Aug Inorganic & Physical Chemistry Part 1 CfE Adv Higher Unit 1 Based on Presentations produced by David P. White University of North Carolina, Wilmington Gordon Watson Chemistry Department, Kelso High School

Aug Introduction Electromagnetic Spectrum Spectroscopy This topic describes the Electromagnetic Spectrum and how it can interact with atoms, Spectroscopy. Electronic Structure Much information about Electronic Structure comes from spectroscopic evidence.

3 The Wave Nature of Light All waves have a characteristic wavelength wavelength, , measured in metres (m) to nanometres (nm) frequencyThe frequency,, of a wave is the number of waves which pass a point in one second measured in Hertz (Hz) or per seconds (s -1 ) speedThe speed of a wave, c, is given by its frequency multiplied by its wavelength: c = f x λ For light, c = 3.00 x 10 8 ms -1 wavenumberAnother unit of ‘ frequency ’ used in spectroscopy is the wavenumber (1/  ), nu nu, measured in m -1 or cm -1 Aug 2016

4 Electromagnetic Radiation Aug 2016

5 Planck Planck: energy can only be absorbed or released from atoms in quanta certain amounts called quanta quantization To understand quantization, consider the notes produced by a violin (continuous) and a piano (quantized): a violin can produce any note by placing the fingers at an appropriate spot on the fingerboard. A piano can only produce certain notes corresponding to the keys on the keyboard. The Particle Nature of Light 1 Aug 2016

6 Electromagnetic Radiation can also be thought of as a stream of very small particles known asphotons particles known as photons Electromagnetic Radiation exhibits wave-particle dual properties. energy The energy (E) of a photon (particle) is related to the frequency (wave) of the radiation as follows: E = hf Planck ’ s constant where h is Planck ’ s constant ( 6.63 x J s ). The Particle Nature of Light 2 Aug 2016

7 E = hf  or E = h c /  energy The energy calculated would be in Joules (J) and would be a very small quantity. one mole of photons Normally, we would calculate the energy transferred by the emission or absorption of one mole of photons as follows: E = Lhf  or E = L h c /  Avogadro Constant Where L is the Avogadro Constant, 6.02 x and E would now be in J mol -1 or kJ mol -1. Energy Calculations 1 Aug 2016

8 For example, a neon strip light emitted light with a wavelength of 640 nm. 640 nm = 640 x m = 6.40 x m. For 1 mole of photons: E =3.11 x x 6.02 x J =1.87 x 10 5 J mol -1 =187 k J mol -1 For each photon: E = h c / λ =6.63 x x 3.00 x 10 8 / 6.40 x =3.11 x J Energy Calculations 2 Aug 2016

9 Atomic emissionspectra Atomic emission spectra provided significant contributions to the modern picture of atomic structure Emission Spectra 1 monochromatic Radiation composed of only one wavelength is called monochromatic continuous Radiation that spans a whole array of different wavelengths is called continuous spectrum White light can be separated into a continuous spectrum of colors. Aug 2016

10 Emission Spectra 2 Aug 2016

11 Hydrogen Emission Spectrum Aug 2016

12 The spectrum obtained when hydrogen atoms are excited excited shows four lines: red, blue-green, blue and indigo Line Spectra Bohr electrons Bohr deduced that the colours were due to the movement of electrons from a higher energy level back to the ‘ ground state ’. fixed energy levels The significance of a Line Spectrum is that it suggests that electrons can only occupy certain fixed energy levels Aug 2016

13 Bohr ’ s Model electron shells These fixed energy levels are what we have always called our electron shells A photon of light is emitted or absorbed when an electron changes from one energy level (shell) to another.

14 Bohr described each shell by a number, principal quantum number, n the principal quantum number, n n = 1 For the first shell, n = 1 n = 2 For the second shell, n = 2 and so on. After lots of math, Bohr showed that n = 1, 2, 3, where n is the principal quantum number (i.e., n = 1, 2, 3, …), and R H is the Rydberg constant = 2.18 x 10  18 J. Principal Quantum Number Aug 2016

15 n=2 Balmer Series The lines detected in the visible spectrum were due to electrons returning to the n=2 level and are called the Balmer Series Lyman Series n=1 ultra-violet Another series of lines called the Lyman Series are due to electrons returning to the n=1 level. The  E values are higher and the lines appear in the ultra-violet region. Hydrogen Spectra Aug 2016

16 converge When we examine spectra we notice that each series of lines converge, i.e the gaps between the lines get smaller and smaller until the lines seem to merge. Ionisation Energy 1 n=1 The line of greatest energy (lowest wavelength, highest frequency), represents an electron returning from the outer limit of an atom to the ground state ( n=1 in the case of Hydrogen). the Ionisation Energy With slightly more energy the electron would have removed from the atom completely, i.e. the Ionisation Energy Frequency Aug 2016

17 Ionisation Energy 2 For example, the wavelength of the line at the convergence Limit of the Lyman series in the Hydrogen spectrum is 91.2 nm nm = 91.2 x m = 9.12 x m. For 1 mole of photons: E = 2.18 x x 6.02 x J =1.31 x 10 6 J mol -1 =1,310 k J mol -1 For each photon: E = h c / λ =6.63 x x 3.00 x 10 8 / 9.12 x =2.18 x J Data Book Value 1,311 kJ mol -1 Aug 2016

18 Subshells - Orbitals High resolution spectra of more complex atoms reveal that lines are often split into triplets, quintuplets etc. Subshells This is evidence that Shells are further subdivided into Subshells Orbitals These Subshells are called Orbitals Quantum Mechanics shapes Calculations using Quantum Mechanics have been able to determine the shapes of these Orbitals Aug 2016

19 s-orbitals s orbitalsspherical Quantum mechanics has shown that s orbitals are spherical in shape An orbital is a region in space where there is a greater than 90% probability of finding an electron. Aug 2016

20 Orbitals and Quantum Numbers Angular Quantum Number, l. This quantum number describes shape s, p, d and f-orbitals the shape of an orbital. l = 0, 1, 2, and 3 (4 shapes) but we use letters for l (s, p, d and f). Usually we refer to the s, p, d and f-orbitals orientation p x p y p z Magnetic Quantum Number, m l. This quantum number describes the orientation of orbitals of the same shape. The magnetic quantum number has integral values between -l and +l. However, we use p x, p y and p z instead. 3 There are 3 possible p -orbitals There are 5 possible d-orbitals There are 7 possible f-orbitals Aug 2016

21 p-orbitals shapedumb-bell The shape of a p-orbital is dumb-bell, (l = 1). three Each shell, from the second shell onwards, contains three of these p-orbitals, ( m l = ). orientationp x p y p z We describe their orientation as ‘ along the x-axis ’, p x ‘ along the y- axis ’, p y and ‘ along the z-axis ’, p z Aug 2016

22 d-orbitals shape The shape of d-orbitals (l = 2) are more complicated. five Each shell, from the third shell onwards, contains five of these d-orbitals, ( m l = ). orientation We describe their orientation as d xy d xz d yz ‘ between the x-and y-axis ’, d xy, ‘ between the x-and z-axis ’, d xz, ‘ between the y-and z-axis ’, d yz, d x 2 - y 2 d z 2 ‘ along the x- and y-axis ’, d x 2 - y 2 and ‘ along the z-axis ’, d z 2 Aug 2016

23 f-orbitals shape The shape of f-orbitals (l = 3) are even more complicated. seven Each shell, from the fourth shell onwards, contains seven of these f-orbitals, ( m l = ). f-orbitals are not included in Advanced Higher so we will not have to consider their shapes or orientations, thank goodness! Aug 2016

24 f-orbitals Couldn ’ t resist it ! Aug 2016

25 Spin Quantum Number Each orbital can hold up to 2 electrons. spin In 1920 it was realised that an electron behaves as if it has a spin A fourth quantum number was needed. spin quantum number The spin quantum number, m s only has two values + 1 / 2 and - 1 / 2 four quantum numbers uniquely Therefore, up to four quantum numbers, n (shell), l (shape), m l (orientation) and m s (spin) are needed to uniquely describe every electron in an atom. Aug 2016

26 Energy Diagram Aufbau diagram Orbitals can be ranked in terms of energy to yield an Aufbau diagram n As n increases, note that the spacing between energy levels becomes smaller. degenerate Sets, such as the 2p-orbitals, are of equal energy, they are degenerate Notice that the third and fourth shells overlap Aug 2016

27 Electron Configurations 1 There are 3 rules which determine in which orbitals the electrons of an element are located. and ….. if there are two electrons in an orbital they must have opposite spins (rather than parallel spins). Pauli Exclusion Principle The Pauli Exclusion Principle states that the maximum number of electrons in any atomic orbital is two…….. Hund ’ s Rule of Maximum Multiplicity For degenerate orbitals, electrons fill each orbital singly before any orbital gets a second electron (Hund ’ s Rule of Maximum Multiplicity). Aufbau Principle The Aufbau Principle states that electrons will fill orbitals starting with the orbital of lowest energy. Aug 2016

28 Electron Configurations 2 Aug 2016

29 Periodic Table Aug 2016

30 Emission Spectroscopy 1 Na line (589 nm): 3p  3s transition Li line: 2p  2s transition K line: 4p  4s transition emission spectroscopy In emission spectroscopy, light of certain wavelengths is emitted as ‘ excited ’ electrons drop down from higher energy levels. The spectrum is examined to see the wavelengths emitted. Aug 2016

31 Emission Spectroscopy 2 characteristic spectrum identify Each element provides a characteristic spectrum which can be used to identify the element. Analysing light from stars etc, tell us a lot about the elements present. intensity quantity Analytical tool The intensity of a particularly strong line in an element ’ s spectrum can be measured. The intensity of the light emitted is proportional to the quantity of the atoms/ions in the sample. Calibration samples can be prepared, intensities measured and unknown concentrations determined. Analytical tool. Aug 2016

32 Absorption Spectroscopy absorption spectroscopy In absorption spectroscopy, light of certain wavelengths is absorbed and electrons are promoted to higher energy levels. The spectrum is examined to see which wavelengths have been absorbed. intensityquantity The intensity of the light absorbed is proportional to the quantity of the atoms/ions in the sample. Calibration samples can be prepared, intensities measured and unknown concentrations determined (PPA) Aug 2016

33 End of Topic 1 Electronic Structure of Atoms Aug 2016