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Ch. 16
Properties of
Atoms & the
Periodic Table
Structure of the Atom
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Element:
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matter made of one type of atom
Abbreviated with a scientific symbol,
usually the first letter or two of the
elements name
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Ex: H=hydrogen, C=carbon, He=helium
Structure of the Atom
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Element:
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Atom: smallest part of matter that still has
the properties of the element
3 parts of an atom:
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Proton: has a positive electrical charge
Neutron: has a neutral charge
Electron: has a negative charge
Protons and neutrons are found in the nucleus of
an atom
Electrons surround the nucleus
Structure of the Atom
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Protons & neutrons are made up
of smaller particles called quarks.
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Quarks are studied by colliding
accelerated charged particles with
protons, which leave tracks in a
bubble chamber.
Six quarks are known to exist
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The 6th quark is known as the top quark
Structure of the Atom
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Scientists use scaled-up models to
represent atoms.
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Early models used a solid sphere.
The current electron cloud model
shows electrons traveling in specific
energy levels around a nucleus of
protons and neutrons.
Masses of Atoms
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Atomic mass:
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composed mostly of the protons and
neutrons in the nucleus
Unit of measurement for atomic
particles is atomic mass unit
(amu) which is one-twelfth the
mass of a carbon atom containing
six protons and six neutrons.
Masses of Atoms
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Atomic number:
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the number of protons in an atom;
number of protons also identifies the
element
The sum of the number of protons
and neutrons in the nucleus of an
atom is
the mass number.
Masses of Atoms
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Isotopes—atoms of the same element
with different numbers of neutrons
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Different isotopes have different
properties.
Number of neutrons is equal to mass
number minus atomic number.
Name of element followed by mass number
identifies the isotope.
Average atomic mass is the weightedaverage mass of an element’s isotopes.
Average atomic mass is closest to its most
abundant isotope.
The Periodic Table
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Elements are organized in the periodic
table by increasing atomic number.
In the late 1800’s, Dmitri Mendeleev
devised the first periodic table based on
atomic mass.
In 1913, Henry G. J. Moseley arranged
the elements by atomic number rather
than atomic mass.
The Periodic Table
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Vertical columns in the periodic table are
groups of elements with similar
properties.
Elements in the same group have the
same number of electrons in their outer
energy level.
The Periodic Table
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Each of the seven energy levels can have
a maximum number of electrons.
Energy level one can contain at most two
electrons.
Energy level two can contain at most
eight electrons.
The Periodic Table
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Each row in the periodic table ends when
an outer energy level is filled.
Electron dot diagrams use the element
symbol and dots to represent outer
energy level electrons.
The Periodic Table
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Periods—horizontal rows of elements
that contain increasing numbers of
protons and electrons.
Elements are classified as metals,
nonmetals, or metalloids (semimetals).
Elements are synthesized in laboratories
all over the world.
The Periodic Table
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The same elements exist all over the
universe.
Hydrogen and helium are the building
blocks of other naturally occurring
elements.
Supernovas spread heavier elements
throughout the universe.