1. Models of the Atom a Historical Perspective

3. Early Models of the Atom
Throughout time, scientists have developed ideas about atoms.
The ideas have become more accurate over time.
For each scientist, you need to list their major contributions, or what made their model different from those that came before.

4. Early Greek Theories
400 B.C. - All matter is made of indivisible particles called “atoms”.
Democritus
Greek word “atomos” means not able to be divided.
Atom: the smallest unit of an element that maintains the properties of an element

5. John Dalton 1800 - Dalton proposed a modern atomic model
based on experimentation not on pure reason.
All matter is made of atoms, atoms are small particles, that cannot be created, divided, or destroyed.
Atoms of an element are identical.
Each element has different atoms.
Atoms of different elements combine in constant ratios to form compounds.

6. Adding Electrons to the Model
JJ Thomson (1897)
Atoms contain negatively charged particles called electrons.
Thought that the rest of the atom
must be positive.
Called the “Plum Pudding” model. (desert of choice at the time)
Electrons: negatively charged particles in an atom

8. Ernest Rutherford (1909) Zinc sulfide screen Thin gold foil Lead block
Radioactive substance
path of invisible -particles
Did an experiment in which he shot alpha particles at gold foil.
Found that an atom is mostly empty space.
Found the dense, positively charged central region of the atom, called the nucleus. Nucleus in made up of protons and neutrons.

9. Relative size of the Atom (Page 548)

11. 1) Dalton’s “Billiard ball” model (1800-1900)
Atoms are solid and indivisible.
Thompson “Plum pudding” model (1900)
Negative electrons in a positive framework.
The Rutherford model (around 1910)
Atoms are mostly empty space.
Negative electrons orbit a positive nucleus.

12. Bohr’s Model (1913)
Electrons are in specific paths called energy levels.
Electrons can move from one energy level to another.
The farther from the nucleus, the more energy the electrons have.

15. Presently
Electrons do not travel in definite paths, electrons path cannot be predicted.
Electron cloud:
Region around the nucleus of an atom where electrons are likely to be found.

16. a unit of mass that describes the mass of an atom
Parts of an Atom
There are 3 types of subatomic particles.
Protons: positive charge, found in nucleus
Neutrons: no charge, found in nucleus
Electrons: negative charge, found in electron clouds
Atomic mass unit:
a unit of mass that describes the mass of an atom
amu = g
Proton: 1 amu
Neutron: 1 amu
Electron: 0 amu (1800 electrons to equal mass of 1 proton)

22. Subatomic Particle Chart
Location
Charge
Mass
Proton
Nucleus +1
1 amu
Neutron
Electron
Outside nucleus, in energy levels -1

23. Atomic Number and Mass Number
The number of protons in an atom, also, the number of electrons.
Example:
lithium atomic number 3 will have 3 protons and 3 electrons
Mass number:
total number of protons and neutrons
Example:
lithium mass number 7 means 7 is the total number of protons and neutrons (3 protons and 4 neutrons)

35. Mass # p+ n0 e–
Atomic # Ca 20 40 20 20 20 Ar 18 40 18 22 18 Br 35 80 35 45 35

36. Energy Level Capacity Chart
Maximum Number of Electrons 1 2 8 3 18 4 32

37. Bohr - Rutherford diagrams
Putting all this together, we get B-R diagrams
To draw them you must know the # of protons, neutrons, and electrons.
Draw protons (p+), (n0) in circle (i.e. “nucleus”)
Draw electrons around in shells He Li
3 p+
4 n0
2e– 1e–
Li shorthand
3 p+
4 n0
2 p+
2 n0
Draw Be, B, Al and shorthand diagrams for O, Na

38. Be B Al O Na 8 p+ 11 p+ 8 n° 12 n° 4 p+ 5 n° 5 p+ 6 n° 13 p+ 14 n°
2e– 8e– 1e– Na
8 p+
8 n°
2e– 6e– O

39. Atoms of the same element that have different numbers of neutrons are called isotopes.
Due to isotopes, mass #s are not round #s.
H( ) is made up of multiple hydrogens.
Isotopes

40. For more lessons, visit www.chalkbored.com
6Li 7Li
3 p+
3 n0
2e– 1e–
3 p+
4 n0
2e– 1e–
For more lessons, visit

41. Periodic Table Dmitri Medeleev
Discovered a pattern to the elements in 1869.
He wrote the names and properties of elements on cards, once he arranged the elements by atomic mass he realized a pattern.
Periodic:
describes something that occurs or repeats at regualr intervals

43. Using the Periodic Table “Groups and Periods”
Groups are Vertical Columns
Elements in same group have similar chemical properties
Elements in same group have same number of electrons in outer energy level
Ex: Lithium, group one, one electron in outer energy level
Periods are horizontal rows
Elements in same period have different chemical properties.
Elements in same period have different number of electrons in outer energy level.
Elements in same period have same number of energy levels.
Ex: lithium, period 2,
2 energy levels

44. Types of Elements Metals 3 or fewer electrons in outer energy level
Left side of P.T.
Nonmetals
5 or more electrons in outer energy level
Right side of P.T.
Metalloids
elements that border the zig-zag line

45. mass protons electrons neutrons group period # of E.L. 11 13 7 3 2
E in outer e.l.
# of E.L.
Type of element
Similar element 11 13 7 3 2
atomic
Symbol

46. Ionic Compound Vocabulary
Compound- 2 or more elements chemically joined Chemical Formula -combination of symbols and subscripts that shows what elements and how many atoms of each are in a compound, Example: Ionic Compound- compound that contains ionic bonds Ionic Bond- force of attraction between oppositely charged ions

47. Ionic Compound Vocabulary
Octet Rule –chemical rule of thumb that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electronic configuration as a noble gas Valence Electron – an electron found in the outermost energy level Ion- charged particle that results from a neutral atom gaining or losing electrons Polyatomic ion- 2 or more atoms that combine and act like one ion

50. A. Naming ionic compounds made of a metal and nonmetal
M-N
Name the metal
2. Name the nonmetal, add –ide ending
*never use prefixes
NaCl
Sodium chloride
Li2O
Lithium oxide

51. Practice
KCl 2. Fe2O KF 4. MgO
5. BeS 6. NaI 7. HBr 8. Sr3N2

52. B. Naming Compounds with Polyatomic Ions
These compounds have 3 or more elements, usually a metal and a polyatomic ion
Name what comes first usually metal
Name what comes second usually PI
Li2 SO4
Lithium sulfate
NaOH
Sodium hydroxide

53. How do Ions form?
What is an ion?
A charged particle that results from a neutral atom gaining or losing electrons to become stable.

57. Writing Balanced Formulas for Ionic Compounds
Sodium oxide
Na O
Na+1 O-2
Na2O
Write the symbols
Pencil in the charges
If the charges=0, you are finished
If the charges do not equal zero, balance the charges by crossing the charges to the subscripts
Rewrite the formula, do not write charges or subscripts of 1.

58. Practice Problems
Strontium fluoride Sodium nitride Lithium phosphate Calcium chloride Aluminum sulfate
Cesium carbonate Magnesium oxide Beryllium chlorate Potassium chromate Aluminum oxide

59. Formula Writing
Write the correct formula for the following Ionic compounds:
Lithium sulfide
Magnesium oxide
Sodium phosphate
Aluminum oxide
Calcium chlorate

60. Calculating Formula Mass of Ionic Compounds
Example Al2O3 Al 2 x 27amu= 54amu O 3 x 16amu= 48amu Formula mass= 102amu
What is formula mass?
The sum of the masses of the ions in a formula unit of an ionic compound

61. “Calculating formula mass, so easy, a Caveman could do it!”
“That’s so condescending!”

62. Covalent Compounds Vocabulary
Covalent compound- a compound containing covalent bonds
Covalent Bond- bond formed by a shared pair of electrons

63. How do covalent compounds form?
Covalent compounds form when 2 or more nonmetals share pairs of electrons to become stable.
Electron dot diagrams are used to show the sharing of electrons. Ne He

64. Use an electron dot diagram to show how the following covalent compounds form.
H2O H2 CH4 CO2 Ne He

65. Prefix Meaning Di 2 Tri 3 Tetra 4 Penta 5 Hexa 6 Hepta 7 octa 8
C. Naming Covalent Compounds (N-N)
Rules
Name left nonmetal, use prefix if needed
Name right nonmetal, use prefix if needed, add –ide
Example:
PBr3
Prefix
Meaning Di 2
Tri 3
Tetra 4
Penta 5
Hexa 6
Hepta 7
octa 8

66. Practice Problems
CF SCl6
3. N2O N3Br4

67. Writing Formulas for Covalent Compounds
1. Diphosphorous pentoxide
3. Nitrogen trioxide
5. Phosphorous tetrafluoride
7. Silicon dioxide
9. Nitrogen octabromide
2. Diselenium trisulfide 4. Carbon oxide 6. Trinitrogen hexasulfide 8. Carbon dioxide 10. Carbon tetrachloride

68. “Yes, it’s me again, and I can do molecular mass, big deal!”
The sum of the masses of the atoms in covalent compounds
CF4
C 1 x 12 = 12 amu
F 4 x 19= 76 amu
88 amu