Law of constant

Composition

Law of multiple

John Dalton – 1803

Based on the way that elements combined in compounds.

Concluded that atoms were the smallest particles of

matter

This view had been expressed by Greek philosophers

at least 2000 years earlierLaw of multiple

proportionsat least 2000 years earlier

Dalton was the first to find EXPERIMENTAL evidence

for this belief

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 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*

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 • 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

demo

amu or dalton = 1/12 of C-12 nucleus

6 p + 6 n

6 X 1023 atoms 12C = 12 g

Table 3.8

Pg 97

Pg 98-103

Pg 100

ions

• Neutral atoms: #p+ = # e-

• Ions – gain or lose of electrons

– Protons are not gained/lost in normal

chemical/physical changeschemical/physical changes

• Gain e, charge…… _____ion

• Lose e-, charge ….. _____ion

We’ll look later at typical charges

For ions

Name # p+ # e- # n Mass # symbol

1 0 0

8135 Br-1

9 10 19

2 0 1

39 K+1

Ions # p+ ≠ # e-

3919 K+1

24 15

Mass # = p + n

Charge = p - e