Download Ch. 3: Atoms History History Law of Conservation of Mass Law of

History
Democritus
named the most basic
particle
atom- means “indivisible”
Aristotle
didn’t believe in atoms
thought matter was
continuous (thought you
could keep dividing it)
Ch. 3: Atoms
3.1 Foundations
History
by
Law of Conservation of Mass
1700s, all chemists agreed:
mass
is neither created or destroyed
during regular chemical or physical
changes
on the existence of atoms
that atoms combined to make
compounds
Still
did not agree on whether
elements combined in the same ratio
when making a compound
Law of Definite Proportions
Law of Multiple Proportions
any
amount of a compound contains
the same element in the same
proportions by mass
No matter
where the
copper
carbonate is
used, it still
has the same
composition
applies when 2 or more elements combine
to make more than one type of compound
the mass ratios of the second element
simplify to small whole numbers
helped to emphasize the idea of atoms
15.9994
15.9994
15.9994
15.9994
31.9988
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Law of Multiple Proportions
Dalton’s Atomic Theory
All matter is made of atoms
Atoms of same element have the same
size, mass, and properties
Atoms can’t be subdivided, created or
destroyed
Atoms of different elements combine in
whole number ratios to make compounds
In chemical reactions, atoms can be
combined, separated, and rearranged.
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Modern Atomic Theory
Some parts of Dalton’s theory were wrong:
atoms are divisible into smaller particles
(subatomic particles)
atoms of the same element can have
different masses (isotopes- atoms of the
same type with different masses)
Most important parts of atomic theory:
all matter is made of atoms
atoms of different elements have
different properties
Ch. 3: Atoms
3.2 Structure of Atom
Structure of Atom
Nucleus:
contains protons
and neutrons
takes up very
little space
contains most of
the particles
Electron Cloud:
contains electrons
takes up most of
space
Subatomic Particles
includes
all particles inside atom
proton
electron
neutron
charge
on protons and electrons are
equal but opposite
to make an atom neutral, need equal
numbers of protons and electrons
2
Subatomic Particles
number of protons identifies the atom as a
certain element
protons and neutrons are about same size
electrons are much smaller
nuclear force- when particles in the nucleus
get very close, they have a strong attraction
Atomic Radius
size of atom
from center of nucleus to outside of electron
cloud
really is one-half the distance between the
center of two identical nuclei bonded together
expressed in picometers (1012 pm = 1 m)
usually 40-270 pm
proton + proton
proton + neutron
neutron + neutron
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