1. Periodic Trends

2. Introduction to ions
Atoms are electrically neutral because they have equal numbers of protons and electrons
When an electron is either gained or lost by an atom, it is no longer electrically neutral and it becomes an ION or a charged atom.
Example: Lithium
3 Protons
3 Electrons
Overall Charge: neutral

3. Positively charged ions: CATIONS
Loss of an electron causes the sodium atom to have more
positive charge in the nucleus than negative charge. Losing
one electron gives it a 1+ charge.

4. Negatively charged ions: ANIONS
Gain of an electron gives chlorine more negative charge
than positive, so it becomes a 1- ion.

5. Ionization Energy
To remove an electron from an atom to make it a cation involves energy.
This is called Ionization Energy and it is measured in kJ/mol.

6. Ionization Energy
The energy needed to remove an electron from an atom or ion in the gaseous state. The higher the ionization energy, the harder it is to remove the electron.

7. Ionization Energy
Ionization energy for Fr (87)_____________________ kJ/mol
Ionization energy for F(9) ______________________kJ/mol
From which atom is it easier to remove an electron?_________
From which atom is it harder to remove an electron?_________

8. Periodic Trends Ionization Energy – Down a group
As you move down a group, the size of the atom increases because it adds more and more orbitals.
The further away the electrons are from the nucleus and its attractive forces, the easier it is to remove.
Lithium
Sodium
Potassium
Rubidium

9. Periodic Trends Ionization Energy – Down a group
Electron Shielding also plays a role as you move down a group.
The inner electrons shield the outermost electrons from the attractive pull of the nucleus.
This causes the electrons to be held less tightly by the nucleus.
This means it will be easy to remove them from the atom.

10. Periodic Trends Ionization Energy – Across a Period
One electron and one proton is added to the atom
If the electron is added to the same energy level, the higher nuclear charge (from the additional proton in the nucleus) attracts the outer electrons more strongly.
Thus the energy required to remove and electron becomes larger. Li Be B C N O F

11. Periodic Trends Ionization Energy Graph – Across a Period Example:
Li has 3 electrons and 3 protons. Neon has 10 electrons and 10 protons. This large number of protons holds the electrons more tightly than Li’s 3 protons can.

12. Periodic Trends Atomic Radius
It’s hard to measure the size of one atom alone.
One method to measure an atom is to calculate the bond radius, which is the length that is half the distance between nuclei of two bonded atoms.

13. Periodic Trends Down a group
Increases as you move down a period due to increase in the number of orbitals
As a result of this, electrons are not pulled close to the nucleus and are easily pulled off

14. Atomic Radius Across a period
Decreases because the added protons pull the electrons closer, making the atom physically smaller

15. Graph of Atomic Radius

16. Periodic Trends Electronegativity
A measure of the ability of an atom to attract electrons. The larger the electronegativity, the more the atom attracts electrons.

17. Electronegativity Across a period
Increases because more protons are added to the nucleus, which allows it to attract negatively charged electrons.

18. Electronegativity Down a group:
Decreases because the larger size of the atom decreases the pull from the nucleus so electrons are not attracted to it.

19. Electronegativity Graph

20. Ionic Radii
When metal atoms lose electrons, they lose an entire energy level.
This makes the atom’s radius smaller.
Normal size
Decreased ionic
size

21. Ionic Radii
When atoms gain an electron, it makes them larger because the electrons repulse (push away from) each other.
Normal size
Increased ionic size