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Atoms…A Matter of Fact!
STRUCTURE of the ATOM
• Atoms are made of smaller particles called
protons, neutrons and electrons.
Parts of the Atom
•
Particle
Charge
Location
Proton
Positive
Neutron
Neutral (no
charge)
Negative
In the
Nucleus
In the
Nucleus
Orbiting the
Nucleus
Electron
Where does an atoms mass
come from?
• The mass of an atom comes from the nucleus.
• The protons and neutrons are responsible
for the mass of the entire atom!
IDENTIFYING AN ATOM
• ATOMS CAN BE IDENTIFIED BY THE
NUMBER OF PROTONS THAT ARE IN
THE NUCLEUS.
• THE NUMBER OF PROTONS
EQUALS THE ATOMIC NUMBER
ATOMIC NUMBER
• Atomic number =
the number of
protons.
• Sodium Na has an
atomic number of
11. Therefore it has
11 protons in the
nucleus.
Neutral Atoms
• Atoms are
neutral
because they
have the same
number of
protons as
electrons.
ISOTOPES
• Atoms with the same number of protons and a
different number of neutrons.
Identifying an Isotope
• Isotopes can be identified by their mass
number.
• Mass numbers are found by adding the
protons and neutrons.
• Atomic mass of an element is the average
mass of all the isotopes of that element.
Isotope example
• Carbon has a mass # of 12 because there are
•
normally 6 protons and 6 neutrons. 6+6=12
Carbon’s isotope has a mass # of 14 because
there are 6 protons and 8 neutrons. 6+8=14
History of the Atom
ATOMIC THEORISTS
•
•
•
•
•
•
JOHN DALTON
J.J. THOMSON
ERNEST RUTHERFORD
NIELS BOHR
JAMES CHADWICK
PRESENT MODERN MODEL
JOHN DALTON
• The first modern scientist to propose the
existence of atoms. He described an atom
as an invisible, indestructible, solid sphere,
like a billard ball.
Thomson Model
• Proposed that the atom is a solid mass of
positively charged material with negative
charges scattered throughout. He is
credited with discovering the electron.
• Described as the “blueberry muffin” or
“plum pudding” model.
RUTHERFORD MODEL
• Says that the atom is mostly empty space.
• Electrons orbit around positively charged
nucleus. He discovered the nucleus.
BOHR’S MODEL
• Proposed that electrons move in different
orbits, or energy levels, around the nucleus
like planets orbit the sun. Each level
contains a certain number of electrons.
CHADWICK’S MODEL
• Discovered the neutron. This explained
why atoms were heavier than the total
mass of their protons and electrons.
Present Modern Model
• Electrons form a negatively charged cloud
around the nucleus. It is impossible to
determine exactly where an electron is at a
given time.