4.2 – Subatomic Particles and the Nuclear Atom

• OBJECTIVES: Students will be able to (SWBAT)

1. Distinguish between the subatomic particles in terms of

relative charge and mass

2. Describe the structure of the nuclear atom2. Describe the structure of the nuclear atom

• 8 lecture/10 reading questions

• 5-sentence summary

Notes: Subatomic Particles and

the Nuclear Atom (4.2)

Parts of the Atom – The Subatomic

ParticlesPart 1: The Electron

Part 2: The Nucleus &

the Proton

Part 3: The Neutron

electron nucleus

proton neutron

Part 3: The Neutron

Opposite charges attract; same or like

charges repel

OPPOSITE CHARGES

LIKE CHARGES

Part 1: THE ELECTRON

JJ Thompson and the Discovery of the

Electron (1897)

• Discovered the electron and the charge to

mass ratio of the electron.

• His experiment:

– Thin beam of electrons (negatively charged) goes – Thin beam of electrons (negatively charged) goes

through a glass tube (cathode ray tube, CRT)

– The beam bends toward a positively charged plate

and away from a negatively charged plate �

beam of electrons must be negatively charged.

Cathode - Charged Plate

Zinc Sulfide Screen

Anode Spinner + Charged

- Charged Plate

+ Charged Plate

Cathode Rays

Thompson's Cathode Ray Tube (CRT)Thompson's Cathode Ray Tube (CRT)

Thompson's Major Results From

Experiment

1. Confirmed existence of electrons.

2. Proposed plum pudding model of atom.

• Negative electrons are spread throughout a

uniform positively-charge atom.uniform positively-charge atom.

Solid Atom with Electrons

ElectronsPositive charge

distributed evenly

throughout

Plum Pudding Model (also called

Chocolate Chip Cookie Model)

Robert Millikan & The Oil Drop

Experiment (1923)

• Determined the Charge and Mass of the

Electron.

• His Experiment: The Oil Drop Experiment

Atomizer

Oil Drops

Beam - Charged Drop

- Charged Plate

Eye piece

Millikan's Oil Drop Apparatus

+ Charged Plates

X-Ray Tube

Millikan’s Results

1. Charge on the electron is 1.6 x 10-19

coulombs � or -1 per electron.

2. The mass of the electron is 9.10939 x10-31 kg

� the mass of a proton1

� the mass of a proton1

1840

Part 2: The Nucleus & the Proton

Rutherford Gold Foil Experiment

• His Experiment:

– A beam of alpha (α) particles, or positively

charged particles, shot at thin sheet of gold foil

– Most of the particles went right through (as – Most of the particles went right through (as

expected) considering plum pudding model

• BUT…many of the particles were deflected at an

angle or completely back toward the source of the

beam

Beam of positive α-particles

Beam

Radiation Source In Lead Cased Box

Screen

Gold Foil

Marsden's Gold Foil Experiment

α-particles source

Large deflections must be caused by

positive particles hitting something

that is also positive.

α Particle Beam

α Particle α

Particle Beam

α

Particle Beam

Gold Nucleus

Rutherford's Conclusions and Model of

the Atom

1. Most of the mass of the atom must be located in the center of the atom (the nucleus).

2. Nucleus must be positively charged to repel the large and positively charged α-particles.

3. Proton then must be the particle in the center of 3. Proton then must be the particle in the center of the nucleus.

4. Electrons orbit the nucleus.

5. Most of atom is empty space between electrons and the nucleus.

Rutherford’s Nuclear Atomic Model

Electrons (-)

Nucleus (+)

Part 3: The Neutron

• James Chadwick discovered that the neutron:

– Has about the same size and mass as a proton

– Is in the nucleus

– Is neutral (has 0 charge).– Is neutral (has 0 charge).

“Relative” – means “compared to”

• Mouse 1 weighs 300 g

• Mouse 2 weighs 600 g

• What is Mouse 2’s mass relative to Mouse 1?

mass of an object

• Mouse 2 is 2 times the mass of Mouse 1.

mass of an object relative mass =

mass of another object

mouse 2 200 g= = = 2

mouse 1 100 g

Relative Mass

1840

-e

Relative Electrical

Charge

0

+p

0n

ElectronsElectrons (-)

Solid Atom with Electrons

Nucleus (+)

Compare the SCIENTISTS.

THOMPSON MILLIKAN RUTHERFORD CHADWICK

EXPERIMENT

PERFORMED

DISCOVERED

WHAT?

MODEL

FORMED

BASED ON

FINDINGS