October 24, 2014 History of the Atom • We know today that all matter is composed of atoms. • Atoms: basic unit of matter. Atoms are the smallest particle of an element that retains its identity. How did scientists figure out the structure of the atom? Can you just "look" at it?
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History of the Atom - OAK PARK USD...October 24, 2014 History of the Atom • We know today that all matter is composed of atoms. • Atoms: basic unit of matter. Atoms are the smallest
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October 24, 2014
History of the Atom
• We know today that all matter is composed of atoms.• Atoms: basic unit of matter. Atoms are the smallest
particle of an element that retains its identity.
How did scientists figure out the structure of the atom? Can you just "look" at it?
October 24, 2014
Democritus and John Dalton
• Democritus: Greek philosopher, believed matter was made of indestructible particles.
• John Dalton: Used the scientific method to test Democritus's ideas and came up with the atomic theory.
• Proton: positively charged particle found in the nucleus (charge opposite of electron)> Mass of 1.0073 amu (2000x bigger than electron)> Atomic number: (Z) # of protons in nucleus,
identifies elements
• Neutron: neutral particle found in the nucleus> Mass of 1.0087 amu (about the same as a proton)> Number of neutrons determines isotopes
• Quantum Mechanical Model of the Atom> Describes electrons as waves> Electrons are found in 3-D atomic orbitals.
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October 24, 2014
Electron Orbitals and Energy Levels
• Principle energy level (shell) (n) indicates the relative size and energy of the various atomic orbitals.> n= integers: n=1, 2, 3...> As n gets bigger
– the orbitals (shell) gets larger– the electrons spends more time away from the
nucleus– the electrons are less tightly bound to nucleus
• Each shell can hold a maximum of 2n2 electrons.> n=1 can hold 2 electrons> n=2 can hold 8 electrons> n=3 can hold 18 electrons> n=4 can hold 32 electrons
• Valence electrons: electrons in outermost shell, involved in forming bonds.
middle school?
October 24, 2014
Parts of the Atom
October 24, 2014
Which element has 35 protons?
Which element is Z=12?
Elements
• Atomic number (Z): Number of protons in their nucleus. Defines elements.