CHEMISTRY QUARTER 1

Democritus

Democritus

Philosopher who was first to theorize that matter was composed of atoms

Joseph priestly

Prepared our oxygen, decomposed mercuric oxide, invented laughing gas/nitrous oxide

Anton Lavoisier

Observed that substances stopped burning when cut off from oxygen, realized that metals got heavier after burning, meaning the mixed with the air, came up with law of conservation of mass

Joseph Proust

Came up with law of definite composition

John Dalton

Summarized theories, came up with 4 postulates, described and predicted chemical behavior

JJ Thomson

Discovered electrons using cathode ray tube, theorized protons

Rutherford

Gold foil experiment, concluded that atom is mostly empty space, theorized that positive charge and most of mass contained in the nucleus, discovered protons

James Chadwick

Confirmed existence of neutron

proton number

Decides element of an atom, atomic number

Electrons

Negatively charged; decide behavior of the atom

Ions

Atoms with same # protons but diff numbers of electrons

Isotopes

Atoms of the same element with different number of neutrons; identified by mass number

Mass number equation

Proton # + neutron #

Atomic mass unit

1/12 mass id a carbon-12 atom; means that proton and neutron are very close but not exactly equal to 1

Atomic mass

Weighted average accounting for abundance of each isotope of an element that occurs in nature

average atomic mass calculation

(Mass of iso. 1 • [%abundance/100]) + (mass of iso. 2 • [%abundance/100)

Henri Becquerel

accidentally discovered radiation by setting uranium salts on a sealed photographic plate

Marie Curie

First to earn Nobel prizes in both physics and chem, named radioactivity, discovered radium, curium, and polonium

Radiation

penetrating rays and particles given off by a radioactive source

Nuclear radiation

occurs bc some nuclei are inherently unstable and the nucleus tries to obtain stability by emitting radiation during radioactive decay

Three main radiation types

alpha, beta, gamma

radioscope

any unstable nucleus

alpha particles

⁴He²⁺ ; made of 2 protons and 2 neutrons; have positive charge of 2

alpha radiation (α)

consists of helium nuclei

Beta radiation (β)

consists of electrons

Change caused by alpha radiation

Atomic mass drops by 4, atomic number drops by 2

changes from Beta decay

atomic number up by 1, mass stays the same

Changes from Gamma radiation

none

changes from electron capture or positron emission

Atomic number drops by 1, mass stays the same

What happens during electron capture?

An atom pulls an electron to a proton to create a neutron

What happens during positron emission

a proton breaks down into a neutron and a positron

positron

₊₁e

electron

_-1e

alpha particle

₄H²⁺

beta particle

_-1e^1-

band of stability

plot of number of protons and neutrons in relation to one another

section of band of stability on top

beta decay

band of stability bottom section

electron capture and positron emission

causes beta decay

too many neutrons

causes positron emission or electron capture

too many protons

half life

time it takes for ½ of a sample to decay

transmutation

changing element of an atom

induced transmutation

changing element of an atom on purpose in a lab

mass defect

when the mass of a nucleus is less than the sum of the masses of protons and neutrons

cause of nuclear chain reaction in nuclear reactors (what happens/what key parts are involved & what they do)

neutrons fired out that hit radioisotopes on other rods

amplitude

wave’s height from zero to crest

wavelength

distance between crests

frequency

number of wave of cycles to pass a given point per unit of time

quantum

minimum amount of energy that can be gained or lost by an atom

radioactive wave frequency in relation to gamma ray frequency

radioactive waves have a lower frequency

photon

massless particle that carries a quantum of energy and moves with a wavelike motion

quantum model

Bohr’s model of an atom, which stated that electrons orbit the nucleus in fixed levels

erwin schrodinger

produced quantum mech. model

parts of quantum mechanical model

electron cloud, energy levels, and energy sublevels

s orbitals

can hold 2 electrons, circle shape

p orbitals

can hold 6 electrons, dumbbell shape

d orbitals

can hold 10 electrons, double dumbell shaped

aufbau principle

each electron occupies the lowest energy orbital available

4 postulates of Dalton’s Atomic theory

all elements are composed of tiny indivisible particles called atoms, atoms of the same element are chemically identical and atoms of any one element are different from those of any other element, atoms of different elements can physically mix together or chemically combine in simple whole-number ratios, chemical reactions occur when atoms are separated, joined, or rearranged; atoms are never transmuted during a chemical reaction

strong nuclear force

holds protons and neutrons in the nucleus; attractive force between subatomic particles that are incredibly close together; has short range

the reason that these neutrons are not attracted to each other by strong nuclear force

the neutrons are too far apart

forces provided by protons?

attractive & repulsive (they repel each other)

forces provided by neutrons

attractive forces

what force wins over strong nuclear force?

repulsion; proton repulsion takes over when there are too many neutrons in between protons

more neutrons → _____ ______ between things→ _______ takes over → _____

bigger distance, repulsion, instability

most stable nuclei are here

in smaller atoms (at. # < 20)

most stable nuclei have this proton to neutron ratio

1:1

What happens when atoms get bigger and protons get farther apart?

their electrostatic repulsion overpowers strong nuclear force, and more and more neutrons are needed to achieve stability

maximum ratio for a stable nucleus

1.5:1 (1.5 is an average, bc. you can’t actually have half a neutron)

amt. of stable isotopes that atoms have

1 (most of the time)

Band of stability

plot of the # of protons in relation to the # of neutrons; where an isotope is found on the band of stability can be used to predict what type of decay can occur

type of decay most likely to happen if an isotope falls in section A of the graph

beta

type of decay most likely to happen when isotope falls in section C of the graph

Alpha decay

type of decay most likely to occur when isotope falls into section B of the graph

Electron capture or positron emission

cause of beta decay

too many neutrons (converts neutron into proton & electon)

cause of positron emission and electron capture

too many protons → balances charges

cause of alpha decay

need to get rid of both neutrons and protons

reason that there are radioisotopes left when they are continuously decaying

every isotope has its own decay rate, some seconds or minutes, some millions of years

half-life

used to measure radioactive decay rates; amount of time that it takes for ½ of a sample of radioisotopes to decay

transmutation

conversion of an atom of one element to an atom of another element; goal of alchemists for centuries; occurs through radioactive decay and induced transmutation

induced transmutation

where change is caused in the nucleus by bombarding it with other subatomic particles; artificial transmutation

transuranium elements

elements following uranium of periodic table; do not occur in nature; produced by induced transmutation; all highly radioactive

mass defect

when the mass of a nucleus is less than the sum of masses of the protons and neutrons; accounted for my einstein’s E=mc² equation where energy and mass can be converted between each other

result of breaking apart or bringing together nuclei

infinitesimally small amounts of matter being converted into huge amounts of energy

fission

breaking down of smaller nuclei after being bombarded with neutrons; produces extra neutrons

Uranium

used for fission; biggest naturally occurring element; biggest thing that we can get from the ground; unstable & breakable

product of one fission reaction

3 new neutrons, which can then cause three new fission reactions, producing 4 neutrons → cause of chain reactions in nuclear reactors

how a nuclear reactor works

fissionable material is shaped into fuel rods which are placed into coolant. As the rods exchange neutrons, more and more energy is released, which heats the coolant which heats the water and causes steam to turn turbine. Rods are placed close together so that neutrons can potentially hit radio isotopes on another rod and continue reacting; gaps in between rods allow control rods to be placed between fuel rods to stop or slow the chain reaction

reasons why not to use more nuclear fission if it is so efficient

cost, safety and protection of workers, production of dangerous waste, location specifics, chernobyl disaster fears

Fusion

when 2 or more small nuclei are forced to combine and form a bigger nucleus and huge amount of energy

attractive qualities of fusion

small nuclei used as fuel are incredibly abundant, products significantly less radioactive than fission, not self-sustaining (won’t explode), everyone has the resources, could bring military in middle east home, could reduce climate change, could provide energy for desalination, won’t have to pay for gas

electromagnetic radiation

energy moving through space like a wave

red light is ____ frequency, purple light is ____ frequency

lower, higher

wavelength _____ as energy/frequency ______

increases, decreases

speed of all electromagnetic radiation

light

photoelectric effect

electrons emitted from the surface of a metal when light of a certain frequency or higher shines on surface

Max Planck

studied metals & wavelengths given off at different temperatures

quantum

minimum amt. of energy that can be gained or lost by an atom

photon

massless particle that carries a quantum of energy & moves with wavelike motion; bundles of energy; make up light in a beam

Einstein said that everything moves in a ______ motion

wavelike