**Chapter 5 Electrons in Atoms**

Electrons in Atoms

5.1 Models of the Atom

5.2 Electron Arrangement in Atoms

5.3 Physics and the Quantum Mechanical Model

5.1 Models of the Atom

Rutherford's model could not explain the chemical properties of elements.

Remember that chemical properties and reactions depend on the behavior of the electrons in atoms.

So Bohr proposed a solution to this....

5.2 Electron Arrangement in Atoms

In atoms, electrons and the nucleus interact to make the most stable arrangement possible.

ELECTRON CONFIGURATIONS - the ways electrons are arranged into various orbitals around the nuclei of atoms

Three Rules - the AUFBAU PRINCIPLE, the PAULI EXCLUSION PRINCIPLE, and HUND'S RULE - tell you how to find the electron configurations of atoms

3 Rules for Electrons

Conclusion

Bohr

electrons are found only in circular paths, or orbits, around the nucleus

electrons around these orbits have fixed energies or are located at specific ENERGY LEVELS

electrons can absorb a QUANTUM to jump to the next energy level (figure 5.3 on pg 129)

Rutherford and Bohr's models were both based on describing the paths of moving electrons. The theoretical calculations and experimental results were inconsistent so Schrodinger devised and solved an equation using the experimental values.

The Quantum Mechanical Model

the modern description for electrons in atoms

from solutions to Schrodinger's equation

no exact path

determines the allowed energies an electron can have and the likelihood of finding the electron in various locations around the nucleus

for each energy level there is a mathematical expression called an atomic orbital, which describes the probability of finding the electron in various locations around the nucleus

ATOMIC ORBITAL: region in space where there is a high probability of finding an electron

energy levels are labeled by the principal quantum number (n), where n=1, 2, 3, 4.....

each energy level may have several orbitals...look on page 131 to see more about energy levels and atomic orbitals....oooo notice the shapes....how many electrons can fit into each of those orbitals? How many can fit in each energy level?

Aufbau Principle - electrons occupy the orbitals of lowest energy first!

the various orbitals for any sublevel of a principal energy level are always of equal energy

for any principle energy level the s sublevel is always the lowest energy

energy levels can overlap so the electron filling does not go in a simple order

exceptions after atomic number 23

Pauli exclusion principle - an atomic orbital may describe at MOST 2 electrons. For two electrons to occupy the same orbital they MUST have opposite spins, in other words the spins must be paired.

Electron spin is a quantum mechanical property of electrons that can be described as clockwise or counterclockwise.

Hund's Rule - electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin as large as possible. Electrons then occupy each orbital so that their spins are paired with the first electron in the orbital.