Transcript Document

Chapter 4 & 5 Review
7/7/2015
Structure of Matter
Students know the structure of the atom
and know it is composed of protons,
neutrons, and electrons.
 Students know how to use the periodic
table to identify elements in simple
compounds.
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Periodic Table
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Students know how to identify regions
corresponding to metals, nonmetals, and inert
gases.
Students know each element has a specific
number of protons in the nucleus (the atomic
number) and each isotope of the element has a
different but specific number of neutrons in the
nucleus.
Students know substances can be classified
by their properties, including their melting
temperature, density, hardness, and thermal
and electrical conductivity.
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Atomic Theory
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As new discoveries were made, the atomic
model changed
– Dalton simple sphere theory
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Basics model still holds true
– Thompson – plum pudding model (1897)
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Electrons floating around in positive pudding
– (Muffin in some descriptions)
Rutherford – gold foil experiment (1911)
– Atoms positive charge concentrated in “nucleus”
– Electrons orbiting at a great distance
– Bohr (1913)
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Electrons in fixes energy orbits around nucleus
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Atomic Theory
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Cloud model (1920).
– Energies of electron orbits not fixed, rather a
spectrum of possible energies within a cloud.
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Modern atomic model.
– Chadwick (1932) discovers a new particle.
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Neutron.
Mass equal to proton.
No electrical charge (neutral).
– Atom now seen as small, concentrated nucleus of
protons and neutron, surrounded by a cloud of
negatively charged electrons.
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Subatomic Particles, Mass,
and
Scale
 Protons
– Positive charge (+1), 1 atomic mass unit (amu)
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Neutrons
– No charge (neutral), 1 atomic mass unit (amu)
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Electrons
– Negatively charged (-1)
– 1/1836 atomic mass unit (~ 0 amu)
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Scale
– Diameter of electron cloud ~ 100,000 times diameter
of the nucleus
– 1 INCH nucleus = 1.6 MILE electron cloud
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Periodic Table
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Mendeleev
– First table constructed by increasing mass.
– Rearranged the elements (63) according to
observable properties.
– Recognized the periodic repetition of many of these
properties.
– Predicted the existence of three new elements.
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Periodic Table
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Modern table
– Now contains 118 known elements
– Seven periods
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Rows from left to right
– Eighteen groups
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Columns of up to eight elements with similar properties
– Constructed by increasing atomic number
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Number of proton in the nucleus
Determines the nuclide identity
Carbon = 6, nitrogen = 7, oxygen = 8 , etc.
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Periodic Table
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Modern table characteristics
– Atomic mass increases
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As you move down
As you move right
Basic information
– Atomic number
– Chemical symbol
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One or two letters (except for un-named elements)
– Element name
– Atomic weight
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Periodic Table
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Metals
– Majority of periodic table
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Ductile (drawn into wire), malleable (hammered into sheet).
Hard, conductive (electricity / heat)
Chemically reactive, generally losing electrons in reactions
Six basic groups
– Alkali metals (group 1)
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Li, Na, K, Rb, Cs, Fr
– Highly reactive,
– Loses one electron during reactions
– In nature only found in compounds, never as pure
element
– Na, K most important examples
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Periodic Table
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Metals
– Alkali earths (group 2)
 Be, mg, ca, Sr, Ba, Ra
– Less reactive than alkali metals,
– Loses two electron during reactions
– In nature, only found in compounds, never as pure
element
– Ca, most important example, needed for many body
functions
– Transition metals (group 3-12)
 Fe, Ag, cu, & Ni some common examples
– Hard and shiny,
– Good conductors
– Less reactive from left to right within a period
– Many used in colorful pigments (cobalt blue, chromium
green, & cadmium red)
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Periodic Table
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Metals
– Mixed group (group 13-15)
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Al, Ga, in, Tl, Sn, Pb, bi
– Minimal reactivity,
– In nature, only found in compounds, never as pure element
– Tin, lead aluminum common example
– Lanthanides
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Period six elements
– In nature, often found in compounds with other lanthanides,
never as pure element
– Often used to alloy other metals
– Sc, & Y (gr3) show similar properties, included in rare earths
– Rare earth neodymium make exceptionally strong magnets
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Periodic Table
– Actinides
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Ac, Th, pa, & U only natural actinides
– All element heavier than U are synthetic
– Uranium used to fuel nuclear power plants
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Synthetic elements
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Using powerful nuclear particle accelerators, scientist have
created element 93 - 118
– Many exist only in the lab, with half-lives < nanosecond
• 10 –9 seconds
• 0.000000001 seconds
– First synthetic element, curium (cm, named after madam
curie) created in 1940 in Chicago by Seaborg
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Periodic Table
– Non-metals
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DO NOT exhibit the characteristics of metals
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Non or semi conductive
Dull
Brittle
Gain or share electrons in reactions
Seven groups or “families”
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Periodic Table
– Carbon family
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C, Si, Ge, Sn, Pb
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4 electrons to share in reactions
C is only non-metal
Si & Ge are semi-metals or “metalloids”
Sn & Pb are metals
– Nitrogen family
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N, P, as, Sb, bi
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3 electrons to share in reactions
N & P are non-metals
As & Sb are semi-metals or “metalloids”
Bi is a metal
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Periodic Table
– Oxygen family
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O, S, se, Te, Po
– 2 electrons to share in reactions
– CO, S, & se are non-metals
– Te & Po are semi-metals or “metalloids”
– Halogen family
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F, Cl, Br, I, at
– 1 electron to share in reactions
– F, Cl, Br, I are non-metals
– At is only semi-metal or “metalloid”
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All are highly reactive, combining with many other
elements to form various salts (HF, HCl)
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Periodic Table
– Inert gases
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He, Ne, Ar, Kr, Xe, Rn
– Often referred to as “noble gases”
– Very non-reactive
– He, lighter than air used in balloons, “neon” lights often
filled with one or more of other inert gases
– Hydrogen
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Alone in the upper left, due to its unique atomic structure and
chemical properties, hydrogen is not included in any group
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90% of all the atoms in the universe are hydrogen
< 1% of earths mass is comprised of hydrogen
Rarely found as pure element
Most hydrogen on earth is in form of H20
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Periodic Table
– Semi-metals
 B,
Si, Ge, as, Sb, Te, Po, at
– Included in groups 13-17
– Si is most common
• Sio2 is primary component of sand & glass
– Si, Ge, & as conduct electricity under specific
condition (varied by temperature, light
exposure, impurities) allowing them to be used
as “semi-conductors”
– Semi-conductors are a crucial part of the
computer, transistor, and laser industries.
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Periodic Table
– Radioactive elements
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Henri Becquerel
– Discovered radioactivity accidentally while studying ore
containing uranium.
– Exposed photographic plates had Becquerel looking for
the source of energy
– Shared information with Marie and Pierre curie
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Madam curie
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Energy originated in the uranium nuclei
Energy emission was spontaneous
Madam curie called the phenomenon radioactivity
Also discovered polonium and radium, each more
“radioactive” than uranium
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Radioactive Decay
As elements emit radiation, they are
transformed into different nuclides
or isotopes.
As they are no longer the original
element, the number of original
atoms gradually decreases – or
decays away
http://www-nds.iaea.org/relnsd/vchart/index.html
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Radioactive Decay
– Three main types of decay
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Alpha emission ()
– Helium nucleus ejected from nucleus of very heavy
atoms – called an “alpha” particle
– Very high energies, > 5 MeV. Very large mass, (4
amu). Large charge (+2), short range
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Beta emission (b)
– Neutron converts to proton within nucleus, electron
emitted from nucleus
– Moderate energy (KeV), small mass (1/1836 amu),
moderate charge (-1), moderate range
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Radioactive Decay
– Gamma emission (g)
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Energetic nucleus emits a high frequency electromagnetic
wave.
Infinite energies are characteristic of the isotope
No mass, no charge, range can be infinite
Similar to x-ray, which originate from the electron clouds of
atoms
– Shielding
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Alpha – single sheet of paper
Beta – thin sheet of aluminum
Gamma – thick concrete block or lead walls
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Radioactive Material Use
– Medical
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Diagnostics
– Tracers and image enhancers
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Treatment
– Radioactive implants,
– Cocktails,
– Direct exposure (gamma knife)
– Industrial
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Instrumentation (density and thickness gauges)
Radiography (metallurgic e-rays)
Biologic process tracers
– Utility
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Fuel for nuclear power stations
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