Chemistry Midterm

SI system

SI system

international system of units, aka metric system, with units such as meter, second, mole, degrees C/K, etc.

mass

measure of the quantity of matter in object

weight

measure of the force that gravity exerts upon an object

conversion factor

a ratio between equivalent units for use in dimensional analysis

accuracy

describes how close a measurement is to the true value

precision

describes the degree to which repeated measures of a value are similar or different

significant figures

digits that represent the precision of the meausring device(s)

scientific method

make observations, develop a hypothesis, test the hypothesis, analyze results, make a conclusion

independent variable

the variable that is manipulated (x)

dependent variable

a variable based on the independent variable (y)

theory

a well-founded explanation for a phenomenon based on repeated observations

law

an essentially confirmed fact that reconciles the results of all experiments relating to and observations of a phenomenon

matter

any substance that has mass and takes up space

volume

the three-dimensional space an object takes up

physical property

a characteristic of matter that can be inherently observed without changing its chemical composition

extensive property

a property that depends on the amount of matter

intensive property

a property that is constant regardless of the amount of matter

chemical property

the ability of a substance to be subject to a certain chemical change

states of matter

solid, liquid, gas, plasma

physical change

a change in which the properties of a substance change but its chemical composition does not

chemical change

a change in which the chemical composition of the substance changes, or more substances are formed

law of conservation of mass

mass is not created nor destroyed; the mass of a reaction's products is equal to that of its reactants

mixture

a physical blend of two or more substances

heterogeneous mixture

a mixture in which components are not uniformly mixed

homogeneous mixture

a solution, in which all components are dissolved

element

simplest form of matter that retains its own properties

compound

chemical combination of elements

pure substance

matter whose components cannot be separated physically (unlike in mixtures)

law of definite proportions

the proportions of the masses of elements in a compound remain constant regardless of the size of the compound

indicators of a chemical reaction

formation of gas, change in color or odor, release of energy (heat or light), formation of a precipitate

precipitate

the insoluble solids formed as a result of a chemical reaction between two solutions

reactants

materials going into a reaction (left side of arrow)

yield

arrow in chemical equation

products

materials produced by a reaction (right side of arrow)

chromatography

a method used to separate the dyes of a mixture; a physical change occurs, in which soluble dyes move quickly up the paper and less soluble dyes move less quickly

thermochemistry

the study of the changes substances undergo in chemical reactions (chemical changes) and changes in state (phase changes)

temperature

the AVERAGE kinetic energy of particles in a thermochemical system

heat

the TOTAL kinetic energy of particles in a thermochemical system

thermoconductivity

the rate at which heat is transferred from one object to another

heat capacity

the amount of heat required to raise the temperature of a substance by 1 degree C

specific heat capacity

the amount of heat required to raise the temperature of 1 GRAM of a substance by 1 degree C

endothermic process

a process that absorbs heat from the surroundings, causing the them to feel cold (Q>0)

exothermic process

a process that releases heat into the surroundings, causing them to feel warm (Q<0)

enthalpy

the heat released or absorbed by a chemical reaction

phase changes

heat of fusion (solid-liquid), heat of solidification (liquid-solid), heat of vaporization (liquid-gas), heat of condensation (gas-liquid)

enthalpy curve

a graph of phase changes and changes in temperature as a function of heat energy

energy

the ability to do work or produce heat

calorimetry

measures the amount of heat absorbed or released

entropy

the measure of the disorder or randomness of the particles that make up a system

average atomic mass

weighted average of the atomic masses of all naturally occurring isotopes of an element

half-life

the time required for half of the nuclei of a radioactive substance to decay

radioisotope

radioactive isotopes

Henri Becquerel

experimented with uranium salts and showed that they emitted radiation

Marie and Pierre Curie

coined the term radioactivity

alpha decay

loss of a helium nuclei (2P 2N); -2 atomic number, -4 atomic mass; low penetrating power; +2 charge

beta decay (negative)

neutron turns into a proton and an electron, which is emitted; +1 atomic number, no change in atomic mass; medium penetrating power, -1 charge

positron emission

proton turns into a neutron and an positron, which is emitted; -1 atomic number, no change in atomic mass; medium penetrating power, +1 charge

electron capture

an electron is drawn into the nucleus and combines with a proton to become a neutron which is emitted; -1 atomic number, no change in atomic mass; medium penetrating power, -1 charge

gamma emission

a gamma ray is emitted; no change in atomic number or mass; extreme penetrating power, 0 charge

transuranium element

elements made in particle accelerators; all elements over 93

uses of nuclear reactions

timekeeping, power, dating

proton

an atomic particle in the nucleus with a charge of +1 and a mass of 1 amu

neutron

an atomic particle in the nucleus with a charge of 0 and a mass of 1 amu

electron

an atomic particle orbiting the nucleus with a charge of -1 and a mass of ~1/1840 amu

nucleus

the small, dense, positively charged center of the atom

fission

the process which occurs when a heavy nucleus is bombarded with atomic particles and splits as in a nuclear bomb, releasing large amounts of energy

fusion

the process which occurs in nature at temperatures of over 40 million degrees C when light nuclei are smashed together and fuse, releasing more energy than fission

alpha particle

a helium nucleus (2P 2N)

positron

an electron with a positive charge

atomic number

the number of protons in the nucleus of an atom

atomic mass/mass number

the sum of the protons and neutrons in the nucleus of an atom

Ernest Rutherford

scientist who conducted the gold foil experiment, shooting alpha particles at an extremely thin sheet of gold foil and discovering they were interacting with and being repulsed by small, dense, sparsely distributed points within the foil

problems with Rutherford's model

failed to describe how electrons moved around the nucleus, unable to describe the chemical properties of electrons, no explanation of why electrons weren't attracted to the nucleus

Democritus

thought of the "atom" is the smallest, indivisible unit of matter (first to coin the term)

John Dalton

devised an atomic theory that said atoms were indivisible, atoms of a given element are identical, and atoms of different elements combine in constant proportions to form compounds

J.J. Thomson

discovered the negatively charged electron using the cathode ray tube

Robert Millikan

used the "oil drop" experiment to determine the mass of the electron

isotope

atoms of the same element with different numbers of neutrons and different mass

ion

atoms of the same element with positive or negative charge

devices used to detect radiation

Geiger counter, scintillation counter, film badge

wavelength

the distance between two crests or two troughs on a wave

amplitude

the height of a wave from origin to crest/trough

crest

the highest point of a wave

trough

the lowest point of a wave

frequency

the number of waves that pass a certain point per unit time

types of electromagnetic radiation

radio waves, microwaves, infrared, visible light (red-violet), UV, X rays, gamma rays

dual wave-particle behavior of light

electromagnetic radiation behaves like a wave and a particle (photon)

atomic emission spectrum

the specific range of frequencies emitted by an atom when its electrons drop from an excited state to a ground state

excited state

energy level occupied by an electron that has absorbed energy; further from the nucleus

ground state

energy level occupied by an electron that has released or not absorbed energy; closer to the nucleus

Bohr model

a model of the atom in which electrons move around a positively charged nucleus, occupying fixed energy levels

problems with the Bohr model

electrons don't really move in circular orbits, unable to describe the chemical properties of anything other than hydrogen

quantum

the specific amount of energy that must be absorbed or emitted by an electron for it to change energy levels

quantum mechanical model

the current best description of the way electrons orbit the nucleus (in probability clouds; orbitals describe areas of highest probability)

Heisenberg's uncertainty principle

it is impossible to know both the location and momentum of a particle with infinite certainty at the same time

sublevel

a subdivision of energy levels (n): s (2 e), p (6 e), d (10 e), f (14 e)

orbital

a region in which there is a high probability of finding an electron

Aufbau principle

electrons occupy the lowest energy levels first and fill higher energy levels as more exist

Pauli exclusion principle

an atomic orbital may describe, at most, two electrons with opposite spins (up/down)

Hund's rule

one electron of a certain spin is placed in each orbital before electrons are paired up in a certain orbital