Download Introductory Chemistry: A Foundation, 6th Ed. Introductory Chemistry

Introductory Chemistry:
A Foundation, 6th Ed.
Introductory Chemistry,
6th Ed.
Basic Chemistry, 6th Ed.
by Steven S. Zumdahl &
Donald J. DeCoste
University of Illinois
Chapter 4
Chemical Foundations:
Elements, Atoms,
and Ions
Elements
•  Over 112 known: 88 found in nature, others
are man made.
•  Each element has a unique one- or
two-letter symbol
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Elements (cont.)
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Elements (cont.)
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Dalton’s Atomic Theory
•  Elements are composed of tiny particles called atoms.
•  All atoms of a given element are identical.
–  All carbon atoms have the same chemical and physical
properties.
•  Atoms of a given element are different from those
of any other element.
–  Carbon atoms have different chemical and physical
properties than sulfur atoms.
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Dalton’s Atomic Theory
•  Atoms of different elements combine to form
compounds.
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Dalton’s Atomic Theory
•  Law of Constant Composition: all samples of a
compound contain the same proportions (by mass) of
the elements that form the compound.
•  Atoms are indivisible by chemical processes.
–  All atoms present at beginning are present at the end.
–  Atoms are not created or destroyed, just rearranged in
chemical reactions.
–  Atoms of one element cannot change into atoms of
another element.
•  Cannot turn lead into gold by a chemical reaction
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Formulas Describe Compounds
•  A compound is a distinct substance that is
composed of atoms of two or more elements.
•  Compounds are identified by the number and type
of each atom in the simplest unit of the compound.
–  Molecules or ions
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Writing Formulas of Compounds
•  Each element is represented by its symbol.
•  The number of each type of atom is indicated by a
subscript written to the right of the element
symbol.
•  If only one atom is present, do not include a
subscript.
•  If polyatomic groups are present in the molecule,
they are written inside parentheses if more than
one group is present.
•  Examples: H2O, NaCl, KNO3, Mg(NO3)2
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What Are Atoms Made Of?
•  J.J. Thomson investigated a beam called a
cathode ray.
•  He determined that the ray was made of tiny
negatively charged particles we now call
electrons.
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The Electron
•  Tiny, negatively charged particle
•  Very light compared to mass of atom
–  1/1836th the mass of a H atom
•  Move very rapidly within the atom
•  Atoms of different elements all produce
electrons; therefore electrons are a
fundamental unit of atoms.
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The Proton
•  If negative electrons exist, must also
have positive particles to balance the
charge and make the atom electrically
neutral
•  Assume “Plum Pudding Model” electrons suspended in a positively
charged electric field
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Rutherford’s Nuclear Model
•  The atom contains a tiny dense center called
the nucleus.
–  The volume is about 1/10 trillionth the volume
of the atom.
•  The nucleus is essentially the entire mass
of the atom.
•  The nucleus is positively charged.
–  The amount of positive charge of the nucleus
balances the negative charge of the electrons.
•  The electrons move around in the empty space
of the atom surrounding the nucleus.
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Components of an Atom
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The Modern Atom
•  Atoms are composed of three main pieces:
protons, neutrons, and electrons.
•  The nucleus contains protons and neutrons.
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The Modern Atom (cont.)
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Isotopes
•  All atoms of an element have the same
number of protons.
•  The number of protons in an atom of a given
element is the same as the atomic number.
–  Found on the periodic table
•  Atoms of an element with different numbers
of neutrons are called isotopes.
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Isotopes (cont.)
•  All isotopes of an element are chemically
identical.
–  Undergo the exact same chemical reactions
•  Isotopes of an element have different masses.
•  Isotopes are identified by their mass
numbers.
–  Mass number = # protons + # neutrons
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Isotopes of Carbon
12C
• 
has 6 protons (atomic number ) and 6
neutrons (atomic mass number = 6 + 6 = 12)
• 
13C
has 6 protons and 7 neutrons (atomic
mass number = 6 + 7 = 13)
• 
14C
has 6 protons and 8 neutrons (atomic
mass number = 6 + 8 = 14)
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Elements
•  Arranged in a pattern called the periodic
table
•  Position on the table allows us to predict
properties of the element
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Elements (cont.)
•  Metals
–  About 75% of all the elements
–  Lustrous, malleable, ductile, conduct heat and
electricity
•  Nonmetals
–  Dull, brittle, insulators
•  Metalloids
–  Also know as semi-metals
–  Some properties of both metals & nonmetals
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The Modern Periodic Table
•  Elements with similar chemical and
physical properties are in the same column.
•  Groups (Families) and Periods
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The Modern Periodic Table (cont.)
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The Modern Periodic Table (cont.)
•  Main group = representative elements
–  “A” columns
•  Transition elements
–  All metals
•  Bottom rows = inner transition elements = rare
earth elements
–  Metals
–  Lanthanides and actinides
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Natural States of Elements
•  Gases: monatomic gases such as noble
gases and diatomic gases such as O2
•  Liquids such as Hg or Br2
•  Solids such as metals or allotropes of
carbon
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Natural States of Elements (cont.)
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Ions
•  Cations: ions that have a positive charge
–  Form when an atom loses electrons
•  Anions: ions that have a negative charge
–  Form when an atom gains electrons
•  Ions with opposite charges attract
–  Therefore cations and anions attract each other
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Ions (cont.)
•  Moving ions conduct electricity.
•  Compound must have no total charge,
therefore we must balance the numbers of
cations and anions in a compound to get 0
total charge.
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Atomic Structures of Ions
•  Metals form cations.
•  For each positive charge the ion has 1 less
electron than the neutral atom.
–  Na = 11 e-, Na+ = 10 e–  Ca = 20 e-, Ca+2 = 18 e-
•  Cations are named the same as the metal
sodium
Na → Na+ + 1e-
sodium ion
calcium
Ca → Ca+2 + 2e-
calcium ion
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Atomic Structures of Ions (cont.)
•  Nonmetals form anions.
•  For each negative charge the ion has 1 more
electron than the neutral atom.
–  F = 9 e-, F- = 10 e–  P = 15 e-, P3- = 18 e-
•  Anions are named by changing the ending
of the name to -ide
–  Fluorine
–  Oxygen
F + 1e- → FO + 2e- → O2-
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fluoride ion
oxide ion
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Ionic Charges and Compounds
•  Charges on the ions of some elements can
be predicted from the periodic table.
•  Cations and anions usually form
simultaneously to yield an ionic compound.
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Ionic Charges and Compounds (cont.)
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Formulas of Ionic Compounds
•  The formula of an ionic compound can be
determined by balancing the positive charge
of the cation(s) with the negative charge of
the anion(s) to yield a net charge of zero.
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