Research Chem Unit 2 - Atoms

Democritus

460 BC

Greek philosopher

Particle Theory of Matter

discovered ATOMS - retain identity in a chemical reaction

John Dalton

1804

Solid Sphere Model

atoms of one element are all the same, combine in whole-number ratios to form compounds, and can’t be broken down

J.J. Thomson

1897

Plum Pudding Model

Discovered electrons in Cathode Ray Tube experiment

Robert Millikan

1909

Oil Drop Experiment

determined negative charge and mass of electrons

Ernest Rutherford

1911

Nuclear Model

Gold Foil experiment →alpha particles deflected by a positive NUCLEUS

Niels Bohr

1913

Planetary Model

Electrons orbit the nucleus at fixed energy levels

Erwin Schrodinger & Werner Heisenberg

1926

Quantum Model

Heisenberg Uncertainty Principle: an electron’s position and velocity of an electron cannot be determined at the same time

James Chadwick

1932

Discovered NEUTRON

Protons

positive subatomic particles found in the nucleus with a mass of about 1 amu. The number of protons = atomic number (z)

Neutrons

neutral subatomic particles found in the nucleus with a mass of about 1 amu. They act as the glue that holds together the nucleus

Electrons

negatively charged subatomic particles found in the electron cloud that have almost no mass

Isotopes

Atoms of the same element with differing numbers of neutrons, resulting in varying atomic masses.

Ions

Atoms that have gained or lost electrons, resulting in a net charge.

Cations

positive ions (lost electrons)

Anions

negative ions (gained electrons)

Average Atomic Mass (AAM)

AAM = (mass1)(% abundance1) + (mass2)(% abundance2)

Nuclear Notation

Radioactivity

the spontaneous emission of radiation in the form of particles or high-energy photons resulting from nuclear reactions

• Pierre & Marie Curie = first to use the term radioactive

• Ernest Rutherford = set the laws for radioactive decay

Nuclear reactions vs Chemical reactions

Nuclear: protons and neutrons in nucleus are rearranged → releases tremendous amount of energy

Chemical: involve electrons

Nuclear stability

the stability of a nucleus is dependent on the neutron (N) to proton (Z) ratio (N : Z)

For light nuclei (elements 1-20), N : Z should be 1 : 1

For heavy nuclei (elements above 20), N : Z should be 1.5 : 1

Nuclear Decay

stabilization of an atom → particles & electromagnetic waves released during nuclear decay

OG atom → alpha/beta/gamma particle + daughter atom

Alpha Decay

• a helium nucleus is the particle released

• poor penetration; can be stopped by paper

Beta Decay

• an electron/negatron released (a neutron emits a negatron and then becomes a proton)

• moderate penetration; can be stopped by aluminum

Gamma Decay

• a gamma photon released (no particles of matter leaves the nucleus; only energy)

• strong, dangerous penetrating ability → can only be stopped by lead or concrete

• can be released with other forms of decay

Radioisotope

an unstable, radioactive atom that decays over time to become more stable

Half-life

the amount of time that it takes for half of a radioisotope sample to decay