9 Quantum Theory- describes mathematically the wave properties of electrons.Definitions:orbital: three-dimensional region around the nucleus that indicates the probable location of an electron. (Each can hold a maximum of 2 electrons.)ground state: lowest energy state electrons in an atom have.excited state: state in which electrons in an atom have a higher energy than ground state.
10 Quantum NumbersSpecify the properties of atomic orbitals and the properties of electrons in orbitals.Symbol DescriptionPrincipal Quantum # n main energy level occupied by an electronAngular momentum # l shape of orbital in a particular sublevelMagnetic Quantum # m orientation of orbitalaround nucleusSpin Quantum # s direction of spin of electron
11 Energy Levels and Sublevels each principal energy level (n) has one or more sublevels.the number of sublevels is the same as the principal quantum numberFirst Principal Energy Level (n=1) has 1 sublevelSecond Principal Energy Level (n=2) has 2 sublevelsThird Principal Energy Level (n=3) has 3 sublevelsEach electron in a given sublevel has the same energy
12 Sublevels continued… Sublevels are named using letters: - the first sublevel is called s- the second sublevel is called p- the third sublevel is called d- the fourth sublevel is called fand so on (g, h …..)If n=1, how many sublevels are there and what are they called?Answer: 1 sublevel called sIf n=2, how many sublevels are there and what are they called?Answer: 2 sublevels called s and p
13 Orbitals Each sublevel contains 1 or more orbitals s - sublevel has 1 orbitalp - sublevel has 3 orbitalsd - sublevel has 5 orbitalsf - sublevel has 7 orbitalsRemember each orbital contains a maximum of 2 electrons.The maximum number of electrons per sublevel:s → 2p → 6d → 10f → 14
14 More OrbitalsAngular Momentum and Magnetic Quantum Numbers
17 Electrons in Energy Levels and Sublevels Principal Sublevels # of orbitals # of electrons Total electronsEnergy available in sublevel possible in for energy levelLevel sublevel(n) (n) (n2) (2n2)1s122s1228p36s123p3618d510s12p36432d510f714
18 Electron Configurations shows the arrangement of electrons in an atomthere are 3 different ways to show electron configurations: Orbital notation2. Electron-configuration notation3. Noble gas notation- electrons are in the ground state unless otherwise noted.unfortunately, there is energy overlap beginning at n = 3.- How can we predict the sublevel order if this occurs?
20 Pauli Exclusion Principle Hund’s Rule- Before a second electron can be placed in any orbital, all the orbitals of that sublevel must contain at least one electron.Pauli Exclusion Principle- In order for two electrons to occupy the same orbital they must have opposite spin.Relates to the Spin Quantum Number (s = +1/2 or -1/2)- Electrons spin clockwise or counterclockwise.
21 Orbital Notation When illustrating orbital notation for an element: 1. Boxes are used to represent orbitals2. Each box is labeled with principal energy level and sublevel.3. Arrows are used to represent electrons.ExamplesHydrogenLithiumAluminum↑↑↑↓1s↑↓↑1s2s↑↓↑↓↑↓↑↓↑↓1s2s2p3s3p
22 Electron Configuration Notation When writing electron configurations for an element:1. Boxes are not used.2. The principal energy level is written, followed by the sublevel.3. The total number of electrons are superscripted on each sublevel.ExamplesHeliumSodiumBromine1s21s2 2s2 2p6 3s11s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
23 Noble Gas NotationNoble gas notation may be used for elements beginning with period 3:1. Find the period the element in question is in.2. Locate the closest noble gas (must have fewer electrons than the element in question).3. Write the symbol of the noble gas in brackets (This represents ‘x’ number of electrons).4. Continue the notation with the principal energy level of the period the element is located in.ExamplesChlorineIronIodine[Ne]3s2 3p5[Ar]4s2 3d6[Kr]5s2 4d10 5p5
25 Blocks of the Periodic Table - The periodic table can be used to predict the order in which electrons enter sublevels.
26 Valence Electrons- Electrons that are located in the highest principal energy level.- The maximum number of valence electrons and element can have is eight.- Usually valence electrons are found only in s and p sublevels.- Electrons that are not valence electrons are inner-shell electrons.ExamplesBromineChlorineIron[Ne]3s2 3p5[Ar]4s2 3d61s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5