1. Ch. 4 - Atomic Structure Structure of the Atom History of the atom
Chemical Symbols
Subatomic Particles

2. Democritus (400 B.C.)
Proposed that matter was composed of tiny indivisible particles
Not based on experimental data
Greek: atomos

3. Alchemy (next 2000 years) Mixture of science and mysticism.
Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.

4. John Dalton (1807) British Schoolteacher Billiard Ball Model
based his theory on others’ experimental data
Billiard Ball Model
atom is a uniform, solid sphere

5. John Dalton Dalton’s Four Postulates
1. Elements are composed of small indivisible particles called atoms.
2. Atoms of the same element are identical. Atoms of different elements are different.
3. Atoms of different elements combine together in simple proportions to create a compound.
4. In a chemical reaction, atoms are rearranged, but not changed.

6. Henri Becquerel (1896) Discovered radioactivity Three types:
spontaneous emission of radiation from the nucleus
Three types:
alpha () - positive
beta () - negative
gamma () - neutral

7. J. J. Thomson (1903) Cathode Ray Tube Experiments Discovered Electrons
beam of negative particles
Discovered Electrons
negative particles within the atom
Plum-pudding Model

8. J. J. Thomson (1903) Plum-pudding Model
positive sphere (pudding) with negative electrons (plums) dispersed throughout

9. Ernest Rutherford (1911) Gold Foil Experiment Discovered the nucleus
dense, positive charge in the center of the atom
Nuclear Model

10. Ernest Rutherford (1911) Nuclear Model
dense, positive nucleus surrounded by negative electrons

11. Niels Bohr (1913) Bright-Line Spectrum Energy Levels Planetary Model
tried to explain presence of specific colors in hydrogen’s spectrum
Energy Levels
electrons can only exist in specific energy states
Planetary Model

12. Niels Bohr (1913) Bright-line spectrum Planetary Model
electrons move in circular orbits within specific energy levels

13. Erwin Schrödinger (1926) Quantum mechanics Electron cloud model
electrons can only exist in specified energy states
Electron cloud model
orbital: region around the nucleus where e- are likely to be found

14. Electron Cloud Model (orbital)
Erwin Schrödinger (1926)
Electron Cloud Model (orbital)
dots represent probability of finding an e- not actual electrons

15. James Chadwick (1932) Discovered neutrons Joliot-Curie Experiments
neutral particles in the nucleus of an atom
Joliot-Curie Experiments
based his theory on their experimental evidence

16. revision of Rutherford’s Nuclear Model
James Chadwick (1932)
Neutron Model
revision of Rutherford’s Nuclear Model

17. Metal that forms bright blue solid compounds.
A. Chemical Symbols
Capitals matter!
Element symbols contain ONE capital letter followed by lowercase letter(s) if necessary.
Metal that forms bright blue solid compounds.
Co vs. CO
Poisonous gas.

18. B. Subatomic Particles in a neutral atom Most of the atom’s mass.
NUCLEUS
ELECTRONS
in a neutral atom
PROTONS
NEUTRONS
NEGATIVE CHARGE
POSITIVE CHARGE
NEUTRAL CHARGE
Most of the atom’s mass.
Atomic Number
equals the # of...

19. B. Subatomic Particles 3 quarks = 1 proton or 1 neutron Quarks He
6 types He
3 quarks = 1 proton or 1 neutron

20. II. Electron Cloud Model Orbital Energy Levels Bohr Model Diagrams
Ch. 4 - Atomic Structure
II. Electron Cloud Model
Orbital
Energy Levels
Bohr Model Diagrams

21. A. Orbital Can’t pinpoint the location of an electron.
Region where there is 90% probability of finding an electron.
Can’t pinpoint the location of an electron.
Density of dots represents degree of probability.

22. A. Orbital
Orbitals have different shapes.

23. B. Energy Levels Electrons can only exist at certain energy levels.
Low energy levels are close to the nucleus.
Each energy level (n) can hold 2n2 electrons.

24. C. Bohr Model Diagrams
Simplified energy levels using Bohr’s idea of circular orbits.
Can replace with: 3p 4n
Lithium
Atomic #: 3
Mass:
# of p: 3
# of e: 3
# of n: 4 e- e- p n
Maximum e-
Level 1 2e-
Level 2 8e-
Level 3 18e-
Level 4 32e- e-

25. C. Bohr Model Activity Choose a number between 1 & 18.
Find your element by the atomic number you picked.
Draw a Bohr Model diagram for your element on your marker board.
Round off the mass listed on the table and subtract the atomic # to find the # of neutrons.
Abbreviate the # of ‘p’ and ‘n’ in the nucleus.
Have a partner check your drawing.
Repeat with a new element.

26. III. Masses of Atoms Atomic Mass Mass Number Isotopes
Ch. 4 - Atomic Structure
III. Masses of Atoms
Atomic Mass
Mass Number
Isotopes

27. A. Atomic Mass 1 proton = 1 u 1 neutron = 1 u 1 u = 1.67  10-24 g
atomic mass unit (u)
1 u = 1/12 the mass of a 12C atom
1 proton = 1 u 1 neutron = 1 u
1 u = 1.67  g
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28. B. Mass Number Always a whole number.
Sum of the protons and neutrons in the nucleus of an atom.
© Addison-Wesley Publishing Company, Inc.
Always a whole number.
# of neutrons = mass # - atomic #

29. C. Isotopes Mass # Atomic # Isotope symbol: “Carbon-12”
Atoms of the same element with different numbers of neutrons.
Isotope symbol:
Mass #
Atomic #
“Carbon-12”

30. C. Isotopes
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31. C. Isotopes Average Atomic Mass reported on Periodic Table
weighted average of all isotopes
Avg.
Atomic
Mass

32. C. Isotopes
EX: About 8 out of 10 chlorine atoms are chlorine-35. Two out of 10 are chlorine-37.
Avg.
Atomic
Mass
35.4 u