Ch 3: Atomic Models and Radioactivity

Law of definite proportions

Compounds form in consistent mass ratios

John Dalton's atomic model

Elements combine in fixed ratios, atoms indivisible

J.J. Thomson's atomic model

Atoms divisible, contain negatively charged electrons

Plum pudding model

Atom has positive 'pudding' with negative electron 'plums'

Ernest Rutherford's atomic model

Atom mostly empty space, with a small positive nucleus

James Chadwick's contribution

Discovered the neutron in the atomic nucleus

Niels Bohr's discovery

Certain elements emit specific colors of light when heated

Planetary model

Electrons orbit nucleus in energy levels

Line spectra

Distinct spectra formed when atoms are heated and viewed through a prism

Quantum model of atoms

Electrons occupy energy levels, exhibit wave-particle duality

Orbitals

Electron clouds around atoms based on energy levels

Subatomic particles

Electron, proton, neutron with respective masses

Atomic number

Number of protons in an atom

Mass number

Sum of protons and neutrons in an atom

Isotope

Atoms with same protons but different neutrons

Valence electrons

Electrons in the outermost energy level

Octet rule

Atoms are most stable with 8 valence electrons

Energy levels

Different orbitals where electrons are located

Radioactivity

Emission of nuclear radiation by unstable nuclei

Alpha particles

2 protons and 2 neutrons, massive with high inertia

Beta particles

High-energy electrons emitted from neutron decay

Gamma rays

Excess energy emitted as high-energy photons

Nuclear fission

Splitting a massive nucleus into smaller ones, releasing energy

Nuclear fusion

Combining small nuclei to form larger ones, releasing energy