KMS 8th grade science
 The
smallest piece of an element that still
represents that element.
 The
atom is made up of two main parts
Electron Cloud
Nucleus
A
small area in the center of an atom

Responsible for most of the atom’s mass
Contains positive charge

 Contained
in the nucleus:
protons
neutrons
Larger than electrons
 Charge: Positive
 Location: Nucleus
 Size:
 Atomic
Mass Unit (amu) = 1 amu
 Size:
About the same size as a proton
 Charge:
Neutral
 Location: Nucleus
 Atomic
Mass Unit (amu) = 1 amu
 Size:
Much smaller than protons and neutrons
 Charge:
 Location:
 Atomic
Negative
Electron Cloud
Mass Unit (amu) = 1/1,840 amu
 The
number of protons located in the atom’s
nucleus.
 Turn
to the periodic table in your text
book…can you find the atomic number in the
following element boxes?



Oxygen
Potassium
Gold
number of protons of the same element
will always be the same
 However, atoms of the same element can
have a different number of neutrons
 For example: every carbon atom has 6
protons, however some have 6, 7, or 8
neutrons.
 The
 Isotopes
- atoms of the same element that
have different numbers of neutrons.
 Most
elements have several isotopes.
 The
 The
sum of protons and neutrons in an atom.
average mass of the element’s isotopes,
weighted according to the abundance of
each isotope.
average atomic mass is weighted
and
based on each isotope’s abundance on Earth
 The
 Approximately
99% of Earth’s carbon is Carbon-12
which is why carbon’s average atomic mass is
close to 12 (12.01)
 Pure
substance made of only one type of
atom
 A substance made from atoms that all have
the same number of protons.
Element
Carbon
6
Symbol
Atomic
Number
C
12.01
Atomic
Mass
 Arranged
by: Dmitri Mendeleev (1834-1907)
 Arranged
in order of: Increasing atomic mass
 Periodic- Describes something that occurs or
repeats in regular intervals.
The three main regions of elements on the
periodic table classify elements as
Metals, nonmetals, or metalloids
 The vertical
(up and
down) columns of the
periodic table are called
groups or families
 There
are 18 groups
 Elements
in the same
group or family have
Similar chemical and
physical properties
 The
horizontal rows of the periodic table
are called periods
 Elements in a period are not alike in properties
 The
first element in a period is usually an
active solid , and the last element in a
period is always an inactive gas .
 Atomic
number (number of protons)
increases from left to right across a period
 Atomic
mass (number of protons +
neutrons) increases from left to right across a
period
 Metals
are on the left
 Non-metals
are on the right
 Different
electrons within an atom have
different amounts of energy
 An
electron moves around the nucleus at a
distance that corresponds to the amount of energy it has.
 Electrons closest to the nucleus have the
least amount of energy.
 Electrons furthest from the nucleus have the
most energy.
Electron Energy Levels
charged electrons are strongly
attracted to positively charged nucleus of an
atom.
 Negatively
 These
OUTERMOST electrons can easily be
attracted to the nucleus of other atoms
 We
call these OUTERMOST electrons valence electrons
 Valence
Electrons - outermost electron of an
atom that participates in chemical bonding.
 These
attractions are what cause chemical bonds