1. Atoms, Molecules, and Ions
Chapter 2

2. Dalton’s Atomic Model First model - early 1800’s
Developed through experiments
All elements are composed of tiny indivisible particles called atoms
All atoms of the same element are identical.

3. Discovery of Electron
1897 – JJ Thomson, using cathode ray tube, discovered the charge to mass ratio of negatively charged particles, later called electrons, to be 1.76 x 108 C/g

4. Millikan’s Oil Drop Experiment
1909 – Robert Millikan discovered the charge of an electron, 1.6 x C
Mass of electron = 9.1 x g

5. “Plum Pudding” Model
Uniform positive sphere with negatively charged electrons embedded within.

6. Radiation Late 1800’s – discovery of radiation Three Types Alpha Beta
Gamma

7. Rutherford Gold Foil Experiment - 1909
Shot alpha particles at gold foil
Most went through foil with little or no deflection.
Some were deflected at large angle and some straight back.

8. Rutherford Gold Foil Experiment - 1909

9. Rutherford Model Conclusions from Gold Foil Experiment
Atom is Mostly Empty Space
Dense positive nucleus
Electrons moving randomly around nucleus

10. Bohr Model Dense positive nucleus
Electrons in specified circular paths, called energy levels

11. Wave Mechanical Model More detailed view of the Bohr Model
Energy levels are divided into sublevels
Electrons are found in Orbitals (in the sublevels)
region of space with a high probability where electron COULD be.
Modern Model
AKA Quantum Mechanical Model, Electron Cloud Model

12. Subatomic Particles Electron Discovered in 1897 by JJ Thomson
Negative charge (-1)
Mass = *10-28g
Approx mass ~ 0
Found outside of nucleus

13. Subatomic Particles Proton Discovered in 1919 by Rutherford
Positive charge (+1)
Mass = *10-24g
Approx mass ~ 1 atomic mass unit (u)
Found inside nucleus

14. Subatomic Particles Neutron Discovered in 1932 by James Chadwick
No charge (0)
Mass = *10-24g
Approx mass ~ 1 atomic mass unit (u)
Just slightly larger than a proton
Found inside nucleus

15. Atomic Structure Atomic Number - number of protons in an element
All atoms of the same element have the same number of protons
Mass Number - number of protons and neutrons in an atom
Isotope – atoms of the same element with different number of neutrons

16. Chemical Symbols
Mass Number
Cl-35
Chlorine-35
Atomic Number

17. Ion
Atom or group of atoms that have gained or lost one or more electrons
Have a charge
Example:
H+, Ca2+, Cl-, OH-

18. Average Atomic Mass Atomic Mass Example
Weighted average based on the relative abundance and mass number for all naturally occurring isotopes
Example
C u 98.9% u
C u 1.1%

19. Periodic Table

20. Molecular Formula Chemical Formula used to represent a molecule
Usually contain nonmetals
Give exact number of atoms of each element in a compound
H2O

21. Empirical Formula
Gives the lowest whole-number ratio of atoms of each element in a compound
C6H12O6 CH2O

22. Structural Formula
Shows order in which atoms are bonded O H
O=C=O

23. Ionic Compounds
Usually contains a metal and a nonmetal or polyatomic ions
Ionic formula is an empirical formula
NaCl

24. Naming Ions and Ionic Compounds
Name positive ion first, then negative ion.
NaCl, Sodium Chloride
Ions of metals that have more than one positive oxidation number need a roman numeral

25. Oxyanions Polyatomic ions often contain oxygen
The most common combination of oxygen and another ion will end with –ate
Nitrate (NO3-), Sulfate (SO42-), Chlorate (ClO3-)
The anion with one less oxygen will end with –ite
Nitrite (NO2-), Sulfite (SO32-), Chlorite (ClO2-)

26. Oxyanions
An anion with two less oxygens will start with Hypo- and end with –ite
Hypochlorite (ClO-)
An anion with one more oxygen that the most common ion will start with Per- and end with –ate
Perchlorate (ClO4-)

27. Naming Acids Acid names are based on the anion in the acid
Anions that end with –ide become hydro_____ic acid
HCl
Chloride  Hydrochloric acid

28. Naming Acids Anions that end with –ate become _____ic acid HNO3
Nitrate  Nitric acid
H2SO4
Sulfate  Sulfuric acid

29. Naming Acids Anions that end with –ite become _____ous acid HNO2
Nitrite  Nitrous acid
H2SO3
Sulfite  Sulfurous acid

30. Naming Molecular Compounds
Use a prefix to indicate the number of atoms for each element
Binary Covalent System
Second element ends in –ide
Exceptions
When there is only one atom of the first element, do not use mono- prefix.
When an element starts with a vowel, drop any o or a at the end of a prefix