Models of the Atom

Bohr’s model… Electrons are found in specific circular paths (orbits) around the nucleus. The electrons have fixed energies called energy levels. (like rungs on a ladder) The amount of energy required to move an electron to another energy level is called a quantum.

The Quantum Mechanical model It is based on the energy and possible location of an electron. how likely it is to find an electron is described in terms of probability. Based on work done by Shrodinger…

n Levels on the Periodic Table Let’s take a look at the periodic table

Atomic Orbitals The energy levels of electrons are labeled by principal quantum numbers (n) Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

Shapes and Orientations of Orbitals

1s Orbital Sphere around the nucleus This means that the electron is in the orbital closest to the nucleus S tells you about the shape

2s Orbital Similar to 1s except the electron is most likely in the region farther from the nucleus

p Orbitals At the first energy level, there is only the 1s orbital, after the second energy level there are 2p orbitals Look like dumbbells In the three directions

Summary: p orbitals and d orbitals p orbitals look like a dumbell with 3 orientations: p x, p y, p z (“p sub z”). Four of the d orbitals resemble two dumbells in a clover shape. The last d orbital resembles a p orbital with a donut wrapped around the middle.

Periodic table arrangement the quantum theory helps to explain the structure of the periodic table. n - 1 indicates that the d subshell in period 4 actually starts at 3 (4 - 1 = 3).

Four Energy Sub-Levels OrbitalOrbital Shape # of Individual Orbitals Number of Electrons Held sSphere12 pDumbbell36 d4-Lobed510 f6-8 Lobed714

Atomic Orbitals

Remember…. MAX NUMBER OF ELECTRONS IN AN ENERGY LEVEL ENERGY LEVELMAX # OF ELECTRONS

Electron Configuration A detailed way of showing the order in which electrons fill in around the nucleus

Electron Configuration Symbols 1s 21s 2 Energy Level Sub Level (s, p, d, f ) # of e - in sub level

We must follow 3 rules… Aufbau priciple Electrons occupy energy levels with lowest energy first.

Pauli exclusion principle If 2 electrons occupy the same energy level they must have opposite spins.

Hund’s rule… Electrons that occupy orbitals of the same energy will have the maximum number of electrons with the same spin. 2p

To start we will use orbital filling diagrams to help us with electron configurations…. Example Boron- has 5 electrons