Chapter 5 Electrons in Atoms Chemistry Adapted from Stephen L. Cotton 1

The Basics Energy level of an electron analogous to the rungs of a ladder The electron cannot exist between energy levels, just like you can’t stand between rungs on a ladder. A quantum of energy is the amount of energy required to move an electron from one energy level to another. 2

Atomic Orbitals Principal Quantum Number (n) = the energy level of the electron: 1, 2, 3, etc. These are called orbitals-regions where there is a high probability of finding an electron. Sublevels- arranged in sections by letters s, p, d, and f. 3

Principal Quantum Number Generally symbolized by “n”, it denotes the shell (energy level) in which the electron is located. 4

Energy Levels Maximum number of electrons in each energy level: 1st Level 2 electrons 2nd Level 8 electrons 3rd Level 18 electrons 4th Level 32 electrons 5

Filling by Energy Level First Energy Level Has only an s orbital only 2 electrons 1s2 2 total electrons Second Energy Level Has s and p orbitals 2 in s, 6 in p 2s22p6 8 total electrons 6

Third energy level Fourth energy level Has s, p, and d orbitals 2 in s, 6 in p, and 10 in d 3s23p63d10 18 total electrons Fourth energy level Has s, p, d, and f orbitals 2 in s, 6 in p, 10 in d, and 14 in f 4s24p64d104f14 32 total electrons Any more than the fourth and not all the orbitals will fill up. You simply run out of electrons. 7

Electron Configuration Rules …are the way electrons are arranged in various orbitals around the nuclei of atoms. Three rules tell us how to arrange them: Aufbau principle- electrons enter the lowest energy first. This causes difficulties because of the overlap of orbitals of different energies – follow the Aufbau diagram! 8

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p

2) Pauli Exclusion Principle- at most, 2 electrons per orbital - but have different spins. 3) Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to.

-We need to account for all 15 electrons in phosphorus. Let’s diagram the electron configuration for Phosphorus using all three rules. -We need to account for all 15 electrons in phosphorus. 11

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p The first two electrons go into the 1s orbital Notice the opposite direction of the spins only 13 more to go... 12

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s The next electrons go into the 2s orbital only 11 more... 13

Increasing energy The next electrons go into the 2p orbital 3d 4d 5d 7p 6d 4f 5f The next electrons go into the 2p orbital only 5 more... 14

Increasing energy The next electrons go into the 3s orbital 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f The next electrons go into the 3s orbital only 3 more... 15

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p The last three electrons go into the 3p orbitals- 3 unpaired electrons The electron configuration for Phosophorus is 1s22s22p63s23p3 16

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p Now lets try Potassium-It’s atomic number 19.

Light The study of light led to the development of the quantum mechanical model. Light is a kind of electromagnetic radiation. Electromagnetic radiation includes many types: gamma rays, x-rays, radio waves. 18

- Page 139 “R O Y G B I V” Frequency Increases Wavelength Longer 19

Parts of a wave Crest Wavelength Amplitude Origin Trough 20

Wavelength and Frequency Are inversely related…As one goes up the other goes down. Energy follows frequency. Different frequencies of light are different colors of light. There is a wide variety of frequencies. The whole range is called a spectrum. 21

Atomic Spectrum Each element gives off its own characteristic colors. Can be used to identify the atom. This is how we know what stars are made of. 22

These are called the atomic emission spectrum Unique to each element, like fingerprints! Very useful for identifying elements 23

Light Production Let’s look at a hydrogen atom with only one electron in the first energy level. 24

Heat, electricity, or light can move the electron up to different energy levels. The electron is now said to be excited. 25

As the electron falls back to the ground state, it gives the energy back as light. 26