Atomic Structure and the Periodic
Table
www.astro.virginia.edu
All Matter is Made of Atoms
 Hydrogen is the most
common atom of our
universe
 Types of atoms in Earth’s
Crust
www.earthshope.org
Iron 5%, Aluminum 8%,
Silicon 28%, Oxygen 47%,
Other 12%
 Types of atoms in Humans
Nitrogen 3%, Hydrogen 10%,
Oxygen 61%, Other 26 %
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Names and Symbols of Elements
 Each element has its own symbol
 Some elements use the first letter of the name:
hydrogen (H), Sulfur (S),Carbon (C)
 Other elements use the first letter of the name
plus another letter: aluminum (Al), Platinum (Pt),
Zinc (Zn)
 The first letter is always capitalized and the
following letters are lower case.
Early Greek Philosophers
determined that atoms are the
building blocks of matter.
John Dalton (1766–1844)
John Dalton’s theory of the
atom started out as a solid
sphere with no charges
Proposed the atomic theory
by investigating atomic
weights of atoms
J.J. Thomson determines that an atom
is made up of negative electrons
embedded in a sea of positive charges .
+
+
-+
- +
www.ucl.ac.uk
Ernest Rutherford did some
experiments with thin metal foils and
found that the positive charge is
located within a central nucleus
www.scientific-web.com
Neils Bohr worked under Rutherford but
found problems with his theory. He
ultimately determined that Electrons are in
circular orbits with increasing energy
levels.
_
_
nobelprize.org
The modern atomic model shows that
electrons occupy regions of space
whose shape is described by complex
mathematical equations. (James
Chadwick)
www.csmate.colostate.edu
History of Atomic Theory
 John Dalton’s theory of the atom started out as a solid
sphere with no charges.
 Then J.J. Thomson figured out there were positive and
negative charges in an atom.
 Rutherford determined that the positive charges
(protons) were located in the center of the atom and the
negative charges (electrons) were scattered around the
nucleus
 Bohr’s theory said that the protons are in the middle and
the electrons travel in specific energy levels and orbits
around the nucleus
 Modern model- protons and neutrons in nucleus,
electrons on energy levels
IP 15: Electron Configuration &
Periodic Table Organization p.
Review
 An atom is made up of protons (+),
neutrons (no charge), and electrons(-).
 The protons and neutrons are found in the nucleus
 There has to be an equal number of protons and
electrons because atoms have no net charge!
 Atomic mass is the number of protons and
neutrons
 Atomic number is the number of protons (which is
the same as the number of electrons)
Vocabulary
Atom: the smallest particle of an element that has the
chemical properties of the element
Nucleus: found in the center of the atom and contains the
protons and neutrons
Proton: a positively charged particle found in the nucleus
of an atom
Neutrons: an uncharged particle found in the nucleus of an
atom
Electron: negatively charged particles that move around
outside the nucleus of the atom
Isotopes: atoms of the same element that have a different
number of neutrons. Chlorine atoms have 17 protons, but some
atoms of chlorine have 18 or 20 neutrons these atoms are the
isotopes of chlorine
Atoms form Ions
Ions: formed when an atom loses or gains one
or more electrons(- or + charge)
Cation: formed when an atom loses an
electron (+ charge)
Anion: formed when an atom gains an
electron (- charge), larger radius.
Elements are organized by similarity
Modern Periodic Table
organized by the atomic
# of the elements
Dmitri Mendeleev began
organizing elements by
their physical and
chemical properties
(1860’s)
How is the Periodic Table organized?
Mendeleev produced
the first periodic table
organized by the
atomic # of the
elements
Named the periodic
table because a
periodic, or repeating
pattern of properties of
the elements
How is the Periodic Table organized?
(Cont’d)
 Period: each row of the periodic
table is called a period. If you
read from left to right one
proton and one electron are
added from one element to the
next
 Group/Family: name for each
column of the table. Read top to
bottom.
-share similar properties.
-divided into Representative
elements= Groups 1-8 &
Trans. Metals
Aufbau Process: lowest energy
orbitals first.
Valence Electrons

Valence Electrons

EXAMPLES:
What
element?
How many
valence
electrons?
What
element?
How many
valence
electrons?
Valence Electrons (Cont’d)
 Determined by the elements’ Group
Lewis Dot Structure
All elements in the 1st group have
only 1 valence electron. All elements
in the first group have a Lewis Dot
Structure like this:
H
Atomic Size on the Periodic Table
Left to right atomic size decreases
Top to bottom atomic size increases
More Properties of Periodic Table
Periodic Table has distinct regions
Reactive: indicates how likely an
element is to undergo a chemical
change
Most elements are somewhat reactive
and combine with other materials
The most reactive are in groups
(up/down) 1 and 17
The least reactive are in group
(up/down) 18
Elements combine by the outside
electrons
 All of the electrons in the combining elements do not interact with
each other to form compounds….
 Valence Electrons: Only the electrons in the element’s outside
energy level interact with each other.
 The most stable configuration has 8 electrons in the outer
energy level.
 Elements in group 1 have 1 electron in outside energy level and
elements in group 17 have 7 electrons in outside energy level so
they react with each other easily to form compounds and fulfill the 8
electron stable configuration.
Metals
Most elements are
metals
Metals are elements
that conduct
electricity and heat,
have shiny
appearance, and can
be shaped by
pounding
(malleability), bending,
or being drawn into a
thin wire (ductility)
Metals (Cont’d)
Reactive metals:
Group 1 (up/down)
most reactive
Transition Metals:
Group 3-12
(up/down)
generally less
reactive than most
metals
Rare Earth Elements
www.riken.jp
 Top row of the two rows of metals that are outside of the main
periodic table
 Also known as Lanthanides because they follow the element
lanthanum (La) on the table
 Scientists once thought these metals were available only in tiny
amounts on the Earth
Actinide
• bottom row of the two
rows of metals that are
outside of the main
periodic table
• The Actinide series is
all radioactive and
some are not found in
nature.
www.chem4kids.com
Nonmetals
Nonmetals: the elements on the right side of
the periodic table
Many are gases at room temperature, dull
surfaces on the solid nonmetals, cannot be
shaped by ductility or malleability
Halogens
Elements in group 17
7 valence electrons
Greek “forming salts
Very reactive nonmetals
Easily form compounds
w/ metals. These
compounds are known
as salts.
Noble Gases
Group 18 on the
periodic table
8 valence e(electrons)
Noble or inert
because they
almost never react
with other
elements
Metalloids
Have properties
of both metals &
nonmetals
Located on
either side of the
zigzag line
separating
metals and
nonmetals
Most common is
Silicon
Summary: 3 N/H
-Valence e-Lewis Dot Structures
-Group characteristics
Poor Metals
Metalloids
Metalloids
Radioactivity
 Radioactivity: the process by
which the nucleus of an atom
releases energy and particles
 Marie Curie was the first person to
isolate two radioactive elements
(polonium and radium)
 An isotope is radioactive if the
nucleus has too many or too few
neutrons
www.achievement.org
 Radioactive atoms
produce energy and
particles from their nuclei
Radioactive Decay
 The identity of these
atoms changes because
the # of protons changes.
(radioactive decay)
 Occurs at a steady rate
characteristic to each
isotope
 The amount of time for
one-half of the atoms to
decay is called the halflife of the isotope
earthsci.org
Radioactive Decay
 Parent decays into daughter isotope.
 Combination of both is 100%
 Parent starts at 100% and decays to 50%
 100% 1 half-life to 50% (daughter 50%)
 50% 2 half-lives to 25% (daughter 75%)
 25% 3 half-lives to 12.5% (daughter 87.5%)
 12.5% 4 half-lives to 6.25% (daughter 93.75%)