Electromagnetic Radiation. is a form of energy that exhibits wavelike behavior as it travels through space.

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1 Electromagnetic Radiation is a form of energy that exhibits wavelike behavior as it travels through space.

2 What are the 7 forms of electromagnetic radiation, in order of INCREASING wavelength? gamma rays (shortest λ), x-rays, ultraviolet light, visible light, infrared, microwave, radio waves (longest λ).

3 What are the colors of the visible spectrum in order of INCREASING wavelength? Violet (shortest λ), blue, green, yellow, orange, red (longest λ)

4 What is wavelength? The distance between corresponding points on adjacent waves.

5 What is frequency? The number of waves that pass a given point in a specific time, usually one second.

6 What are the units of frequency? Units are waves/s, also called cycles/s. 1 wave/s = 1 Hz (Hertz)

7 What is the relationship between frequency and wavelength? c = λν Since the speed of light is a constant, as λ increases ν must decrease, and verse visa. Relationship between λ and ν

8 Gamma rays have a wavelength of ~10-2 nm, Microwaves have a wavelength of ~10 1 cm. Compare the frequency, and speed of these two types of radiation. Gamma rays have a HIGHER frequency than microwaves Gamma rays and microwaves travel at the same speed (c = the speed of light) Relationship between λ and ν

9 Indigo colored light has a wavelength of 440nm. What is the frequency of this light? ν = 6.8x1014Hz

10 X rays have a frequency of approximately 4.0x10 17 Hz. What is the wavelength in meters? In nm? λ= 7.5x10 10m λ = 7.5x10 1nm Practice Problem #2

11 Max Planck What was Planck s contribution to the particle theory of light? He suggested that hot objects emit EM radiation in discrete packets like a particle (not in a continuous wave). He called these small, specific amounts of energy quanta.

12 Al s explanation of the Photoelectric Effect How did Einstein explain the photoelectric effect? Electromagnetic radiation is absorbed by matter only in whole numbers of photons. For an electron to be ejected from a metal surface, the electron must be struck by a single photon possessing at least the minimum energy required to knock the electron loose. This corresponds to a minimum radiation frequency. Electrons in different elements are bound to the nucleus more or less tightly, so different metals require different minimum frequencies to exhibit the photoelectric effect.

13 How does the photoelectric effect support the particle theory of light? Only light whose frequency was above a minimum would cause the emission of electrons from a metal when light shines on the metal. Light can be thought of as a stream of particles (photons). In order to emit electrons, the metal must be struck by a photon of light containing a quantum of energy, E=hν

14 Sodium emits yellow light with a wavelength of approximately 570 nm. What is the frequency of this radiation in Hz? 5.3x10 14 Hz

15 How are spectral lines formed? An electron absorbs a photon and jumps to a higher energy level (excited state). When it moves back to the ground state (or another lower energy state) it emits a photon of light whose energy is equal to the difference in energy between the two levels. This photon shows up as a line on the spectrum, the wavelength can be used to calculate the energy of the photon.

16 The line spectrum for hydrogen shows a blue line (λ= 434nm) and a red line (λ= 656nm). Which line results from an electron going from n=4 to n=2, and which one results from a jump from n=3 to n=2? Blue is n=4 to 2 (bigger jump=more energy, therefore smaller λ Red is n=3 to 2 (smaller jump=less energy, therefore larger λ E= hc λ

17 In addition to lines in the visible range of the spectrum, hydrogen also produces lines in the ultraviolet range (Lyman series) and infrared range (Paschen series). Which series results from greater jumps? Lyman series lines have more energy (uv is higher frequency than IR), which means the jumps were bigger. E=hν

18 Who first suggested that electrons act as waves in an orbital? de Broglie suggested that electrons were waves confined to the space around the nucleus the waves could only exist at certain frequencies that corresponded to specific energies the quantized energies of Bohr s orbits (where E = hν).

19 Werner Heisenberg What is Heisenberg s Uncertainty Principle? It is impossible to determine simultaneously both the position and velocity of an electron or any other quantum particle.

20 What was Shrodinger s contribution to Quantum Theory? Schrodinger developed an equation that treated electrons as waves. The solution to Schrodinger s wave equation are the first 3 quantum numbers, which are like GPS coordinates for the location of an electron (they describe the energy level, shape, and orientation of orbitals).

21 What is an orbital? An orbital is a three dimensional region around the nucleus that indicates the probable location of an electron. Orbitals are like clouds showing the region of probable electron locations.

22 What is the relationship between n (the first quantum number) and the amount of energy an electron possesses? As n increases, the electron s energy and average distance from the nucleus increases. n=1 n=2 n=3

23 What is the shape of each orbital? s orbital spherical p orbital dumbell shape d orbital cloverleaf shape f orbital a bunch of leaves

24 What is the relationship between n and the total number of sublevels and orbitals? For each main energy level (n), there are n sublevels, and n 2 total orbitals in each main energy level. n sublevels orbitals 1 s 1 2 s,p 1 in s; 3 in p 3 s,p,d 1 in s; 3 in p; 5 in d 4 s,p,d,f 1 in s; 3 in p; 5 in d; 7 in f

25 How many total orbitals are contained in the third main energy level? n=3 contains s,p,d sublevels. Each s sublevel contains 1 orbital, p sublevel contains 3 orbitals, d contains 5 orbitals, therefore, there are 9 total orbitals in the 3 rd main energy level.

26 What sublevels are contained in the 4 th main energy level? s,p,d,f which means there can be a total of 32 electrons in the 4 th main energy level (n=4)

27 How many electrons could be contained in the 3 rd main energy level? The total number of electrons in a main energy level is 2n 2. For n=3, the total number of electrons is 18 contained in the s,p,d sublevels.

28 How many electrons can each orbital hold? A single orbital can hold a maximum of two electrons, which must have opposite spins.

29 What is the Aufbau principle? An electron occupies the lowest-energy orbital that can receive it. In other words, each electron is placed in the lowest energy orbital that still has room in it. The orbitals within a sublevel are filled following Hund s rule. Once all of the orbitals within a sublevel are full, the next lowest energy sublevel would be used.

30 What is the Pauli exclusion principle? No two electrons in the same atom can have the same set of four quantum numbers. Thus electron pairs in orbitals must be of opposite spin. Electrons spin about their axis in opposite directions. Wolfgang Pauli:

31 What is Hund s Rule? Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron (i.e., everybody on the bus would prefer to have their own seat and only share if there are no other open seats), and all electrons in singly occupied orbitals must have the same spin. The rule above minimizes electron-electron repulsion. Notice how the 3p electrons are all up arrows before you start filling with down

32 The electron configuration for an atom is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 4 How many electrons does it have? 34 What element is it? Selenium Se What is the valence shell? n=4 In which sublevels are the valence electrons located? 4s and 4p sublevels How many unpaired electrons does this atom have? 2

33 What is an octet of electrons? How many electrons are in an octet? An octet of electrons is 8 in the valence shell, giving the atom the same electronic configuration as a noble gas

34 Identify the element having the following electron configuration: [Kr] 5s 2 4d 10 5p 2 How many unpaired electrons are there in this atom? Tin (Sn) 2 unpaired electrons

35 Identify the element having the following electron configurations: Contains one paired and three unpaired electrons in its outermost main energy level n=4 Arsenic 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 3

36 Identify the element having the following electron configurations Contains four electrons in its outermost main energy level n=3 Silicon 1s 2 2s 2 2p 6 3s 2 3p 2

37 Is the following electron configuration for gallium (Ga) correct? If not, rewrite it correctly. 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 1

38 Is the following electron configuration for Chromium (Cr) correct? If not, rewrite it correctly. [Ar]4s 2 3d 4 [Ar]4s 1 3d 5 This configuration represents the lowest energy configuration (even though it violates the Aufbau principle)