 n

a magnesium atom

The third shell of a magnesium atom is not filled. Atoms with partially filled shells tend to be unstable, so this atom is unstable.

–

–

–

– –

– –

–

–

–

––

12 p 12 n

a magnesium atom

The third shell is

not filled, so this atom is

unstable

In order to become stable, this atom will (click) lose these two electrons in the third shell

–

–

–

– –

– –

–

–

–

––

12 p 12 n

a magnesium atom

In order to become

stable, this atom will lose

these two electrons

Like this

–

–

–

– –

– –

–

–

–

––

12 p 12 n

a magnesium atom

This is no longer called a magnesium atom, we must now (click) call it a magnesium ion.

–

–

– –

– –

–

–

–

–

12 p 12 n

a magnesium atom

a magnesiu

m ion

In an ion, the number of electrons is NOT equal to the number of protons. We have 12 protons, but only 10 electrons here, so this is an ion

–

–

– –

– –

–

–

–

–

12 p 12 n

In an ion, the number of electrons is NOT equal

to the number of

protons

a magnesiu

m ion

This ion is stable.

–

–

– –

– –

–

–

–

–

12 p 12 n

This ion is stable. It has

the same electron

arrangement as the noble

gas neon: completely

filled first and second shells

a magnesiu

m ion

(start new sentence) Because it has 10 electrons, it has the same electron arrangement as the noble gas neon:

–

–

– –

– –

–

–

–

–

12 p 12 n

This ion is stable. It has

the same electron

arrangement as the noble

gas neon: completely

filled first and second shells

a magnesiu

m ion

With completely filled first,

–

–

– –

– –

–

–

–

–

12 p 12 n

This ion is stable. It has

the same electron

arrangement as the noble

gas neon: completely

filled first and second shells

a magnesiu

m ion

And second shells

–

–

– –

– –

–

–

–

–

12 p 12 n

This ion is stable. It has

the same electron

arrangement as the noble

gas neon: completely

filled first and second shells

a magnesiu

m ion

This ion has 12 protons,

–

–

– –

– –

–

–

–

–

12 p 12 n

12 protons (+)

a magnesiu

m ion

But only 2 plus 8, or 10 electrons

–

–

– –

– –

–

–

–

–

12 p 12 n

12 protons (+)10 electrons (–)

a magnesiu

m ion

12 protons means the ion has 12 positive charges

–

–

– –

– –

–

–

–

–

12 p 12 n

a magnesiu

m ion

12 protons (+)10 electrons (–)++++++++++++

And 10 electrons means it has 10 negative charges

–

–

– –

– –

–

–

–

–

12 p 12 n

12 protons (+)10 electrons (–)++++++++++++–– – – – – – – – –

a magnesiu

m ion

Negative and positive charges neutralize each other, and what’s left over is called..

–

–

– –

– –

–

–

–

–

12 p 12 n

12 protons (+)10 electrons (–)++++++++++++–– – – – – – – – –

a magnesiu

m ion

The net charge

–

–

– –

– –

–

–

–

–

12 p 12 n

12 protons (+)10 electrons (–)++++++++++++–– – – – – – – – –Net charge: +

+Net charge:

+2

a magnesiu

m ion

Which are two positive charges in this case.

–

–

– –

– –

–

–

–

–

12 p 12 n

++++++++++++–– – – – – – – – –Net charge: +

+Net charge:

+2

a magnesiu

m ion

12 protons (+)10 electrons (–)

We can also state this by saying that the charge on this ion is positive 2.

–

–

– –

– –

–

–

–

–

12 p 12 n

++++++++++++–– – – – – – – – –Net charge: +

+Net charge:

+2

a magnesiu

m ion

12 protons (+)10 electrons (–)

Which can also be written as 2 plus

–

–

– –

– –

–

–

–

–

12 p 12 n

++++++++++++–– – – – – – – – –Net charge: +

+Net charge:

2+

a magnesiu

m ion

12 protons (+)10 electrons (–)

In the box on the periodic table, the top right hand corner shows the charge on the most common ion of magnesium. We see it is (click) 2 plus

–

–

– –

– –

–

–

–

–

12 p 12 n

++++++++++++–– – – – – – – – –Net charge: +

+Net charge:

2+

The ion charge

a magnesiu

m ion

12 protons (+)10 electrons (–)

The same as the net charge on our magnesium ion here.

–

–

– –

– –

–

–

–

–

12 p 12 n

12 protons (+)10 electrons (–)++++++++++++–– – – – – – – – –Net charge: +

+Net charge:

2+

The ion charge

a magnesiu

m ion

Looking on the periodic table, Group 1 metals, or alkali metals all lose 1 electron (click) to form an ion with a positive 1 charge.

Group 1 (Alkali Metals) all lose one electron to

form an ion with a1+ charge

Group 2 metals, or alkaline earth metals all lose 2 electrons (click) to form an ion with a positive 2 charge. In general, metals tend to lose electrons in order to form stable positive ions.

Group 2 (Alkaline Earth

Metals) all lose two electrons to form an ion

with a2+ charge