History of the Atomic Model

Who proposed the Atomic Theory in 1805?

John Dalton. (1766-1844)

What did Dalton say all matter is composed of?

Small, indivisible particles called atoms.

According to Dalton, atoms of a given element have what?

Unique characteristics and weight.

What were Dalton’s three types of atoms?

Simple, compound, and complex atoms.

How did Dalton view the atom?

As a solid sphere, like a billiard ball.

Who discovered the electron?

J.J. Thomson. (1856-1940)

What device did Thomson use to discover electrons?

The Cathode Ray Tube (CRT).

What was Thomson’s model of the atom called?

The Plum Pudding Model.

In the Plum Pudding Model, what are the electrons compared to?

Raisins in positive pudding.

Who discovered the nucleus of the atom?

Ernest Rutherford. (1871-1937)

What experiment did Rutherford use to discover the nucleus?

The Gold Foil Experiment.

What did Rutherford conclude about the atom?

It contains a tiny, dense, positively charged nucleus.

What type of particles did Rutherford use in his experiment?

Alpha particles.

What happened to some alpha particles in Rutherford’s experiment?

They bounced backward, showing a dense core.

What are the three types of radiation?

Alpha, beta, and gamma radiation.

What did Rutherford’s experiment not explain?

The arrangement or position of electrons.

Who proposed that light is an electromagnetic wave?

James Maxwell. (1831-1879)

What two components make up an electromagnetic wave?

Electric and magnetic components.

What part of the electromagnetic spectrum is visible to humans?

Visible light.

What does it mean that the electromagnetic spectrum is continuous?

All values or wavelengths are possible.

Who studied black body radiation and discovered that light behaves as particles?

Max Planck. (1858-1947)

What happens when a solid is heated, according to Planck?

It glows as it emits electromagnetic energy.

What is Planck’s equation for energy?

E = h × f.

What does “h” stand for in Planck’s equation?

Planck’s constant (6.63 × 10⁻³⁴ J/Hz).

Who explained the photoelectric effect using quantum theory?

Albert Einstein. (1879-1955)

What happens in the photoelectric effect?

Light causes electrons to flow from a metal surface.

What did Einstein call the particles of light energy?

Photons.

What determines whether electrons are released in the photoelectric effect?

The frequency of the light.

Does increasing light intensity affect electron energy in the photoelectric effect?

No, only frequency affects energy.

What determines the kinetic energy of released electrons?

The light’s frequency.

What do different metals have in the photoelectric effect?

Different threshold frequencies for current generation.