1. The Atom, The History, and The Periodic Table (Chemical Naming and Formula Writing)
Unit #3
Part I
Chemistry

2. Theories Involving Matter and Atoms
Democritus
Greek
400 B.C. – Greeks: “all matter is
composed of 4 fundamental
substances”
Earth, air (wind), water & fire
Democritus: “matter is composed
of small, indivisible parts,” (Greek –
“atomos”)
No experiments to test; no definitive conclusion
First scientist to discover the idea of an atom

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. Theories cont. Aristotle Greek Rejected the idea of atoms
Expanded on idea of 4
elements
Reasoning from logic & observation
Also in line with religion

5. Theories cont. Lavoisier French chemist “Father of Modern Chemistry”
Experimented and measured the masses of reactants and products of various reactions
Law of Conservation of Matter

6. Theories cont. Proust French chemist
Showed that a given compound always contains the same proportion of elements by mass
Law of Definite Proportions

7. Theories cont. John Dalton (1803) English schoolteacher
Thought about atoms as particles that might compose elements
Billiard Ball Model
atom is a uniform, solid sphere
Elements combine in the ratio of small whole numbers
Law of Multiple Proportions

8. 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.

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

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

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

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

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

14. 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

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

16. 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

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

18. 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

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

20. Atoms Best current representation of the atom is a charged-cloud
Smallest particle of an element that retains its properties
Electrically neutral; # Protons = # electrons
 Parts of an atom
Nucleus (contains both protons and neutrons)
Electron Cloud (contains electrons)

21. Parts of an Atom Nucleus Small, dense center of positive charge.
Protons
Positively charged particles within the nucleus
Neutrons
Particles within the nucleus with no charge
About the same mass as protons

22. Parts of an Atom cont. Electron Cloud Empty Space
Holds electrons, which are densely packed
Negatively charged particles found outside the nucleus
Much smaller than protons and neutrons
Proton/neutron mass = 1.67 x g
Electron mass = 9.11 x g
More about electron behavior later

23. Picture of an atom e-
Electrons
Neutrons p+
Nucleus
Protons no

24. Atoms and Elements
What is the difference between an element and an atom?
An atom is a single example of an element.
An element is the collective term for many atoms of a single substance.

25. Periodic Table of Elements Structure
Listed in order of inc. atomic #
Columns = Families or GROUPS
Have similar chemical properties
Referred to by the number and letter (A or B) over the column
Many have special names
Rows = PERIODS
Contains info on physical properties
(i.e. mp, bp, density, physical states, etc)

26. Element Characteristic
Each square usually contains
Element name
Element symbol
Atomic number
The number of protons
Symbolized at “Z”
Atomic mass or mass number
Atomic mass: decimal mole weight
= to the average mass numbers of all isotopes
Mass number: rounded mole weight
Mass number: The sum of the number of the protons and the number of neutrons
State of matter (usually)

27. Short Handing Element Characteristics
Symbolizing
AzX
A = mass # (NO DECIMALS!)
Z = atomic # (# of protons & electrons)
X = symbol of the element

28. Isotopes
Isotopes
Atoms with the same number of protons but a different number of neutrons
Atoms of the same element have the same atomic number but different mass numbers

29. Isotopes cont. Potassium-39 Potassium-40 Potassium-41 Protons 19
Neutrons 20 21 22
Electrons

30. Isotopes cont.

31. Isotopes cont.
The diagram shows three oxygen isotopes. Each nucleus has eight protons (gray) and eight, nine, or ten neutrons (green).

32. Oxidation Numbers Indicate the charge on the ion
Found on the periodic table
Common oxidation numbers are given in additional table
Note:
Group 8 elements do not form ions; No ox #
Transition metals have multiple ox #’s

33. Valence Electrons Electrons in the outer most shell
The electrons on an atom that can be gained or lost in a chemical reaction
More on this to come with Electron Configurations….

34. Alkali Metals Group IA (except H) Li, Na, K, Rb, Cs, Fr
Soft, gray metals
Very reactive
Especially with water
React with water to form bases
“Alkali” = basic

35. Alkali Metals cont. Why are they so reactive?
One electron in their outer shell
Only 1 electron away from a full outer shell
Want to lose that electron: easily react
So reactive – don’t occur as free elements

36. Interesting Tidbits Li – used as depression medication
Cs – used in atomic clocks
Fr – predicted by Mendeleev in 1870s; discovered in 1939
Less than 1 oz. of Fr exists at any given time

37. Alkali Earth Metals Group IIA Be, Mg, Ca, Sr, Ba, Ra
Shiny, silvery-white metals
Harder and denser than Group IA
Distributed in rock formations
Reactive but not as reactive as Group IA
2 outer electrons
Want to lose 2 to have a complete outer shell
+2 oxidation number

38. Interesting Tidbits Used in pyrotechnics and fireworks
Mg – white; Sr – red; Ba – green

39. Calcium Widely distributed as limestone
Important biologically for bones and teeth
Compounds of Calcium
- CaCO3 = limestone]
- CaO = “lime” or “quicklime”
- Ca(OH)2 = “limewater”; treat antacid

40. Nobel Gases He, Ne, Ar, Kr, Xe, & Rn
Group VIIIA
He, Ne, Ar, Kr, Xe, & Rn
Aka “Inert Gases” b/c they are unreactive
Aka “Rare Gases” b/c they are very rare on Earth
Colorless, tasteless, odorless

41. Nobel Gases cont. Why are they unreactive? Their outer shells are full
Recall: the outer shell electrons are the ones involved in bonding
When the outer shells are full, these electrons can’t bond and, therefore, react with other elements
Used in:
Lighting
Fill light bulbs, neon lights, black lights, flashlight bulbs, strobe lights, headlights, etc.

42. Halogens F, Cl, Br, I, At Non-metals
Group VIIA
F, Cl, Br, I, At
Non-metals
- Exist in all 3 states at room temperature:
* Solid: I, At
* Liquid: Br
* Gas: F, Cl
Very reactive
Most often, bond with metals
Diatomic (F2, Cl2, etc.)

43. Halogens cont. Why are the halogens diatomic?
1 electron away from a full outer shell
Too reactive/unstable by itself
Bonds with another atom so both have 8
Dot diagrams
What is the mole weight of chlorine gas?
Which is more reactive, F2 or Cl2? F2

44. Transition Metals Middle section of the periodic table
Exhibit metallic properties
Ductile
Malleable
Good conductors of heat and electricity
Silvery luster (except Cu and Au)

45. Ions Atoms that have a positive or negative charge
To become an ion, an atom gains or loses electrons
Cation = positively charged ion;
Lose electron(s)
Metals form positive ions
Anion = negatively charged ion;
Gain electron(s)

46. Polyatomic Ions
Def: tightly bound groups of atoms that behave as a unit and carry a charge
Ion composed of more than one atom
List of common polyatomic ions
Ex:
SO4-2
NO ** Must memorize these
CO polyatomic ions! **
PO4-3
OH-1
C2H3O2-1
NH4+1