The Atom
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Transcript of The Atom
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The AtomReview Class #1
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Greeks◦ Matter is made up of tiny, discrete particles
Fire, Earth, Wind, Water Boyle
◦ Found gold and silver as being elemental Dalton’s Theory
◦ All elements are composed of indivisible atoms◦ All atoms of a given element are identical◦ Atoms of different elements are different, that is,
they have different masses◦ Compounds are formed by the combination of
atoms of different elements
Theories of the Atom
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JJ. Thomson◦ Cathode ray tube to show smaller units make up atom◦ Light ray deflected in a magnetic field◦ Came up with idea of electrons
PLUM PUDDING MODEL Nucleus
◦ Rutherford Bombarded atom with alpha particle Alpha particle got deflected Concluded atoms have a dense core – NUCLEUS
Because particles repelled, nucleus must be positive too Also concluded atom is mostly empty space
Electrons are distributed in the empty space
Experimental Parts of Atom – pg .3
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Bohr◦ Dense nucleus◦ Electrons found in orbits
Electrons have required energy to keep them in orbit Not too much or too little Called this the planetary model
Wave Mechanical Model – modern model◦ Energy and matter can act as waves and particles
Solar panels◦ Dense positive center◦ Electrons are in “regions of probability”
Modern Atomic Model
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RB pg. 4, 1-12
Questions
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Nucleus contains 2 types of particles◦ Neutrons and protons
This is where the mass comes from Subatomic particles
◦ Mass of a proton is found on 1st page of reference tables
◦ 1 amu = mass of a proton = mass of 1 proton◦ Mass of electron is negligible
Structure of the Atom
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Sum of number of protons and neutrons equals the mass number◦ Found in the periodic table as atomic mass◦ Measured in amu (atomic mass units) NOT grams
If measured in grams would be atomic mass * mass of an atom
Subatomic particles
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All type of element on periodic table have the same number of protons◦ Protons define the element
Neutrons can vary from atom to atom for 1 element◦ Same # protons but different number neutrons =
isotopes Examples:
◦ Carbon – 12 = 6 protons and 6 neutrons◦ Carbon – 13 = 6 protons and _ neutrons
Isotopes
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Mass number for element must be integer◦ We can’t have part of a proton or neutron◦ Why are atomic masses of elements not integers?
Weighted atomic mass◦ The atomic mass is an average of all the different
isotopes.◦ If have of the carbon isotopes were carbon 12 and
half were carbon 13 Weighted atomic mass would be 12.5 Is this the weighted atomic mass for carbon? Which isotope is more abundant?
Atomic masses
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Found in space around a nucleus of an atom Energy Levels
◦ Orbitals in an atom form series of energy levels S holds 2 electrons P holds 6 electrons D holds 10 electrons
This is where S, P, and D block names come from
Electrons can move between energy levels◦ You can walk up a set of stairs, takes a certain
amount of energy◦ Certain amount of energy is needed for e- to jump
between energy levels (it is quantized)
Location of electrons
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Ground state – e- in lowest energy◦ Ground state is given in periodic table on ref. tables◦ If e- configuration doesn’t match ground state, it has to
be excited state Excited state
◦ Electrons possess more energy than they would if they were in ground state
Spectral lines◦ Visible light that is emitted when electrons fall back to
their ground state◦ Must first add energy to be excited – we can’t see this
Ground vs excited state
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RB pg. 7, 13-36
Questions
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Read 9 – 16 for Wed. morning