1. Trends in the Periodic Table
Periodicity
Review of Atomic Forces
Atomic Radius
Ionization Energy
Ions are their sizes
Electronegativity

2. Periodicity The word Periodic means recurring at regular intervals
The Periodic Table is an organization of the atoms such that their properties repeat on each row
This means that elements in the same group (column) have similar properties.
We will learn why elements in the same group have similar properties and why elements are more or less reactive depending on which period they are in.

3. Review of Atomic Forces
Opposite charges attract and like charges repel
Increasing protons in the nucleus increases the attraction of electrons pulling them closer to the nucleus
Increasing electrons in the electron cloud, increase the repulsion between the electrons
The closer electrons are to the nucleus the stronger the attraction to the nucleus
Electrons in the same energy level are about the same distance from the nucleus, electrons in higher energy levels are farther from the nucleus.

4. Trends in the Periodic Table
Atomic Radius
The outside edge of the atom is defined by the electron cloud
As you move down a group, the size of the atom increases
the number of energy levels increases making the electron cloud bigger, so atomic radius increases
As you move across a period from left to right, the size of the elements decreases.
The number of e- increases but the additional e- are on the same energy level, which does not increase the size of the atom.
The number of protons in the nucleus increases which means there is a greater inward attraction of the electrons.

5. Ionization Energy
First Ionization Energy – the amount of energy required to remove the first e- from an atom
The higher the ionization energy, the harder it is to remove an e-
As you move down a group, the ionization energy decreases (e- are easier to remove from an atom)
Electrons close to the nucleus are held more tightly because they are closer to the protons
As you move down a group the outer e- are farther and farther away from the nucleus, making them easier to remove
Electrons in lower energy levels shield the outer energy levels from the full force of the protons, making outer e- easier to remove.
Ionization energy increases as you move across a period
The number of protons in the nucleus increases which means there is a greater inward attraction of the e-, making it more difficult to remove an e-.

6. Ionization Energy (Continued)
Second, Third, and Fourth Ionization Energies
With each e- removed, it gets harder to remove additional electrons, because the ratio of protons to electrons increases.
There are the same number of protons pulling on fewer electrons.

7. Electronegativity
Electronegativity – the ability of an atom to attract electrons
A large value indicates that the atom strongly attracts e-
If two atoms are fighting over an electron, the atom with the greater electronegativity will win the battle
Electronegativity decreases as you move down a group
Electrons in higher energy levels are not attracted as strongly because they are father from the nucleus
Electrons in lower energy levels shield the outer energy levels from the full force of the protons
Electronegativity increases as you move left to right across a period
Atoms with more protons tend to have a stronger attraction of e-

8. Comprehension Check Summary of Trends
6.3
Comprehension Check
Summary of Trends
What is the underlying cause of periodic trends?

9. Record on your Periodic Table
6.3
Record on your Periodic Table
Decreases
Increases
Electronegativity
Nuclear Charge
Ionization energy
Atomic Size
Decreases
Properties that vary within groups and across periods include atomic size, ionic size, ionization energy, electronegativity, nuclear charge, and shielding effect. Interpreting Diagrams Which properties tend to decrease across a period?
Increases

10. Comprehension Check
1. Which of the following sequences is correct for atomic size?
Mg > Al > S
Li > Na > K
F > N > B
F > Cl > Br
2. Which of the following is the most electronegative? Cl Se Na I

11. Other Trends in the Periodic Table