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CHAPTER 4 ATOMIC STRUCTURE
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• Aristotle (Greek)
• Thought all substances were built from either fire, earth, air, water
• Thought that atoms of a liquid are smooth and round
• Thought atoms of a solid were rough and prickly
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• Dalton’s Atomic Theory (1766)
• Evidence for atoms
• Measured the masses of elements
• Compounds have fixed composition
• All matter is made up of individual particles called atoms, which cannot be divided
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• 1 All elements are composed of atoms• 2 All atoms of the same element have the
same mass, and atoms of different elements have different masses
• 3 compounds contain atoms of more than 1 element
• 4 in a particular compound, atoms of different elements always combine the same way
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• Evidence for subatomic particles– Mass and charge are spread throughout the
atom– Earnest Rutherford- (1871-1937)
• Alpha particles---fast moving positive charged• All the atoms positive charge is in the nucleus• The nucleus is the positively charged mass located
in the center of the atom• Ques.1-5 pg. 105
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SECTION 4-2
• Properties of subatomic particles
• Protons-- + charged particles, varies among elements
• Each nucleus contains at least one positively charged particle
• +charge = proton
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• Electron
• - charge 1-
• Found outside the nucleus in an electron cloud or (shell)
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• Neutron
• No charge
• Found in the nucleus
• Mass almost = to a proton
• Protons, electrons and neutrons can be distinguished by mass, location in an atom and the charge
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ATOMIC NUMBER AD MASS NUMBER
• The atoms of any element contain the same number of protons
• Example there is one proton in the nucleus of every hydrogen atom. There hydrogen has an atomic number of 1
• ATOMIC NUMBER = NUMBER OF PROTONS
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• Atoms of different elements have different numbers of protons
• Sulfur= atomic #= 16 because it has 16 protons in the nucleus
• Each positive charge is balanced by a negative charge SO hydrogen has 1 proton and 1 electron sulfur 16 protons and 16 electrons
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• MASS NUMBER= the sum of the protons and neutrons in the nucleus of the atom
• Ex Aluminum= 13 protons+14 neutrons= an atomic mass of 27
• Number of neutrons= mass#-atomic number
• Ex. Aluminum 27-13= 14 (#of neutrons)
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ISOTOPES
• When an atom does not have the same number of neutrons
• Same atomic number but different mass #’s
• Ex. Oxygen-16, 17, and 18
• All oxygen atoms have 8 protons, but some have 9 or 10 neutrons
• Ques. 1-7 pg. 112
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• Energy levels
• 1 one orbital max 2 electrons
• 2 four orbitals max 8 electrons
• 3 nine orbitals max 18 electrons
• 4 sixteen orbitals max 32 electrons
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• Electron configuration—arraignment of electrons in the orbitals of an atom
• Lowest levels get filled before higher energy levels----inner to outer
• Stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies (ground state)
• Ques. 1-5 pg. 118
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4-3 Modern Atomic Theory
• Niels Bohr-1885-1962 Danish physicist focused on electrons in the electron cloud
• Energy levels
• Each electron has a fixed amount of energy
• Electrons closer to the nucleus have less energy than further away from the nucleus
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• They move in a less than predicable way
• Atomic orbitals– The electron cloud represents all the orbitals in
an atom– An orbital is a region of space around the
nucleus figure 15 page 117 (copy into notes)– Draw in your notes the Thomson, Rutherford,
Bohr, and electron cloud models (pg 115)
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• An electron in an atom can move between energy levels when the atoms gain or lose energy
• The size of the jump between orbitals determines the amount of energy gained or lost
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• Evidence for movement from one level to another is light---light is a form of energy-----heat is another cause of movement of electrons from one orbital to another
• Electron cloud-how electrons behave in their orbitals
• Electrons move like planets in the solar system around the nucleus, they move in a less than predicable way
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• When electrons move to a higher energy level they are considered in an excited state
• Ex. He, Ne, Ar Kr, Xe find out the names of these elements
• Page 118 questions 1-5
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