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Chapter 2

Chemistry Review Chapter 2.docx

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Scott Browning

Chemistry Review CHAPTER 2 MATTER CLASSIFIED INTO 3 TYPES (based on comp) 1) Elements: simplest type of matter with unique P + C props - Only one kind of atom - SO, CAN’T be broken down into simpler matter Mdensity) different becauseach element is unique because the properties of its atoms are unique submicroscopic props -re Different states, but many in molecular form different - Molecules: independent structure of 2(+) atoms bound together - Ex) O 2 diatomic molecules 2) Compounds: consist of 2(+) elements that are bonded chemically Ratio!!!! - Many consist of molecules (BUT… Na Sulfate/Silicon Dioxide) Ex) Amm = 14 parts N and 3 parts 3element has a fixed mass fraction by mass - B/c each unit of compound made of a fixed # of atoms of each - 1N = 14xm of H - each amm molecule = 1N +3H elements - Props are diff. from props of its component elements - CAN be broken into its elements by C-Change! 3) Mixtures: consist of 2(+) substances, elements OR compounds, physically intermingled - C ompounds of a mixture CAN vary in their parts by mass Ex) Salt water… - Many properties retained from its components Water boiled out - Sep into components by P-Change! ELEMENTS = FIXED COMP = 1 type of atom! COMPOUND = 2(+) elements chemically combined = C-CHANGE SEP. MIXTURES = 2(+) mixed subs = components keep properties = P=CHANGE Needed to explain: 1) LAW OF MASS CONVERSION: “Total mass of subs does not change” during a C-Reaction - # of subs can BUT total amount of matter = constant - based on all c-experience - Matter can’t be created/destroyed - (Einstein: not exact same, some convert to energy) - C-Reaction: en change small - Nuc-Reaction: en change huge 2) LAW OF DEFINITE COMPOSITION: “no matter what its source, a particular compound is made of same elements in same parts (fractions) by mass” - AKA…………Any sample of a given compound has same elements present in same parts by mass - Definition: part of compounds mass that each elements contributes (me/mc) - Percent by mass: Fraction by mass (me/mc) x 100 me depends on sample’s mass, BUT mass fraction is fixed no matter what the size of sample m% = EX) draw. %amu/element mass emu mc in sample (given) x me in compound (calculate) EQWASHUN YO: For me in sample mc (calculate) = MULTIPLER PROPOERTIONS LAW, “If elements A + B react to form 2 compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole #s” a) Divide mass % to find masses in 100g b) Divide m ba m fibed mass * In 2 compounds of same elements, m off1 element is relative to other changes in increments based on ratios of small whole #s * Postulates of Atomic Theory 1) All matter made of atoms: tiny invisible particles of an elements that can’t be created/destroyed 2) Atoms of 1 element CAN’T convert into atoms of a different element - In C-reactions, they recombine 3) Atoms of 1 elements are identical in mass/props, diff from atoms of other elements 4) COMPS = C-combination of a specific ratio of atoms of different elements: law of definite comp! Explains Mass Laws: (POST 2) MASS CONVERSIONS: - Atoms can’t be created/destroyed/converted, therefore in c-reactions, there is not mass change in the recombination of atoms Mass conserved during a reaction because atoms keep their identities, they’re just combined differently (POST 4) DEFINITE COMP: - Compounds = combinations of SPECIFIC ratio of different atoms with particular mass - Therefore each elements in a compound constitutes a fixed fraction of the total mass Compounds have a fixed mfof its element because it is made of a fixed # of each type of atom (POST 1+3) MULTIPLE PROPORTIONS: - Atoms of elements have same mass + indivisible - m of element B combine with fixed m of A = small, whole #ratio because different B #s combine with each A in different compounds Different compounds of same element show multiple propoertions because they consist of whole #s e + Props AKA, “Cathode Rays” “Passed current through nearly evacuated glass tubes with metal electrodes. When power ON, a ray seen striking phosphor coated end, making light” - Originated from (-) electrode AKA CATHODE, moved on to (+) ANODE Cathode rays made of (-) charged particles found in all matter Ex) Neon signs, Aurora Borealis, TV + CPU monitors Mass + Charge of e - 1) JJ THOMSON, measured the ratio of mass of a cathode ay particle to its charge - Weighed less than 1/1000 as much as H = DALTON’S ATOMIC THEORY, because atoms have even smaller particles! 2) ROBERT MILLIKAN, measured charge of an e - Method: Fine mist of oil sprayed into apparatus> droplets fall through hole in (+) charged plate> x-ray knock efrom air molecules + they stick to drops> electric field OFF> measure mass of drops from its rate of fall; TTL charge of various droplets always some whole # multiple of a min charge: if diff drops got diff #s of e, its because of min charge = charge of e itself -19 - 1.602x10 C!!!!!!! Conclusion: e’s mass/charge ratio + e’s charge can find e’s mass = VERY SMALL = 9.109x10 =28g Atomic Nucleus Q: Matter is electrically neutral, SO atoms are too, but they contain (-) charged e with very tiny mass. What is (+) with larger mass? Thomson: PLUM PUDDING MODEL, (+) charged matter with e embedded like raisins Rutherford: Experiment: (+) charged Alpha partic
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