1. I. From Philosophical Idea to Scientific Theory (p. 66-71)
Ch. 3 – The Atom
I. From Philosophical Idea to Scientific Theory (p )
Foundations
Dalton’s Theory
Modern Theory
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2. A. Foundations Law of Conservation of Mass
In a chemical reaction, matter is neither created or destroyed
In the 1790’s a new emphasis was placed on the quantitative study of matter in chemical reactions. Aided by improved balances, investigators began to accurately measure the masses of elements and compounds they were studying. This led to the discovery of 3 basic laws…
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3. A. Foundations Law of Definite Proportions
A chemical compound contains the same elements in the same proportions regardless of the size of the sample
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4. A. Foundations Law of Multiple Proportions
the ratio of elements that makes up a compound is always a whole # ratio
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5. B. Dalton’s Atomic Theory
All matter is composed of atoms
The atoms of any one element (Na) are all alike, but differ from the atoms of other elements (C)
Atoms cannot be divided, created, or destroyed
The atoms of elements combine in whole # ratios to form compounds
Atoms are combined, separated, or rearranged in a chemical reaction
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6. C. Modern Atomic Theory Correction to Dalton’s Theory…
Atoms are composed of even smaller particles called protons, neutrons, and electrons
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7. II. Atomic Structure (p. 72-76)
Ch. 3 – The Atom
II. Atomic Structure (p )
Subatomic Particles
Thomson’s Cathode Ray
Rutherford’s Experiment
Composition
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8. A. Subatomic Particles equal in a neutral atom Atomic Number
NUCLEUS
ELECTRONS
equal in a neutral atom
PROTONS
NEUTRONS
NEGATIVE CHARGE
QUARKS
Atomic Number
equals the # of...
POSITIVE CHARGE
NEUTRAL CHARGE
Most of the atom’s mass.
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9. A. Subatomic Particles Quarks component of protons & neutrons 6 typesHe
3 quarks = 1 proton or 1 neutron
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10. B. Thomson’s Cathode Ray Experiment
Play “Cathode Ray Tube” by dchummer 2:49 on YouTube
Famous experiment that led to the discovery of the Electron

11. B. Thomson’s Cathode Ray Experiment
Thomson concluded that the particles in the beam had a negative charge and a very small mass

12. C. Rutherford’s Gold Foil Experiment
If an atom were the size of a large football stadium, the nucleus would be about the size of a marble….the atom is mostly empty space.

13. D. Composition of the Atomic Nucleus
The atom’s nucleus are made of two kinds of particles- protons and neutrons
Protons have a (+) charge equal in magnitude to the (-) charge of an electron
Neutrons are neutral; they contain no charge
Atoms are neutral because they contain equal #’s of protons and electrons

14. D. Composition of the Atomic Nucleus
The atom’s nucleus takes up most of the atom’s mass while electrons take up most of it’s volume.
Nuclear Forces allow protons and neutrons to be closely packed together without repelling one another
Generally, like-particles repel each other, yet there is a strong attraction between the protons in the nucleus.

15. D. Composition of the Atomic Nucleus
Did You Know?
Unleashed nuclear forces provide the energy associated with nuclear power or the detonation of an atomic weapon.

16. Ch. 3 – The Atom II. Masses of Atoms (p. 75-80) Mass Number Isotopes
Relative Atomic Mass
Average Atomic Mass
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17. A. Atomic Number
An element’s Atomic Number is the # of protons in its nucleus and is used to identify that element. The Periodic Table organizes elements in order of increasing atomic #’s from
Hydrogen’s (H) atomic # = 1
Helium’s (He) atomic # = 2
Lithium’s (Li) atomic # = 3
Etc…
The IDENTITY of the atom is determined by the # protons. The # of electron/neutrons can vary and the atom will still be of the same element. But if the # of protons changes, then the atom becomes an atom of a different element.
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18. A. Mass Number mass # = protons + neutrons always a whole number
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always a whole number
NOT on the Periodic Table!
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19. B. Isotopes
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20. B. Isotopes
There are 3 types of Hydrogen (H) atoms, each with a diff. # of neutrons
We call these “isotopes” of Hydrogen
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21. B. Isotopes 1) Nuclear symbol: Mass # Atomic #
Isotopes are atoms of the same element with different #’s of neutrons and therefore different mass numbers. 2 methods for specifying:
1) Nuclear symbol:
Mass #
- The atoms of many naturally occurring elements have different #’s neutrons.
Atomic #
2) Hyphen notation: carbon-12
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22. B. Isotopes # neutrons = mass # - atomic # C. Johannesson
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The # of neutrons is found by subtracting the atomic # from the mass #
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23. B. Isotopes
How many protons, electrons, and neutrons are there in an atom of Chlorine-37?
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24. B. Isotopes Chlorine-37 atomic #: mass #: # of protons:
# of electrons:
# of neutrons: 17 37 20
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25. B. Isotopes
How many protons, electrons, and neutrons are there in an atom of Bromine-80?
-35 protons, 35 electrons, 45 neutrons
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26. What is the nuclear symbol for Carbon-12, Carbon-13, & Carbon-14?
B. Isotopes
What is the nuclear symbol for Carbon-12, Carbon-13, & Carbon-14?
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27. B. Isotopes
Write the hyphen notation for the isotope with 15 electrons and 15 neutrons
Phosphorus-30
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28. C. Relative Atomic Mass
Relative Atomic Mass: mass of a particular isotope of an element.
Ex- naturally occurring Copper (Cu) consists of
69.15% Copper-63; atomic mass = amu
30.85% Copper-65; atomic mass = amu
- Most elements occur naturally as mixtures of isotopes.
- The % of each iso. Is nearly always the same no matter where the element is found.
- This % is taken into account when calculating the element’s avg. atomic mass.
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29. D. Average Atomic Mass
Average Atomic Mass: weighted average of all isotopes
on the Periodic Table
round to 2 decimal places
- Most elements occur naturally as mixtures of isotopes.
- The % of each iso. Is nearly always the same no matter where the element is found.
- This % is taken into account when calculating the element’s avg. atomic mass.
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30. D. Average Atomic Mass or Avg. Atomic Mass Avg. Atomic Mass
- Most elements occur naturally as mixtures of isotopes.
- The % of each iso. Is nearly always the same no matter where the element is found.
- This % is taken into account when calculating the element’s avg. atomic mass.
Avg.
Atomic
Mass
= (mass)(decimal) + (mass)(decimal)
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31. D. Average Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Avg.
Atomic
Mass
16.00
amu
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32. D. Average Atomic Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Avg.
Atomic
Mass
35.40 amu
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33. Practice Problems…
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34. According to the Law of Conservation of Mass, what mass would compound AB have, if the atomic mass of A = 2 mass units and that of B = 3 mass units? 5
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35. What two regions make up an atom?
Nucleus, Electrons
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36. What are the two kinds of particles that make up the nucleus of an atom?
Protons, Neutrons
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37. It is equal to the # protons
In a neutral atom, how do you determine the # of electrons?
It is equal to the # protons
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38. Where is the majority of an atom’s mass located?
The Nucleus
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39. Where is the majority of an atom’s volume located?
Electrons
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40. Total # of protons + neutrons
What is the mass # of an isotope?
Total # of protons + neutrons
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41. Write the hyphen notation for an isotope who’s atomic # = 2 and mass # = 4?
Helium-4
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42. Write the hyphen notation for an isotope who’s atomic # = 19 and mass # = 39?
Potassium-39
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43. Protons = 11, Electrons = 11, Neutrons = 12
How many protons, electrons, and neutrons are there in an atom of sodium-23?
Protons = 11, Electrons = 11, Neutrons = 12
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44. Protons = 20, Electrons = 20, Neutrons = 20
How many protons, electrons, and neutrons are there in an atom of calcium-40?
Protons = 20, Electrons = 20, Neutrons = 20
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45. Protons = 29, Electrons = 29, Neutrons = 35
Protons = 29, Electrons = 29, Neutrons = 35
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46. Protons = 47, Electrons = 47, Neutrons = 61
Protons = 47, Electrons = 47, Neutrons = 61
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47. Silicon-28 Write the Nuclear Symbol and Hyphen Notation for:
- an isotope with a mass # = 28 and an atomic # = 14
Silicon-28
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48. Iron-56 Write the Nuclear Symbol and Hyphen Notation for:
- an isotope with 26 protons and 30 neutrons
Iron-56
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