isotopes. are all atoms of an element the same? not necessarily. some atoms have an unequal number...
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Isotopes
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•Are All Atoms of an Element the Same?• Not necessarily. Some atoms have an unequal number of protons and neutrons. We call these atoms isotopes.
• In an isotope, the number of protons in an element always remains the same. The neutrons change.
• Let’s look at an example…
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How are they different?
Proton
Electron
Proton
Electron
This is a Hydrogen Atom This is a Hydrogen Atom Isotope
Neutron
The isotope has 2 particles which means it has greater mass.
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Properties of Isotopes
•Each element has a limited number of isotopes that occur naturally
•Some isotopes have unique properties because they are unstable
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Properties of Isotopes
•An atom that is unstable means that the nucleus has the ability to change the numbers of neutrons that are in the nuclear space.
• Isotopes that are unstable are also called radioactive.
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Properties of Isotopes•Simply stated…Isotopes share almost all of the same physical and chemical characteristics.
• For example, Oxygen isotopes are colorless, odorless gases at room temperature (physical).
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How Can We Tell One Isotope from
another?•Each element has a mass number which identifies the isotope of the element.
•Mass number = protons + neutrons in an atom
•Electrons have such small mass they are not included in this calculation
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Naming Isotopes• Let’s go back to our earlier example of the hydrogen atom and the hydrogen isotope.
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Name That Isotope!
Proton
Electron
Proton
Electron
There is 1 proton and 0 neutrons so the name of this
atom is Hydrogen-1
There is now 1 proton AND 1 neutron so the name changes
to Hydrogen-2
Neutron
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So How Do I Figure Out The Number of Protons And Neutrons?•As an example, we’ll look at the carbon isotope, with a mass number of 12 (found on the Periodic Table) It’s called Carbon-12.
Mass Number 12
- # Protons (atomic number) -6 Number of neutrons 6
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Try One• Determine the number of protons, neutrons, and electrons in an aluminum-27 (Al).
• 13 protons, 14 neutrons, and 13 electrons
• How did we get the number of electrons?
• It’s the same as the number of protons.
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Let’s Try One!•Use what you know about Carbon-12 to create Carbon-13.
•Using your Periodic Table • create Hydrogen-2 (H), Helium-3 (He), and Carbon-14 (C).
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Where Have I Heard Carbon-14 Before?
•The isotope carbon-14 is used in radio-carbon-dating of animal and plant fossils.
•Uranium-238, uranium-235, and thorium-232 are isotopes that scientists use to tell the age of rocks and meteorites.
BrainPOPIsotopes
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Calculating the Mass of an Element•Most elements found in nature contain a mixture of two or more stable (nonradioactive) isotopes
•The Atomic Mass is the average of the masses of all the naturally occurring isotopes of an element.
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Let’s try it!•The metal thallium occurs naturally as 30 percent thallium-203 and 70 percent thallium-205. Calculate the atomic mass.
204.4 amu