2 Bohr’s Model Why don’t the electrons fall into the nucleus? Move like planets around the sun.In circular orbits at different levels.Amounts of energy separate one level from another.
3 Bohr’s Model Nucleus Nucleus Electron Electron Orbit Orbit Energy LevelsEnergy Levels
4 Bohr postulated that: Fixed energy related to the orbit Electrons cannot exist between orbitsThe higher the energy level, the further it is away from the nucleusAn atom with maximum number of electrons in the outermost orbital energy level is stable (unreactive)
5 How did he develop his theory? He used mathematics to explain the visible spectrum of hydrogen gas
9 Bohr’s Triumph His theory helped to explain periodic law Halogens are so reactive because it has one e- less than a full outer orbitalAlkali metals are also reactive because they have only one e- in outer orbital
10 DrawbackBohr’s theory did not explain or show the shape or the path traveled by the electrons.His theory could only explain hydrogen and not the more complex atoms
11 } Fifth Fourth Increasing energy Third Second First Further away from the nucleus means more energy.There is no “in between” energyEnergy LevelsFifthFourthThirdIncreasing energySecondFirst
12 The Quantum Mechanical Model Energy is quantized. It comes in chunks.A quanta is the amount of energy needed to move from one energy level to another.Since the energy of an atom is never “in between” there must be a quantum leap in energy.Schrödinger derived an equation that described the energy and position of the electrons in an atom
13 Atomic OrbitalsPrincipal Quantum Number (n) = the energy level of the electron.Within each energy level the complex math of Schrödinger's equation describes several shapes.These are called atomic orbitalsRegions where there is a high probability of finding an electron
14 S orbitals 1 s orbital for every energy level 1s 2s 3s Spherical shapedEach s orbital can hold 2 electronsCalled the 1s, 2s, 3s, etc.. orbitals
15 P orbitals Start at the second energy level 3 different directions 3 different shapesEach orbital can hold 2 electrons
20 Electron Configurations The way electrons are arranged in atoms.Aufbau principle- electrons enter the lowest energy first.This causes difficulties because of the overlap of orbitals of different energies.Pauli Exclusion Principle- at most 2 electrons per orbital - different spins
21 Electron Configurations First Energy Levelonly s sublevel (1 s orbital)only 2 electrons1s2Second Energy Levels and p sublevels (s and p orbitals are available)2 in s, 6 in p2s22p68 total electrons
22 Third energy levels, p, and d orbitals2 in s, 6 in p, and 10 in d3s23p63d1018 total electronsFourth energy levels,p,d, and f orbitals2 in s, 6 in p, 10 in d, and 14 in f4s24p64d104f1432 total electrons
23 Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p
24 Electron Configuration Hund’s Rule- When electrons occupy orbitals of equal energy they don’t pair up until they have to .Let’s determine the electron configuration for PhosphorusNeed to account for 15 electrons
25 Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p The first to electrons go into the 1s orbitalNotice the opposite spinsonly 13 more
26 Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p The next electrons go into the 2s orbitalonly 11 more
27 Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p The next electrons go into the 2p orbitalonly 5 more
28 Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p The next electrons go into the 3s orbitalonly 3 more
29 Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s The last three electrons go into the 3p orbitals.They each go into separate shapes3 unpaired electrons1s22s22p63s23p3
30 Orbitals fill in order Lowest energy to higher energy. Adding electrons can change the energy of the orbital.Half filled orbitals have a lower energy.Makes them more stable.Changes the filling order
31 Write these electron configurations Titanium - 22 electrons1s22s22p63s23p64s23d2Vanadium - 23 electrons 1s22s22p63s23p64s23d3Chromium - 24 electrons1s22s22p63s23p64s23d4 is expectedBut this is wrong!!
32 Chromium is actually 1s22s22p63s23p64s13d5 Why? This gives us two half filled orbitals.Slightly lower in energy.The same principal applies to copper.
33 Copper’s electron configuration Copper has 29 electrons so we expect1s22s22p63s23p64s23d9But the actual configuration is1s22s22p63s23p64s13d10This gives one filled orbital and one half filled orbital.Remember these exceptions
34 Great site to practice and instantly see results for electron configuration.
35 PracticeTime to practice on your own filling up electron configurations.Do electron configurations for the first 20 elements on the periodic table.