Review for Exam 2 PDF

Unit 1.4 Learning Objectives Interpret mass spectrometry / mass spectra (MS) Explain similarities and differences between isotopes Use elemental analysis and mass spectra to identify a compound’s empirical formul...

Unit 1.4 Learning Objectives Interpret mass spectrometry / mass spectra (MS) Explain similarities and differences between isotopes Use elemental analysis and mass spectra to identify a compound’s empirical formula and molecular formula Chemical Thinking  Gallium’s atomic mass is 69.723 from periodic table 69.723 (100%) = 68.9256 (X %) + 70.9247 (Y %) Chemical Thinking 69.723 (100%) = 68.9256 (X %) + 70.9247 (100-X %) Solve for X X = 60.11 % The other percent must be 100 – 60.11 = 39.89 % 69.723 (100%) = 68.9256 (60.11%) + 70.9247 (39.89%)  Another way Gallium’s atomic mass is 69.723 from periodic table Chemical Thinking 69.723 (1) = 68.9256 (X) + 70.9247 (1-X) Solve for X X = 0.6011 1-X = 0.3989 (60.11%) (39.89%)  From Atoms to Molecules Mass spectrometry can also be used to determine the mass of molecules and analyze their structure. However, in this case it is important to realize CH4+ that the molecules will CH3+ break apart into Chemical Thinking several fragments. CH2+ ? CH+ C+ Methane CH4  Let′s Think This is the mass spectrum for methanol (CH3OH): Which molecular fragment CH3O+ CH3OH+ corresponds to the major peak? Chemical Thinking A. CH3OH+ CH3+ B. CH3OH C. CH3O+ D. CH3+  Base Peak and Molecular Ion Base peak Molecular ion Chemical Thinking  This peak is the molecular ion. All 12C, molar mass = 84 g/mol 12 + 12 + 12 + 12 + other pieces = 84 12 + 12 + 12 + 13 + other pieces = 85 Chemical Thinking Mostly 12C but one 13C, so this peak’s molar mass is 85 g/mol  Unit 2.1 Learning Objective Relate frequency and wavelength Interpret absorbance spectra, transmission spectra, and emission spectra Explain how the energy changes in an electron relates to specific wavelengths of light (both energy increases and Chemical Thinking decreases) Convert between energy, frequency, and wavelength for single photons and moles of photons – Use Planck’s constant and conversion factors (J to kJ, etc.)  Absorption vs Transmission Absorption spectroscopy data can be represented in various ways Transmission Ethanol Spectrum (C2H6O) Chemical Thinking At which l is Maximum absorption absorption maximum for this substance?  High frequency = high energy / big change A causes transition from 1 to 2 A low frequency = low energy B causes transition B Chemical Thinking from 1 to 3 C causes transition C from 1 to 4 high frequency = high energy  Review Slide: Converting Units E = hc/l l = 122 nm (1 m / 109 nm) = 122 x 10-9 m c = 3.00 x 108 m/s h = 6.626 x 10-34 J s 8 m 3.00 x10 Chemical Thinking c s En 1 n 2 h 6.6262 x10  34 J  s x  122 x10  9 m per photon 1.63 x 10-8 J/photon * (1 kJ / 1000 J) * (6.022 x1023 photons / 1 mol) = 9.82 x 102 kJ/mol of photons  Unit 2.2 Learning Objectives Explain bond strength and electron sharing within bonds Interpret infrared (IR) spectra to determine how atoms are connected in a molecule Explain the “shell model” of atomic structure Interpret photoelectron spectra (PES) Chemical Thinking Organize an atom’s electrons into shells, subshells, and orbitals Match an element with its electron configuration  Let’s Think Consider this IR spectrum of a substance: Wavenumber = 1/l Wavelength ↑ as frequency ↓ but Wavenumber ↑ as frequency ↑ Chemical Thinking Which bond in this molecule is likely the strongest? a) O-H b) C-H stretch c) C-H bend d) C-O  Let’s Think O-H stretch (Smallest atoms) Higher wavenumber = higher frequency = stronger bond Chemical Thinking Which bond in this molecule is likely the strongest? a) O-H b) C-H stretch c) C-H bend d) C-O  Molecular compounds result from the combination of nonmetallic elements. Many nonmetallic elements Valence 4 3 2 1 0 seem to have fixed bonding capacities (valence) or number of bonds they can form: Chemical Thinking Nonmetallic elements C  4 bonds N, P  3 bonds O, S  2 bonds Valence is a periodic property H, F, Cl  1 bond (elements from the same column behave similarly)  Each Row Adds Another Shell Electrons in 1st shell Electrons in 2nd shell Electrons in 3rd shell Chemical Thinking Electrons in 4th shell Electrons in 5th shell  Let’s Think IE IE Chemical Thinking 1s2 2s1 1st IE