Honors Chemistry Unit 3 ELECTRONS IN ATOMS

Transcription

1 Honors Chemistry Unit 3 ELECTRONS IN ATOMS

2 I. RADIATION A. Particles 1. alpha particle - helium nucleus with 2 protons, 2 neutrons 2. beta particle - electron or positron ejected from nucleus B. Energy - gamma rays (like x-rays)

3 II. SPECTRA A. EM (electromagnetic) energy Equations: E = hv v = frequency (Hz) E = energy h = Planck's constant (6.626 x J/Hz) λ = c/v c = speed of light (3.00 x 10 8 m/s) λ = wavelength (nm) Relationships: E/v = constant (direct) λv = constant (inverse) E and λ are inversely related So high energies are associated with high frequencies and lower wavelengths

4 EXAMPLE What is the wavelength of light (in nm) whose frequency is x Hz? λ = c/ν So λ = 3.00 x 10 8 m/s = 4.00 x 10-5 m x /s Change to nm: 4.00 x 10-5 m 1 x 10 9 nm = 4.00 x 10 4 nm 1 m

5 TYPES OF SPECTRA B. Emission spectrum: wavelength given off by energized electrons in the element Ground state: lowest energy state of an atom Excited state: atom has higher potential energy than in ground state C. Absorption spectrum: wavelength absorbed as light passes through the element vapor

6 SPECTRA EXAMPLES

7 III HISTORY OF QUANTUM MECHANICS Led to Electron Cloud model of atom A. DeBroglie studied relationships between velocity, mass, and wavelength 1. electron had wavelike properties 2. wave-particle duality of nature - we only see the wave nature when particles are small and velocity is near c (speed of light)

8 B. HEISENBERG 1. can't know position and momentum of electron at the same time because finding one changes the other 2. uncertainty principle -the more you know about position the less you know about momentum

9 C. SHRÖDINGER Developed a mathematical equation to describe the wave-like behavior using the amplitude of the wave

10 D. MAX BORN Found the probability of an electron's position at any time

11 IV. QUANTUM NUMBERS - DESCRIBE AN ELECTRON IN 4 WAYS: 1. PRINCIPLE QUANTUM NUMBER (n) energy level, distance from nucleus, size of cloud a. given in whole numbers (1,2,3) b. lower energy if closer to the nucleus c. higher numbers mean higher energy and larger cloud d. maximum electrons in an energy level = 2n 2 If n=1 2e-, n=2 8e-, n=3 18e-

12 2. ANGULAR MOMENTUM QUANTUM NUMBER (L) - SHAPE OF ORBITALS IN SUBLEVEL a. Possible numbers are 0,1,...n-1 b. 0 = s sphere 1 = p peanut 2 = d double peanut 3 = f flower c. number of shapes possible on the level = n: Level 1 = 1 shape (s), Level 2 = 2 shapes (s,p)

13 3. ORBITAL QUANTUM NUMBER (M) - POSITION IN SPACE RELATED TO X,Y,Z AXES a. given values of -l to +l b. each orbital can hold two electrons s sublevel has 1 orbital: 0 p sublevel has 3 orbitals: -1,0,+1 d sublevel has 5 orbitals: -2,-1,0,+1,+2 f sublevel has 7 orbitals: -3,-2,-1,0,+1,+2,+3

14 4. SPIN QUANTUM NUMBER (S) - DIRECTION OF SPIN a. clockwise: +1/2 (preferred - first assigned) b. counterclockwise: -1/2

15 A. PAULI EXCLUSION PRINCIPLE: No two electrons in the same atom can have the same four quantum number Example: (4,3,2,-½) only exists ONCE in an atom Must differ in at least one of the numbers (4,3,2,+½) could exist different spin

16 B. APARTMENT BUILDING ANALOGY Energy Level - Floor Orbital shape (sublevel) Type of Apartment: s -1 bedroom, p-3 bedroom, d-5, f-7 Orbital position - Which bedroom in apartment (1 person in each room before adding a roommate) Spin - Which bed in bedroom? Bed by window is first taken (clockwise), bed by door (counterclockwise)

17 V. ELECTRON FILLING ORDER - RULES 1. Aufbau Principle: electrons will occupy lowest energy levels and shapes first (follow diagram) 2. Hund s Rule: electrons will be alone in an orbital if possible - put one in each equal energy orbital before doubling up in any orbital in the same sublevel Orbitals with the same energy requirement are called degenerate orbitals

18 3. EXAMPLE: OXYGEN Atomic number 8, so has 8 electrons Assign quantum numbers for each electron (see board)

19 B. QUANTUM SHORTHAND 1. Orbital Notation - shows all properties described by the four quantum numbers 1s Orbitals shown by line, electron represented by arrow (up-clockwise, down-counterclockwise) 2. Electron Configuration - shows electrons down to the sublevels Energy level and sublevel with superscript of how many electrons present 1s 2 2s 2 2p 6

20 3. ELECTRON DOT NOTATION Shows outer energy level only (energy level with the highest number in front) a. Dot arrangement: E (draw in numbers to show dot order) b. 8 dots maximum: next energy level begins to fill after the p sublevel - only highest level is shown even if lower level is not complete

21 C. SHORTHAND EXAMPLES See board

22 NOBLE GAS CONFIGURATION Begin the configuration with the symbol for the noble gas from the row above your element. Put it in brackets with the number of electrons above it (the atomic number of the gas). Beginning with the s level of the period that contains your element, continue to fill orbitals until the total number of electrons (all superscripts added together) matches your element s atomic number.

23 EXAMPLES Phosphorus Atomic number 15 Find noble gas above P put in brackets [Ne] (has 10 electrons already only need to show 5 more) Start with s electrons on energy level of period that P is on 3 rd period so begin with 3s electrons Continue filling until electrons equal atomic number [Ne] 3s 2 3p 3 Indium Atomic number 49 [Kr] 5s 2 4d 10 5p 1

24 END OF UNIT 3 Study for Test! Keep up with Homework! Do Insurance It really helps!