Periodic Trends

Summary

Name	Description	Trend
#Atomic Radius	The distance between the two nuclei of adjacent atoms
#Ionization Energy	The energy required to move an electron from an atom
#Electron Affinity	The energy given off when an electron is added to an atom
#Electronegativity	The energy required to remove an electron from an atom in its ground state

Atomic Radius

Definition

The distance between the two nuclei of adjacent atoms

Factors affecting atomic radii:

Principle Quantum Number (n)
- Bohr: energy levels
- As , atomic radius
  - Electrons end up further because more shells exist
- ⇅ with family
Effective Nuclear Charge ()
- Number of Protons
- As , atomic radius
  - Electrons end up closer because the electrons are pulled in more from the increased protons
- <-> with period

always takes precedent over

Example

A neutral atom will have a smaller atomic radius than the anion of the same element
- E.g - has larger A.R because the extra electron means the electrons will repel more
A neutral atom will have a larger atomic radius than the cation of the same element - E.g - has larger A.R because it loses a shell

Figure

The largest atoms are found on the lower left, and smallest on the top right

Ionization Energy

Definition

The energy required to move an electron from an atom

The 1^st I.E is the energy required to remove the weakest held electron from the neutral atom

Factors affecting ionization energy:

Principle Quantum Number ()
- As , ionization energy
  - Electrons are further apart, so the hold of electrons is weaker
- ⇅ with family
Effective Nuclear Charge ()
- Number of Protons
- As , atomic radius
  - The hold on the electrons is stronger, so the ionization energy required is greater
- <-> with period

Example

Lithium gas

1^st IE is 520 kJ/mol
- Lithium has 1 valence electron, so it wants to lose it
2^nd IE is 7297 kJ/mol
- After losing 1 valence electron, lithium is stable

Figure

Smaller atoms are more electronegative

Electron Affinity

Definition

The energy given off when an electron is added to an atom

Example

Fluorine (F) has 7 valence electrons, so it has a high electron affinity. When given an electron, it gives off a lot of energy.

The 1^st E.A results in the formation of an anion with a charge of -1
Trends in electron affinity are more irregular than those for atomic radius and ionization energy

Figure

Smaller elements have higher I.E

Electronegativity

Definition

The electron-attracting ability of an atom, ranging from 0.7 (Francium) to 4.0 (Flourine)

Subtracting electronegativities can provide information about the strength and type of bond present between atoms (see Molecular Compounds#Types of Bonds)

Info

Non metals have high EN, while metals have low EN

0.7	4.0
- Atom doesn't want electrons	- Atom wants electrons
- More metallic	- More non-metallic

Figure