Download Section 4.6 Introduction to the Modern Concept of Atomic Structure

Chapter 4
Chemical Foundations:
Elements, Atoms, and
Ions
Chapter 4
Table of Contents
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
The Elements
Symbols for the Elements
Dalton’s Atomic Theory
Formulas of Compounds
The Structure of the Atom
Introduction to the Modern Concept of Atomic
Structure
Isotopes
Introduction to the Periodic Table
4.9
4.10
4.11
Natural States of the Elements (see Part 2)
Ions (see Part 2)
Compounds That Contain Ions (see Part 2)
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Section 4.1
The Elements
•
•
•
114 known (officially named)
88 found in nature, 26 are man made.
Just as you had to learn the 26 letters of the
alphabet before you learned to read and write,
you need to learn the names and symbols of
the chemical elements before you can read and
write chemistry.
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Section 4.1
The Elements
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Section 4.1
The Elements
How the Term Element is Used
•
•
•
Could mean a single atom of that element
(Ar or H).
Could mean molecules of an element (H2),
which is hydrogen found in its natural state
(diatomic).
Could mean atoms of elements are present in
some form (sodium found in the human body).
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Section 4.1
The Elements
•
•
Most elements are very reactive.
Elements are not generally found in
uncombined form.
 Exceptions are:
• Noble metals – gold, platinum and silver
• Noble gases – Group 8
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Section 4.1
The Elements
Diatomic Molecules
•
Nitrogen gas contains N2
molecules.
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• Oxygen gas contains O2
molecules.
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Section 4.1
The Elements
Diatomic Molecules
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Section 4.1
The Elements
•
Atoms can form ions by gaining or losing electrons.
 Metals tend to lose one or more electrons to form
positive ions called cations.

Cations are generally named by using the name of
the parent atom.
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Section 4.1
The Elements
•
Nonmetals tend to gain one or more electrons to form
negative ions called anions.
•
Anions are named by using the root of the atom name
followed by the suffix –ide.
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Section 4.1
The Elements
Ion Charges and the Periodic Table
•
The ion that a particular atom will form can
be predicted from the periodic table.
Group or Family
Alkali Metals (1A)
Alkaline Earth Metals (2A)
Halogens (7A)
Noble Gases (8A)
Charge
1+
2+
1–
0
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Section 4.1
The Elements
Ion Charges and the Periodic Table
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Section 4.1
The Elements
•
•
Ions combine to form ionic compounds.
Properties of ionic compounds


High melting points
Conduct electricity
•
•
If melted
If dissolved in water
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Section 4.1
The Elements
•
•
Ionic compounds are electrically neutral.
The charges on the anions and cations in the
compound must sum to zero.
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Section 4.1
The Elements
Formulas for Ionic Compounds
•
•
Write the cation element symbol followed by the anion
element symbol.
The number of cations and anions must be correct for
their charges to sum to zero.
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Section 4.2
Symbols for the Elements
•
•
•
Each element has a unique one- or two-letter symbol.
First letter is always capitalized and the second is not.
The symbol usually consists of the first one or two
letters of the element’s name.

•
Examples:
Oxygen
Krypton
O
Kr
Sometimes the symbol is taken from the element’s
original Latin or Greek name.

Examples:
Gold Au
Lead Pb
aurum
plumbum
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Section 4.2
Symbols for the Elements
Names and Symbols of the Most Common Elements
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Section 4.4
Formulas of Compounds
Chemical Formulas Describe Compounds
•
•
Compound – distinct substance that is
composed of the atoms of two or more
elements and always contains exactly the
same relative masses of those elements.
Chemical Formulas – expresses the types of
atoms and the number of each type in each
unit (molecule) of a given compound.
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Section 4.4
Formulas of Compounds
Rules for Writing Formulas
1. Each atom present is represented by its element
symbol.
2. The number of each type of atom is indicated by a
subscript written to the right of the element symbol.
3. When only one atom of a given type is present, the
subscript 1 is not written.
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Section 4.4
Formulas of Compounds
Exercise
The pesticide known as DDT paralyzes insects by
binding to their nerve cells, leading to uncontrolled firing
of the nerves. Before most uses of DDT were banned in
the U.S., many insects had developed a resistance to it.
Write out the formula for DDT. It contains 14 carbon
atoms, 9 hydrogen atoms, and 5 atoms of chlorine.
C14H9Cl5
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
The atom contains:
•
•
•
Electrons – found
outside the nucleus;
negatively charged
Protons – found in the
nucleus; positive charge
equal in magnitude to
the electron’s negative
charge
Neutrons – found in the
nucleus; no charge;
virtually same mass as a
proton
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
•
The nucleus is:
 Small compared with the overall size of the
atom.
 Extremely dense; accounts for almost all of
the atom’s mass.
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
Why do different atoms have different chemical
properties?
•
•
•
The chemistry of an atom arises from its
electrons.
Electrons are the parts of atoms that
“intermingle” when atoms combine to form
molecules.
It is the number of electrons that really
determines chemical behavior.
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
• 1
EARTH = 6.775235700E9 PEOPLE
• 1 PURE COPPER
• 1
PENNY = 2.4E22 ATOMS
MOLE OF ANY SUBSTANCE = 6.022E23 ATOMS
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Section 4.7
Isotopes
Isotopes
•
•
•
Atoms with the same number of protons but
different numbers of neutrons.
Show almost identical chemical properties;
chemistry of atom is due to its electrons.
In nature most elements contain mixtures of
isotopes.
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Section 4.7
Isotopes
Two Isotopes of Sodium
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Section 4.7
Isotopes
Isotopes
A
Z
•
•
•
X
X = the symbol of the element
Z = the atomic number (# of protons)
A = the mass number (# of protons and
neutrons)
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Section 4.7
Isotopes
Isotopes – An Example
14
6
•
•
•
C
C = the symbol for
carbon
6 = the atomic number
(6 protons)
14 = the mass number
(6 protons and 8
neutrons)
12
6
C
• C = the symbol for
carbon
• 6 = the atomic number
(6 protons)
• 12 = the mass number
(6 protons and 6
neutrons)
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Section 4.7
Isotopes
Exercise
A certain isotope X contains 23 protons and 28
neutrons.
• What is the mass number of this isotope?
• Identify the element.
Mass Number = 51
Vanadium
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Section 4.8
Introduction to the Periodic Table
The Periodic Table
•
The periodic table shows all of the known elements in
order of increasing atomic number.
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Section 4.8
Introduction to the Periodic Table
The Periodic Table
•
•
•
Metals vs. Nonmetals
Groups or Families – elements in the same
vertical columns; have similar chemical
properties
Periods – horizontal rows of elements
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Section 4.8
Introduction to the Periodic Table
The Periodic Table
•
•
•
Most elements are metals and occur on the left side.
The nonmetals appear on the right side.
Metalloids are elements that have some metallic and
some nonmetallic properties.
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Section 4.8
Introduction to the Periodic Table
• ATOMIC NUMBER - the number of protons in the
nucleus of an atom
• # OF ELECTRONS (NEGATIVELY CHARGED) EQUALS THE # OF
PROTONS (POSITIVELY CHARGED)
• MASS NUMBER – total number of protons and neutrons
in the nucleus
• # OF NEUTRONS = MASS # - ATOMIC #
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Section 4.8
Introduction to the Periodic Table
NAME
SYMBOL
ATOMIC
#
PROTONS
NEUTRONS
MASS
#
ELECTRONS
OSMIUM
24
36
Er
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Section 4.8
Introduction to the Periodic Table
Physical Properties of Metals
1. Efficient conduction of heat and electricity
2. Malleability (they can be hammered into thin
sheets)
3. Ductility (they can be pulled into wires)
4. A lustrous (shiny) appearance
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