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problem, question, answer, solution
problem: a situation that presents difficulty, uncertainty, or perplexity
question: a request for data; inquiry, interrogation, query
answer: a spoken or written reply, as to a question
solution: something worked out to explain, resolve, or provide a method for dealing with and settling a problem
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Units (5)
- (1) time [seconds]
- (2) length [meters]
- (3) mass [grams]
- (4) amount [moles]
- (5) temperature [Kelvins]
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Qualitative vs. Quantitative
• qualitative observations: describe properties oroccurrences in ways that do not rely on numbers
• quantitative observations are measurements thatconsist of a number a unit and a label
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hypothesis
a tentative explanation for the observations that may not be correct, but puts the scientist’s understanding of the system being studied into a form that can be tested
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experiments:
• tests the validity of the hypothesis
• are systematic observations or measurements made under controlled conditions, in which the variable of interest is clearly distinguished from any others
• if experimental results are reproducible, they are summarized in a law
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law
a verbal or mathematical description of a phenomenon that allows for general predictions that describes what happens and not why and is unlikely to change greatly over time unless a major experimental error is discovered
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theory
attempts to explain why nature behaves as it does which is incomplete and imperfect and evolves with time to explain new facts as they are discovered
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Scientific Method
a procedure that searches for answers to questions and solutions to problems, which consists of
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Law of Conservation of Mass
- mass, or matter, can be neither created nor destroyed
- *the total mass of substances does not change during a chemical reaction
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Law of the Conservation of Energy
energy cannot be created or destroyed [1st Law of Thermodynamics]; this only applies to systems not involving nuclear reactions or velocities approaching the velocity of light
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Law of Definite Proportions
when two or more elements combine to form a compound, their masses in that compound are in afixed and definite ratio (this data helps justify an atomic view of matter)
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Law of Multiple Proportions
when two elements combine to form more than one compound, the mass of element A which combines in the first compound with a given amount of element B has a simple whole number ratio with the mass of element A which combines in the second compound with the same given mass of element B
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accuracy
how closely measured values agree with the correct value
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precision
how closely individual measurements agree with other measurements
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Significant Figures
- • start at the left and proceed to the right
- • if the number does not have a decimal point, count until there are no more non-zero numbers
- • if the number has a decimal point, start counting at the first non-zero number and continue counting until you run out of decimal places
- Multiplication/Division Rule
- • product has the smallest number of significant figures of multipliers
- - ex. 4.242 x 1.23 = 5.22 (3 sig figs)
- Addition/Subtraction Rule
- • answer contains smallest decimal place of the addends
- - ex. 8.7937 - 2.123 = 6.671
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chemistry
science that describes matter; its properties, composition, structure, the changes it undergoes, and the energy changes that accompany those processes
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matter
anything that has mass and occupies space (*has volume)
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energy
- the capacity to do work or transfer heat; chemical reactions always involve energy changes
- - most processes lead to a lowering of the system's energy
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chemical properties
observed only during chemical change/reaction; they describe the characteristic ability of a substance to react to form new substances
- ex. rusting or oxidation, flammability and corrosion
- a chemical change: is a change in the composition or identity of a substance (naturally accompanied by changes in physical & chemical properties
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physical properties
can be measured/observed without changing the composition or identity of a substance
- ex. mass, color, volume, amount of space occupied by the sample
- physical change: a change in physical properties without any change in the composition or identity of a substance
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extensive properties
• those properties that depend upon the amount of substance present
-ex. mass, volume, energy, etc.
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intensive properties
• other units apply to quantities which do not depend on 'sample size'
-ex. density or temperature
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the states of matter
• solids: have a fixed shape & volume; volume independent of temperature & pressure
• liquids: have indefinite shape but fixed (definite) volume; assume the shape of their containers; volume independent of temperature & pressure
• gasses: have indefinite shape & indefinite volume; expand to fill their containers; volume strongly dependent on temperature & pressure
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aqueous
a substance which has been dissolved in water
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atomic number (Z)
- number of protons in the nucleus of an atom of an element
- -different for each element
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atomic symbol
- abbreviation used to represent an atom in chemical formulas
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ion
atoms or groups of atoms with a + or - charge formed by the addition or removal of electrons from an atom
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essential elements
elements that are abolutely required in the diets of humans
- • found only in the first two periods (rows) of the periodic table (2 exceptions: Mo & I)
- • a deficiency in such an element causes abormality; can only be rectified using supplement of said element
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bulk elements (5)
- C, H, O, N, S (chons...)
- • building blocks of compounds that make up organs/muscles and consitute the bulk of our diet
- • carbon, hydrogen, oxygen, nitrogen, sulfur
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macrominerals (6)
elements that provide essential ions in body fluids & form major structural components of the body
- • Na, Mg, K, Ca, Cl, P
- (sodium, magnesium, potassium, calcium, chlorine, phosphorous)
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trace elements (7!)
remaining essential elements; present in small amounts
- • V, Cr, Ni, F, Sn, Si, As
- (vanadium, chromium, nickel, flourine, tin, silicon, arsenic)
- • many compounds of trace elements are toxic
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mass number
- number of protons + neutrons in an atom
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density
- • mass per unit volume; mass/volume = kg/m3
• liquids & solids: g/cm3 - • gasses: g/L
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atomic mass
the mass of a certain element (given in amu's); the one listed on the periodic table is the weighted average of the masses of said isotopes
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isotope
- atoms that have the same number of protons but different numbers of neutrons
- • all isotopes have the same chemical properties (b/c they have the same # of protons & electrons), they only differ in their atomic MASS
- • ex. Carbon 12, 13, & 14
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mass v. weight
- • mass: a measure of the quantity of matter in an object
- - the more mass something has, the more weight it will have
• weight: the force that gravity exerts on an object
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heat v. temperature
• heat: the transfer of thermal energy from a warm object TO a cooler object
• temperature: a measure of the amount of thermal energy an object contains
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Conversion between Celcius and Kelvin
• Tcelcius = Tkelvin - 273.15
• Tkelvin = Tcelcius + 273.15
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volume
• product of three lengths; for a rectangular solid = l * w * h m 3
- • metric volume units for fluid = Liters (L)
- - 1 L = 1 dm3- 1 mL = 1 cm3
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electrostatic attraction/repulsion
• attraction: (+ & -) force between oppositely charged particles cause them to move TOWARD each other
• repulsion: (+&+ or -&-) force between 2 particles that have the same charge causes them to repell each other
-when attractive electrostatic forces are stronger than repulsive ones, atoms form chemical compounds and the interactions between atoms are called chemical bonds
- • forces are dependent on
- 1) mass (distance): the further away electrons/protons are from each other, the weaker the charge (regardless of charge, heavier atoms are larger than lighter ones)
- 2) charge: the more charge, the stronger the forces (so charges of 4 and 1 are more attractive/repulsive than those of 1 and 1)
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ionic bonding
one atom transfers electrons to another atom and the resultant oppositely charged particles 'stick together'
- • involves a metal (cation) and either a 1) nonmetal (anion) or 2) polyatomic ion
- • bond forms from the attraction between 2 oppositely charged particles
- • the metal donates 1 or more electrons, forming a positively (+) charged ion = cation
- • these electrons then enter the non-metal, causing it to form a negatively charged ion = anion
- - electronegativity difference of 1.7 or more
- -ex. NaCl or Al2O3
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IONIC COMPOUNDS ARE NOT MOLECULAR BECAUSE
- ionic compounds are not molecular
- • there are NO discrete pairings (act in a group)
• covalent compounds CAN have molecular formulas; they CAN be discrete (Covalent Can)
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ionic compounds
• metals lose electrons to become cations (+ charged) & nonmetals gain electrons to become anions (- charged)
• ionic compounds are held together by attractive electrostatic interactions between cations and anions
• physical properties: form hard, crystalline solids that have high melting points (& are resistant to evaporation)
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binary ionic compounds
- • ionic compound that contains only 2 elements, one present as a cation and one as an anion
- • formula subscripts can be obtained using charges
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polyatomic ions
- • groups of atoms that have a net electrical charge
- • atoms IN polyatomic ion are held together by covalent bonds
- • more polyatomic ions than monatomic ions
- • more polyatomic ANions than cations
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covalent bonding
- • bonds formed from atoms sharing electrons (therefore they stay near each other)
- • occurs between 2 non-metals
- - electronegativity difference of less than 1.7
- -ex. O2, CH4
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compounds
- a substance composed of two or more elements which are chemically united in fixed proportions by mass (due to law of definite proportions)
- • can be separated by chemical but NOT physical means
- -characters of each individual element are lost when they form a compound
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molecules
the smallest unit of a compound that retains the characteristics of the compound
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chemical formula
gives the composition of molecular compounds; is chemical symbols and the number of each representing composition
1) empirical: simplest ratio of elements that does not represent the actual number and is non-positional
2) molecular: gives only the number of each kind of atom present; chemical symbols and number of each element in a compoind; denotes actual composition but not position
3) structural: shows which atoms are present & how they connect; chemical symbols and numbers of each element that represents both number and position
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types of structural formulas (4)
1) condensed: ex. CH 3OH
2) ball & stick model
3) space filling model
4) wedge-dash model (or perspective drawing)
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waters of hydration
- ionic compounds that contain specific ratios of loosely bound water molecules
- • can be removed by heating
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