1. Objectives
To understand how the principal energy levels fill with electrons in atoms beyond hydrogen
To learn about valence electrons and core electrons
To learn about the electron configurations of atoms with Z < 18
To understand the general trends in properties in the periodic table

2. A. Electron Arrangements
Orbital Notation for Carbon
  _ _ __
1s 2s 2p
Electron Configuration for carbon
1s22s22p2

3. “Orbital Filling Rules”
Aufbau Principle
Electrons fill the lowest energy orbitals available
Pauli Exclusion Principle
Orbitals can hold a maximum of two electrons; two electrons in one orbital must have opposite spins.
Hund’s Rule
Electrons fill equal energy orbitals one at a time until each is occupied by one electron; Electrons in singly occupied orbitals have the same spin.

4. A. Electron Arrangements in the First 18 Atoms on the Periodic Table
Classifying Electrons
Valence electrons – electrons in the outermost (highest) principal energy level of an atom
Core electrons – inner electrons
Elements with the same valence electron arrangement show very similar chemical behavior.

5. B. Electron Configurations and the Periodic Table
Orbital filling and the periodic table

6. A. Electron Arrangements in the First 18 Atoms on the Periodic Table

7. B. Electron Configurations and the Periodic Table
Look at electron configurations for K through Kr

8. C. Atomic Properties and the Periodic TableNe Na Mg F O
1s22s22p  filled outer energy level
1s22s22p63s1  can lose 1 electron to have a filled energy level
1s22s22p63s2  loses 2 electrons
1s22s22p  gains 1 electron
1s22s22p  gains 2 electrons

9. C. Atomic Properties and the Periodic Table
Metals and Nonmetals

10. C. Atomic Properties and the Periodic Table
Metals
Conduct electricity
Left side of the periodic table
Form (+) ions; lose electrons
Nonmetals
Do not conduct electricity
Right side of the periodic table
Form (-) ions; gain electrons

11. C. Atomic Properties and the Periodic Table
Atomic Size
Measured as the atomic radius (distance from the center of an atom to its outermost electrons
Remember:
The locations of electrons are not exact  atomic radius is an approximation.

12. C. Atomic Properties and the Periodic Table
Atomic Size

13. C. Atomic Properties and the Periodic Table
Atomic Radius
Trends:
1. Atoms increase in size as you move down a group on the periodic table
Why?
Outermost electrons are in higher energy levels. Orbital size increases with energy level.

14. C. Atomic Structure and the Periodic Table
Trends (cont.) - Atomic Radius
Atoms decrease in size as you move from left to right across the periodic table.
Why?
It is the result of increasing nuclear charge going left to right. As the number of protons increases, there is a stronger attraction for the outermost electrons. (which are located in the same energy level. The electrons will be held closer to the nucleus.

15. C. Atomic Properties and the Periodic Table
Ionization Energies
Ionization Energy – energy required to remove an electron from an individual atom (gas)

16. C. Atomic Properties and the Periodic Table
Ionization Energy

17. C. Atomic Properties and the Periodic Table
Ionization Energies
Trends:
I.E. increases as you go from left to right on the periodic table
Why?
Increasing nuclear charge as you move to the right; the nucleus has a stronger attraction for the outer electrons
I.E increases as you move up a group on the periodic table.
Electrons are closer to the nucleus as you move up a group; there is a stronger attraction to the nucleus

18. Atomic Properties and the Periodic Table
Ionization Energies
I.E. can also be explained in terms of atomic radius.
The smaller an atom is…the greater the attraction between the nucleus and outer electrons… and the greater the I.E.

19. Which element (Cs, Hf, Au) has the smallest atomic radius? Au
Practice
Which element (Cs, Hf, Au) has the smallest atomic radius? Au
2. Arrange the following elements in order of decreasing ionization energy: Li, O, C, K, Ne, F
Ne, F, O, C, Li, K
For each of the following pairs of elements select the largest atom.
C, O Sr, Mg
Si, N Li, Mg