Atomic Structure
Elements
All elements are composed of only one type of
atom. In these atoms are three subatomic
particles:
Protons
Neutrons
Electrons
Elements
-Protons have a positive charge (+)
-Neutrons have no charge (neutral)
-Electrons Have a negative charge (-)
• Most of the mass of an atom is found in the
nucleus which contains the neutrons and
protons.
Atomic number
• Atomic number tells you how many protons
that elements has.
• If the number of protons changes, the
element changes.
Atomic number
• Since the atom of an element is neutral, then
the atomic number also tells you how many
electrons you have.
Atomic # = # of protons = # of electrons
Atomic Mass
• Atomic mass is the total number of protons
and neutrons found in the nucleus of an atom.
• # of protons + #of neutrons = atomic mass
Neutrons
• To find out how many neutrons and element
has:
a) Round atomic mass to nearest whole number
b) Subtract atomic number from atomic mass to
get number of neutrons
Atomic Mass – Atomic Number = # of neutrons
Example
• Na (sodium)
• Atomic mass is 22.989
• Atomic mass rounded 23
• Atomic number is 11
Atomic Mass – Atomic Number = # of neutrons
• 23-11= 12
• Na has 12 neutrons.
Try these!!!
Co (Cobalt)
Ag (Silver)
• Atomic mass is
58.933
• Atomic mass
rounded 59
• Atomic number 27
• 59-27= 32
• Atomic mass is
107.868
• Atomic mass
rounded 108
• Atomic number 47
• 108-47 = 61.
Bohr’s model
• Is a physical drawing that shows where all the
subatomic particles are located in a particular
atom of an element.
• The Bohr’s model is similar to our very own
solar system.
Bohr’s Model
• Protons and neutron are always found in the
nucleus of the atom of an element.
• Electrons are around the atom in an area
called the electron cloud.
• In this electron cloud are orbitals where
electrons move around the nucleus of the
atom.
Bohr’s Model
• Each orbital can only hold a certain amount of
electrons:
• 1st orbital- 2 electrons
• 2nd orbital- 8 electrons
• 3rd orbital- 8 electrons
• 4th orbital- 18 electrons
• The elements found in a group have similar
properties because they have the same
number of valence electrons.
• The horizontal rows on the periodic table are
called a period. Periods tell you how many
orbitals will be on your drawing.
• Ex. Na (sodium) is in Period 3, it will have 3
orbitals in its Bohr’s Model.
• The vertical columns on the periodic table are
called groups. Groups tell you how many
valence electrons the element has.
• Ex. Na (sodium) is in Group 1 so it has 1
valence electron.
• Valence electrons are the electrons that
occupy the last orbital of an element.
• Orbitals are also called energy levels.
Boron (B)
5 p+
6n
Al
13 p+
14 n
Lewis-Dot Structure
• The amount of dots you draw for
a Lewis Structure (LS for short) is
equal to the # of Valence
Electrons in an Atom
Valence Electrons
• The # of Valence e- an atom
has is dictated by the Group
that the Element is in
• Groups are the Vertical
Columns on the Periodic
Table!!! It’s So Simple!!!!
• Isotopes are atoms of a given element that
have different numbers of neutrons and
different mass numbers.
• Ex. Oxygen-16; has 8 neutrons
Oxygen-17; has 9 neutrons
Oxygen-18; has 10 neutrons
These are all still oxygen atoms.
• Elements on the periodic table are classified
as one of the following:
• Metals
• Nonmetals
• Metalloids