12, September 2007 Dr. Stevens Gen. Chem. 1 Homework Help -Sunday through Thursday (7-9pm) 237 -Question 6: 2 sig figs (only pennies, no fractions) 5 extra tries -Email etiquette -Whitworth acct. -Use the subject line to tell the information Factor-Label Questionnaire Volumes liters (L/mL/etc.) - cubic measurement (xyz) -ft^3, cm^3, etc. Conversion 1mL = 1cm3 Example Density of N2 gas = 2.0 g/L. What is the mass in 1.0 in^3? d=m/v -> m=dv; m=2.0g/Lx1.0in^3 1in=2.54cm, 1in^3=(2.54cm)^3 2.0x1.0x(2.54)^3x(1/1000) = 3.3e-2 Chapter 2 Objectives -Know structure of the atom -Write isotopes in proper notation -Understand layout of the Periodic Table -Know and use ionic notation for # e/p/n. -Write empirical and molecular formulas -Name ionic and molecular compounds Atomic Theory Dalton (c. 1808) -elements are composed of atoms -atoms of an element are identical -compounds are composed of ratios of atoms of 2+ elements in fixed proportions -fixed proportions = integer of simple fraction (ex: 2/5, 3/1, etc.) -a chemical reaction involves the separation/combination/rearrangement of atoms 1900-1950 -showed internal structure of atom 1st time -Thomson (U.K.) & Millikan (US) working separately (1908) -cathode ray tube creates negative discharge ray which was deflectable with magnet a of a negative charge -negatively charged particle in atoms -Rutherford (N.Z.) -gold foil and alpha particles (nucleus of He atom)
-bombarded foil with alpha particles -results: vast majority (99.99%) passed through foil; .01% bounced back. -conclusion: massive center to an atom so that when you happen to hit the center, then it'll bounce back -approx. 99% of atom=empty space, with small but massive center -also able to detect that center massive area = + -if atomic r = 100pm, then nuclear center = .005pm Chadwick (U.K.) 1932 -mass rates of molecules of atoms -expected mass ratios to be equal to number -He/H = 4/1 ratio -extra particle that has mass, but no charge (neutron) Particle Proton (p) Neutron (n) Electron (e) Mass 1.672e-24g 1.675e-24g 9.09e-28g Relative mass 1g 1g 0.00055g Charge +1 0 -1
Electron approx. 1800x's smaller than p/n Atomic Number = Z = #p in nucleus Mass Number = A = #p + #n in nucleus Isotopic Notation: A
Z
X
(A/Z X)
Z defines an atom (integer on PT) A can vary #n can vary (integer not on PT) X is chemical element symbol #e = can be inferred from any charge given only e- can come or go in an atom (anion/cation) -+ = cation (lost e-) - - = anion (gained e-) Examples 1. 24Na(+4) #p=11, #n=24-11=13, e=11-4=7 12/6C #p=6 #n=6 #e=6