This document summarizes key models of the atom and concepts about electrons in atoms. It discusses Thomson's "plum pudding" model, Rutherford's discovery of the nucleus, Bohr's model of electrons in energy levels, and the modern quantum mechanical model. It also describes electron configurations, orbital notation, Hund's rule, the Aufbau principle, and the Pauli exclusion principle.

1. Chapter 4 Electrons in Atoms

2. Thomsons’s Model Atom has postitive pieces and negative pieces. Thought they were all mixed up together. Called a “plum pudding” model.

3. Rutherford’s Model Discovered the nucleus Small dense and positive Electrons moved around in Electron cloud Rutherford’s Model Discovered the nucleus Very small and positively charged Most of the atom is empty space with electrons moving around

4. Bohr’s Model 2, 8, 8, …thing Electrons are in “rings” or energy levels. Energy separates one level from another. Electrons can never be found in between two levels.

5. More details about energy levels. All orbits are not sphere-shaped. It can only tell us the probability of finding an electron a certain distance from the nucleus. The Modern Model (the Quantum Mechanical Model)

6. There is one s orbital in every energy level Sphere shaped Each s orbital can hold 2 electrons Called the 1s, 2s, 3s, etc.. orbitals. S orbitals

7. p orbitals Start at the second energy level Peanut-shaped 3 different directions Each peanut (orbital) can hold 2 electrons

8. d orbitals Daisy shaped (except the 5 th picture) 5 d orbitals can hold 10 electrons Each d orbital can hold 2 electrons

9. f orbitals Start at the fourth energy level “ Funny” shaped Each funny shape holds up to 2 electrons (total= up to14 electrons)

10. Electron Configurations Tells the way electrons are arranged in atoms. Gives more details than Bohr Electrons must fill in this order 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 …

11. Electron Configurations Lowest energy fill first. The energy levels overlap (ex: …4s 2 3d 10 4p 6 …) Electrons must fill the spaces in order and cannot leave any empty spaces This is called the Aufbau Principle

12. Orbital Notation Start with electron configuration and add one box for every orbital. Show electrons by putting arrows in the boxes. (Pointing opposite ways.) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 4

13. Orbital Notation Notice in the last box the electrons spread out before doubling up. This is Hund’s Rule (=bus rule) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 4

14. Orbital Notation Notice that only the boxes of the last part (4d 4 ) can have empty spaces. They have to be filled in order according to the Aufbau Principle 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 4

15. Pauli Exclusion Principle The 2 arrows have to point opposite ways. Two electrons in the same orbital (box) must be spinning in opposite directions according to the Pauli 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 4