Exploring InnerExploring Inner
TEKS 8.5A describe the structure of atoms including the masses, electrical charges and
locations, of protons and neutrons in the nucleus and electrons in the electron cloud
TEKS 8.5B identify that protons determine an element’s identity and valence electrons
determine its chemical properties, including reactivity
Each element on the Periodic
Table is made of the same
kind of atom.
Each atom in anEach atom in an
element has theelement has the
same number ofsame number of
The number of protons presentThe number of protons present
in the atom is what determinesin the atom is what determines
thethe element’s identity and isand is
shown by theshown by the atomic number.
On your Periodic Table, fill in thisOn your Periodic Table, fill in this
# protons = element’s identity = atomic
Atoms are made up ofAtoms are made up of
Each particle in the atomEach particle in the atom
has specific properties,has specific properties,
such as location,such as location,
electric charge andand
Since each proton andSince each proton and
neutron in the nucleus has aneutron in the nucleus has a
mass ofmass of 11 atomic mass unitatomic mass unit
(amu), we can(amu), we can add thethe
number of protons andnumber of protons and
neutrons together to findneutrons together to find
thethe atomic mass..
Fill in this information on yourFill in this information on your
Periodic Table!Periodic Table!
# protons + # neutrons = atomic
How many protons are in
the element lithium?
Lithium has 4 neutrons,
what is its atomic mass?
The Periodic Table showsThe Periodic Table shows
the mass for each elementthe mass for each element
as aas a decimal. When we use. When we use
the atomic mass to findthe atomic mass to find
the number of protons orthe number of protons or
neutrons, weneutrons, we round thethe
mass number.mass number.
If the mass number isIf the mass number is
known, and you know theknown, and you know the
number of protons, how cannumber of protons, how can
you find the number ofyou find the number of
neutrons?neutrons?Mass # -Mass # - #protons = #neutrons= #neutrons
fill in this information onfill in this information on
your Periodic Tableyour Periodic Table
Atomic mass - # protons = # neutrons
Surrounding the nucleus is an
area called the electron cloud.
Inside the electron cloud,
electrons orbit around in
different energy levels.
The electrons are so small
that they basically have no
mass, so they are not
included in finding the
As a general rule, each energy levelAs a general rule, each energy level
only holds so many electrons at aonly holds so many electrons at a
given time.given time.
TheThe first energy level, which isenergy level, which is
closest to the nucleus, holds up toclosest to the nucleus, holds up to 2
TheThe second energy level holds up toenergy level holds up to
TheThe third energy level may holdenergy level may hold 8 oror
How many electrons are
in each energy level of
the element Lithium? 1st
– 2, 2nd
By numbering the periods
(rows) on the Periodic Table,
you can determine how many
energy levels are in an atom.
For example, Lithium is in
period 2, therefore it has 2
energy levels.Number the first three periods on your
How many energy
levels does sodium
Period 3, 3 energy levels
Valence ElectronsValence Electrons
The numbers of electrons
in an atom’s outermost
energy level are called
These electrons areThese electrons are
important because theyimportant because they
determine howdetermine how reactive thethe
element is with otherelement is with other
For example, Lithium has only 1
valence electron. Since the
second energy level may hold up
to 8 electrons, Lithium would
need 7 additional electrons in
order for its outermost energy
level to be filled. But, it is
easier for Lithium to give away 1
Charges on particlesCharges on particles
Protons carry aProtons carry a positive electricelectric
Electrons carry aElectrons carry a negative
electric charge.electric charge.
Neutrons haveNeutrons have no charge.charge.
The most stable form of an
atom is electrically
neutral. This means that
the number of protons and
electrons is equal.
For example, look at the
element oxygen. Oxygen is
atomic number 8, which
means it has 8 protons (+).
Therefore, in a stable
oxygen atom, there are 8
electrons (-). The positive
and negative charges are
Look at your
Find the element
How many positive
does carbon have?
How many negativeHow many negative
charges (electrons)charges (electrons)
does carbon have?does carbon have?
What is the mass of carbon?
How can the number of neutrons
(atomic mass - # protons = # neutrons)
Carbon has 6 neutrons.
Write this on your Periodic
Atomic mass - # protons = # neutrons
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