Transcript Atoms and Periodic Table Review

Atoms and
Periodic Table
Review
Dalton’s Concept
• John Dalton, an English schoolteacher
proposed the following ideas about matter:
1. Matter is made up of atoms.
*2. Atoms cannot be divided into smaller pieces.
*3. All the atoms of an element are exactly alike.
4. Different elements are made of different
kinds of atoms.
• Dalton pictured an atom as a hard sphere that was
the same throughout.
Thomson’s Atomic Model
• Thomson pictured a
sphere of positive
charge.
• The negatively charged
electrons were spread
evenly among the
positive charge.
• The atom is neutral.
• Plum pudding model (chocolate chip cookie)
Rutherford’s Gold Foil Experiment
Rutherford’s Model
• Most of atom is empty space
• Electrons surrounding
• Nucleus- very dense positively charged area.
The Proton
• In 1920 scientists identified the
positive charges in the nucleus as
protons.
• A proton is a positively charged
particle present in the nucleus of all
atoms.
Neutron
• Electrons are very light weight
• Mass of atom should be equal to the number of
protons.
• But mass is about 2X the number of protons
• Hypothesized a new particle.
neutron (NEW trahn),
would have the same
mass as a proton and
be electrically neutral.
The Electron Cloud Model
• The new model of the
atom allows for the
somewhat unpredictable
wave nature of electrons
by defining a region
where electrons are
most likely to be found.
• Electrons travel in a
region surrounding the
nucleus, which is called
the electron cloud.
Atoms by the Numbers
• Atomic Number- the number of protons in an
atom. (Z)
• The mass number of an isotope is the number of
neutrons plus protons. Also called the atomic
mass. Designated A
Isotope Identification
Name of element followed by mass number identifies
the isotope.
• Hyphen notation
• Carbon-14 or C-14
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Mass number
Atomic number
14
6C
C
Development of the Periodic Table–
Mendeleev’s Table of Elements
• A Russian chemist, Dmitri Mendeleev (men
duh LAY uhf), published his first version of
the periodic table 1869.
• When Mendeleev arranged the elements in
order of increasing atomic mass, he saw a
pattern.
• He noticed repeating patterns of properties.
Moseley’s Contribution
• Although Mendeleev’s table correctly
organized most of the elements, a few
elements (cobalt and nickel, tellurium and
iodine) seemed out of place.
• In the early twentieth century, the English
physicist Henry Moseley realized that
Mendeleev’s table could be improved by
arranging the elements according to atomic
number rather than atomic mass.
Today’s Periodic Table
• In the modern periodic table, the elements
still are organized by increasing atomic
number.
• The rows or periods are labeled 1-7.
• A period is a row of elements in the periodic
table whose properties change gradually and
predictably.
Today’s Periodic Table
• The periodic table has 18 columns of
elements.
• Each column contains a group, or family, of
elements.
• A group contains elements that have similar
physical or chemical properties.
Element Key
Color- book only not reference sheet
Blue – Metal
Green – Metalloid
Yellow - Nonmetal
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Common elements - Uncommon Names
Sodium
Potassium
Iron
Copper
Silver
Tin
Antimony
Tungsten
Gold
Mercury
Lead
Na
K
Fe
Cu
Ag
Sn
Sb
W
Au
Hg
Pb
Review Electron Configuration
• The properties of an element are determined by the
arrangement of electrons in the outer energy level.
• The number of electrons in the outer energy level of
main group elements can be determined by the group
number of the element.
• Group 1 and 2: number of electrons = group number.
• Group 13-18: number of electrons = group number - 10
Groups
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Group 1 – alkali metals 1 outer electron
Group 2 – alkaline earth metals - 2 outer electrons
Group 3-12 – Transition Elements (Medals)
Group 13 – 3 outer electrons
Group 14 – 4 outer electrons
Group 15 – 5 outer electrons
Group 16 – 6 outer electrons
Group 17 – halogens - 7 outer electrons
Group 18 – noble gases – 8 outer electrons