Structure of the Atom
What’s in an Atom?
An Atom is the smallest part of matter. Matter is anything that takes up space.
What are Subatomic Particles?
Subatomic Particles are the smallest parts of an atom- Protons, Neutrons & Electrons
Subatomic Particle
Charge
Location
Mass
Proton
Positive
In the Nucleus
1 amu
Neutron
Neutral
In the Nucleus
1 amu
Negative
Orbiting around the
nucleus in a region
called the electron cloud
Extremely smaller
than 1 amu
Electron
Atomic structure of helium
nucleus
_
electrons
+
+
_
protons
neutrons
energy level
NOTE: If the atom is neutral, then the number of protons will be the same as the
number of electrons.
# of POSITIVES = # of NEGATIVES
# of PROTONS = # of ELECTRONS
4 protons = 4 electrons
Atomic #
Protons
Electrons
Same #
Understanding the Atom
What’s an Atomic Number?
 The number of protons in the nucleus of an atom is called the atomic number. The
atomic number identifies the element.
1
Ex:
H
All Hydrogen atoms have:
Atomic Number of _1_
_1 Protons
_1_ Electrons
1.008
Hydrogen
All Oxygen atoms have:
Atomic Number of _8_
8 Protons
_8_ Electrons
8
O
15.999
Oxygen
What’s the Atomic Mass of an Atom?
 The atomic mass is the average mass of an atom of a particular element. Atomic
mass is located on the element key and is written exactly as it appears on the
Periodic Table.
11
Na
22.990
Sodium
For example, sodium has an atomic mass of 22.990. This means that of
all the sodium atoms, they have an average mass of 22.990. Some
sodium atoms may have a larger mass and other sodium atoms may have
a smaller mass.
What’s the Mass Number of an Atom?
 The mass number is the sum of the protons and neutrons in a
nucleus of an atom.
 It is the Atomic Mass rounded.
4 protons
+ 5 neutrons
mass number 9
11
Na
22.990
Sodium
Rounded to
23
How can you determine the mass number of an element?
Example 1: Count the number of protons and neutrons and add them together.
4 protons
+ 5 neutrons
mass number 9
Example 2: Find the atomic mass on the periodic table. Round that number and it
becomes the mass number.
4
Be
9.012
Beryllium
9.012 rounds to 9
Mass Number = 9
How can you determine the number of neutrons of an element?
Example 1: Count them. (Remember that neutrons are located in the nucleus and are
neutral)
# of Neutrons = 5
Example 2: Find the mass number. Then subtract the Atomic Number (number of
Protons) from the mass number, this equals the neutrons.
17
Cl
35.453
Chlorine
Mass number
- Atomic number
Neutrons
Atomic mass rounded = mass number
35.453 rounds to 35
Atomic number = # of protons = 17
35
- 17 protons
18 neutrons
Electrons and Energy Levels
Where are electrons located?
 In the energy levels; this is a region around the nucleus.
 Also called
o Electron Cloud
o Orbital
o Shells
 Electrons move around the nucleus, but do not travel in a fixed path.
 Energy levels represent the most likely location of an electron in the electron
cloud.
 The location of the electron depends on how much energy it has.
- Electrons with the lowest energy are found in the energy levels
closest to the nucleus.
- Electrons with the highest energy are found in the energy levels
farther from the nucleus.
 Energy levels can hold only a certain number of electrons.
Nucleus contains protons & neutrons
_2_ electrons in the 1st shell
_8_ electrons in the 2nd shell
_8_ electrons in the 3rd shell
Why is the arrangement of the electrons important?
 The electron arrangement is what gives an element its chemical properties....
What are Valence Electrons?
 Electrons in the last energy level. They are used in chemical bonding. They
determines the elements bonding ability (what that element can bond with)
Structure of the Atom
What’s in an Atom?
What are Subatomic Particles?
Subatomic Particle
Charge
Location
Mass
Proton
Neutron
Electron
Atomic structure of helium
1.___________
_
4.___________
+
+
_
2.___________
3.___________
5.___________
NOTE: If the atom is neutral, then the number of protons will be the
same as the number of electrons.
# of ____________ = # of _____________
# of PROTONS = #of ELECTRONS
__ protons = __ electrons
A_____
P______
E______
S_______
Understanding the Atom
What’s an Atomic Number?
 The number of____________ in the nucleus of an atom is called the
atomic number. The atomic number ___________________________.
Ex: All Hydrogen atoms have:
Atomic Number of _____
_____ Protons
_____ Electrons
All Oxygen atoms have:
Atomic Number of _____
_____ Protons
_____ Electrons
1
H
1.008
Hydrogen
8
O
15.999
Oxygen
What’s the Atomic Mass of an Atom?
 The atomic mass is the _____________________ of an atom of a particular
element. Atomic mass is located on the element key and is written exactly as it
appears on the Periodic Table.
11
Na
22.990
Sodium
For example, sodium has an atomic mass of ____________. This means
that of all the sodium atoms, they have an average mass of 22.990. Some
sodium atoms may have a larger mass and other sodium atoms may have
a smaller mass.
What’s the Mass Number of an Atom?
 The mass number is the sum of the _______________and the _______________ in
the nucleus of an atom.
 It is the Atomic Mass __________________________
11
Na
22.990
Sodium
Rounded to
_______
How can you determine the mass number of an element?
Example 1: Count the number of protons and neutrons and add them together.
Example 2: Find the atomic mass on the periodic table. Round that number and it
becomes the mass number.
4
Be
9.012
Beryllium
How can you determine the number of neutrons of an element?
Example 1: Count them. (Remember that neutrons are located in the nucleus and are
neutral)
# of Neutrons = _____
Example 2: Find the mass number. Then subtract the Atomic Number (number of
Protons) from the mass number, this equals the ____________.
17
Cl
35.453
Chlorine
M___________
- A____________
N___________
Electrons and Energy Levels
Where are electrons located?
 In the __________________; this is a region around the nucleus.
 Also called
o __________________________
o _______________
o _______________
 Electrons move around the nucleus, but do not travel in a _______________.
 Energy levels represent the ____________________ of an electron in the
_______________________
 The location of the electron depends on how much
it has.
- Electrons with the __________ energy are found in the energy levels
____________to the nucleus.
- Electrons with the __________ energy are found in the energy levels
__________ from the nucleus.
 Energy levels can hold only a certain number of electrons.
Nucleus contains __________ & __________
____ electrons in the 1st shell
____ electrons in the 2nd shell
____ electrons in the 3rd shell
Why is the arrangement of the electrons important?
 The electron arrangement is what gives an element its _________________.
What are Valence Electrons?
 Electrons in the ______ energy level. They are used in ________________. They
determines the elements bonding ability (what that element can bond with)
Drawing Bohr Models:
1.
8
O
15.999
Oxygen
Example 2:
2.
15
P
30.974
Phosphorus