Atomic Theory. Quantum Mechanics

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Lynette Robinson
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1 Atomic Theory Quantum Mechanics

2 Quantum Mechanics The ol solar system model of the atom does have some practical uses It tells us that protons and neutrons are in the nucleus, and electrons are in orbitals around the nucleus The closer the orbital is to the nucleus, the lower the energy of the orbital

3 But Electrons do not travel in specific pathways in the orbital as shown in the previous picture Orbitals are not trails around the nucleus This model went out with Model-T Fords and Al Capone Al Capone

4 The New Look Atom Electrons are in orbitals, but orbitals are clouds of probability that show where an electron could be For example, suppose you go to a school dance. Your mom knows that there is a large probability that you are in the school gym, but cannot pinpoint where in the gym at any one time

5 Orbitals have different sizes and shapes, depending on their energy level Every orbital can accommodate up to two electrons each electron spins in a different direction

6 The Lowest Energy Orbital The 1s orbital is spherical in shape and is the smallest orbital, and is closest to the nucleus This is the lowest energy orbital in any atom as it is closest to the nucleus. The one or two electrons that occupy this orbital would be the lowest energy electrons in the entire atom!

7 Orbitals represent probability clouds. We know the electron(s) are somewhere in the orbital, but we don t know where There is a greater chance that the electron(s) are closer to the nucleus as then they will be lower energy probability cloud like a dartboard

8 The 1s orbital is the only orbital at energy level 1. The next orbital is the 2s (energy lev. 2), which is the same shape as the 1s, only larger 1s 2s

9 Hydrogen How many electrons does hydrogen have? 1 In its stable state, the hydrogen electron is in the 1s (lowest energy) orbital. This is called the ground state If the electron becomes excited, it can be promoted to the 2s orbital (excited state), where it will eventually emit the excess energy and return to the 1s level

10 The next orbitals after the 2s are the 3 different 2p orbitals. Each 2p orbital can hold up to two electrons, for a total of six electrons. The three 2p orbitals are the 2p x, 2p Y, and 2p z orbitals, depending on their orientation

11 The 2p Orbs all together Remember these are probability clouds that represent where the electron(s) could be!

13 Think back to Science 10 How did the electron shells go again? 2, 8, 8, 18 How many orbitals in energy level 1 in our new model how many electrons? Only 1s, therefore 2 electrons In the second energy level? 2s, 2p x, 2p Y, 2p z, therefore 8 electrons Notice a trend? Our energy levels are the same as the shells you learned about before

14 Energy Level 3 The third energy level has 3s, 3p x, 3p Y, and 3p z orbitals. They look the same as their energy level 2 counterparts, except that they are larger and are higher energy. There are also five 3d orbitals that can each hold two electrons

15 Here s how they look combined

16 Energy Level 4 The 4 th energy level has a 4s orbital, three 4p orbitals, five 4d orbitals, and seven 4f orbitals. The s, p, and d orbitals look like the level 3 orbitals except they are larger and higher energy The seven 4f orbitals look like this

18 Energy Levels 5, 6, 7 Levels 5, 6, and 7 all have one s orbital, three p orbitals, five d orbitals, and seven f orbitals respectively As the level number increases, both the size and energy of the orbitals increase

19 Electron Configurations Every atom or ion has an electron configuration - a map of where the electrons are We show the electrons in the ground state the lowest energy arrangement Hydrogen only has one electron what orbital would it be in? You re right!! The 1s orbital

20 How many electrons does Helium have? 2. Where would they be located? In the 1s orbital, filling it up (each orb can only hold 2 electrons!) Orbital Diagrams Opposite spins Energy Increase

21 Try Lithium. Beryllium? 2 ways to show elec. config.

22 Write electron configurations using both methods for Boron, Carbon, and Nitrogen. What do you notice here? The three 2p orbitals are written together. The 2p orbitals all together hold 6 electrons

23 p Orbitals Freidrich Hund p orbitals will fill by one electron going into each p orbital (p x, p Y, p z ), and then doubling up after. This is a lower energy arrangement as it minimizes electron repulsion This is called Hund s Rule The same goes for d and f orbitals

24 Write electron configurations both ways for oxygen, fluorine, and neon Summary

25 Orbitals will be filled from lowest to highest energy. See the relative energies of each orbital below: Notice that the 4s orbital is lower in energy than the 3d orbital!

27 Orbital Filling Order

28 Practice Give electron configurations both ways for Silicon, Calcium, and Iron how many electrons for each? 14 for Si, 20 for Ca, 26 for Fe

29 What order do the orbitals get filled again? The periodic table gives the order by its layout! 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d

30 Trends Cell phones and ipods are so hot right now!! Oh, I mean periodic table trends Give the electron configurations for hydrogen, lithium, sodium, and potassium. What is similar about each config? Correct! They all end in s 1

31 Where are these four elements found on the table? In the first column - The s 1 block!

32 The d 3 block! The s 2 block! The p 1 block! The f 5 block! The p 6 block!

33 Quantum Numbers Quantum numbers are a way of keeping track of electrons Each electron in an atom has a different set of 4 quantum numbers The 1 st quantum number is called n and tells what energy level the orbital occupies n values can be 1, 2, 3, 4, 5, 6, or 7

34 Keep in mind that energy and orbital size increases as the n value increases The 2 nd quantum number is L L tells the shape of the orbital is it an s, p, d, or f orbital? The 3 rd quantum number is m m tells the orientation of the orbital s has no orientation as it is a sphere p can be p x, p Y, or p z d and f are more complicated and you don t have to know these

35 The 4 th quantum number is m s m s gives the spin of the electron either +1/2 or 1/2 Electrons can have one, two, or three of the same quantum numbers, but never all four or we are describing the same electron! Pauli Exclusion Principle

36 Core Notation Give the electron configuration for Titanium Core Notation for Ti: [Ar] 4s 2 3d 2 The core is the configuration that is identical to the nearest previous noble gas then write the configuration for the remaining outer electrons

37 Practice Give core notation for As, Cl, K, Cr, Ar

38 Core Notation for Ions If you have an anion (ion with negative charge), then the extra electrons go into the lowest energy orbital available Give core notation for P 3- P atom is [Ne] 3s 2 3p 3 The 3- charge means three extra elecs. P 3- is [Ne] 3s 2 3p 6 Give core notation for Cl -, O 2-

39 A cation (positively charged ion) has less electrons than the neutral atom RULE: Electrons are removed from p orbitals first, then s orbitals, then d orbitals when in core notation (p before s before d) People Should Dream Give core notation for Ca 2+ First, do core notation for Ca [Ar] 4s 2.no p orbs outside of core, so take out the two s electrons.therefore Ca 2+ is [Ar]

40 Practice Give core notation for Fe 2+, Al 3+, Li +, Mn 2+, Fe 3+, Pb 4+ What do you notice about the electron configuration of many of the ions? They have the same configuration as noble gases! (and are happy) Ions which have identical electron configurations to noble gases are said to be isoelectronic with the noble gas

41 The Hulkster, like ions, in fact, is all CHARGED UP!!! Mean Gene Okerlund

42 Special Stability of Full and Half-Full d orbitals Any configuration that ends in d 4 or d 9 will undergo electron elevation, meaning an s electron moves up to a d orbital Ag [Kr] 5s 2 4d 9 is actually [Kr] 5s 1 4d 10 Ag + [Kr] 5s 1 4d 9 is actually [Kr] 4d 10 Cr [Ar] 4s 2 3d 4 is actually [Ar] 4s 1 3d 5

43 ONLY FOR d 4 and d 9!! The elevation of an s electron to half fill or fully fill a d orbital is due to the special stability that results it is unexpected and a phenomenon that is not well explained! Who knows?

44 Valence Electrons Valence electrons are the electrons that take part in chemical reactions Can lose valence electrons to become an ion (or gain valence electrons) Or, valence electrons can be used to bond with other atoms to make a compound (covalent cmpds.)

45 Valence electrons are all the electrons that are not in the core, and not in filled d or f orbitals How many valence electrons in each of the following? Al Ga V Xe Al 3+ S 2-

46 Ions Valence electrons react in order to create a situation where an atom has filled orbitals (think about combining capacities of each chemical family)

47 Do your assignment or Well Barry Horowitz will make you and, believe you me you don t want that.

Unit 8: Atomic Theory. Quantum Mechanics

Unit 8: Atomic Theory. Quantum Mechanics Unit 8: Atomic Theory Quantum Mechanics 1 Unit 8: Atomic Theory 1. Historical Views of the Atom 2. The 'New' Look Atom 3. Electron Configurations 4. Electron Configurations & the Periodic Table 5. Quantum