Transcript Chemistry II Chapter 2 Notes

History of the ATOM
AP Chemistry
History of the Atomic Theory
• Democritus (460370 BC) thought
that matter must be
made up of tiny
particle called
“atomos” which
means invisible in
Greek.
History of the Atomic Theory
• Plato (428-348 BC)
and later Aristotle
(384-322 BC)
believed there could
be no “ultimate
particle”. This view
was preferred by
most until the late
1700s.
Fundamental Chemical Laws
• Law of Conservation of Mass-proved
through Lavoisier’s careful measurements
of masses of reactants and products that
mass is neither created nor destroyed.
• Law of Definite Proportions-Proust
showed that a given compound always
contains exactly the same proportion of
elements by mass.
Fundamental Chemical Laws
• Law of Multiple Proportions-Dalton
found that when two elements form a
series of compounds, the ratios of the
masses of the second element that combine
with 1 gram of the first element can always
be reduced to small whole numbers.
• These laws led to….
Dalton’s Atomic Theory
• In the early 1800s John Dalton
revived the “atoms” concept.
• “Everything is made of atoms.”
• His theory proposed that atoms were
invisible and indestructible.
Dalton’s Theory Cont’d
• He also stated that atoms of one element
are all the same and different from those of
other elements
• Atoms combine in small whole number
ratios to form compounds.
• In chemical reactions atoms are just
rearranged.
Gay-Lussac and Avogadro
• Gay-Lussac first determined the formula
for water by measuring the volumes of
gases that combined to form a given
volume of water.
• Avogadro’s hypothesis-based on this
work stated that equal volumes of gases at
standard temperature and pressure contain
equal numbers of particles.
J.J. Thomson and e
• Using cathode ray tubes, Englishman J.J.
Thomson found the ratio between charge
and mass for subatomic particles that we
know as electrons.
• This proved part of Dalton’s theory wrong.
Robert Millikan finds the mass
of the electron. Plum-pudding
• Using Thomson’s experiments and his own
data he determined the mass of the electron
and found it to be very small, about 9.1 x
10-28g.
• With this information, Thomson proposed
a model of the atom that had positive and
negative charges in the atoms like plums in
a pudding. (“plum pudding” model)
Rutherford’s Gold Foil
Experiment. A look inside.
• Ernest Rutherford tried to determine the
internal arrangement of atoms by shooting
a particles at VERY thin gold foil.
• If the charges inside the atom were evenly
spaced the particles would pass through
unchanged.
• That wasn’t the case, a few were deflected
at large angles.
Rutherford’s Nuclear Atom
• The results of the gold foil experiment led
Rutherford to realize that there was a small
positive mass in the center of atoms that
contained most of the mass of the atoms,
called the nucleus, and electrons must orbit
the nucleus.
• He called the positive particles that made
up the nucleus “protons”.
3 Subatomic Particles
• Protons are found in the nucleus. They
have a positive charge. They have a mass
1840 x that of the electron.
• Neutrons are found in the nucleus. They
have no charge. They have a mass about
1840 x that of the electron.
• Electrons are found in the orbital and have
a negative charge. Table 2-1
Atomic Number
• All atoms of the same element have the
same number of protons, this is their
atomic number.
• For neutral atoms, the number of protons is
the same as the number of electrons.
• Atomic number (Z) = # of protons= # electrons
Isotopes
• Some atoms of an element have different
numbers of neutrons. There weight is
different from other atoms of the same
element.
• These are called isotopes.
• Mass number (A) is the number of protons
and the number of neutrons.
Covalent Bonds form molecules.
-
ee-
-
e-ee-e
e- e- e- ee-ee- ee- e
-ee
e
e
e
e-ee--ee- e- e- e-
Nonmetallic
NonmetallicMolecule
Atom
Atom
• Covalent bonds occur
between atoms that
result in the sharing of
electrons between two
nonmetallic atoms so
that each achieves a
noble gas
configuration.
Forming covalent molecules
• Only nonmetals are bound.
• Enough electrons are shared so that each
atom “thinks” that it has a full outer shell.
• A molecule is formed that has an overall
charge of zero.
Representations of Molecules
Ball-and-Stick Model
Space-filling model
Ionic Bonds form ions.
• Ionic Bonds are
formed when
electrons are given by
metallic atoms
to nonmetallic
atoms so that each
achieves noble gas
configuration.
e-
e- ee-- ee- ee- ee- eee- ee-- e-
Metallic
Ion
Metallic
+1Atom
Cation
Nonmetallic
Nonmetallic
IonAtom
-1 Anion
Forming ionic compounds
• The metal gives electrons to the nonmetal.
• The number of electrons given and
received must be equal, the sum of the
charges = 0.
• Sometimes more than one ion of each is
necessary to equal zero
The Periodic Table
PT Organization
• To the left of the staircase are the metals.
• To the right are the nonmetals.
• Metalloids are touched on two sides by the
staircase (except boron and aluminum).
• Groups or families are the columns (they
are alike)
• Periods are the rows.
PT by Group
• Alkali metals – group 1, most reactive
metals, form ions with a +1 charge
• Alkaline earth metals – group 2, still
pretty reactive, form ions with a +2 charge
• Halogens- group 17, most reactive
nonmetals, form ions with a -1 charge
• Noble Gases- group 18, very stable