Transcript Chapter 18

Chapter 18
Properties of Atoms and the
Periodic Table
Section 1-Structure of the Atom
• Chemical Symbolsconsist of one capital
letter or a capital letter
plus one or two small
letters
ex: table 1—pg. 544
Atomic Components
• Atoms—the smallest
piece of matter that still
retains the property of
the element
• Atoms: Contain protons
and neutrons in the
nucleus
• Electrons—contained in
electron cloud
• Quarks—smaller particles
that comprise protons and
neutrons
• Scientists have confirmed
the existence of six
uniquely different quarks
• The search for the
composition of protons and
neutrons is an ongoing
effort
Models of the Atom
• Democritus—”uncuttable”
composed of tiny, solid
particles that could not be
subdivided—(atomos)
**Dalton—solid sphere
**Thomson Model—”cookie
dough”
charged particles were
evenly embedded
throughout a positively
charged sphere
(more models)
• Rutherford Model—
proposed almost all the
mass of an atom (& +
charges) were
concentrated in a central
nucleus surrounded by
electrons
• Bohr Model—
– Hypothesized electrons
traveled in fixed orbits
Electron Cloud Model
(Quantum Mechanical)
• 1926—current model
• Electron cloud—area around
the nucleus of an atom
where its electrons are
most likely found
• Energy levels are areas of
the cloud where electrons
are more likely 2 B found
Section 2—Masses of Atoms
• AMU—unit of measurement
used for atomic particles
• Mass of 1 proton or 1
neutron is almost 1 amu.
• Atomic number—the
number of protons in an
atom
• Mass number—the sum of
the number of protons and
the number of neutrons in
the nucleus
• Atomic mass = decimal
number under the symbol
on the periodic table
• NOT THE SAME THING AS
ATOMIC NUMBER
• It is the average weight of
all atoms of the element
(including isotopes)
• Mass number-does not
account for isotopes
Calculating neutron number
• If you know the mass
number and atomic
number of an atom, you
can find the number of
neutrons as well,.
• Neutron # = mass # atomic #
Isotopes
• Carbon-12 is the most
common form of carbon
• However, Carbon-14 is a
radioactive form of carbon
• WHY?
• Not all the atoms of an
element have the same
number of neutrons
ISOTOPES
• Isotopes—atoms of the
same element that have
different numbers of
neutrons
• Average atomic mass—the
weighted average mass of
an element’s mixture of
isotopes (used because
most elements have more
than one isotope)
The Periodic Table
• Dimitri Mendeleevarranged all the elements
known in order of
increasing atomic masses
and discovered a pattern
• Today’s Periodic Table—
elements are arranged by
increasing atomic number
and by changes in
physical and chemical
properties
• Mendeleev-left blank
spaces to keep elements
in line according to
chemical properties
• He predicted the
existence of two
elements not yet
discovered
Groups
• The vertical columns
in the periodic tablealso called families
• Periodic Table—pg.
556 and 557
Electron Cloud Structure
• In neutral atoms, the
electron number = the
proton number
• SO: Atomic number
tells how many protons
AND how many
electrons the element
has
• Elements in the same
group have the same
number of electrons in
their outer energy levelcalled VALENCE
ELECTRONS
• This number determines
properties of the
elements
Number of Atoms in Energy Levels
•
•
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•
Energy Level 1—holds 2 e
Energy Level 2—holds 8 e
Energy Level 3—holds 18 e
Energy Level 4—holds 32 e
• Octet Rule—explains that
atoms are most stable with
an outer valence holding 8
electrons
Periods/Rows
• Horizontal groups
across the periodic
table
• Each row ends with an
element with a full outer
valence (8 electrons)
• Periods increase by
one proton and one
electron going L to R
Metals
• Metals are on the lefthand side of the
periodic table
• Most are shiny, ductile,
malleable and are
good conductors
• Ductile—drawn into wire
• Malleable-can be
hammered into sheets
Non-metals
• Non-metals are on the right
side of the periodic table
• Most are gases, brittle, and
poor conductors
Metalloids
• Metalloids-run along
the middle zig-zag line
• Metalloids have some
of the properties of both
metals and non-metals
• Carbon-14
has 6 protons and 8
neutrons
Isotopes—atoms of the same
element that have different
numbers of neutrons
Radioactive isotopes—those
isotopes that are unstable
and become radioactive
Identifying Isotopes
• Average atomic mass—the
weighted-average mass of
the mixture of its isotopes
• Ex: 4 out of 5 atoms of B
are boron-11 and 1 out of
five is boron-10
• Weighted average =
4/5 (11) + 1/5(10) = 10.8 AMU
Periodic Table websites:
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www.chemicool.com
www.Ptable.com
www.periodictable.com
www.webelement.com