chapter 2 atomic structure
TRANSCRIPT
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Life’s Chemical BasisChapter 2
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Elements• Fundamental forms of
matter
• Can’t be broken apart by normal means
• 92 occur naturally on Earth
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Most Common Elements in Human Body (98%)
Oxygen
Hydrogen
Carbon
Nitrogen
Calcium
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What Are Atoms?• Smallest particles that retain
properties of an element
• Made up of subatomic particles:
– Protons (+) located in the nucleus
– Neutrons (no charge) located in the nucleus
– Electrons (-) located in space around the nucleus
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Atomic Number(whole # on the periodic table)
• = the # of protons• All atoms of a specific element have
the same atomic #• Atomic # of hydrogen = 1• Atomic # of carbon = 6• Atomic # of helium = 2• If you change the # of protons, you
change the atom into a different element
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Atomic Mass (decimal # on the periodic table)
Number of protons
+Number of neutrons
So why is it a decimal number? You’ll soon
find out….
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What is the role of neutrons?
• Since protons have a + charge, they repel each other
• Neutrons are neutral and help to stabilize the nucleus – think police
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The Organization of the Periodic Table: Based on ELECTRONS!
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Why Electrons Matter
• Atoms acquire, share, and donate electrons
• Whether an atom will interact with other atoms depends on how many electrons it has
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Electrons
• Carry a negative charge• Also repel one another • Attracted to protons in the
nucleus• Move in volumes of space
that surround the nucleus
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Shell Model• The shell model of electron orbitals
diagrams electron vacancies, filled from inside out
• Each shell represents an energy level:– 1st shell: (2 electrons)– 2nd shell: (8 electrons)– 3rd shell: (8 electrons)
• Atoms with vacancies in their outer shell tend to give up, acquire, or share electrons
CALCIUM20p+ , 20e-
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Electron Vacancies
• Unfilled levels make atoms more likely to react with other atoms
• Hydrogen, carbon, and nitrogen are examples of elements with vacancies in their outer levels
CARBON6p+ , 6e-
NITROGEN7p+ , 7e-
HYDROGEN1p+ , 1e-
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Ion Formation• Atoms that lose electron(s),
become positively charged ions (cations)
• Atoms that gain electron(s), become negatively charged ions (anions)
• Electronegativity:– A measure of an atom’s
ability to pull electrons from another atom
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proton
neutron
electron
He
Atomic Structure: Helium
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N
Atomic Structure: Nitrogen
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HYDROGEN
electron
proton
neutron
Atomic Structure of Hydrogen
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Isotopes: What are They?• Atoms of an element with the SAME # of
protons, but a DIFFERENT # of neutrons
• The atomic mass # on the periodic table is an avg. mass of all the different isotopes possible for the element
• How do you figure out the number of neutrons in an atom? Atomic mass – atomic number = #
neutrons
“Carbon 12” has 6 protons, 6 neutrons
“Carbon 14” has 6 protons, 8 neutrons
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Special Isotopes: Radioactive Isotopes
• Have an unstable nucleus
that emits energy or some
of the subatomic particles
(protons or neutrons)• Some are used in research
and medical applications (pacemakers, radiation therapy, MRI)
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Radioactive Isotopes Can be Used as Tracers
• A tracer is a substance with a radioactive isotope attached to it
• Emissions from the tracer can be detected with special devices
• Following the movement of tracers is useful in many areas of biology and medicine
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Next Lecture…
Chemical Bonds!
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Lab 3: Making Conversions Between Various Lab 3: Making Conversions Between Various Measuring SystemsMeasuring Systems
• Purpose of this lab:
To become familiar with several systems of measurement and make conversions from one unit to another as well as learn to read syringes and graduated cylinders