Presentation on theme: "Electron House Where do the electrons live?. Energy Levels & Floors Recall that Bohr was the first scientist to describe electrons using specific energy."— Presentation transcript:
Energy Levels & Floors Recall that Bohr was the first scientist to describe electrons using specific energy levels Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus Each possible electron orbit in Bohr’s model has a fixed energy know as energy levels – The 1 st energy level could hold a maximum of 2 electrons – The 2 nd energy level could hold a maximum of 8 electrons – The 3 rd energy level could hold a maximum of 18 electrons – The 4 th energy level could hold a maximum of 32 electrons – Mathematical equations for electrons in energy levels is 2n 2 where n is the energy level
Energy Levels & Floors Your House – The house itself, represents the electron cloud – In your house each floor is a different energy level On the periodic table each row is an energy level – Each bedroom represents a sublevel within an energy level. Sublevels are labeled as s, p, d, or f – Each bed represents an orbital within the sublevel. Two people (electrons) can occupy the same bed at the same time.
What is an Energy level? energy levels the specific energies an electron in an atom can have – The number of energy levels equals the period number To move from one energy level to another, an electron must gain or lose just the right amount of energy. – A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level. the higher the energy level, the farther it is from the nucleus.
Sleeping Arrangements Electron will occupy the lowest energy level first – Would you want to walk up steps if you don’t have to. One electron will occupy each orbital (bed) before they pair up – Would you want to sleep with your younger brother – A maximum of two electron can occupy each orbital (each bed) Think it through…. – How many bed rooms are in the first energy level? – How many beds are available in the first energy level? – So how many electrons can be in the first energy level total?
Sleeping Arrangements Second energy level – How many bed rooms – How many bed – How many electrons total can it hold Third energy level – How many bed rooms – How many bed – How many electrons total can it hold Third energy level – How many bed rooms – How many bed – How many electrons total can it hold
Electron’s locations Relative locations of electrons described by – Energy level--floors in the electron house – Sub-level--different rooms on each floor – Orbitals—beds in the room
Seven energy levels observed to hold electrons First energy level closest to nucleus, increasing in distance as subsequent levels needed Period = energy level 1 2 3 4 5 6 7
Sub-levels Four known types, additional proposed* (s, p, d, f, g*, h*) Each type has a different ‘shape’ or zone of probability Number of types of sub-levels increases as the energy level does – 1 st energy level has one sub-level, s only – 2 nd energy level has 2 sub-levels, s & p – 3 rd energy level has 3 sub-levels, s, p & d – 4 rd energy level has 4 sub-levels, s, p, d & f
s sub-level Spherical in ‘shape’ or zone of probability Lowest energy electrons in energy level Present in all 7 energy levels Has 1 orbital (1 bed)
p sub-level Dumbbell shaped (2 lobes where electrons have a high probability of being) Arranged spatially along x, y, and z axes Present in all energy levels except 1 st 3 different orbitals (3 beds)
d sub-levels Most have 4 leaf clover shape Much more complex geometrically than s, & p Lobes arranged (mostly) between axial lines Present in 3 rd energy level and above 5 different orbital shapes (5 beds)
Electron Configuration Rules In an atom, electrons and the nucleus interact to make the most stable arrangement possible. The ways in which electrons are arranged in various orbitals around the nuclei of atoms are called electron configurations. Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms
1. Aufbau Principle aufbau principle, electrons occupy the orbitals of lowest energy first. The orbitals for any sublevel of a principal energy level are always of equal energy. within a principal energy level the s sublevel is always the lowest-energy sublevel. range of energy levels within a principal energy level can overlap the energy levels of another principal level.
2. Pauli Exclusion Principle Pauli exclusion principle, an atomic orbital may describe at most two electrons. To occupy the same orbital, two electrons must have opposite spins the electron spins must be paired. A vertical arrow indicates an electron and its direction of spin (↑ or ↓). An orbital containing paired electrons is written as
3. Hund’s Rule Hund’s rule states that electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible. – three electrons would occupy three orbitals of equal energy as follows:
Electron Configuration Arrow Diagram Arrow Diagrams use boxes and arrows to represent the atomic orbitals and each electrons location in the orbitals S sublevel has ONE orbital so it gets 1 box P sublevel has THREE orbitals so it gets 3 boxes D sublevel has FIVE orbitals so it gets 5 boxes F sublevel has SEVEN orbitals so it gets 7 boxes
Arrow Diagrams The electrons will fill the lowest energy sub- levels first before moving to the next sub-level (Aufbau Principle) Electrons will not pair up until each orbital has one electron in it (Hund’s Rule) and when they pair up they have opposite spin (Pauli Exclusion Principle) Note that the sum of the arrows equals the number of electrons in the atom.
Arrow Diagram You must label the energy level (1, 2, 3,…..) and the sub-level (s, p, d, f). The boxes represent the orbitals (beds) Use arrows to show each electron
Arrow Diagram Remember to follow the three rules – Lowest energy level & sub level first – Don’t pair up until each orbital of same energy has 1 electron – Can only pair if have opposite spins It does not matter which way the 1 st arrow faces!!! Complete Arrow diagram practice
Electron Configuration A convenient shorthand method for showing the electron configuration of an atom – write the energy level and the symbol for every sublevel occupied by an electron. – indicate the number of electrons occupying that sublevel with a superscript. – Example: oxygen= 1s 2 2s 2 2p 4. Note that the sum of the superscripts equals the number of electrons in the atom.
Example For Chlorine Becomes 1s 2, 2s 2, 2p 6, 3s 2, 3p 5 Use the periodic table like a book and you have to read the elements like words on a page You MUST always start on the 1 st element.
Noble Gas Electron Configuration Abbreviated Electron Configuration With larger elements writing out the location of EVERY electron can get a bit cumbersome – W: 1s 2, 2s 2, 2p 6, 3s 2, 3p 6, 4s 2, 3d 10, 4p 6, 5s 2, 4d 10, 5p 6, 6s 2, 4f 14, 5d 4 A short hand notation was created using the NOBLE GAS that comes before the element to abbreviate most of the electrons Will still have to show the location of electrons that come after the noble gas A noble gas can NOT be its own abbreviation – W the noble gas before it is Xe – W: [Xe] 6s 2, 4f 14, 5d 4
Noble Gas Electron Configuration Abbreviated Electron Configuration Tin (Sn) [Kr] 5s 2, 4d 10, 5p 2 Al [Ne] 3s 2, 3p 1 Rn [Xe] 6s 2, 4f 14, 5d 10,6p 6 Ra [Rn] 7s 2
Identifying Elements from Configurations Two methods of using Electron Configuration too find the element 1.Look at the last item in the configuration and match its location on the periodic table. 2.Add up the exponents and see the number of electrons in the element and match it to the correct element. Example: 1s 2, 2s 2, 2p 6, 3s 2, 3p 4 3p 4 refers to 3 rd period, p-block, 4 th element over = S has 16 electrons so is element # 16 = S
Identifying Elements from Configurations Example: 1s 2, 2s 2, 2p 6, 3s 2, 3p 4, 4s 2, 3d 10, 4p 6, 5s 2, 4d 4 4d4 refers to the 2 nd row of the transition metals = Mo Has 42 electrons = Mo Example: [Xe] 6s 2, 4f 10 4f 10 refers to 1 st row of f-block, 10 th element = Dy [Xe] = 54 e- + 12 e- = 66 e- = Dy Practice 1: 1s 2, 2s 2, 2p 6, 3s 2, 3p 4, 4s 2, 3d 10, 4p 5, 4p5 refers to 4 th period, p-block,5 th element = Br 35 electrons = Br Practice 2: [Kr] 5s 2, 4d 7, 4d 7 refers to 2 nd row d-block, 7 th element = Rh [Kr]= 36 e- + 9 e- = 45 e- = Rh
Valance Electrons Valance electrons are the electrons in the outer energy level of the atom Valance electrons are the electrons that participate in forming bonds – Note: Protons determine identity of element – NOTE: electrons determine chemical properties of element
Valance Electrons ALL elements: write the electron configuration and see how many electrons are in HIGHEST energy level. [Kr] 5s 2, 4d 10, 5p 2 – 5 th energy level is highest and has 4 electrons so has 4 valance electrons 1s 2, 2s 2, 2p 6, 3s 2, 3p 5 3rd energy level is highest and has 6 e- so valance electrons = 6 [Kr] 5s 2, 4d 7, 5 th energy level is highest and has 2 e- so valance electrons = 2
Valance Electrons – Representative Elements (s & p blocks ONLY) LOOK at 1’s digit in group number – Ca is in group 2 or 2a so it has 2 valance e- – Sb is in group 15 or 5a so it has 5 valance e- – Rn is in group 18 or 8a so it has 8 valance e- – YOU GIVE IT A TRY In Sr S Fr I In = 3 valance e- Sr = 2 valance e- S = 5 valance e- Fr = 1 valance e- I = 7 valance e-
Quantum Mechanical Model videos Origins of quantum theory (minuet physics): http://www.cleanvideosearch.com/media/action/ yt/watch?videoId=i1TVZIBj7UA http://www.cleanvideosearch.com/media/action/ yt/watch?videoId=i1TVZIBj7UA Schrodinger’s Cat (minuet physics) http://www.cleanvideosearch.com/media/action/ yt/watch?videoId=IOYyCHGWJq4 http://www.cleanvideosearch.com/media/action/ yt/watch?videoId=IOYyCHGWJq4 Wave/particle duality(Double Slit Experiment and Example in Nature) http://www.cleanvideosearch.com/media/action/ yt/watch?videoId=tu57B1v0SzI http://www.cleanvideosearch.com/media/action/ yt/watch?videoId=tu57B1v0SzI