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Teacher Instructions:
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Go to www.Brainpop.com
Login: edhpop
Password: edhpop1
Go to Science
Go to “Matter and Chemistry”
Go to “Atoms” view video
Have students complete quiz (graded) as a class, then go
through the powerpoint. Have students define protons,
neutrons and electrons on the page that they will complete
the table on slide 13.
• Students must turn table and definitions in to their science
teacher.
Atoms,
Molecules,
and Ions
Basic Atomic Structure
EARLY THEORIES
Democritus’s 460 – 370 B.C.
• Matter is composed of empty space through which
atoms move.
• Atoms are solid, homogeneous, indestructible, and
indivisible.
• Different kinds of atoms have different sizes and
shapes.
• The differing properties of matter are due to the
size, shape, and movement of atoms.
• Apparent changes in matter result from changes in
the groupings of atoms and not from changes in the
atoms themselves.
Atomic Theory of Matter
The theory that atoms are
the fundamental building
blocks of matter
reemerged in the early
19th century, championed
by John Dalton.
Dalton’s Postulates
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Each element is composed of extremely small
particles called atoms.
All atoms of a given element are identical to one
another in mass and other properties, but the atoms of
one element are different from the atoms of all other
elements.
Atoms of an element are not changed into atoms of a
different element by chemical reactions; atoms are
neither created nor destroyed in chemical reactions.
Compounds are formed when atoms of more than one
element combine; a given compound always has the
same relative number and kind of atoms.
The Electron
• Streams of negatively charged particles were found
to emanate from cathode tubes.
• J. J. Thompson is credited with their discovery
(1897).
Millikan Oil Drop Experiment
Robert Millikan (University of Chicago)
determined the charge on the electron in
1909 [ – 1] and he calculated the mass of
an electron [9.1 × 10-28 g].
The Atom, circa 1900:
• “Plum pudding” model, put
forward by Thompson.
• Positive sphere of matter
with negative electrons
imbedded in it.
Discovery of the Nucleus
Ernest Rutherford shot
 particles at a thin
sheet of gold foil and
observed the pattern of
scatter of the particles.
The Nuclear Atom
Since some particles
were deflected at large
angles, Thompson’s
model could not be
correct.
THE NUCLEAR MODEL
According to Rutherford,
most of the atom
consists of electrons
moving rapidly through
empty space and a
very dense, positively
charged nucleus.
Other Subatomic Particles
• By 1920 , Rutherford had refined his concept
of the nucleus: He concluded that the very
dense nucleus contained positively particles
called protons.
• James Chadwick, a coworker, showed that
the nucleus also contained a neutral particle
in 1932. This was the neutron – a particle
with nearly equal mass as a proton.
Properties of Subatomic Particles
Relative Actual mass
Particle Symbol Location Charge
mass
(g)
Electron
Proton
Neutron
e-
p+
n0
Around
nucleus
Nucleus
nucleus
1–
1+
0
1
1840
9.11×10-28
1
1.673×10-
1
24
1.675×1024
Atomic Structure and the Periodic
Table
Symbol
Name
14
Si
28.086
Silicon
Atomic number = # protons & #
electrons (if neutral atom)
Atomic Mass: Round to a
whole #:
28 = Relative mass of nucleus
-14 = # protons
14 = # neutrons
Practice From the Periodic Table
Complete the following chart:
Name
Symbol
Relative
#
#
# protons
mass
neutrons electrons
Lithium
Mg
26
16