1. ELECTRON CONFIGURATIONS “THE ADDRESSES OF ELEMENTS”
ELECTRONS IN THE ATOM
ELECTRON CONFIGURATIONS
“THE ADDRESSES OF ELEMENTS”

2. EQ’s What do the chemical properties of atoms depend on?
What is the quantum mechanical model?
How is the quantum mechanical model organized?
What is the Aufbau Principle?

3. ELECTRONS: The chemical properties of atoms, ions, and molecules
are related to the arrangement of electrons.

4. EVOLUTION OF THE ATOM
To understand this concept, let’s take a look at the history of the atomic models.
Dalton – solid indivisible mass

5. EVOLUTION OF THE ATOM
Thomson - The atom is a ball of positive charge with electrons stuck into the ball.
Electron
Positive charge

6. EVOLUTION OF THE ATOM
Rutherford – Most of an atom’s mass is concentrated in the small, positively charged nucleus. The electrons surround the nucleus and the rest of the atom is empty space.

7. EVOLUTION OF THE ATOM
Bohr – Electrons are arranged in concentric circular paths around the nucleus.

8. 90% probability of finding the electron within this space
EVOLUTION OF THE ATOM
Quantum Mechanical Model – Modern atomic theory describes the electronic structure of the atom as the probability of finding electrons within certain regions of space.
90% probability of finding the electron within this space

9. WHERE ARE THE ELECTRONS?
The quantum mechanical model is a theoretical mathematical approach to the study of atomic and molecular structure – a very complex theory! So let’s not go there. Instead we will learn some of the basic concepts using a visual that we can all relate to: an apartment building.
Vs.

10. ELECTRON APARTMENTS
The apartment building has different floors [principal energy level], different apartments on each floor [sublevel], and rooms [orbitals] within each apartment.

11. PRINCIPAL ENERGY LEVELS
There are seven “floors” in our building. Each of these “floors” is assigned a number. These are called the principal quantum numbers (n). Principal energy levels are assigned values in order of increasing energy: n = 1, 2, 3, 4, and so forth.

12. PRINCIPAL ENERGY LEVELS
Take a look at your periodic table. How many periods are there?

13. Hummmm – do you think there may be a connection here?
Seven levels, seven periods!
So floor 2 (n = 2) would be the second period;
Floor 5 (n = 5) would be the 5th period

14. SUBLEVELS
The “apartments” (sometimes called blocks or shells) within our Principal Energy Levels are identified with a letter: s, p, d or f.

15. If you are looking for apartment 6s, it would be found here
Principal energy level n = 1 is a bit strange, because the sublevel s is split into two areas.
If you are looking for apartment 6s, it would be found here
Apartment 4p, would be found

16. ORBITALS
Each sublevel (apartment) contains a very specific number of rooms (orbitals):
s – blocks contain 1 orbital
p – blocks contain 3 orbitals
d – blocks contain 5 orbitals
f – blocks contain 7 orbitals
Each orbital can contain a maximum of 2 electrons.

17. Orbitals are difficult to show until we learn a couple of principles and one rule.
A good way to remember the number of orbitals is to count (horizontally) the number of elements in a block and divide that by 2.
s-block; 2 elements = 1 orbital
p-block; 6 elements = 3 orbitals
d-block; 10 elements = 5 orbitals
f-block; 14 elements = 7 orbitals

18. ELECTRON CONFIGURATION
The electron configuration actually gives us the location of any element on the periodic table. We simply have to be able to count as we fill in boxes!
The way we read the configuration is to account for every electron in the atom – time to remember that as elements progress across the periodic table, the number of protons and electrons increase by one.
A little practice is all it takes.

19. Hydrogen: s1
Helium:1s2
Chlorine: 1s22s22p63s23p5
Iron: 1s22s22p63s23p63d6

20. PAULI EXCLUSION PRINCIPLE
An atomic orbital may describe at most two electrons.
To occupy the same orbital, two electrons must have opposite spins.
Arrows are used to indicate the electron and its direction of spin (↑ or ↓).
An orbital containing paired electrons is written as ↑ ↓

21. HUND’S RULE
When electrons occupy orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with parallel spins.
p orbitals
When the 4th electron is needed, it will occupy the first orbital and so on - - -

22. AUFBAU PRINCIPLE Electrons enter orbitals of lowest energy first 7p 6d
Increasing Energy

23. Hydrogen (H):

24. Helium (He):

25. Beryllium (Be):

26. Aluminum (Al):

27. Sulfur (S):