1. Ionization Energy and Electron Affinity

2. Intro to Ionization Energy and Electron Affinity
An electron can be removed from an atom if enough energy is supplied.
When a neutral atom loses an electron, it forms an ion with a positive charge.
When a neutral atom gains an electron, it forms an ion with a negative charge.

3. More about ions
An ion is an atom that either a positive or negative charge.
An ion with a positive charge is called a cation.
An ion with a negative charge is called an anion.
Go over examples on the board for determining the number of protons, neutrons, and electrons for an ion

4. You try it…
How many electrons must be removed from a neutral sodium atom to form the Na2+ cation?

5. Answer
2 electrons must be removed from the neutral sodium atom to form the Na2+ cation.

6. Ionization Energy
The energy required to remove ONE electron from a neutral atom of an element is the first ionization energy or IE1.

7. Ionization Energy
What is second ionization energy?

8. Second Ionization Energy
Second ionization energy is the energy required to remove TWO electrons from a neutral atom (IE2).

9. Trends Ionization energy decreases down a group.
Ionization energy increases across a period.

10. Why do we see these trends?
We know that as we go across the row to the noble gases that they do not want to lose or gain any electrons so ionization energy increases as you move across to the noble gases.

11. A closer look…
We also see that as we go across a period, the atomic number increases.
An increase in atomic number means an increase in the number of protons and an increase in positive charge.
A large positive charge is able to hold the electrons more strongly to the nucleus.
More energy is going to have to be supplied to knock one of these electrons free from the strong positive charge.

12. Why?
Why when you move down a group does the ionization energy decrease?
We see that as we go down a group, the rings or orbitals around the atom are increasing meaning the electrons are getting further and further away from the nucleus as we move down a group.

13. Why?
As you move further from the nuclues, the electrons do not feel that strong positive charge as much and you don’t have to apply as much energy to get it to lose an electron.

14. One more thing…
The more electrons you remove, requires more and more energy.
For example, for lithium (Li) the
first ionization energy = 520 kJ/mol
second ionization energy = 7,298 KJ/mol
third ionization energy = 11,815 kJ/mol

15. Why?
As you remove electrons, there are less electrons to shield from the positive charge of the nucleus, making the attraction between the nucleus and electrons stronger and stronger.

16. Electron Affinity
The energy change that occurs when an electron is gained by a neutral atom is called the atom’s electron affinity.
Most atoms release energy when they gain an electron.
A + e- → A- + energy
When energy is released, it is indicated by a negative number.

17. Electron Affinity
However, some atoms, such as the noble gases, must be “forced” to gain an electron by the addition of energy.
A + e- + energy → A-
The alkaline-earth metals must also be forced to gain an electron by the addition of energy.

18. Electron Affinity Trends
We know that out of all the elements, the halogens want to gain an electron the most because then they will have a noble gas configuration.
Therefore, the halogens release the most energy when they gain an electron.
They have the most negative electron affinity values.

19. Electron Affinity Values

20. Electronegativity
Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons.
Those elements that want electrons are going to have a high ability to attract electrons.

21. Electronegativity Trends
Nitrogen, oxygen, fluorine, and chlorine are the four most electronegative elements.
Fluorine is the most electronegative element.