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Everything is made of Atoms
-Richard Feynman
• Review of scientific
• A brief history of the
• Composition of Earth’s
• Avagadro’s Number
• How many atoms are in
your body?
How many seconds are in a year?
606024365 = 31536000
= 3.1536107
 3.15107
(to 3
significant digits)
Review: Scientific Notation
How many years are in a second?
1/3.1536 x 107 = 0.0000000317098
= 3.1709810-8
 3.1710-8
(to 3
significant digits)
Review: Scientific Notation
How many atoms are in my body?
Review: Scientific Notation
A brief history of the atom
In the 5th cent. B.C. the Greek
philosophers Democritus and
Leucippus proposed that matter
was made up of tiny, indivisible
particles in constant motion.
Aristotle, however, did not
accept the theory, and it was
ignored for centuries.
atoma= non-divisible
A brief history of the atom
Modern atomic theory began
with the publication in 1808 by
British chemist and physicist
John Dalton of his experimental
conclusions that:
1. all atoms of an element have
the same size and weight, and
2. atoms of elements unite
chemically in simple numerical
ratios to form compounds.
Definition: Element
A single or isolated group of
particles composed of only one
species of atoms.
A brief history of the atom
In 1897, British physicist J.J.
Thomson discovered the
electron, a subatomic particle
(i.e., a particle smaller than
the atom). For this work, he
was awarded a Nobel prize in
His discovery of the electron
led to Thomson’s proposed
plum-pudding model for the
A brief history of the atom
In 1911, New Zealander Ernest
Rutherford explained an atom's
structure in terms of a positively
charged nucleus surrounded by
negatively charged electrons
orbiting around it.
His famous gold
foil experiment
showed that
atoms are mostly
empty space.
Perspective on the atom: If the nucleus
could be enlarged to the size of a pea
and placed at the centre of a football
stadium, the electrons would be like
flies buzzing around the cheap seats.
A brief history of the atom
In 1913 Danish physicist Neils
Bohr used quantum theory to
explain why electrons could
remain in certain allowed orbits
without radiating energy.
Bohr model for the atom.
Modern view of the atom
Atom (definition): The smallest unit of matter
that possesses the properties of an element.
Nucleus (not to scale)
Electrons (clouds)
Modern view of the atom
• Atoms are composed of subatomic
particles: protons, neutrons and electrons.
• Protons and neutrons reside in the nucleus
of the atom - the central core where virtually
all of the mass of the atom is located.
• Electrons exist outside the atomic nucleus
in a cloud of orbitals.
Nucleus (not to scale)
Electrons (clouds)
Important characteristics of the electron
• they orbit the nucleus in a cloud (or shell)
• they are bound to atoms because their
negative charge is attracted to the positive
charge in the nucleus
• the chemical behaviour of atoms and
elements is largely controlled by the number
and configuration of electrons
Physical facts of subatomic particles*
Mass (kg)
* There are actually a lot
more known subatomic
particles than those listed
How many elements are there in the world?
•At this time, scientists know of 116
different elements, of which 92 occur in
nature (the rest are man-made).
• The naming convention for new elements is
to name them after people or places (e.g.,
Einsteinium or Gallium).
How many elements are there in the world?
“The first full-scale hydrogen bomb
explosion in the Pacific in late 1952
produced two new chemical elements,
atomic scientists disclosed today.
The researchers recommend that the
new elements be named after Dr.
Albert Einstein and Dr. Enrico Fermi,
who played major roles in the birth
of the atomic age”
(New York Times, August 1955)
Composition of Earth’s crust
(8 Major Elements)
Element (Symbol)
Oxygen (O)
Silicon (Si)
Aluminum (Al)
Iron (Fe)
Calcium (Ca)
Sodium (Na)
Potassium (K)
Magnesium (Mg)
Percent by weight
Periodic Table of the Elements
• Ordered by increasing atomic weight and
atomic number (Z = number of protons in the
nucleus of one atom).
• Atomic weight (grams/mol) is given below the
element symbol.
Atomic Number (Z )
Atomic Symbol
Atomic Weight
Avogadro’s Number
• Avogadro’s number was
determined experimentally in the
20th century, but was named in
honour of 19th century Italian
• The 2002 CODATA
recommended value for
Avogadro's number is
6.0221415 x 1023 mol-1
Avogadro’s Number
• Avogadro’s number (N ) gives the
number of atoms in 1 mole of an
• Magnitude of N:
If the Earth was
covered by N peas,
the peas would be
piled to a height of
0.5 km!
How many atoms are in my body?
• Suppose that I am made entirely of carbon
• Suppose that I weigh … 72.0 kg
•Number of moles (mol) of carbon
1 mol
12.01 g
X mol
7.20×104 g
X = 7.2x104/12.01
= 6.00x103 mol
• Number of carbon atoms  6.00 ×10
mol ×
6.022 × 1023 atoms/mol  3.61 × 1027 atoms
Review: Scientific Notation
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