Lecture 1.4 – Atomic Radius

What is atomic radius?

I. Atomic Radius

• Atomic Radius – The distance from the center of the nucleus to the edge of the electron cloud

Outer edge of electron cloud

Nucleus

What are the trends for atomic radii?

I. Atomic Radius Trends

• Atomic radius increases as you go down a group• Atomic radius decreases as you go across a period

Why do these trends exist?

I. Why Radii Increases Down a Group

• As you add more electron shells to an element, the element becomes “bulkier”.

• This means that as you go down a group, more orbits are added, so the radius becomes bigger.

II. Why Atomic Radius Decreases Across a Period

• As you move across a period, more protons are added to the nucleus.

• This means there is a larger positive and negative charge, which results in a higher attraction and a decrease in the radius.

What is ionization energy?

I. Nuclear Attraction• The negatively charged electrons are

attracted towards the positively charged nucleus.

II. Ionization Energy• Ionization energy is the energy that is

required to remove an electron.

What are the trends for ionization energy?

I. IE Trends• As you move down a group the IE

decreases.• As you move across a period, the IE

increases.

Why do these trends exist?

I. Why IE Decreases Down a Group• As you go down a group more orbits are

added.• IE decreases because it requires less

energy to remove an electron due to shielding of orbits.

II. Why IE Increases Across a Period• As you move across a period you add

more protons and electrons within the same orbit.

• The larger amount of protons show an increased attraction for electrons.

What is electronegativity (electron affinity?

I. Electronegativity

• Electronegativity is the measure of the ability of an atom to attract electrons.

What are the trends for electronegativity?

I. Electronegativity Trends• As you go down a group, the electronegativity

decreases.• As you go across a period, the electronegativity

increases.

Class Example

• Order the elements from smallest to largest electronegativity: oxygen, beryllium, lithium,

Table Talk

• Order the elements from largest to smallest electronegativity: chlorine, bromine, fluorine

Stop and Jot

• Order the elements from smallest to largest electronegativity: silicon, aluminum, sulfur

Why do these trends exist?

I. Why Electronegativity Decreases Down a Group

• As you go down a group more orbits are added.• Electroneg. decreases because there is a

decreased ability of the nucleus to attract electrons because of larger distance.

II. Why Electronegativity Increases Across a Period

• As you move across a period you add more protons and electrons within the same orbit.

• The larger amount of protons in the nucleus and electrons in orbit show an increased attraction, which leads to increased electroneg.