Atomic Radius Ionic Radius

4.2 Periodic trends

Unit 4: The periodic table

Let's think

How would you measure an atom? From where to where?

Open Ended

How would you measure an atom? From where to where?

Atomic Radius

• It is the distance from the center of an atom's nucleus to its outermost electron

• The more electrons it has, the more protons it has as well (in ground state). Therefore, the more protons, the closer the electrons are, as they are more attracted by protons (and since protons are bigger, they have more attraction)

Atomic Radius

• Atomic radius increases as you move down by series in the periodic table

• Because as you move down, new shells are added, electrons are further from the nucleus (basically above the other orbitals of the lower energy levels)

• Board example

Multiple Choice

What element has the biggest atomic radius?

• B

• Tl

• Al

• In

Atomic radius

• This is also seen as you move horizontally in the periodic table, thanks to the attraction principles we mentioned.

• The more you move to the right, the atomic radius decreases. ​

Multiple Choice

Which of the following elements have a bigger atomic radius?

• Magnesium

• Silicon

• Chlorine

• Argon

Ionic Radius

• Basically, it is the atomic radius of ions (cations and anions)

• When an atom loses an electron, the atom becomes smaller, when it gains one, it gets bigger

• Board example: Li and Be

Ionization energy

• In order to form compounds, atoms have to lose or take electrons to some extent. but some lose them easily, while others stubbornly hold on to them

• The ionization energy refers to the energy needed for an atom to lose an electron (become cation)

• It increases as you move right inside a period.

• It also increases as you move up as shown in the chart:

Multiple Choice

Which element has a higher ionization energy?

• Calcium (Ca)

• Bromine (Br)

• Germanium (Ge)

• Iron (Fe)