1. C HAPTER 4.3 – M ODERN A TOMIC T HEORY

2. T HE B OHR M ODEL OF THE A TOM The Bohr model of the atom is commonly used in science classes to help visualize where electrons are found in the electron cloud. This model shows atoms in electron energy levels that orbit around a central nucleus. The level closest to the nucleus has the lowest energy and can only hold two electrons. The energy of these electron levels increases with each added ring.

3. E NERGY L EVELS If an atom gains or loses energy, the energy level of an electron can change. Lets say that an atom gains (absorbs) energy and this causes an electron to “jump” up an energy level or two. When this electron gives off this extra energy it may give off visible light. Fireworks show this energy change. The explosion causes energy to be absorbed by electrons. When the electrons give off energy, it is in the form of the colorful light you see. The color emitted depends on the material used.

4. O RBITALS An orbital is an area outside the nucleus where an electron is likely to be found. In an atom, only a certain number of electrons can exist per level of the electron cloud Level 12 electrons Level 28 electrons Level 318 electrons (* we will only go to 8 in PS) This is where we get the maximum numbers of electrons that can exist in each energy level.

5. G ROUND STATE When all electrons in an atom have the lowest possible energies, this is called the ground state for an atom. The ground state is what is shown in the diagrams we made of atoms in class. When electrons absorb energy, we call this the excited state. Atoms in the excited state are less stable (less likely to exist) than in those in the ground state. The reason that neon and many gases glow is that they are giving off energy as light as they return to a ground state from an excited state.

6. T HE E LECTRON C LOUD M ODEL OF THE ATOM The modern model of the atom is the electron cloud model. This model shows that electrons exist in a cloud as it is difficult to find the fast moving electron. The dense areas of the cloud show where it is most probable to find an electron. Dense regions