Transcript atom

Chemistry Chapter 3
Atoms
Building Blocks of Matter
Not the history of the atom itself, but
the history of the idea of the atom
Philosophical Idea
• Greeks
– Only theoretical
– 400 BC thought matter could be divided into
smaller particles until basic particle found
– Democritus
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460-370 BC
Coined the term atom
atoma (sg. atomon) or "indivisible units"
Believers of Democritus theory called atomists
– Aristotle
• 384-322 BC
• claimed that there was no smallest part of matter
and that different substances were made up of
proportions of fire, air, earth, and water
• As there were of course no experimental means
available to test either view, Aristotle's prevailed
mainly because people liked his philosophy better.
• Followed this idea until 18th century
Robert
Boyle
(1600’s)
• 1st true “chemist”
• Discovered a relationship between
pressure and volume (Boyle’s Law)
Contributing Principles to Atom
• Antoine and Marie Lavoisier
• (1700’s)Conducted experiments
• that eliminated the 4 element idea
• Underlying the new chemistry is the
assumption that matter is
conserved. Weight becomes the tool for
determining if a product is simpler or
more complex than an ingredient.
• Joseph Louis Proust
• Created Law of definite Proportions
or Proust Law
states that a chemical compound always
contains exactly the same proportion of
elements by mass
Robert
Bunsen
• Found that when heated, different
elements produced different colors in a
flame
Atomic Theory
• John Dalton 1766-1844
– English school teacher, hobby meteorology
– 1st individual to recognize the importance of Democritus theory
– Daltons Theory
• All matter is composed of extremely small particles called atoms
• Atoms of a given element are identical in size, mass, and other
properties; atoms of different elements differ in properties.
• Atoms cannot be subdivided, created, or destroyed
• Atoms of different elements can combine in simple, whole number
ratios to form compounds
• In chemical rxn, atoms are combined, separated, or rearranged
• Proposed the “Billiard-ball model” of the
atom
Atomic theory accepted
• Explained the Laws of conservation of
mass and definite composition
• Exceptions to theory
– Atoms are divisible—discovery of the
subatomic particles
– An elements atoms can have different
mass***discovery of isotopes
Atom and conservation of mass
• “if atoms are indivisible and atoms of
different elements can combine in
chemical reactions then it must be that
mass is conserved in a chemical reaction.”
Law of Multiple Proportions
• Created by John Dalton
• States: If two or more different compounds are
composed of the same two elements, the
masses of the second element combined with a
certain mass of the first element can be
expressed as ratios of small whole numbers
• Carbon Monoxide vs Carbon Dioxide
Structure of the Atom
• Defn. atom: smallest particle of an element that
can exist alone or in combination with other
atoms
• Defn. atomic structure: the identity and
arrangement of smaller particles w/in atoms
• Regions of atom
– Nucleus
• DENSE central part
• Is positive in charge
– Outer energy levels (shells, rings)
• Contain negative particles
Subatomic particles
• Discovery of Electron
– John Joseph (JJ) Thomson
• English physicist
• Measured ration of the charge of a cathode-ray
particle to mass
• Found ratio always the same regardless of metal
used to make the cathode or the gas used
• Concluded all cathode rays were composed of
negative particles
• Called particles ELECTRONS
Plum pudding model
Charge and Mass of Electron
• Robert Millikan
– American physicist
– Found mass of e- to be 1/2000 of mass of H
atom
– Accepted mass of an electron is 9.109 x 1028 grams
– Electron present in all matter
Inferences
• Because atoms are neutral, must also
contain a positive charge
• Because e- are so small, there must be
other particles present to account for the
mass
Discovery of Atomic Nucleus
• Ernest Rutherford, Hans Geiger, and
Ernest Marsden
– Studied the bombardment of thin metal foil
with alpha particles (+)
– Rutherford concluded: The force of repulsion
must be caused by very densely packed
bundles of matter with a positive charge
– Called the bundle the NUCLEUS
• Nucleus
– Has a positive charge
– Contains nearly all mass of the atom
– Takes up an insignificant fraction of volume
– Composition
• Protons
– Positive charged
– Equal in magnitude to the negative charge of an electron
• Nuclear Model of the Atom
Discovery of Neutron
• James Chadwick
• Chadwick made a fundamental discovery
in the domain of nuclear science: he
proved the existence of neutrons elementary particles devoid of any
electrical charge.
Henri Becquerel
(December 15, 1852-August 25, 1908)
•Accidentally discovered
radioactivity
•Alpha particles (+2 charge)
•(Also beta particles, gamma
rays)
Niels Bohr
• Created first accepted model
Of the atom using the work of previous
scientists
Stated that electrons orbit the nucleus in
specific energy levels
Will be expanded in next chapter
Arnold Sommerfeld
• Expanded the Bohr model
Electrons travel in orbitals, but
the orbitals are not the same shape
-- this leads to the electron cloud model of
the atom
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Erwin Schrödinger (1887 – 1961) and Louis Victor de Broglie
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Model: The Wave Mechanical Model (Also the Quantum Mechanical
Model)
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Schrödinger used the new quantum theory to write and solve
mathematical equations to describe the location and energy of an electron
in an atom.
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The model is derived from mathematical solutions to the Schrödinger
equation.
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Schrödinger’s model is primarily mathematical; there are few (if any)
analogies in real life.
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The Quantum Mechanical Model – a modern description of electrons in
atoms
• Wolfgang Ernst Pauli (25 April 1900 – 15
December 1958)
– an Austrian theoretical physicist noted for his
work on spin theory, and for the discovery of
the exclusion principle underpinning the
structure of matter and the whole of
chemistry.
• Werner Heisenberg (December 5,1901 –
February 1, 1976) was a German
theoretical physicist who made
foundational contributions to quantum
mechanics and is best known for asserting
the uncertainty principle of quantum
theory.
Properties of Subatomic particles
• See table 1 page 76
Important Information for Counting
Atoms
• Atomic number called the Z number
• Atomic mass is the average of the atomic masses of the
naturally occurring isotopes of the element
– Isotopes are atoms from same element having different numbers
of neutrons
• Nuclear Symbol:
• Hyphen notation: Name---mass
– When using masses, round to the nearest hundredth
– Mass must be relative (ie expressed in a unit)
• Formula mass in u or amu (atomic mass unit)
• Ex.: Hydrogen is 1.01 u or 1.01 amu
• A mole (mol) is a counting unit that
describes the amount of substance that
contains as many particles as there are
atoms in 12g of Carbon-12
• Molar mass: the mass of one mole of a
substance expressed in grams/mol
– For elements that is the atomic mass in g/mol
Amedeo
Avogadro
Lorenzo Romano Amedeo Carlo Avogadro, conte di Quaregna e di Cerreto (1776 1856)
• at the same temperature and pressure,
equal volumes of gases contain the same
number of particles
Avogadro’s hypothesis
• Avogadro’s Number
6.022E23 atoms=1mole