Exam 1 - CHEM 1551

chemical change

any change that’s hard to reverse - flammable, corrosion, oxidation, acidity, toxicity.

physical change

changes the shape or state, composition - smell, taste, boiling point, melting point, density

observation

data, helps to formulate a hypothesis

experiment

conducted to test a hypothesis, through the manipulation of variables

hypothesis

an explanation of observations, an educated guess about why something is happening (proven false through testing)

scientific law

related observations; summarizes old observations and predicts future ones, through testing. these have been proven through consistent observations or results

theory

why something happens; best model at current time to explain why/how nature behaves the way that it does

element

pure substance that is the only thing present

compound

pure substance that is created of two or more atoms of elements bonded together

homogeneous mixture

mixture of two or more substances that can’t be separated (appears to be one mix); ex. tea

heterogeneous mixture

mixture of two or more substances that can separate; ex. sand and water

decanting

pouring a liquid from one container to another to separate it from sediment (separation based on density)

distillation

separation based on boiling points

filtration

process where mixture is poured through filter paper in a tunnel

solid

fixed volume and shape; crystalline: organized pattern; amorphous: no long-range order

liquid

fixed volume, but takes shape; molecules slide by each other

gas

alot of space between molecules; compressible; fits into space it has

intensive property

independent of amount of substance (constant no matter what); ex. density

extensive property

dependent on amount of substance (amount matters, will change); ex. mass

precision

how close to one another each result is to one another

accuracy

how close each result is to the actual value

mega

x 10⁶

kilo

x 10³

deci

x 10^-1

centi

x 10^-2

milli

x 10^-3

micro

x 10^-6

nano

x 10^-9

density formula

mass/volume (m/V)

atomic number

number of protons (Z)

mass number

number of protons plus neutrons (A = Z + N)

cation

positively charged ion, more protons than electrons; ex. Na³⁺ would have 11 protons and 8 electrons

anion

negatively charged ion, less protons than electrons; ex. Ca^2- would have 20 protons and 22 electrons

millikin

found charge of electron through oil drop experiment; c = -1.6E19 C

thomson

found the electron through cathode ray experiments; plum pudding model, the atom as uniform sphere of positive charge with negatively charged electrons embedded within it

rutherford

tested the plum pudding model (thomson), concluded that positive charge is in the nucleus and had nothing to do with mass, found the nucleus (nuclear theory of atom - most volume of atom is empty space w/ electrons dispersed, protons and electrons must have same amount to be neutral); gold foil model

chadwick

the mass unaccounted for was neutrons, neutrons have no charge, but nearly same mass as protons

ionic compounds

metal w/ nonmetal (use of roman numerals to balance based on charge)

molecular compounds

two nonmetals used together (have prefixes)

acids

composed of hydrogen and one or more nonmetal (-ide, hydro & ic; -ate, ic; -ite, ous)

group 1A

alkali metals (1+ ion)

group 2A

alkali earth metals (2+ ion)

group 7A

halogens (1- ion)

group 8A

noble gases

group 3A

3+ ion

group 5A

3- ion

group 6A

2- ion