Lecture 2: The basics: atoms, moles, energy & light

Transcription

1 Lecture 2: The basics: atoms, moles, energy & light Read: BLB Chap ; ; 6.1 HW: BLB 2:4,23,25,31; 5:3,25,28 Sup 2:1 3; 6:1,3,4,5 do NOT do Sup 6.2! Know: the mole atomic structure protons, neutrons, electrons atomic weights kinetic & potential energy conservation of energy energy: system & surroundings wavelength, frequency of light E = hν Pre-quiz must be taken by midnight tonight; log onto ANGEL (cms.psu.edu), navigate to Chem110: Sections Lessons. Get started on the Skill Check Tests (on ANGEL). Bonus deadline for Skill Check Tests #1 (basic math) & #2 (metric measurements) is tomorrow, Jan 15. Form a study group, use the CRC, take advantage of SI (starting soon, info on web), use the online resources, and work those problems practice, practice, practice Sheets Page 1 Lecture 2

2 Big picture issues to keep in mind what is the structure of an atom? what are the properties of atoms? Remember: structure effects function! where are the electrons anyway? what is the energy of an electron? Sheets Page 2 Lecture 2

3 The MOLE the critical concept! A mole is a number just like a dozen but a lot bigger! N A = Avagadroʼs number = 1 dozen green peas = 12 green peas 1 mol green peas = green peas makes it easier to refer to large numbers a mole same of something (atoms, molecules, green peas, coffee beans) BUT different objects different masses (or volumes); cannot experimentally measure a mole, can measure mass & volume # atoms or molecules mole g, ml (measurable quantities) Sheets Page 3 Lecture 2

4 Components of atom mass (amu) proton p ~1 electron e or e ~0 neutron n ~1 charge neutral atom: p: e: n: 19 F 9 ion: p: e: n: 39 + K 19 element: defined by number of isotope: atoms of a given element with different numbers of Sheets Page 4 Lecture 2

5 Atomic mass & molar mass atomic mass (or weight): in units of amu (atomic mass units); what one atom weighs. for a molecule or compound, we refer to a formula or molecular weight molar mass: in units of g/mol; what one mole of that atom (or molecule) weighs. Example: 1 atom of 16 O has an atomic weight of 16 amu. 1 mol of 16 O has a mass of g. 1 molecule of NaOH has a mass of amu, and 1 mol of NaOH has a mass of g. Sheets Page 5 Lecture 2

6 Energy thermodynamics: the study of energy and its transformations thermochemistry: the study of the relationship between chemical reactions and energy changes kinetic energy mechanical (moving mass: 1/2mv 2 ) potential energy mechanical (mass in a place where force can act) electrical (electrostatic: Q 1 Q 2 /d) chemical (bonds) nuclear (binding energy) electrical (moving charge) light (photons) sound (molecules moving uniformly) heat gravitational (molecules moving (mgh, where g = randomly) 9.8 m/s 2 ) Sheets Page 6 Lecture 2

7 Units of energy SI: Joule (J) 1 J = 1 kg m 2 /s 2 [equal to 2 kg object moving at 1 ms 1 (from 1/2 mv 2 ) or ~100 g at h = 1 m (from mgh)] in chemistry (!!!) kilojoule calorie Calorie (dietary) 1 kj = 10 3 J 1 cal = J 1 Cal = 10 3 cal = 1 kcal Sheets Page 7 Lecture 2

8 The first law of thermodynamics qualitative definition: energy can be converted between various forms, but total energy is law of conservation of energy = first law of thermodynamics all energy lost by a system under observation must be gained by the (and vice versa) during energy conversion, some heat is always produced Sheets Page 8 Lecture 2

9 The first law of thermodynamics internal energy (E): associated with any system; sum of all sources of kinetic & potential energy quantitative definition: ΔE = E final E initial ΔE = q + w E is a state function (path independent; more about this later) Sheets Page 9 Lecture 2

10 Does this make sense?? Exothermic: energy is released by the system; ΔE Endothermic: energy is absorbed by the system; ΔE Note for our purposes this semester: we are using enthalpy and energy interchangeably. Enthalpy is heat (another form of energy) at constant pressure. Sheets Page 10 Lecture 2

11 Electromagnetic radiation light and other electromagnetic radiation behaves as a wave properties of waves λ = wavelength: distance between maxima (m) ν = frequency: # maxima per second (s 1 ) cycles/s = hertz (Hz) c = speed of light: m/s [vacuum]; know this! c = λν know this! light can undergo diffraction (wave nature); but also has momentum (particle nature) Sheets Page 11 Lecture 2

12 Sheets Page 12 Lecture 2

13 Light quanta energy can be released (or absorbed) by atoms in discrete energy packets or quanta E = hν energy of a photon know this! h = J s (Planckʼs constant) energy is always absorbed or emitted in whole-number multiples of hν (hν, 2 hν, 3 hν, ); only certain, discrete energies allowed total energy in a light beam is [n hν] with n large (n = number of atoms or molecules of substance emitting light) Duality of light: light has characteristics of both (c = λν) and (E = hν) experimental support black-body radiation (Planck) photoelectric effect (Einstein) line spectra of hydrogen (Bohr) Sheets Page 13 Lecture 2

14 Before next class: Read: BLB 2.1, 2.2; HW: BLB 6:4,10,13,23,26 Sup 6:1,3,4,5 do NOT do Sup 6.2! Know: E = hν c = λν photons: quantized energy photoelectric effect line spectra Bohr model electronic transitions Sheets Page 14 Lecture 2