atoms - chm 131 spring 2011

1. John Dalton – 1803
Based on the way that elements combined in compounds.
Law of constant
Concluded that atoms were the smallest particles of
Composition
matter
This view had been expressed by Greek philosophers
Law of multiple
at least 2000 years earlier
proportions
Dalton was the first to find EXPERIMENTAL evidence
for this belief

2. Postulates of Dalton’s atomic theory
• Matter made of discrete particles called atoms
– An atom is the smallest particle of matter*
• Atoms of a given element are identical to other atoms of that
element and different from atoms of other elements*
• Atoms of different elements combine together to form
compounds
– A given compound will have the same number and same type of
elements
• Chemical rx involves rearrangement, separation or
combinations of atoms
• Atoms are not created or destroyed*

3. Changes
• Matter made of discrete particles called atoms
– An atom is the smallest particle of matter*
• Atoms have subatomic particles (p+, e-, n)
• Atoms of a given element are identical to
other atoms of that element and different
from atoms of other elements*
– Isotopes
• Atoms are not created or destroyed*
– E=mc2 conversion between mass and energy

4. demo

6. Table 3.8
Pg 97
amu or dalton = 1/12 of C-12 nucleus
6p+6n
6 X 1023 atoms 12C = 12 g

7. Pg 98-103

8. Pg 100

10. ions
• Neutral atoms: #p+ = # e-
• Ions – gain or lose of electrons
– Protons are not gained/lost in normal
chemical/physical changes
• Gain e, charge…… _____ion
• Lose e-, charge ….. _____ion
We’ll look later at typical charges
For ions

11. Ions # p+ ≠ # e-
Name # p+ # e- #n Mass # symbol
1 0 0
81 Br-1
35
9 10 19
2 0 1
39 K+1
19
24 15
Mass # = p + n
Charge = p - e