Glow in the Dark

Chemistry Sheds Light on Our LivesUnit 4 Atoms and Light

Glow in the Dark

4.1 Development of Atomic Theory

4.2 Atomic Structure

4.3 Electron Structure

4.4 Periodic Table

4.5 Periodicity

4.6 Light

4.7 Light and Matter

4.1 & 4.2 Atomic Theory and Atomic Structure

Objectives

• Determine the location, charge, and relative mass of protons, neutrons, electrons.

• Use symbols in writing isotope notation.

• Identify isotopes using mass number and atomic number and determine the number of protons, neutrons and electrons.

• Differentiate actual atomic mass of an element from the mass number of an isotope

• Calculate average atomic mass from % abundances of an isotope

Atomic Structure Timeline

On Wednesday’s quiz, you will be expected to…

match scientists to their experiments and discoveries

place the models in chronological order

Democritus (400 B.C.)

• Proposed that matter was composed of tiny indivisible particles

• Not based on experimental data

• Greek: atomos

Alchemy (next 2000 years)

• Mixture of science and mysticism. • Lab procedures were developed, but alchemists did not perform controlled

experiments like true scientists.

John Dalton (1807)

British Schoolteacher

based his theory on others’ experimental data

Billiard Ball Model

atom is a uniform, solid sphere

John Dalton

Dalton’s Atomic Theory

1. All matter is made of tiny particles “atoms”2. Atoms cannot be created, divided, destroyed

or changed into other types of atoms3. Atoms of the same element have identical

properties4. Atoms of different elements have different

properties5. Atoms of different elements combine in

whole-number ratios to form compounds6. Chemical changes join, separate or

rearrange atoms in compounds

Henri Becquerel (1896)

Discovered radioactivity

spontaneous emission of radiation from the nucleus

Three types:

alpha () - positive

beta () - negative

gamma () - neutral

J. J. Thomson (1903)

Cathode Ray Tube Experiments

beam of negative particles

Discovered Electrons

negative particles within the atom

Plum-pudding Model

Cathode Ray Tubes

Metal plate (cathode) releases stream

Cathode ray

A cathode ray is a ray of light traveling in a vacuum (no other particles inside)

Metal plate (anode) to which stream travels

The ray travels from one metal plate to another as the plates are connected to electricity

Cathode Ray Tubes & Charge

-

+

Negatively charged plate

Positively charged plate

Ray is deflected away from negative plate and towards positive plate

In the late 1800’s, JJ Thomson put charged plates outside the tube

It made no difference what type of metal he used in the tube—all material produced this stream that curved towards the positive charge

J. J. Thomson (1903)

Plum-pudding Model

positive sphere (pudding) with negative electrons (plums) dispersed throughout

Chocolate Cookie Model

Dough is positive area and chips are negative electrons

Robert Millikan (1909)

• Balanced the downward gravitational force and the upward electrical and buoyant forces of charged oil droplets suspended between two metal plates.

• Discovered the charge of an electron

Ernest Rutherford (1911)

Gold Foil Experiment

Discovered the nucleus

dense, positive charge in the center of the atom

Nuclear Model

Ernest Rutherford (1911)

Ernest Rutherford (1911)

Nuclear Model

dense, positive nucleus

Mainly empty space filled with electrons

Niels Bohr (1913)

Bright-Line Spectrum

tried to explain presence of specific colors in hydrogen’s spectrum

Energy Levels

He stated that electrons can only exist in specific energy states

Planetary Model

Niels Bohr (1913)

Planetary Model

electrons move in circular orbits within specific energy levels

Bright-line spectrum

Erwin Schrödinger (1926)

Quantum mechanics

electrons can only exist in specified energy areas

Electron cloud model

orbital: region around the nucleus where e- are likely to be found

James Chadwick (1932)

Discovered neutrons

neutral particles in the nucleus of an atom

Joliot-Curie Experiments

based his theory on their experimental evidence

James Chadwick (1932)

Neutron Model

revision of Rutherford’s Nuclear Model

Make a chart like the one below and fill it in to help you study for your quiz.

Scientist Experiment Discoveries New model described

New model drawing

Dalton (1809) Other’s data 6 postulates(two were later proven incorrect)

Billiard Ball Model

Thomson (1903)

Millikan (1909)

Rutherford (1911)

Bohr (1913) Bright-Line Spectrum

Schrödinger (1926) N/A

Chadwick (1932) N/A