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Chapter 17
Properties of Atoms and
the Periodic Table
Structure of the Atom

Elements are
abbreviated in scientific
shorthand- first letter or
two of an element’s
name.
Structure of the Atom- Cont.

Atom- smallest piece of
matter that still has the
properties of the element.




Protons have electrical
charge of +1.
Neutrons do not have an
electrical charge.
Electrons have electrical
charge of -1.
Protons and neutrons are in
the nucleus of an atoms;
electrons surround the
nucleus.
electron
neutron
proton
Structure of the Atom- Cont.

Protons and neutrons are made up of smaller
particles called quarks.

Six quarks are known to exist; the sixth is called
the top quark.
Structure of the Atom- Cont.

Scientists used
scaled-up models
to represent
atoms.

Early models of
atoms used a solid
sphere.
These are the actual wood spheres that
Dalton used as models for atoms. They are
about 200 years old. Notice the holes drilled
in them. He probably used them to connect
atoms to other atoms to make compounds.
Structure of the Atom- Cont.

Current electron cloud
model shows electrons
traveling in specific
energy levels around a
nucleus of protons and
neutrons.
Masses of Atoms

Atomic Mass- composed mostly of the
protons and neutrons in the nucleus.



Unit of measurement of atomic particles is atomic
mass unit.
Atomic Number- 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- Cont.
Element
Element
Atomic Number
Symbol
Mass Number
Masses of Atoms- Cont.

Isotopes- atoms of the same element with
different numbers of neutrons.


Different isotopes have different properties.
Number of neutrons is equal to the mass number
minus atomic number.
Masses of Atoms- Cont.
Masses of Atoms- Cont.

Name of element followed by mass number
identifies the isotopes.
Masses of Atoms- Cont.


Average atomic mass is the weighted-average
mass of an element’s isotopes.
Average atomic mass is the closest to its most
abundant isotope.
The Periodic Table

Elements are organized in the periodic table
by increasing atomic number.
The Periodic Table- Cont.

In the late 1800’s, Dmitri
Mendeleev derived the
first periodic table based
on atomic mass.
The Periodic Table- Cont.
The Periodic Table- Cont.

In 1913, Henry G. J.
Moseley arranged the
elements by atomic
number rather than
atomic mass.
The Periodic Table- Cont.

Vertical columns in the periodic table are
groups of elements with similar properties.


Elements with the same group have the same
number of electrons in their outer energy level.
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- Cont.
The Periodic Table- Cont.

Each row in the periodic
table ends when an outer
energy level is filled.
The Periodic Table- Cont.

Electron dot diagrams use the elements symbol
and dots to represent outer energy level
electrons.
The Periodic Table- Cont.

Periods- horizontal row 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- Cont.
The Periodic Table- Cont.

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.