1. Atomic Theory The Bohr-Rutherford Model of the Atom

2. Atomic Theory Modern atomic theory has evolved a lot in the last 200 years. Dalton first came up with the idea that matter is made up of small particles called atoms. Other scientists soon discovered negatively charged electrons that could be transferred between atoms. Later, others discovered positively charged protons, and neutral neutrons.

3. JJ Thompson JJ Thompson theorized that the positive charge in an atom was spread out, and the negative charges were dotted throughout it. This is called the “raisin bun” model, with electrons being like raisins in the bun.

4. Ernest Rutherford Ernest Rutherford discovered that atoms had a dense, positive nucleus. This is how he did it. Rutherford fired positive particles through a thin piece of foil only a few hundred atoms thick. He expected them to pass straight through. Instead, some were deflected, indicating a dense positive point in the atom. The nucleus.

5. Niels Bohr Bohr further adaped the model of the atom by discovering that electrons exist in specific energy levels.

6. Excited Electrons Bohr was able to discover this because when atoms are excited they release light. When an element is excited by adding energy (light, heat or electricity) the atom releases light. A neon sign is one example of this.

7. Excited Electrons Electrons in the neon atoms get when electricity runs through them. When they do this, they move faster. Once they move faster, they have to “jump” to a higher energy level. As they fall they need to release the energy, in this case as red coloured light.

8. Representing Atoms There are several different ways to represent atoms. The Bohr-Rutherford model is one such way. Ex: Al 13 27

9. An Easier Way This method is an extension of the Bohr- Rutherford model. Instead of representing the electrons as dots, we just count how many are in each shell. Ex: Al 13 27

10. An even EASIER way The Lewis dot diagram is an even easier way to show atoms. It shows only the outer shell of electrons. Since only the outer shell is involved in bonding, this is ideal for us. Note: You need to know the pattern in the periodic table. Ex: NaEx: S