Download Atoms, Molecules, and Ions

Atoms, Molecules, and Ions
Chapter 2
The atomic theory of matter
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Democritus
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Atomos – indivisible
Plato and Aristotle
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No indivisible particles
Continuous
The atomic theory of matter
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Dalton
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Atomic Theory
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Each element is composed of extremely small particles called
atoms.
All atoms of a given element are identical; the atoms of
different elements are different and have different properties.
Atoms of an element are not changed into different types of
atoms by chemical changes; atoms are neither created nor
destroyed in chemical reactions.
Compounds are formed when atoms of more than one element
combine; a given compound always has the same relative
number and kind of atoms.
Father of modern atomic theory
The atomic theory of matter
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Dalton’s theory
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Explained the law of constant composition(Proust).
Explained the law of conservation of
mass(Lavoisier)
Helped deduce the law of multiple
proportions(Dalton).
The discovery of atomic structure
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Crooke - cathode rays(1850’s)
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Thomson(1897)
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(-) to (+)
Could be deflected in electric or magnetic fields
Nature of the rays was identical regardless of cathode material
Concluded that rays are not waves but particles with mass
Calculated a value of 1.76 x 108 coulombs per gram for charge to
mass ratio of electron
Millikan(1909)
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Oil drop experiment to find the charge of an electron(1.6 x 10-19
Coulombs)
Radioactivity
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Becquerel(1896)
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Found that uranium minerals emit high energy
radiation spontaneously.
Rutherford(1909)
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Found 3 types of radiation
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Alpha – helium nuclei, massive, slow, paper deters it
Beta – high speed electrons, fast, negative, metal foil
deters it
Gamma – similar to x-rays, no particles, no charge, very
harmful to living tissue
Rutherford’s gold foil experiment
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1910
Used alpha particles shot at gold foil.
Some passed through the foil. Some were
deflected at an angle. Some bounced back.
Major contribution to understanding the atom.
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The atom is mostly space.
There is a dense, central core called the nucleus.
The nucleus is positive.
Further information
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Rutherford discovered the proton in 1919 in the
cathode ray tube in much the same way that
Thomson discovered the electron.
Chadwick discovered the neutron in 1932.
They were more difficult to find.
Models of the atom
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Dalton – spherical but no charges
Thomson – plum pudding model; positive
sphere with negative electrons in it.
Rutherford – nuclear atom with lots of empty
space; nucleus is positive and dense; electrons
are randomly spaced outside the nucleus.
Bohr – nuclear atom but placed electrons in
energy levels outside the nucleus. No electrons
anywhere but in the energy levels. Only certain
numbers of electrons in each level.
The modern view of the atom
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Schoedinger model
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Has all the parts that the Bohr atom had but has fine structure
added to explain bright line spectra.
Has protons, electrons, and neutrons.
Discusses the position of electrons in terms of probability of
finding them in a location.
Has sublevels(s, p, d, f, g, h…) inside the main energy levels
Atoms are very small. Masses are expressed in amu
and radii are expressed in Angstroms(non-SI) or
picometers.
The modern view of the atom
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With the discovery of the neutron, Dalton’s atomic
theory had to be revised. Now there was the possibility
that two atoms of the same kind could have different
masses(isotopes) and that two different atoms could
have the same masses.
Isotopes have the same number of protons(atomic
number; identity) but different numbers of neutrons.
Thus a nuclide would be written 12C for carbon-12 and
13C for carbon-13. The superscript is called the mass
number(p + n).
The Periodic Table
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Families(groups)
Representative groups
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1A Alkali metals(active at the bottom of column)
2A Alkaline Earth metals
3A(13) Boron group
4A(14) Carbon group
5A(15) Nitrogen group
6A(16) Chalcogens
7A(17) Halogens(active at the top of column)
8A(18) Noble gases(inert)
The Periodic Table
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Transition metals
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Include lanthanides and actinides
B-groups
Have more than one oxidation number
Metals
Nonmetals
Metalloids
Compounds
Molecules and
Formula Units
Types of bonding
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Ionic bonding occurs when two or more ions
join. It occurs between a metal and a nonmetal.
Ions are formed when an atom loses or gains
an electron.
Oppositely charged ions are attracted to one
another and a formula unit is made.
Covalent bonding occurs when two nonmetals
share electrons and a molecule is made.
Types of formulas
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Molecular formulas are those that indicate the
actual numbers of each kind of atom present.
Empirical formulas are those that indicate the
relative numbers of atoms present. They may
or may not indicate an actual compound.
Structural formulas indicate the way in which
atoms are attached to one another. Two
compounds may have the same formula but
may have differing structures and hence will
have different properties.
Ions and Ionic Compounds
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Ionic compounds are formed from cations(positive
ions) and anions(negative ions).
A cation is formed when a metal atom loses one or
more electrons.
An anion is formed when a nonmetal atom gains one
or more electrons.
Representative elements form predictable ions
whereas transition elements do not. (Exceptions: Cd,
Zn, and Ag)
Molecular Compounds
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Molecular compounds are made when two
nonmetal atoms share electrons.
This forms a covalent bond.
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Pure covalent
Polar covalent
Coordinate covalent
Metallic covalent