# 3/25/2017 Electrons Model of atoms.

## Presentation on theme: "3/25/2017 Electrons Model of atoms."— Presentation transcript:

3/25/2017 Electrons Model of atoms

The Wave Nature of Light
Light was first recognized as manifestation of electromagnetic energy and it was called electromagnetic radiation 3/25/2017

3/25/2017

Produced by motion of electrically charged particles
3/25/2017 Produced by motion of electrically charged particles Move through vacuum (at x 108 m/s or 186,282 mi/hr), air and other substances Have characteristic wavelengths/frequencies Visible radiation has wavelengths between 400 nm (violet) and 750 nm (red) As electromagnetic wave, light has some characteristics in common with all forms of electromagnetic energy

Substance or material that carries wave
Wave: disturbance of medium which transports energy without permanently transporting matter Medium Substance or material that carries wave Merely carries wave from source to other location 3/25/2017

Light is a repeating waveform in motion
Rest Position: no energy present 3/25/2017 (amt. energy found in wave)

If frequency ↑, wavelength ↓
Frequency, wavelength, and velocity are inversely proportional to each other If frequency ↑, wavelength ↓ Ex. Purple light has a frequency of x Hz.  What is its wavelength? c =  3.00 x 108 m/s = 7.42 x 1014 Hz ()  = 4.04 x 10-7 3/25/2017

3/25/2017

Photons: packets of energy that make up light
3/25/2017 Photons: packets of energy that make up light Each carries specific energy related to its wavelength Photons of short wavelength (blue light) carry more energy than long wavelength (red light) photons Einstein successful explained photo-electric effect within context of quantum physics

Particulate Theory of Light
3/25/2017 Light is series of energy packets passing through space Size of energy packets vary/change color of light Quantized: electron limited to specific quantities of energy, not random value of energy Distance between energy packets = wavelength # photons passing point in period of time = frequency Particulate Theory of Light

3/25/2017

One of simplest working models of atom developed by Niels Bohr
3/25/2017 Suggested H’s electron moves around nucleus in only certain allowed orbits Smaller orbit, lower energy level Larger orbit, higher energy level Electron can have different energy levels Ground state: lowest level Excited state: atom gains energy One of simplest working models of atom developed by Niels Bohr

Assigned quantum number, n, to each orbit
Electron in ground state (1st energy level, n = 1) Does not radiate energy Quantum jump: electron moves from one energy level to another by gaining energy (excited state) or losing energy (ground state) in continuously changing amounts Electron drops from higher to lower energy orbit Photon with specific energy emitted as light Shown as different colored line spectrums (atomic spectrum) Every element has its own 3/25/2017

Atomic emission spectrum (amount of electromagnetic radiation of each frequency gas emits when heated/excited) Photon hits metal, is absorbed as electron takes up energy Einstein deduced each photon possesses energy Different metals require different minimum frequencies for electrons to exhibit photoelectric effect Above threshold frequency, # electrons ejected depend on intensity of light If photon’s frequency below minimum, electron remains bound to metal surface 3/25/2017

3/25/2017

3/25/2017 Fe

h = Planck's constant, 6.626 x 10-34 J·s ν= frequency of radiation
Ephoton = nhν n = # photons h = Planck's constant, x J·s ν= frequency of radiation Convert wavelength from nanometers to meters: 1 x 10-9 meters = 1 nm 3/25/2017

Groups of lines observed in emission spectrum of hydrogen atoms
UV visible IR IR IR 3/25/2017

Calculate the energy of a photon of yellow light with a frequency of 5
Calculate the energy of a photon of yellow light with a frequency of 5.09 x 1014 s-1. E= nhn = (1)(6.626 x J.s)(5.09 x 1014 s-1)= 3.37 x J Calculate the energy of a photon of wavelength x 104 nm (infrared). E = nhn = nhc/l = (1)(6.626 x J·s)(3.00 x 108 m/s) (5.00 x 10-5 m) = 3.98 x J Calculate energy of mole of photons of yellow light with a frequency of 5.09 x 1014 s-1. E = nhn = (6.022 x 1023)(6.626 x J·s) (5.09 x 1014 s-1) = 2.03 x 105 J 3/25/2017

What is the frequency in hertz of blue light having a wavelength of 425 nm?
7.06 X 1014 Hz A certain substance strongly absorbs infrared light having a wavelength of 6,500 nm.  What is the frequency in hertz of this light? 4.62 X 1013 Hz Yellow light has a wavelength of 600 nm. What is its frequency in hertz? 5.00 X 1014 Hz Green light has a wavelength of 550 nm. What is its frequency in hertz? 5.45 X 1014 Hz 3/25/2017

Intense microwaves have a frequency of 9. 5 X 1011 Hz
Intense microwaves have a frequency of 9.5 X 1011 Hz. What is the wavelength of these particular microwaves? 3.16 X 10-4 m  =  mm = 316 micrometers = 3.16 X 105 nm Infrared waves can be seen if you look down the railroad tracks or a road on a hot day. They heat the air as they go past causing the air to refract or bend the light.  If infrared rays of 9.75 X 1013 Hz are being reflected off the tracks or road what will be the size of  the wavelengths in micrometers? 3.08 X 10-6 m  = 3.08 micrometers A sunbather forgot their sunblock. On the beach they get a unheathy dose of UV radiation of 5.66 X 1016 Hz.  What is the wavelength of these particular UV waves? 5.30 X 10-9 m  = 5.00 nm 3/25/2017

Sodium vapor lamps are used to sometimes light streets
Sodium vapor lamps are used to sometimes light streets. If the frequency of the light coming from them is 5.09 X 1014 Hz what is the energy in each photon? 3.37 X J/photon What is the energy of each photon of red light that has a frequency of 4.0 X 1014 Hz? 2.65 X J/photon Calculate the energy in joules/photon for green light having a wavelength of 550 nm. 3.62 X J/photon 3/25/2017

Microwaves are used to heat food in microwave ovens
Microwaves are used to heat food in microwave ovens. The microwave radiation is absorbed by moisture in the food. This heats the water, and as water becomes hot, so does the food.   How many photons having a wavelength of 3.00 mm would have to be absorbed by 1.00 g of water to raise its temperature by 1oC? 6.63 X J/photon; 6.31 X 1022 photons The wavelengths of X-rays are much shorter than those of ultraviolet or visible light. Show quantitatively why continued exposure to X-rays is more damaging than exposure to sunlight. X-rays: 6.63 X J/photon, UV rays: X J/photon, X-rays are 100 times more powerful than UV rays. 3/25/2017

Flame Tests 3/25/2017 Prepare 0.5 M solutions of barium/calcium/potassium lithium/sodium/ and strontium chloride (nitrates can be used). Fold the end of a nichrome or platinum wire into a ball and tap the straight end to a wooden stick. Dip the end into dilute hydrochloric acid, hold it in the burner until no color shows. Dip the end into a test tube of one of the solutions, place it in the flame, record color on chart.

Homework: Read 5.1, pp. 116-126 Q pg. 126, #8-10
3/25/2017 Read 5.1, pp Q pg. 126, #8-10 Q pp , #33, 36, 37, 65, 66, 70, 71, 74, 76 Homework:

de Broglie (de-broy-lee) 1924
By the mid-1920s, scientists convinced Bohr atomic model was incorrect, formulated new explanations of how electrons arranged in atoms de Broglie (de-broy-lee) 1924 If light could act as both particles and waves, so could electrons Since energy E of photon equals Planck’s constant times frequency f, or E = hf, momentum p of electron would equal Planck’s constant divided by wavelength 3/25/2017

3/25/2017

3/25/2017

Heisenberg’s Uncertainty Principle applied de Broglie’s hypothesis
Impossible to determine with perfect accuracy both position and momentum of particle simultaneously Making measurements on object alters location/ momentum enough to disturb accuracy of reading location/momentum More certain we are about particle's position, less certain we are about its velocity, and vice versa Bohr ran into trouble because he tried to predict electron’s movement too precisely Restricting electron to certain locations and having it move in orbits violated Heisenberg Uncertainty Principle 3/25/2017 Heisenberg’s Uncertainty Principle applied de Broglie’s hypothesis

3/25/2017

Is light a wave or a particle?
Electromagnetic radiation has dual "personality“ Acts like waves/photons with no mass Displays behaviors characteristic of any wave (reflection, refraction, diffraction, interference, exhibits Doppler effect) that would be difficult to explain with pure particle-view 3/25/2017 Is light a wave or a particle?

3/25/2017

3/25/2017

Principles of Quantum Mechanics (Schrödinger)
Equation contains both wave and particle terms Electrons do not have planetary orbit Location of electron is probability, not certain position 3/25/2017

Quantum Theory 3/25/2017 Describes mathematically wave properties of electrons and other very small particles Cloud shapes now called orbitals 3-D region around nucleus that indicates probable location of electron (“probability regions”) Electrons not confined to fixed circular path

Quantum numbers 3/25/2017 Specify properties of atomic orbitals/electrons in orbitals 1st 3 from Schrödinger equation (main energy level, shape, and orientation of orbital) 4th is spin quantum number Electrons have specific energy levels (1st, 2nd) Different energy levels associated w/different orbits Those nearer nucleus have lower energy than those farther away Electrons cannot exist between energy levels

Quantization of energy
3/25/2017 Place a ball at the top of the stairs and roll it gently toward the flight of stairs. Observe the motion and intermittent resting points of the ball as it moves down the stairs. What is its final resting place on one step analogous to? Toss a small ball toward the top of the stairs with as little spin as possible. Where does it come to rest? What happens if you throw it harder (use more energy)? What is the amount of energy you use analagous to?

Principal Quantum Number, n
3/25/2017 Main energy level occupied by electron/ size of orbital As n becomes larger, atom becomes larger and electron is further away from nucleus Principal Quantum Number, n

Cartesian coordinate system (x, y, and z axes) as frame of reference; nucleus located at origin
Boundary surface diagrams: volume of space that encloses 90% probability of finding electron within orbital’s boundary surfaces 3/25/2017

Azimuthal Quantum Number, l (angular momentum)
3/25/2017 Shape of cloud Divides shells into subshells (sublevels) (l) in each principal energy level (l = n-1) Azimuthal Quantum Number, l (angular momentum) n = 1, 1 sublevel (s) n = 2, 2 sublevels (p) n = 3, 3 sublevels (d) n = 4, 4 sublevels (f)

Divides subshell into orbitals which hold electrons
3/25/2017 Divides subshell into orbitals which hold electrons Specifies 3-D orientation of each orbital around nucleus Magnetic Quantum Number, ml (effect of different orientations of orbitals 1st observed in presence of magnetic field)

Each orbital has specific # sublevels
s has 1 sublevel p has 3 sublevels (px, py, pz) d has 5 sublevels (dxy, dyz, dxz, dx2-y2, dz2) f has 7 sublevels 3/25/2017

Magnetic Quantum Number, ms (spin quantum number)
3/25/2017 Specifies orientation of spin axis of electron Creates magnetic field because it spins, oriented in one of two directions Pairs (diamagnetic) not attracted to magnets Unpaired (paramagnetic) weakly attracted to magnets Magnetic Quantum Number, ms (spin quantum number)

Each sublevel can contain maximum of two electrons
s has lowest energy (max 2 electrons) p (max 6) d (max 10) f has highest energy (max 14) Must have opposite spins 1st electron to fill orbital has a ↑/+ spin 2nd electron to fill the orbital has a ↓/- spin You can use /, N/S, +/- 3/25/2017

3/25/2017

Homework: Read 5.2, pp. 127-134 Q pg. 134, #13, 15, 16
3/25/2017 Read 5.2, pp Q pg. 134, #13, 15, 16 Q pg. 146, #42, 45, 49, 52, 56, Homework:

All orbitals related to energy sublevel are of equal energy (All three 2p orbitals are of equal energy) Sublevels w/in principal energy level have diff. energies (Three 2p orbitals are of higher energy than 2s orbital) In order of increasing energy, sequence of energy sublevels within principal energy level is s, p, d, and f Orbitals within one principal energy level can overlap orbitals related to energy sublevels within another principal level (Orbital related to atom’s 4s sublevel has lower energy than five orbitals related to 3d sublevel) 3/25/2017 Aufbau (“building up” in German) principle: each electron occupies lowest energy orbital available

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f
3/25/2017

Pauli exclusion principle -atomic orbital has at most 2 electrons
3/25/2017 No more than 2 electrons, each with opposing spin (↾⇂), can be located in energy level No two electrons can have the same set of quantum numbers If 1 energy level is available, then 2 electrons can be accommodated Pauli exclusion principle -atomic orbital has at most 2 electrons

n l m Subshell notation # orbitals in subshell # electrons needed to fill subshell Total # electrons in subshell 1 1s 2 (± ½) 2 2s -1,0,1 2p 3 6 8 3s 3p -2,-1,0,1,2 3d 5 10 18 4 4s 4p 4d -3,-2,-1,0,1,2,3 4f 7 14 32 3/25/2017

3/25/2017

3/25/2017

3/25/2017 Hund’s rule: Orbitals of equal energy are each occupied by one electron before any orbital is occupied by 2nd electron, and all electrons in singly occupied orbitals must have same spin WRONG RIGHT

3/25/2017

3/25/2017

Exceptions to electron configuration rules
Half filled 4s and 3d is more stable than expected electron configuration expected 1 observed 3/25/2017

3/25/2017

Electron Configurations of Ions
3/25/2017 1. Which of the following sets of atomic number and configuration represent the ground state electron configuration of an atom or ion? State which atom or ion it is.        a)   A = 8,  1s2 2s2 2p4        b)   A = 11,  1s2 2s2 2p6        c)   A = 14,  1s2 2s2 2p6 3s2        d)   A = 22,  1s2 2s2 2p6 3s2 3p6 4s2 2. Write the correct electron configurations for:        a)  Pb4+        b)  S2-        c)  Fe3+        d)  Zn2+ Electron Configurations of Ions

3. Give the electron configurations for the following transition metal ions:        a)  Sc3+        b)  Cr2+        c)  Ag1+        d)  Ni3+ 4. Of the following species (Sc0, Ca2+, Cl0, S2-, Ti3+), which are isoelectric? 5. Identify the group containing the element composed of atoms whose last electron:         a)  enters and fills and 's' subshell.         b)  enters but does not fill an 's' subshell.         c)  is the first to enter a 'p' subshell.         d)  is the next to the last in a given 'p' subshell.         e)  enters and fills a given 'p' subshell.         f)   is the first to enter a 's' subshell.         g)  half fills a 'd' subshell. 6. Write the electron configuration for argon. Name two positive and two negative ions that have this configuration. 3/25/2017

6. 1s2 2s2 2p6 3s2 3p6 4s2 = Ar = S-2, Cl-1, K+1 and Ca+2
1. a)   oxygen as a neutral atom     b)   lithium as a +1 ion     c)   silicon as a +2 ion     d)   titanium as a +2 ion 2. a)  Pb4+   1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d8     b)  S2-      1s2 2s2 2p6 3s2 3p6     c)  Fe3+    1s2 2s2 2p6 3s2 3p6 4s2 3d3     d)  Zn2+    1s2 2s2 2p6 3s2 3p6 4s2 3d8 3. a)  Sc3+    1s2 2s2 2p6 3s2 3p6     b)  Cr2+    1s2 2s2 2p6 3s2 3p6 4s2 3d2     c)  Ag1+    1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s0 4d10     d)  Ni3+    1s2 2s2 2p6 3s2 3p6 4s2 3d5 4. Ca2+and  S2-have the same electronic configuration with 18 electrons each. 5.  a)  The alkali earth metals      b)  The alkali metals      c)  The boron group      d)  The halogens      e)  The noble gases      f)   The alkali metals      g)  The manganese group 6.  1s2 2s2 2p6 3s2 3p6 4s2   = Ar = S-2, Cl-1, K+1 and Ca+2 3/25/2017

3/25/2017 Read 5.3, pp Q pg. 141, #25, 27 Q pp , #60, 64, 78 a/d, 79 a-d, 80 a/c/f Test practice, pg. 149, all questions Use link for quiz and submit as before. e/science.php?qi=520 Homework: