Download Drawing Bohr Atoms An atom consists of a dense nucleus

Drawing Bohr Atoms
An atom consists of a dense nucleus surrounded by electrons moving in space.
Nucleus
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A nucleus is made of protons and neutrons
o
Protons and neutrons both have a mass of 1 µ
o
Protons have a positive charge(+), neutrons have no charge
The total mass of the atom is equal to the mass of the protons and
neutrons in the nucleus
If an atom were the size of a football stadium, the nucleus would be the size
of a marble.
o
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The atomic number of an atom is equal to the number of protons in the
nucleus
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The atomic mass is expressed in atomic mass units (µ) and is the sum of the
number of protons and neutrons.
Electrons
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Electrons travel around the nucleus in specific paths called shells or orbits.
o
Shells exist whether there is an electron in them or not.
o
Electrons occupy certain shells depending on the atom. For example,
hydrogen has a single electron in the first shell; Sodium has two in the
first shell, eight in the second shell and one in the third shell.
o An atom can have a maximum of two electrons occupying the first
shell, eight in the second shell and eight in the third shell. We will not
study the structure of atoms with more than three levels of shells.
Each shell must be filled before electrons occupy the next one.
o
Electrons are so light they are considered to have zero mass Electrons have a negative electric charge (-).
Drawing a Bohr Atom
Example: Nitrogen
The following steps will help you draw Bohr atoms.
1. Determine the number of protons, neutrons and electrons in the atom.
Number of protons = atomic number = 7 protons
Number of neutrons = atomic mass - atomic number = 14 - 7 = 7 neutrons
Number of electrons = number of protons = 7 electrons
2. Draw a small circle to represent the nucleus of the atom.
3. Label the number of protons and neutrons in the nucleus
4. Draw a larger circle around the nucleus and place two tiny circles
representing electrons opposite each other on the larger circle. A maximum
of two electrons is allowed in the first shell.
5. Draw another, larger, circle around the one already there and place
electrons on it. The electrons should be equally spaced. A maximum of eight
electrons is allowed in the second shell. Remember, the number of electrons
is equal to the number of protons (atomic number) in an atom.
If needed, draw a third shell larger than the second. The third shell can also hold a
maximum of eight electrons. You will not be asked to draw Bohr atoms with more
electrons than three shells.
Adapted from Manitoba Education – Grade 9 Science - WebCT