Lesson 2 Matter
Periodic Table and Atomic Structure
All atoms have the same basic structure, but how do atoms of different elements differ?
B2.35 Stylized model of an atom
An atom is made up of three particles: electrons, protons, and neutrons. Electrons have a negative charge, protons have a positive charge, and neutrons have no charge—they are neutral. Due to the presence of an equal number of negative electrons and
positive protons, the atom as a whole is electrically neutral.
The protons and neutrons (collectively called nucleons) are located in a small nucleus at the centre of the atom. Due to the presence of protons, the nucleus is positively charged.
The protons and neutrons (collectively called nucleons) are located in a small nucleus at the centre of the atom. Due to the presence of protons, the nucleus is positively charged.
Watch This
What Is an Atom? @ YouTube MonkeySee
This video is a good summary of the structure of the atom.
Periodic Table and Atomic Structure
Now that you understand the basic structure of an atom, let’s look at how different elements are structured. Throughout this course, we will use a modified Bohr model to help visualize the structure of the atoms of the first 20 elements.
Here is the structure of the modified Bohr model.
Here is the structure of the modified Bohr model.
B2.36 Modified Bohr model of an atom
A special name is given to the last energy level that contains electrons; it is called the valence energy level. This concept will be very important later on when we talk about the bonding of atoms to form compounds.
In order to model an element using the modified Bohr diagram, there are three key pieces of information that are needed: the number of protons, the number of electrons, and the number of neutrons. This information is readily available from the periodic
table found in your data booklet. If you do not have a copy of the Science 10 data booklet, please contact your teacher.
Key information about the composition of atoms is listed on the periodic table.
Key information about the composition of atoms is listed on the periodic table.
B2.37 Legend of the periodic table
Some of the information is self-explanatory, such as element name and symbol. The following clarifies the other terms and information.
The atomic number is the number of
Examples
Click on the video beside each example to see a teacher work through the example.Example 1: An atom is found to have 35 protons in its nucleus. What element is this atom? https://adlc.wistia.com/medias/5opgb5dlc9
Bromine
Atomic molar mass
Isotopes are different forms of the same element. They differ by having a different number of neutrons. We will discuss this concept in more detail later on.
Mass number,
Using mass number and atomic number, you can calculate the number of neutrons in an isotope.
The symbol of an isotope is slightly different, as it specifies the mass number and the number of protons for that specific isotope.
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Symbols for the two stable naturally occurring isotopes of nitrogen are
«math»«mstyle mathsize=¨24px¨»«mmultiscripts»«mo»§#160;«/mo»«mprescripts»«/mprescripts»«mn»7«/mn»«mn»14«/mn»«/mmultiscripts»«mi mathvariant=¨normal¨»N«/mi»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«mmultiscripts»«mo»§#160;«/mo»«mprescripts»«/mprescripts»«mn»7«/mn»«mn»15«/mn»«/mmultiscripts»«mi mathvariant=¨normal¨»N«/mi»«mo»§#160;«/mo»«/mstyle»«/math»
The element name of a specific isotope is also slightly different, as it includes the mass number of that isotope.
For example, nitrogen consists of two stable isotopes that are named nitrogen-14 and nitrogen-15.
Digging Deeper
Some isotopes are extremely important, such as the isotope carbon-14, which is used for carbon dating. Watch this video.
B2.42 Fossils
This website identifies all of the isotopes for each element on an interactive periodic table.
Learn More
You may wonder why the atomic molar mass is listed as 14.01 on the periodic table when the two isotopes have mass numbers of 14 and 15; shouldn’t the average be 14.5? But remember that it is based on percent abundancy. Of all the naturally occurring nitrogen, approximately 99.6% is nitrogen-14 whereas approximately only 0.4% is nitrogen-15.
Examples
Click on the video beside each example to see a teacher work through the example.
B2.40 potassium from the periodic table
The atomic number represents the number of protons. An atom is neutral, so it will have the same number of electrons.
Protons = 19 and electrons = 19
Determine the number of neutrons by subtracting the number of protons (atomic number) from the mass number.
Number of Neutrons = Mass Number – Atomic Number
Number of neutrons = 41 – 19
Number of neutrons = 22
Protons = 19 and electrons = 19
Determine the number of neutrons by subtracting the number of protons (atomic number) from the mass number.
Number of Neutrons = Mass Number – Atomic Number
Number of neutrons = 41 – 19
Number of neutrons = 22
Example 2: Identify the number of protons, electrons, and neutrons in an atom of copper-65. https://adlc.wistia.com/medias/7syc003bpb
B2.41 copper from the periodic table
The atomic number represents the number of protons. An atom is neutral, so it will have the same number of electrons.
Protons = 29 and electrons = 29
Determine the number of neutrons by subtracting the number of protons (atomic number) from the mass number.
Number of Neutrons = Mass Number – Atomic Number
Number of neutrons = 65 – 29
Number of neutrons = 36
Protons = 29 and electrons = 29
Determine the number of neutrons by subtracting the number of protons (atomic number) from the mass number.
Number of Neutrons = Mass Number – Atomic Number
Number of neutrons = 65 – 29
Number of neutrons = 36
The ion charge and ion name are very important and will be discussed more in Section 2 of this unit.