Download (atomic #).

The Atom
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The Atom: Learning Goals
• Democritus: explain his ideas about the atom
• Dalton: explain points of his atomic theory
• Subatomic particles protons, neutrons, electrons:
Identify them in terms of mass, charge, and position
• Rutherford: describe atom’s internal structure from his
model
• Isotopes: identify similarities & differences
• Atomic Number and Mass Number: calculate # of
protons, neutrons, and electrons
• Atomic Mass: calculate atomic mass of an element from
isotopes
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The Atom
Warm-up
Structure of the Atom
The subatomic particles in
an atom’s nucleus are
the _______________
protons
and _______________.
neutrons
electrons are
The ______________
outside the nucleus in a
“cloud.”
protons and neutrons are in the nucleus of the atom.
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The Atom
We can determine the number of protons
an atom has by looking at its
Atomic Number
____________
_____________.
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The Atom
•
Isotopes
What is an Isotope?
• An Isotope is a “Version” of the same
element that contains a different number
of NEUTRONS. Isotopes have the same
number of protons (atomic #).
Ex: Carbon-12 and Carbon-14 are
ISOTOPES of Carbon. Both C-12 & C-14
have 6 protons. C-12 has 6 neutrons,
but C-14 has 8 neutrons.
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The Atom
Defining the Atom
Democritus
• among first to
suggest existence
of atoms
• believed atoms
were indivisible &
indestructible
(ca. 460 BC – ca. 370 BC)
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The Atom
John Dalton
Defining the Atom
English Chemist & School Teacher
(1766 – 1844)
Dalton’s Atomic Theory
(Early 1800’s)
1. Elements are made of atoms
2. Atoms of same element are
identical; atoms of one element
different from atoms of another
element
3. Atoms of different elements
can combine to form compounds
4. atoms cannot be changed chemically
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The Atom
Plum Pudding Atom
Defining the Atom
J.J. Thomson
English Physicist
Discovered electrons by making cathode ray
tube
(1856 – 1940)
1897: Discovered the electron
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Ernest Rutherford
The Atom
Defining the Atom
•Gold Foil Experiment
•Shot alpha particles at gold foil
•Some particles bounced off
foil, indicating presence of
nucleus
1911: Discovered that
atoms have a nucleus
Click on foil pic for youtube video
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Niels Bohr
The Atom
Defining the Atom
•Electron moves in a
circular orbit at fixed
distances from nucleus
negative
electrons
on their
orbitals
1913: Discovered
electron orbitals
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The Atom
Defining the Atom
RECAP - History and Discoveries
Democritus
(ca. 460 BC – ca. 370 BC)
Greek Philosopher
Existence of atoms; indivisible
& indestructible
John Dalton
J. J. Thomson
(1766 – 1844)
English Chemist &
School Teacher
(1856 – 1940)
English Physicist
Atomic Theory: 4 key points
Discovered electron;
cathode ray tube;
atom as “Plum Pudding”11
The Atom
Defining the Atom
RECAP - History and Discoveries
Ernest Rutherford
(1871 – 1937)
British-New Zealand
Chemist & Physicist
Discovered
NUCLEUS;
Gold Foil Experiment
Niels Bohr
(1885 – 1962)
Danish Physicist
Discovered electron ORBITALS
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The Atom
•
Review
Who was the first to realize there was a
smallest part of matter?
Democritus
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The Atom
•
Review
Who discovered that atoms have a
nucleus?
Rutherford
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The Atom
Subatomic Particles: PROTONS
•
•
•
•
•
•
Protons Identify the element!
The number of protons cannot change.
# of protons is same as Atomic Number
Protons are located inside nucleus
Protons have a Positive charge (+)
Proton’s Mass is 1 amu
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The Atom
Subatomic Particles: NEUTRONS
•
•
•
•
•
Neutrons are located inside nucleus
Neutrons have no charge at all (0)
Neutron’s Mass is 1 amu
The number of neutrons can CHANGE.
# neutrons = Mass number – Atomic number
• Oxygen’s # neutrons = 16 – 8 = 8
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The Atom
Subatomic Particles: ELECTRONS
•
•
•
•
•
Electrons are located outside of nucleus
# of electrons is same as # protons in neutral atom
Atomic number = # of electrons in neutral atom
Electrons have a Negative charge (-)
Electron’s Mass is 1/1840 amu
•
Because protons and electrons have equal but opposite charges, a
neutral atom must contain equal numbers of protons and electrons
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Subatomic Particles
&
Reading Periodic Table Squares
The Atom
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Subatomic Particles
&
Reading Periodic Table Squares
The Atom
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The Atom
•
Isotopes
What is an Isotope?
• An Isotope is a “Version” of the same
element that contains a different number
of NEUTRONS. Isotopes have the same
number of protons (atomic #).
Ex: Carbon-12 and Carbon-14 are
ISOTOPES of Carbon. Both C-12 & C-14
have 6 protons. C-12 has 6 neutrons,
but C-14 has 8 neutrons.
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The Atom
Defining the Atom
Atomic Number and Mass Number
Atomic Number Is the Number of Protons of the Nucleus
Isotopes: Calculating # of neutrons
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