Atoms

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Atoms

• - the smallest unit of an element

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• Each element is made up of only one type of atom
  (the element Carbon is only made up of carbon
  atoms).
• Atoms are so small they cannot be seen with a
  microscope.

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Structure of the Atom

• The center of the atom is called the nucleus.

• The nucleus contains two types of particles
  protons and neutrons.

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Structure of the Atom

• Protons have a positive charge ().

• Neutrons have no charge. They are neutral.

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Structure of the Atom, contd

• Electrons are always moving or spinning around
  the nucleus, like planets orbiting the sun.

• The space where the electrons orbit is called the
  electron cloud.

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Structure of the Atom, contd

• Electrons have a negative (-) charge.

• Electrons are much smaller than protons.

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• The number of protons in an atom equals the
  number of electrons in an atom. Therefore an
  atom is electrically neutral.
• protons electrons
• What makes atoms different from one another is
  the number of protons, neutrons and electrons
  that they have.

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Structure of an Atom

• Label the picture of an atom using the following
  codes
• P Proton
• N Neutron
• E - Electrons
• Color the protons blue.
• Color the neutrons red.
• Color the electrons brown.
• Write the charges beside each one.

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Structure of an Atom
E

• Label the picture of an atom using the following
  codes
• P Proton
• N Neutron
• E - Electrons
• Color the protons blue.
• Color the neutrons red.
• Color the electrons brown.
• Write the charges beside each one.

o
N
P
P
N

o

E
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Atomic Number Atomic Mass
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• The periodic table includes each elements
• atomic number
• atomic mass
• symbol
• name

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Atomic Number

• The atomic number is the number of protons an
  element has.
• The periodic table lists elements in order by
  their atomic number.
• Remember, the number of protons is the same as
  the number of electrons.

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Atomic Mass

• The atomic mass (also called mass number) is the
  weight of one atom of the element.
• Atomic mass will also give you the average number
  of neutrons in the nucleus by the following
  formula
• protons neutrons atomic mass

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• What is the atomic number?

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• How many protons?

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• How many electrons?

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• What is the atomic mass?

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• How many neutrons?

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Isotopes

• All atoms of a certain element will always
  contain the same number of protons, however the
  number of neutrons can vary.
• Isotopes are atoms that have the same number of
  protons, but different numbers of neutrons.

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Isotopes

• Carbon-12 has 6 protons and 6 neutrons.
  Carbon-14 has 6 protons and 8 neutrons.
• The atomic mass is an average of the isotopes so
  is not always a whole number.
• Isotopes are useful in determining age of
  fossils, diets of animals, and origins of wood.

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Atomic Mass

• Scientists have chosen the most common isotope of
  carbon (carbon-12) as a reference.

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• An atom of carbon-12 is assigned a mass of 12
  atomic mass units (amu).
• The masses of all other atoms are compared with
  this mass.

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• One atomic mass unit is 1/12 the mass of a
  carbon-12 atom.
• The mass of an atom expressed in atomic mass
  units is called its atomic mass.

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• The atomic mass of an element found in the
  periodic table is actually calculated from the
  masses of the elements isotopes.
• It is a weighted average of the masses of the
  isotopes you must take into consideration the
  percent abundance of each element.

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• Example
• There are two isotopes for lithium lithium-6
  makes up 7.4 of all lithium atoms and lithium-7
  makes up the other 92.6.
• Calculate the average atomic mass.

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• SOLUTION
• (6amu x 0.074) (7amu x 0.926) 0.44 6.482
• 6.922 6.9amu

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• Now its your turn