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Atoms Each element on the periodic table has an atomic number, which tells how many protons an atom of that element has. Each element also has an mass number. Mass number = # of Protons + # of Neutrons
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Introduction to Atoms, Ions and Isotopes
What are atoms?• The atom is a basic unit of
matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons.
• While all atoms have protons, neutrons and electrons, atoms of different elements have different numbers of these.
Atoms• Each element on the periodic table
has an atomic number, which tells how many protons an atom of that element has.
• Each element also has an mass number.
• Mass number = # of Protons + # of Neutrons
Electrons• Neutral atoms have the same
number of electrons (negative charge) as they do protons (positive charge).
• # of electrons = atomic number
• ONLY IN NEUTRAL ATOMS
Let’s Practice!• Find Boron on the periodic table.• How many protons does an atom of Boron
have?• How many neutrons?
– Assume the mass number is 11• How many electrons?
Ions• An atom or small molecule with an
overall positive or negative charge due to an imbalance of protons and electrons.– # of protons does not change– # of electrons changes.– Positive charge = loss of electrons– Negative charge = gain of electron
Ions Continued…• Ions are represented by a superscript
charge on the element symbol.– Examples: F-, Mg2+, Al3+
Practice:• How many protons, neutrons, and
electrons does Al3+ have?
Isotopes• All neutral atoms of the same
element have the same number of protons, and therefore the same number of electrons.
• The number of neutrons CAN vary.• Isotopes: atoms of an element
that have the same number of protons, but a different number of neutrons.
Average Atomic Mass• The mass shown on your periodic
table as a decimal is the average atomic mass.– Average mass of all isotopes of an atom
in nature.
Example: Lithium• 2 Isotopes are found in nature:
Lithium-6 and Lithium-7 (Lithium-8 is radioactive and quickly decays)
• Atomic mass is listed as 6.94.• How is that possible?
– 94% of Li atoms have an atomic mass of 7, and 6% have an atomic mass of 6.
– Avg. Atomic Mass = (7 x .94) + (6 x .06)
Let’s Review!• ________ are charged atoms.
– _________ ions have LOST electrons.– _________ ions have GAINED electrons.
• An atom of Cu2+ with mass number 63 has:– ________ protons– ________ neutrons – ________ electrons
More Review• ____________ are atoms of the same
element that have different numbers of neutrons in the nucleus.
• What does average atomic mass represent?
Complete Atomic Structure WS #1 Front and Back
Hint: Chromium-52 means Chromium with a mass number of 52. 26Fe means
iron with atomic number 26.
Related Book Work
• Read section 5.1• Pg. 134-143• Answer the following questions on
page 162 1-3, 6, 7, 29, 31, 32, 38, 65, 71-76.
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