Atoms

J.J. Thomson

Electrons exist and are negative

Millikan

Measured the charge of an electron

Rutherford

Atoms have a dense nucleus

Thomson’s Plum Pudding

Electrons float in a positive “pudding”

Rutherford’s Model

Electrons orbit a small, dense nucleus

What is the smallest piece of matter that still has the properties of that substance?

An atom

How big is an atom?

10^{-10} meters (1 angstrom)

What did the cathode ray tube experiment show?

That atoms contain negatively charged particles called electrons

What’s the mass of an electron?

9.11×10^-31 kg

What did Rutherford’s gold foil experiment show?

Atoms are mostly empty space with a dense nucleus

What’s the Plum Pudding Model?

Electrons are embedded in a positively charged “pudding.”

What’s the Rutherford Model?

Electrons orbit a small, dense, positively charged nucleus

What happens when an electron drops to a lower energy level?

It emits light (a photon).

What is the Balmer series?

A set of light wavelengths from electrons falling to the second energy level

What causes ionization?

A photon with enough energy kicks an electron out of the atom.

What does absorption spectrum show?

Which wavelengths are absorbed by atoms (missing colors).

What do we usually ignore in nuclear physics?

Electrons

What causes emission spectra?

Electrons drop from higher to lower energy levels, releasing photons

What is the Balmer series?

when electron jumping for transitions ending at energy level n = 2 in hydrogen.

What is the Rydberg equation used for?

determines the wavelengths of the lines

What’s the equation for photon energy?

E=hf or E=hc/λ

What are the constants in photon energy equations?

h = 6.626×10^-34 m²kg/s and c = 3.00×10⁸ m/s

Steps to find wavelength from energy levels

Find E=E₂−E₁ then Use 𝜆 =ℎ𝑐 / 𝐸 

What are the three types of radiation?

• Alpha (α): He nucleus, +2 charge and mass # of 4

• Beta (β): electron or positron, ±1 charge mass number 0 and comes with Anti-
  Neutrino

• Gamma (γ): photon, no charge

the nucleus will spontaneously decay if

the q value is > than 0

What is nuclear fission

Splitting a heavy nucleus into smaller ones, releasing energy and neutrons.

What is nuclear fusion?

Combining light nuclei to form a heavier nucleus, releasing energy.

What is binding energy?

Energy released when nucleons bind to form a nucleus.

Why is Fe-56 highly stable?

It has one of the highest binding energies per nucleon.