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CHAPTER 3
ATOMIC STRUCTURE
 3.1 Defining the Atom
 Why can you see this?
Chapter 3
Atomic Structure
 Can you still see it?
 NO?
 Of course not, it’s been reduced to the size of an
atom.
 An atom is the smallest particle of an element that
retains its identity in a chemical reaction.
Continuing section 3.1
 Democritus
 He was a Greek philosopher (460BC – 370 BC) that was
the first to suggest that all things were made up of small
indivisible and indestructible particles, he called atoms.
 He had no scientific support, so what makes him right?
3 Basic Laws of Chemistry
 1. Law of conservation of mass:
 Matter can neither be created nor destroyed by
ordinary chemical reactions.
 Mg + HCl
H2(g) + MgCl2
 2. law of definite proportions:
 Chemical compounds contain the same elements in
exactly the same proportions by mass regardless of
the size or source of the sample
3 Laws cont.
 3. Law of multiple proportions: if two or more
different compounds are composed of the same two
elements, then the ratios of the masses of the second
element combined with a certain mass of the first
element is always a ratio of small whole numbers.
 In CO
1.33 g of O combine with 1 g C
 In CO2 2.66 g of O combine with 1 g of C
 Both ratio of masses 1.33g and 2.66g are a 2 to 1
ratio
Continuing section 3.1
 John Dalton’s Atomic theory
 2000 yrs after Democritus, Dalton established his atomic
theory.
 Using science he transformed Democritus ideas into a
scientific theory.
 Dalton studied the ratios in which elements combine in
chemical reactions.
Continuing section 3.1
 Dalton Atomic Theory
 1. all elements are composed of tiny indivisible
particles called atoms.
 2. atoms of the same element are identical. Atoms of
one element are different from another element.
 3. Atoms of different elements can physically mix
together (chemically combine) in whole-number
ratios to form compounds.
Continuing section 3.1
 4. Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms of one
element are never changed into another element
from a chemical reaction.
Fun Info
 Atoms are so small that if you lined up 100,000,000
atoms of copper (Cu) it would only make a line about
1 cm long.
 Copper atoms
Silicon Atoms
 Electron tunneling microscope images
FermiLab, Chicago 17 mile circumference
Particle collisions