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Atomic Notes
The Structure of Matter (key points)
• Matter is anything that has mass and takes up space.
• All matter is made of minute particles known as atoms. Atoms are composed of protons, neutrons and
electrons.
• An element is a substance made up of only one type of atom.
• Atoms can react with other atoms to form compounds. A compound is made up of two or more different
types of atoms.
• Both before and after a chemical reaction, the number of atoms and the total mass stay the same.
Atoms and their subatomic particles
• All matter is made up of minute particles called atoms. Scientists see these atoms as the basic building
blocks of matter.
• The three most important part of these particles are: Protons, Neutrons and Electrons
Protons
• The proton is a particle with a (+) positive electrical charge and a mass of 1 atomic mass unit (amu).
• Protons are located inside the nucleus of the atom.
• The nucleus is the dense center of the atom.
Neutrons
• The neutron is a neutral particle with no electrical charge.
• It has approximately the same mass as the proton (1 amu).
• Neutrons are located in the nucleus of an atom.
Electrons
• Electrons are small particles with a negative (-) electrical charge.
• They move around the nucleus at very high speeds.
• They have no significant mass.
• Scientists believe that electrons move in different energy levels (shells) around the nucleus in the
electron cloud.
Apply what you have learned
Atomic Electrical Location
Mass
Charge in atom
• Proton:
_______ _______ ________
• Neutron:
_______ _______ ________
• Electron:
_______ _______ ________
Model the structure of an atom that has 3 protons, 4 neutrons and 3 electrons. Label the protons, neutrons,
electrons and nucleus in your drawing. What element is this? _________________
Atomic Symbols
• To identify each type of atom, or element, scientists use a symbol of one or two letters, based on its
name.
• The first letter is capitalized, but not the second.
• For example, the symbol for hydrogen is H, and the symbol for carbon is C. The symbol for helium is
He, and iron is Fe.
Atomic Numbers – use Periodic Table
• Every type of atom has its own unique atomic number. This equals the number of protons each atom of
the element has. For example:
 Hydrogen has an atomic number 1. This means that hydrogen has 1 proton.
 Helium has an atomic number of 2. this means helium has 2 protons.
 Carbon has an atomic number of 6 because it has 6 protons.
Lithium Element - Periodic Table example
Now you try
Look at your periodic table. What are the following atomic numbers, # of protons?
1. Oxygen –
2. Aluminum –
3. Boron –
4. Krypton –
5. Gold Electrical charge
• When an atom is not combined with other atoms, it is electrically neutral. This means it has no
electrical charge.
• This is because an uncombined atom ALWAYS has the same number of (+) charged protons and (-)
charged electrons.
• So…the atomic umber also tells us the number of electrons in that atom.
Use this to help you remember…
Ions
•
•
When atoms of one element combine with atoms of another element to form compounds---atoms
sometimes give away of take electrons from one another.
When an atoms does this, it is now called an ion and takes on a positive (cation) or negative (anion)
charge.
Atomic Mass
• Scientists measure the mass of an atom by its atomic mass units.
•
•
The two particles with mass in an atom are its protons and neutrons. (An electron has almost no
significant mass.)
To determine the mass of a single atom – the amount of matter it contains – scientists simply add the
number of its protons and neutrons together.
Now you try it!
Look on your periodic table. Do you see where the number of protons and neutrons have been added together?
What is the atomic mass of:
1. Carbon – ______________
2. Neon – _______________
3. Silver - _______________
How can we tell the number of neutrons?
• The atomic mass is the number of protons PLUS neutrons. The atomic number is the number of protons.
Simple math from there….
• Atomic mass – atomic number = number of neutrons
Let’s figure some out…
Atomic mass minus atomic number = #N
• Lithium  7-3 =
• Sodium  23 – 11 =
• Chlorine  35-17 =
• Radon  222 – 86 =
Atomic Mass
Let’s just address why Hydrogen is a freak and get it over with …
1. Hydrogen has 1 proton and 1 electron – it has the atomic number 1.
2. Hydrogen has an atomic mass of 1.008. That number is protons + neutrons. 1 proton has a mass of
1amu….that means hydrogen does not have a neutron.
3. Furthermore, it is a non-metal on the wrong side of the table.
Show me what you know!
1. An atom of nickel has an atomic number of 28. It has an atomic mass of 59.
• How many:
1. Protons
2. Neutrons
3. Electrons
2. Why do atoms of elements have neutral charges?
A. All atoms contain neutrons which have no charge
B. The number of protons and the number of neutrons are equal.
C. The number of protons and the number of electrons are equal.
D. The number of electrons and the number of neutrons are equal.
3. What region of the atom determines the volume of the atom?
A. The nucleus because it is extremely dense.
B. The nucleus because almost all of an atom’s mass is located there.
C. The electron cloud because it is very dense.
D. The electron cloud because almost all of an atom’s mass is located there.
4. The opposite charges of which two subatomic particles result in the attractive force between the nucleus and
the electron cloud of an atom?
A. Element and atom
B. Proton and neutron
C. Neutron and electron
D. Proton and electron
5. Where are electrons with less energy found?
A. On energy levels closer to the nucleus
B. On energy levels farther from the nucleus
C. On energy levels directly inside the nucleus
D. On energy levels between the nucleus and electron cloud
6. An atom of nitrogen has 7 protons, 7 electrons and 7 neutrons. What is its atomic mass and atomic number?
Draw here