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CHAPTER 3
Chemical Foundations
3.1 THE ELEMENTS
• 118 elements
•92 occur naturally, the rest are synthesized
•All matter in the universe can be chemically broken
down into elements
•Compounds are made by combining atoms of elements
like words are formed from letters of the alphabet.
Words
Compounds
ABUNDANCE OF
ELEMENTS
• 9 elements make up about 98% of Earth
• Elements of the human body: CHNOPS
THE WORD ELEMENT CAN
HAVE SEVERAL MEANINGS
Element
Element
Element
Microscopic form
Single atom of that
element
Macroscopic form
Sample of that
element large enough
to weigh on a balance
Generic form
When we say the human body contains the element
sodium or lithium, we do not mean that free
elemental sodium or lithium is present. Rather we
mean that atoms of these elements are present in
some form.
NAME AND SYMBOLS
FOR THE ELEMENTS
• Each element has a unique name and symbol
• Symbol usually consists of first one or two letters of
elements name
• Oxygen = O
• Krypton = Kr
• Sometimes the symbol is taken from the original Latin or
Greek name
FORMULAS OF
COMPOUNDS
• The types of atoms and the number of each type is
shown using chemical symbols and subscripts.
• Write the formula for each of the following, listing the
elements in the order given
• One atom of sulfur and three atoms of oxygen
• Two atoms of nitrogen and five atoms of oxygen
• give the number of each atom in the following:
• Ca(NO3)2
• AlPO4
• Al2(SO4)3
• 2H2O
3.2 EARLY IDEAS ABOUT
MATTER
• Greek philosophers – formed explanations based on life
experiences
•Proposed four ‘elements’
DEMOCRITUS – 400 BC
•Believed matter was made of tiny particles called atomos
• Cannot be created, destroyed, or divided
•Aristotle disagreed
ALCHEMY
• Origin of the word Chemistry
• Tried to make gold out of abundant elements
• Invented many of the techniques still used today like
filtration and distillation
ANTOINE LAVOISIER
• 1743-1794
• French scientist known as the “Father of Chemistry”
• Made Chemistry quantitative by taking accurate
measurements
• Wrote 1st chemistry textbook
• Beheaded in 1794 for being funded by taxes
PROUST (1754-1826)
• Proposed the Law of Constant Composition (1794):
• A given compound always contains the same proportion by mass of
the elements of which it is composed.
JOHN DALTON (1803)
• Revived and Revised Democritus’ idea
• Came up with his own Atomic Theory
• All elements are composed of tiny particles called atoms
which cannot be broken into smaller parts.
• All atoms of the same element are identical, atoms of
different elements are different
• Atoms of one element can combine with atoms of other
elements to form compounds. A given compound always has
the same relative numbers and types of atoms
• Chemical reactions take place when atoms rearrange. Atoms
are not created or destroyed during chemical reactions.
3.3 DEFINING THE ATOM
• The smallest particle of an element that retains the
properties of the element
•Atoms are very small
 One Cu atom = 1.28 x 10-10 m
 Solid copper penny = 2.9 x 1022 atoms
 If 1 atom = size of an orange, an orange would be as big as
the earth!
• Scanning tunneling microscope (STM) allows individual
atoms to be seen
 Scans across the surface of atoms
 silicon
J.J. THOMSON – 1897
Worked with a cathode ray tube
Discovered cathode ray was attracted to positively
charged plate
What 2 things did Thomson learn from this experiment?
By measuring the effects of both magnetic and electric
fields on a cathode ray, Thomson determined the mass of
the charged particle is less than the hydrogen atom (the
lightest atom known)
Why is this significant?
What subatomic particle did Thomson discover?
•Thomson’s model
 Matter is neutral so some positive charge needs to balance
out the negative electrons
 Plum pudding model
ERNEST RUTHERFORD 1911
• In 1911, Rutherford and his coworkers at the University of
Manchester, England, directed a narrow beam of alpha
particles at a very thin sheet of gold foil.
• Based on Thomson’s model of the atom he expected
the alpha particles to pass through the foil but not all did!
What conclusion can Rutherford draw from this result?
Rutherford concluded:
 Atom consists of mostly empty space
 If an atom had a diameter of 2 football fields the nucleus would be
the size of a nickel
 Almost all + charge & mass are found in nucleus
Rutherford Model of the atom
ATOMIC STRUCTURE
Ernest Rutherford showed that atoms
have internal structure.
 The nucleus, which is at the center of the
atom, contains protons (positively charged)
and neutrons (uncharged).
– Electrons move around the nucleus.
JAMES CHADWICK - 1932
What we knew
1.
Electrons & Protons have opposite charges
2.
Neutral atom has same number of electrons as
protons
3.
Mass of atom was too much to just be made of
protons & electrons
Showed nucleus contained
a particle with the same
mass as a proton but no
charge – neutron
Particle
Electron
Proton
Neutron
Symbol
Location Charge
Mass
The number of protons in an atom identifies it as a
particular element
Number of protons = atomic number
Periodic table is organized in order of increasing atomic
number
All atoms are electrically neutral therefore
# of protons =
Determine the number of protons and electrons in an
atom of Molybdenum
MASS NUMBER
Mass number = protons + neutrons
Neutrons =
Mass numbers are given in atomic mass units (amu)
 1 amu = 1/12 mass of Carbon-12 atom
ATOMIC SHORTHAND
• Beryllium- - -atomic number 4
mass number 9
The atomic number is written as a subscript.
The mass number is written as a superscript.
Be
Element
Atomic
Number
Protons
35
10
Electrons
Neutrons
19
20
Mass
number
80
20
ISOTOPES
Atoms with the same number of protons but different
number of neutrons
• Most naturally occurring elements have two or more
stable isotopes
 One is usually more common than the others
 Oxygen – 16, oxygen – 17, oxygen - 18
• mass number vs. atomic mass
• Mass number = protons + neutrons
• Atomic mass (on periodic table) = weighted average of all
the isotopes of an element
CALCULATING ATOMIC
MASS
Unknown element X has two isotopes. 6X has an atomic
mass of 6.015 amu and a 7.59 % abundance. 7X has an
atomic mass of 7.016 amu and a 92.41% abundance.
What is the atomic mass of the unknown element? What
is the identity of the unknown element?
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.
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.
Element
Atomic
#
Protons Electrons Neutrons
O2Al3+
19
14
6C
Potassium - 41
18
Mass
number
Ion charges can be predicted from the periodic table
WHAT CAN CHANGE IN
AN ATOM?
Protons – NEVER!!!
Neutrons – if changed an isotope is formed
Electrons – if changed an ion is formed
PROTON CHANGED
Whole new atom!!!
Oxygen loses a proton it becomes Nitrogen
Oxygen gains a proton it becomes Fluorine
NEUTRON CHANGED
Different version of the same atom is formed (isotope)
Oxygen – 16 has 8 Neutrons
Oxygen – 17 has 9 Neutrons
Oxygen – 18 has 10 Neutrons
ELECTRONS CHANGED
Charged version of the same atom is formed (ion)
Oxygen gains 2 electrons – 10 electrons & 8 protons
 Anion
Oxygen loses 2 electrons – 6 electrons & 8 protons
 Cation
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
 Total positive charge must cancel out total negative charge
FORMULAS FOR IONIC
COMPOUNDS
Write cation symbol followed by anion symbol
The number of cations and ions must be correct so their
charge sums to zero
• Write the formula for compounds containing the
following ions:
 Potassium and oxygen
 Calcium and sulfur
 Magnesium and nitrogen
3.4 INTRODUCTION TO
THE PERIODIC TABLE
• In 1913 our current periodic table was developed by
Henry Moseley who arranged the atoms by atomic
number
• Periodic law – when elements are arranged according
to increasing atomic number, there is a periodic
repetition of chemical and physical properties
THE MODERN PERIODIC
TABLE
•Columns = groups
 Numbered 1 – 18
 Correspond to the number of outermost electrons
• Have similar properties
 Some have special names
•Rows = periods
 Numbered 1 – 7
 Correspond to outermost energy level
PHYSICAL STATES AND
CLASSES OF ELEMENTS
•Most elements are solid at room temperature
•Br & Hg are liquid
•N, O, F, Cl, and Noble gases are gas
METALS
•Shiny
•Solid at room temperature
•Good conductors of heat & electricity
•Malleable
•Ductile
•Found to the left of the staircase
• 1 exception =
Alkali metals – group 1 elements
 Except for
 Very reactive
 # of valence electrons =
Alkaline earth metals – group 2 elements
 Also highly reactive
 # of valence electrons =
Transition metals – group 3 – 12 (d block)
 Number of valence electrons varies
Inner transition metals – f block
 Number of valence electrons varies
 Lanthanide & actinide series
NONMETALS
•Gasses or dull looking solids
• 1 exception =
•Poor conductors of heat and electricity
•Found to the right of the staircase
Halogens – group 17
 Highly reactive
 # of valence electrons =
Nobel gases – group 18
 Extremely unreactive
 # of valence electrons =
METALLOIDS
Border the staircase
Have properties of both metals and nonmetals
Semi-conductors = conduct electricity only under certain
conditions
NATURAL STATES OF 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
NATURAL STATES OF THE
ELEMENTS
Diatomic Molecules
Nitrogen gas contains
N2 molecules.
Oxygen gas contains
O2 molecules.
NATURAL STATES OF THE
ELEMENTS
Diatomic Molecules
NATURAL STATES OF THE
ELEMENTS
Elemental Solids
Carbon
atoms
Diamond
Graphite
Buckminsterfullerene