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Chapter 4
“Chemical Foundations”
Section 4.1
Objective: to learn about relative abundance of the elements
and learn some names of elements
The Elements
Element Name
•
•
•
•
•
•
•
•
•
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
hydrogen
Relative Abundance
•
•
•
•
•
•
•
•
•
49.2%
25.7%
7.5%
4.71%
3.39%
2.63%
2.4%
1.93%
0.87%
4
How the Term Element is Used
•
Could mean a single atom of that element
▫
•
Could mean molecules of an element
▫
•
(H2, N2, O2, F2, Cl2, Br2, I2), which are found in
their natural states.
Could mean atoms of elements are present in
some form
▫
•
(Ar or H).
(sodium found in the human body).
Look at each particular case to determine its
proper use.
Section 4.2
Objective: to learn the symbols for the elements
6
•
•
115 known: 88 found in nature, others 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.
Names & Symbols
• One or two letter
▫ Fluorine F
Neon
Ne
• First letter is CAPATALIZED, the second is not
▫ Silicon Si
Argon
Ar
• Not always first two letters of element
▫ Zinc
Zn
Chlorine
Cl
• Sometimes based on other languages
▫ gold (aurum) Au
Iron (ferrum) Fe
9
Law of Constant Composition
•
A given compound always has the same
composition, regardless of where it comes
from.
 Water always contains 8 g of oxygen for every 1 g
of hydrogen.
 Carbon dioxide always contains 2.7 g of oxygen
for every 1 g of carbon.
Section 4.4
objective: to learn how a formula describes a compound's composition
11
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.
12
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.
13
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
Section 4.9
Objective: to understand diatomic molecules
Diatomic Molecules
• Most elements quite reactive
▫ so they form compounds to
become more stable
▫ When found alone in nature,
(not combined with other
elements in compounds),
these elements exist only as
two covalently bonded atoms
• Some we give a special name
to:
▫ Diatomic molecules
 Molecules made up of two
atoms
17
Copyright © Cengage
Learning. All rights reserved
Diatomic Molecules
•
Nitrogen gas contains N2
molecules.
• Oxygen gas contains O2
molecules.
Section 4.8
Objective: learn various features of the periodic table
19
Mendeleev’s Table
Russian chemist Dmitri Mendeleev
developed and published the
basic arrangement of the periodic
table between 1869 and 1871.
Mendeleev arranged the elements in order of
increasing relative atomic mass (protons
had not been discovered yet). The elements
on the modern periodic table are arranged
in order of increasing atomic number.
He also grouped elements with similar
properties into columns and rows so that
the properties of the elements varied in a
regular pattern (periodically).
2-
The Periodic Table:
A Preview
 A “periodic table” is an
arrangement of elements in which
the elements are separated into
groups based on a set of repeating
properties
The periodic table allows you to
easily compare the properties of
one element to another
The Periodic Table: Row vs Group
Each horizontal row (there are
7 of them) is called a period
Each vertical column is called
a group, or family
Elements in a group have
similar chemical and physical
properties
Identified with a number and
either an “A” or “B”
Families
Rare Earth Metals are the collective group of
lanthanide and actinide series
23
Periodic Table
•
•
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
Helium
Neon
Argon
Krypton
Xenon
Metal vs Nonmetal vs Metalloid
Properties of Metals
•
•
•
•
Efficient conductors of heat and electricity
Malleable (hammered into thin sheets)
Ductility (pulled into thin wires)
Lustrous (shiny) appearance
Atoms
Sizing up the Atom
 Elements are able to be subdivided into
smaller and smaller particles – these are the
atoms, and they still have properties of that
element
If you could line up 100,000,000 copper
atoms in a single file, they would be
approximately 1 cm long
Despite their small size, individual atoms
are observable with instruments such as
scanning tunneling (electron) microscopes
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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
atomic number
Neutrons –
found in the nucleus
no charge
virtually same mass as a
proton

-atomic mass p+n
29
•
The nucleus is:
 Small compared with the overall size of the
atom.
 Extremely dense; accounts for
almost all of the atom’s mass.
Subatomic Particles
Particle
Charge
Mass (g)
Location
Electron
(e-)
-1
9.11 x 10-28
Electron
cloud
Proton
(p+)
+1
1.67 x 10-24
Nucleus
Neutron
(no)
0
1.67 x 10-24
Nucleus
We have had many models of the atom (we will discuss this
more in detail in a later chapter), but for now we will look at the
Bohr Model and Lewis Dot Structures
Neil Bohr’s Atomic Model
electrons orbit nucleus like planets around sun
Example 1 (3D model)
“Jimmy Neutron”
Example 2 (2D model)
Atomic Number
• Atoms are composed of identical
protons, neutrons, and electrons
▫ How then are atoms of one element
different from another element?
• Elements are different because they
contain different numbers of PROTONS
• The “atomic number” of an element is
the number of protons in the nucleus
Atomic Number
Atomic number (Z) of an element is
the number of protons in the nucleus
of each atom of that element.
Element
# of protons
Atomic # (Z)
Carbon
6
6
Phosphorus
15
15
Gold
79
79
Question:
How do I know how many electrons each
element has?
4
Be
Beryllium
9.012
• On the periodic
table the ATOMIC
NUMBER also tells
you how many
electrons there are
• Because:
▫ #of protons = # of
electrons
Atoms have an overall neutral charge
• # of p+ = # of e-
▫ number of protons equals the number of electrons
• example….helium has atomic number of 2
▫ Protons = +2
▫ Neutrons = 0
▫ Electrons= -2
---------------------
• Total charge
0
 Remember this is ONLY true on the periodic table.
 It is not true in “real life”
37
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.
Specifically VALENCE ELECTRONS
Valence Electrons
• Electrons found in the outermost energy level of
an atom.
▫ Determine:
 1. Chemical properties
 2. Atoms ability to form bonds
• Every atom has between 1 and 8 valence
electrons
• Group number helps to determine valence
electrons
Stop Bohr model
Lewis Dot Structures
• What are the valence electrons?
▫ They determine a elements unique properties
▫ They are also the electrons that are used in bonding
• Only these outer electrons want to bond? Why?
▫ all other electrons (in their energy levels) are happy
▫ therefore scientists want to focus their attention on
these specific electrons
• Lewis dot structures
▫ Show only the valence electrons
• How do we figure out the number of valence
electrons?
▫ GROUP NUMBER
So where are the electrons?
• If Bohr model isn’t accurate and Lewis’s just
shows us valence electrons where are the
electrons exactly?
• MODERN ATMOIC THEORY
▫ Electrons are found in orbitals/clouds (regions
around the nucleus where the electrons are likely
to be found)
▫ best scientists can do is calculate chance of finding
electron in certain place within an atom
▫ Electron move very fast.
Modern Atomic Theory
Figuring out the number of
protons, electrons, neutrons
•
•
•
•
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Determining subatomic particles in elements (GENERIC)
Element symbol (X)one/two/three letter symbol for element
Atomic number (Z) number of protons found in the element
Mass number (A)number of protons + the number of neutrons
The periodic table will give you all the information you need in order
to calculate protons, neutrons and electrons
Superscript →
Mass
number
Atomic
Subscript →
number
X
Atomic Number = Number of
protons and number of
electrons.
On the periodic table all
elements are neutral.
Therefore p = e
4
Be
Beryllium
9.012
Element Symbol =
symbol for element:
usually first letter or two
letters of its name.
However, not in all cases.
WHY?
Element Name =
Full name of the element
Average Atomic Mass
Number = Number of
protons and number of
neutrons. Sometimes p = n
Sometimes p = n
Mass Number
Mass number is the number of
protons and neutrons in the nucleus
of an isotope: Mass # = p+ + n0
p+
n0
e- Mass #
8
10
8
18
Arsenic - 75
33
42
33
75
Phosphorus - 31
15
16
15
31
Nuclide
Oxygen - 18
Symbols

Find each of these:
a) number of protons
b) number of
neutrons
c) number of
electrons
d) Atomic number
e) Mass Number
80
35
Br
Symbols

If an element has an atomic
number of 34 and a mass
number of 78, what is the:
a) number of protons
b) number of neutrons
c) number of electrons
d) complete symbol
Symbols
 If an element has 91
protons and 140 neutrons
what is the
a) Atomic number
b) Mass number
c) number of electrons
d) complete symbol
Symbols
 If an element has 78
electrons and 117 neutrons
what is the
a) Atomic number
b) Mass number
c) number of protons
d) complete symbol
Isotopes
Isotopes
•Atoms of the same element can
have different numbers of
neutrons.
•Thus, different mass numbers.
•These are called isotopes.
Isotopes
• Frederick Soddy (1877-1956)
proposed the idea of isotopes in
1912
• Isotopes are atoms of the same element having
different masses, due to varying numbers of
neutrons. (same P, different N)
• Soddy won the Nobel Prize in
Chemistry in 1921 for his work with
isotopes and radioactive materials.
Isotopes are atoms of the same element having
different masses, due to varying numbers of
neutrons.
Isotope
Protons Electrons
Neutrons
Hydrogen–1
(protium)
1
1
0
Hydrogen-2
(deuterium)
1
1
1
1
1
2
Hydrogen-3
(tritium)
Nucleus
Naming Isotopes
•We put the mass number
after the name of the
element:
▫carbon-12
▫carbon-14
▫uranium-235
Isotopes
• Isotopes- an element with the different numbers of
neutrons
▫ Most element have a number of different isotopes
 For example C-12, C-13, and C-14.
• We use C-14 to carbon date fossils
▫ Scientists take an average of these atomic masses
▫ In this calculation the abundance of the isotope is also
calculated
 For example the atomic mass of C is 12.01
• Can you hypothesize which C isotope is most
abundant
▫ ***therefore rare isotopes have little effect on the
atomic mass
Atomic Masses
Atomic mass is the average of all the
naturally occurring isotopes of that element.
Isotope
Symbol
Carbon-12
12C
Carbon-13
13C
Carbon-14
14C
Composition of
the nucleus
6 protons
6 neutrons
6 protons
7 neutrons
6 protons
8 neutrons
Carbon = 12.011
% in nature
98.89%
1.11%
<0.01%
Isotopes
Elements occur
in nature as
mixtures of
isotopes.
Remember:
Isotopes are
atoms of the
same element
that differ in
the number of
neutrons.
57
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
Remember an element is determined
by the number of protons it has*
• What happens if you change the number of protons of an
element?
▫
•
You have a completely different element
What happens if you change the number of neutrons?
▫ you still have same element but this element has a different
number of neutrons then the original element…….
 This is an isotope
• What happens if you change the number of electrons?
▫ You have the same element….but the element has a charge
(either positive or negative)
 This is called an ION
Ions
Ions
• Are atoms of an element with an unequal
number of protons and electrons
• Everything is based off the electron
• ion charge also called Oxidation Number
• Represented as Mg+2 or OH -1
▫ Cation = + ion (loses an electron, therefore has
more protons (+) then electrons)
▫ Anion = - ion (gains an electron, there has
more electrons (-) then protons)
61
Ions
•
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.
62
Ions
•
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.
Oxidation Number
*remember atoms want to be stable
*everyone wants to be like the last column (noble gases)
and have ______ valence electrons. Exceptions?
• How do atoms do this?
▫ Atoms want to get to that stable outer valence shell of
8 electrons.
• Oxygen has ______ valence electrons; therefore it
needs _____ more to get to eight.
• IF AN ATOM NEEDS TO GAIN ELECTRONS THE
OXIDATION NMUMBER IS NEGATIVE. THE
ATOM IS IN NEED. LIKE A DEBT……THE ATOM
NEEDS MORE MONEY (electrons)
• If an atom needs 2 more electrons; its
oxidation number is -2 (negative 2)
•Fluorine has _________ valence electrons;
therefore it needs ________ more to get to
eight.
•If an atom needs 1 more electron; its
oxidation number is -1 (negative 1)
• Nitrogen has ________ valence electrons:
therefore it needs _____ more to get to eight
•If an atom needs 3 more electrons; its
oxidation number is -3 (negative 3)
• NEXT
Lithium has _____ valence electrons: how does it
get to be stable?
What is easier to gain 7 electrons or get rid of
one?
IF AN ATOM HAS EXTRA ELECTRONS THE OXIDATION
NUMBER IS POSITIVE. THE ATOM HAS MORE THEN
IT NEEDS. LIKE A CREDIT……YOU HAVE EXTRA
MONEY (ELECTRONS)TO LOAN
Lithium has ________ valence electrons:
therefore it can loan ______ more to become
stable
What is easier to gain 7 electrons or get rid of
one?
IF AN ATOM HAS EXTRA ELECTRONS THE OXIDATION
NUMBER IS POSITIVE. THE ATOM HAS MORE THEN
IT NEEDS. LIKE A CREDIT……YOU HAVE EXTRA
MONEY (ELECTRONS)TO LOAN
Lithium has ________ valence electrons:
therefore it can loan ______ more to become
stable
If an atom can loan 1 electrons; its
oxidation number is +1 (positive 1)
There is a trend in the oxidation
number on the periodic chart. Can
you find it?
• Beryllium has ___________ valence electrons;
therefore it can loan ________more to become
stable.
• I f an atom can loan 2 electrons; its oxidation
number is +2 (positive 2)
• Carbon has __________ valence electrons; it is
right in the middle; therefore it can gain or loan 4
electrons
• 1... if an atom can gain OR loan 4 electrons; its
oxidation number is +/- 4 (positive or negative 4)
Oxidation trend in the periodic table
Section 4.11
Objective: learn how ions combine to form neutral compounds
72
Compounds that Contain Ions
•
•
Ions combine to form ionic
compounds.
Properties of ionic
compounds


High melting points
Conduct electricity

•
•

If melted
If dissolved in water
Ionic compounds are
electrically neutral.
The charges on the anions
and cations in the compound
must sum to zero.
73
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.
This chapter will be referred to on a daily basis
from here on out. If you do not know and
understand this chapter YOU WILL BE LOST!