Chemistry Unit 3 Electrons in Atoms Chapter 5

5.1 The Evolution of Atomic Models The work of Dalton, Thomson and Rutherford began an age of exploration that culminated with a model of the atom that described a dense nucleus surrounded by electrons. This model continued to be modified as more data was collected.

Bohr model- Electrons are arranged in concentric circular paths (orbits) around the nucleus Called the planetary model Electrons have particular paths with fixed energy, which he called its energy level

Quantum mechanical model It comes from the mathematical solutions to the Schrodinger equation The probability of finding an electron within a certain volume of space surrounding the nucleus can be represented by a cloud (electron cloud) The cloud represents where the electron can be found approximately 90% of the time. Sodium atom

In Summary…

Energy level - region around the nucleus where the electron is likely to be moving. -An electron can jump from one level to another by absorbing energy.

Quantum - the amount of energy required to move an electron from its present energy level to the next higher energy level

Atomic orbital – the region in space where the electron is likely to be found A quantum mechanical model of a hydrogen atom, which has one electron, in its state of lowest energy. The varying density of the spots indicates the relative likelihood of finding the electron in any particular region.

Electrons can be described by a series of 4 quantum numbers Electrons can be described by a series of 4 quantum numbers. You must be familiar with these!

1. Principle quantum number (n) -describes the principal energy level an electron occupies -values of 1,2,3,4,etc 1 2 3 4 5 6 7

Question What energy level are the following elements in? Sr Pb

2. Azimuthal quantum number (l) -describes the shape of atomic orbitals -s orbitals are spherical, p orbitals are peanut shaped, d orbitals are daisies and f orbitals are fancy -designates a sublevel -values of 0 up to and including n-1 0=s, 1=p, 2=d, 3=f

s orbital Spheres

p orbitals Peanuts

d orbitals Daisies or Doughnuts

Fancy f orbitals

Where do I find the orbital shapes?

3) Magnetic Quantum Number We therefore need a third quantum number, known as the magnetic quantum number (m), to describe the orientation in space of a particular orbital.

4) Spin Quantum number Each of these orbitals can accommodate up to two electrons (with opposite spins), forming the basis of the periodic table.

Movie: periodic table of the elements: t10-20 ml ms 1 0(s) 3d ENERGY 4s 2 0(s) 3p 1(p) -1, 0, 1 3s 3 0(s) 2p 1(p) -1, 0, 1 2s 2(d) -2, -1, 0, 1, 2 1s 4 0(s) Movie: periodic table of the elements: t10-20

Question: What would the quantum numbers be for the outer electron of a chlorine atom?

Quick and Easy Electron Configuration First, number the periods 1-7, 3-6 and 4-5 as shown by your teacher. 1 2 3 4 5 6 7 S 3 4 5 6 P D 45 F