history (Dalton, J. J. Thomson, Rutherford, Maxwell, Planck, Einstein)

Dalton Atomic Theory

1. All matter was composed of small indivisible particles termed atoms

2. Atoms of a given element possess unique characteristics and weight

3. Three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules)

what did Thomson discover

electrons and showed that it was part of the structure of the atom.

what did Thomson theorize

electrons were much like raisins in pudding, where the pudding is the positive particle

Radiation comes in 3 types (rutherford)

1. Alpha particles (helium nuclei; 2 protons, 2 neutrons, NO electrons)

2. Beta particles (electrons only)

3. Gamma waves (high energy electromagnetic waves)

what did Rutherford theorize

according to Thomson’s model of the atom alpha particles should pass through atoms unaffected

what did Rutherford conclude?

the atom contained a tiny, dense core that was positively charged.

rutherford gold experiment

• bombarded very thin sheets of gold foil with fast moving alpha particles

• a very small percentage of alpha particles bounced off the gold foil at very large angles

• He concluded that all of the positive charge and the majority of the mass of the atom must be concentrated in a very small space in the atom's interior (nucleus)

rutherford electron problem/experiment flaws

• failed to explain why individual atoms produce discrete line spectra

• electrons orbit the nucleus in a circular fashion. If this was in fact true, then as electrons accelerate around the nucleus, the acceleration would cause the electron to radiate energy, meaning lose energy. its velocity would decrease, causing it to spiral and eventually smash into the nucleus, meaning not stable, which is false.

Maxwell what did he propose

light is an electromagnetic wave (electric + magnetic component). visible light is just a small part of the entire range of the Electromagnetic Spectrum (range of all possible waves)

black body radiation (Planck)

idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence

When a solid is heated, it begins to glow. The hotter the object, the more energy the electromagnetic waves emitted by the object have

Planck theory and solution

if light is a continuous wave, then the math predicts a curve that is not experimentally observed. Planck was able to find a mathematical formula that fit the empirical data IF he treated light as if it was a particle instead of a wave.

The photoelectric effect (Einstein)

the process where light (made of particles called photons) hits a material and knocks electrons loose

occurs when electromagnetic waves (light) is shone on a metal plate, which results in flowing electrons. It is the collision of photons with electrons that breaks them free from the atom. The higher the energy/frequency, the greater the chance the collision will break an electron free. The light frequency determines the kinetic energy of the released electron

about the photoelectric effect

• The frequency (colour/energy) of the light determines how much energy the freed electron has

• Intensity (brightness) does not change the energy of the electrons; it only increases the number of photons → current unaffected

• Threshold Frequency: Every metal has a specific minimum energy level required to release an electron

What 3 characteristics of the nucleus of an atom did Rutherford’s gold foil experiment determine?

• all mass is centered in the middle → dense

• nucleus is positive

• nucleus verrry small (cuz only a very small portion managed to deflect the gold foil)

Planck’s constant

6.63 x 10^-34 J/Hz