Atomic trends

Mr.Yeung

How would you find the radius of these?

• The atomic radius is the distance between two nuclei when two like atoms are bonded together.

• In the figure above, the distance between the two nuclei in the molecule is 50 pm (1 pm = x 10−12m).

• The atomic radius of the atom is then 25 pm.

Atomic Radii

Atomic Radii Trends• Trends in atomic radius down a group

– the atoms get bigger as you go down groups (moving to higher energy level). Adding more electrons, more shielding, electrons further away from nucleus, reducing forces

• Trends in atomic radius across periods – atoms get smaller as you go across a period. – Adding proton but still same energy level

shielding remains constant more force to pull on the electron smaller atomic radius

– Exclude the noble gas

Shielding – Inner electrons tend to

screen or shield the force of the nucleus

from the outer electrons. So outer electrons can move

further away.

Ionic Radii

• Negative ions are larger– More electron – electron

repulsion – Electrons outnumber

protons, less forces on pulling the electrons in

• Positive ions are smaller– Less electrons – less

electron-electron repulsion stronger forces pulling on the electrons

– More protons more forces

What is it my

master Splinter? Patience.Ionization energy is the amount of energy needed to remove an electron from a gaseous atom

Like – A(g) + energy → A+(g) + 1e−

Ahh… so what would affect the

energy?Well, it depends on the

force on the electron. The stronger the force, the more

energy is required to remove the electron, the

higher the ionization energy.

Well, since the atomic radii decreases as we go across

the periodic table, would the ionization energy

increase across since the atoms are smaller, and

tighter?

Yes! You are absolutely right. The distance

between the nucleus and the outer electrons are

closer together so they are held tighter making it more

difficult to remove the electrons

What about going down the periodic

table? What do you think

Ummm… since the atomic radii is increasing as we go down due to

a new energy level and more shielding effect (as stated by He-

Man), ummm I would think the energy required to remove the

outer electron will decrease lowering the ionization energy

Very well my young grass hopper. You are learning quickly

So the ionization energy increases as we go across the periodic table, and decreases

going down the table.

Is that all master Splinter?

Some atoms can come in different ionic charges.

What about the ones that have 1 electron removed,

and then 2 and so on? Like this A+(g) → A2+ + 1e−

Look at this table I made with my turtles.

Do you see any patterns?

Yes, it seems like the numbers are getting bigger as more electrons are removed.

But what does this mean?

Ah my inquisitive student, it means the ionization

energy increases as more electrons are removed.

The more electrons you remove, the tighter the

electrons are held.

Since you are removing electrons, the same number of protons will attract

and hold the electrons tighter increasing the

ionization energy

Is that all master?

There is one thing left… The stable gases to the

right.

The Noble gases?

Yes my son. They are very stable and do not

like to be disturbed like a calm lake.

When can you remove electrons from noble

gases? What about Na+, or Al3+

Where they have removed enough electrons to

achieve the noble gas configuration

Look at this energy chart that I made.

I see the ionization energy 2 went up dramatically! Is it

because it is in the noble gas configuration since all the valence (outer)

electrons are removed?

Yes, because the outer valence electrons are removed, the next

electrons that can be removed are in the lower energy level where the

orbital is completely full. The electrons are also closer to the nucleus having a stronger hold

with the nucleus.

Now is that all?

Yes. You have done well my young grass hopper.

I have provided you with a summary table for your

atomic journey

Thank you master

Ionization Energy•Ionization energy tends to increase across a period and decrease down a group. •Ionization energy tends to increase with each successive electron removed •Ionization energy tends to increase greatly when removing electrons from a noble gas configuration.

Atomic radius tends to decrease across a period and increase down a group.

Ionic radius tends to decrease for every electron removed and increase for every electron added.