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Chem 101 Week 1 Notes

by: Noemie Trocher

Chem 101 Week 1 Notes CH 101

Marketplace > Boston University > CH 101 > Chem 101 Week 1 Notes
Noemie Trocher
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About this Document

These notes covered what we covered in class.
General Chemistry
Dr. Dill
Class Notes




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This 3 page Class Notes was uploaded by Noemie Trocher on Wednesday September 7, 2016. The Class Notes belongs to CH 101 at Boston University taught by Dr. Dill in Fall 2016. Since its upload, it has received 8 views.

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Date Created: 09/07/16
CH101 Lecture September 9, 2016 For Today: - Air in room SCI/109 - Atoms, elements, and isotopes - Isotopes ->atomic weight - Chemist’s dozen: the mole *Next Lecture: Ch3, naming things, molecular mass specter Liquid Volume of Air in SCI/109 - Mass of air: 2400 kg 3 - Liquid air density: 1g/cm - Use formula Volume = mass x (1/density) 3 3 V = 1cm x 2400 kg x 10 g x 1L x 1gal x 1jug 1 g 1 1kg 10 cm 4L 5gal = 2400 x 1 jug/(4 x 5) = 2400/20 = 120 jugs Atoms, Elements, and Isotopes - Atoms come in different kinds *elements* - Atoms of each kind come in different flavors *isotopes* - Atom anatomy: ● Mostly wispy *cloud of negatively charged electrons* ● About 10 cm in diameter ● Nucleus is about 10 cm in diameter ○ really dense area of positively charged protons - Element example: 19 <- number of protons/electrons K Potassium 39.0983 <- atomic weight (average of isotopes) Isotopes -> atomic weight - Atoms with the same number of protons but different number of neutrons are chemically the same but have different masses *isotopes* ● Electron are the only thing that affect the chemical properties - Atomic mass unit u ● 1u is defined as exactly (1/12) mas of 1 atom of 12C ● Exactly 12g of 12C contains N A 6.02214 x 10 23atoms *Avogadro's number* ○ mass of one 12C i 12g/NA= 1.99265 x 10 g-23 ○ so 1u = 1/12 x 1.99625 x 10 = 1.6054 x 10 -24 *(1/N A* Mass spectrometer - Mass spectrometer “weighs” atoms ● What it does ○ strip one electron from the atom ○ accelerates positive ions ○ deflect them in a magnetic field ○ less deflection = heavier massive ● Mass spectrum is the graph that goes with it ○ vertical axis: relative abundance of ions ○ horizontal axis: mass of ions ○ relative peak heights on graph -> isotope abundance CH101 Discussion September 8, 2016 Significant Figures: ● All non-zero integers are significant ● Zeros: ○ Not significant- ■ 1.) 0.009 *zeros come before the first non-zero integer* -> there is one significant figure ■ 2.) 2000 * there is no decimal at the end* -> there is one significant figure *Tip: putting the number in scientific notation helps figure out how many significant figures there are ○ Significant: ■ 1.) 101 *is in between non-zero integers* -> there are 3 sig. figs. ■ 2.) 21.0 * is after the decimal point* -> there are 3 sig. figs. ■ 3.) 20. * is between a non-zero integer and a decimal* -> there are 2 sig. figs. ● Rules: ○ When adding or subtracting: ■ use least accurate apparatus -> 2.56 - 2.512 ■ 2.56 is the least accurate apparatus because it has the least amount of sig. figs. after the decimal -> answer would be .048 ■ Ex: 15-12.37 -> answer would be 3 rather than 2.63 because 15 has not sig. figs. after the decimal ○ When multiplying or dividing: ■ still use least accurate apparatus ■ Ex: 4.31x5.0 -> answer would be 22 rather than 21.55 because 5.0 has only 2 sig. figs. ○ *ALWAYS ROUND AT THE END*


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