Chemistry Honors Wilson Chapter 3 & 4

Atom

The smallest particle of an element that retains the chemical properties of that element.

Dalton's (Billiard Ball) model

The atom is a solid, indivisible sphere; atoms of different elements differ in mass and properties.

Thomson's (Plum Pudding) model

The atom is a positively charged "pudding" with negatively charged electrons embedded throughout.

Rutherford's (Nuclear) model

The atom has a small, dense, positively charged nucleus surrounded by mostly empty space where electrons move.

Bohr's (Planetary) model

Electrons orbit the nucleus in fixed energy levels (like planets orbiting the sun).

Quantum Mechanical model

Electrons exist in probability regions called orbitals, not fixed paths; their positions are described by wave functions.

Thomson's Cathode Ray Tube experiment

It revealed the existence of electrons — negatively charged particles smaller than atoms.

Millikan's Oil Drop experiment

It measured the charge and mass of the electron.

Rutherford's Gold Foil experiment

Most of an atom is empty space, with a small, dense, positively charged nucleus.

Hydrogen Emission Spectrum

Electrons occupy specific energy levels; light is emitted or absorbed when electrons change levels.

Electron movement and energy

When electrons absorb energy, they move to higher energy levels; when they fall back, they release energy as light.

Electromagnetic spectrum

The range of all types of electromagnetic radiation, from radio waves to gamma rays, arranged by wavelength or frequency.

Subatomic particle locations

Proton: nucleus; Neutron: nucleus; Electron: electron cloud.

Mass and charge of protons, neutrons, and electrons

Proton: +1 charge, ≈1 amu; Neutron: 0 charge, ≈1 amu; Electron: -1 charge, ≈0 amu.

Atomic number, mass number, and neutrons relationship

Mass number = protons + neutrons; Atomic number = protons; Neutrons = mass number - atomic number.

Finding number of electrons in an ion

Electrons = protons - charge.

Calculating average atomic mass

Multiply each isotope's mass by its percent abundance (as a decimal) and add them together: (mass₁ × %₁) + (mass₂ × %₂) + ...

Alpha, beta, gamma, and positron radiation

Alpha (α): +2 charge, heavy (4 amu); Beta (β⁻): -1 charge, tiny mass; Gamma (γ): no charge, no mass (energy only); Positron (β⁺): +1 charge, tiny mass.

Balancing a nuclear equation

Both the mass numbers and atomic numbers on each side of the equation.

Nuclear equation for alpha decay of Uranium-238

²³⁸₉₂U → ⁴₂He + ²³⁴₉₀Th

Factors influencing nuclear stability

Strong nuclear force, neutron-to-proton (N/P) ratio, and band of stability.

When alpha decay occurs

In very heavy nuclei that need to reduce mass and charge.

When beta decay (β⁻) occurs

When a nucleus has too many neutrons; a neutron turns into a proton and emits an electron.

When positron emission (β⁺) or electron capture occurs

When a nucleus has too many protons; a proton changes to a neutron.

Critical mass

The minimum amount of fissionable material needed to sustain a nuclear chain reaction.

Subcritical, critical, and supercritical conditions

Subcritical: reaction dies out; Critical: reaction sustains itself; Supercritical: reaction grows uncontrollably.

How nuclear reactors generate electricity

Through fission — splitting large nuclei (like U-235) to release energy that heats water and produces steam to spin turbines.

Safety measures controlling nuclear reactions

Control rods absorb excess neutrons; coolant removes heat; containment structures prevent radiation leaks.

Half-life

The time it takes for half of a radioactive sample to decay.

Ways to solve half-life problems

1. Chart method: halve the amount after each half-life. 2. Equation: A = A₀(½)^(t/t₁/₂).

alpha decay nuclear equation

beta decay nuclear equation

positron emission nuclear equation

electron capture nuclear equation

bombardment nuclear equation