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Topic OutlineLearn Major ElementsThe Atom Subatomic Particles Modern Atomic Theory Organizing the ElementsPeriodic TableClassifying ElementsAtomic Models
Defining the AtomAtom – the smallest particle of an
element that retains its identityCan not see with naked eyeNanoscale (10-9 m)Seen with scanning
tunneling electronmicroscope
DemocritusDemocritus was a Greek to first
come up with idea of an atom.
His belief: atoms were indivisible and indestructible. = WRONG!
Atom comes from “atmos” - indivisible
Dalton’s Atomic Theory2000 yrs later, John Dalton used
scientific method to transform Democritus’s idea into a scientific theory
Dalton put his conclusions together into his Atomic Theory (4 parts)
Dalton’s Atomic Theory2. Atoms of the same element are
identical. Atoms of different elements are different
The ElectronParticle with negative charge
Discovered by J.J. Thomson
Used cathode ray (electron) beam and a magnet/charged plate.
Millikan found the charge and mass
The Proton and NeutronAn atom is electrically neutral
If there is a negative particle then there must be positive particle
Proton – particle with positive charge
Chadwick discovered neutron – neutral charge
Rutherford’s Atomic ModelThe nucleus is the central part of the
atom containing protons and neutronsPositive chargeMost of the mass
Electrons are located outside the nucleusNegative chargeMost of the volume
Atomic Number An element is defined only by the
number of protons it contains
Atomic Number – number of protons
Number of protons = number of electronFor a neutral element
Identify the number of Protons1. Zinc (Zn)
2. Iron (Fe)
3. Carbon (C)
4. Uranium (U)
1. 30
2. 26
3. 6
4. 92
Mass NumberNucleus contains most of the mass
Mass Number – total protons and neutrons
Number of neutron = Mass # – Atomic #
Identify # of Subatomic Particles
1. Lithium (MN = 7)
2. Nitrogen(MN = 14)
3. Fluorine(MN = 19)
**MN = Mass Number
1. 3 p+ , 3 e-, 4 n0
2. 7 p+ , 7 e-, 7 n0
3. 9 p+ , 9 e-, 10 n0
Differences in Particle NumberDifferent element: different number of
protons
Ions – same number of proton, different number of electrons
Isotope – same number of proton, different number of neutronsDifferent Mass Numbers
Two Notations for AtomsNuclear Notation
Write the element symbolOn left side, superscript = Mass NumberOn left side, subscript = Atomic Number
Isotope –Hyphen NotationWrite full name of elementOn right side, put a dashOn right side put Mass Number after dash
Hydrogen - 3
Ex: Three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18.
Write the nuclear symbol for each.
Ex: Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope?
Atomic MassAtomic Mass Unit (amu) – one-twelfth
of the mass of the carbon-12 atom
Different isotopes have different amu (mass) and abundance (percentage of total)
Atomic Mass – weighted average mass of the naturally occurring atoms.Isotope MassIsotope Abundance