1. Chapter 14: Periodicity!!!
What does periodic mean? Why is this wonderful tool called the PERIODIC TABLE???
The elements were originally grouped according to similar properties.
Dobreiner’s Triads = groups of 3
Mendeleev built on this by arranging according to atomic mass… he noticed regular repeating patterns! He used these patterns to leave spaces for undiscovered elements!

2. Mosely: arranged by increasing atomic number or increasing number of protons
Periodicity: the property of having regular, repeating patterns
The modern periodic table is arranged in such a way that we can predict the properties of even undiscovered elements!

3. WHY are all of these patterns predictable????
Electrons!!!
You know that the periodic table helps with electron configuration, that’s because this electron configuration determines the properties of the elements!

4. Noble gases: the outermost p and s orbitals are full.
Representative elements: the outermost p or s orbitals are only partially filled
Transition metals: electrons in the d orbital
Inner transition metals: electrons in the f orbitals

5. These trends, and some rules, are the HEART of electron configuration!
Aufbau principle: Electrons enter orbitals of lowest energy first
Pauli exclusion principle: only 2 electrons in each orbital (configuration)
Hund’s rule: when electrons occupy orbitals od equal energy, on electron enters each orbital until all the orbitals contain one electron. (Seats on a bus rule)

6. Orbital Diagrams
Now you can actually sketch where each electron is located in an atom!
Orbital diagram: representation of the energy levels, sublevels, and orbitals

7. Let’s try it!
Pg 396, 1-5
Pg 409, 10-16

8. Atomic Radius
The volume of an atom is taken up mostly by its electrons. But, we can’t know EXACTLY where these electrons are, so how do we determine size of atoms?
Nonbonding atomic radius: determined by freezing a sample of an element and measuring the distance between the center of two adjacent atoms. The atoms are NOT bonded together, just very, very close to one another.
Also called van der Waals radius

9. Another way to define the size of an atom is called the bonding atomic radius or covalent radius
Nonmetals: one half the distance between two atoms bonded together
Metals: one half the distance between two of thee atoms next to each other in a crystal of the metal

10. General Trend As you move down a group, radius increases
As you move left to right, it generally decreases.
Negative ions of an atom are smaller. WHY????

11. Periodic trends in the size of atoms

12. More Trends!
Ionization energy: the energy required to remove an electron from an atom or ion in the gaseous state.
Energy required to remove first electron? FIRST IONIZATION ENERGY, and so on.
Trends: decrease as you move down a column/group. Increases left to right across a period. WHY????

14. Electron Affinities and Metallic Character
These characteristics also exhibit periodic trends!
Electron Affinity: the energy change associated with gaining an electron
Usually negative because an atom usually releases energy when it gains an electron
There is not much of an observable trend down a group
Becomes more negative as you move left to right across a group. WHY???

15. Metallic Character Conductivity, Malleability, ductility, shiny
General Trend: As you move left to right across a row, metallic character decreases
As you move down a column, metallic character increases

17. Trends in Electronegativity
Electronegativity: the tendency for an atom to attract electrons.
Fluorine is the most electronegative. WHY???
General trend: increases as you move left to right
Increase as you move from bottom to top

18. You try it!
Pg 406, 6-9
Pg 409, 10-29