Transcript Chemistry Ch. 5

Periodic Table of Elements
Mendeleev
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In 1869, Dmitri Ivanovitch
Mendeléev created the first accepted
version of the periodic table.
He grouped elements according to
their atomic mass, and as he did, he
found that the families had similar
chemical properties.
Blank spaces were left open to add
the new elements he predicted
would occur.
The Current Periodic Table
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Mendeleev wasn’t too far off.
Now the elements are put in rows by
increasing ATOMIC
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NUMBER!!
The horizontal rows are called periods and
are labeled from 1 to 7.
The vertical columns are called groups or
families and are labeled from 1 to 18.
Elements
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Science has come
along way since
Aristotle’s theory of Air,
Water, Fire, and Earth.
Scientists have
identified 90 naturally
occurring elements, and
created about 28
others.
Elements
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The elements, alone or in
combinations, make up our
bodies, our world, our sun,
and in fact, the entire
universe.
Almost all elements are
made up of 3 sub atomic
particles. Protons (+),
neutrons (0) & electrons (-)
The most abundant element in the
earth’s crust is oxygen.
Periodic Table
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The periodic table organizes the elements in a
particular way. A great deal of information about an
element can be gathered from its position in the
period table.
For example, you can predict with reasonably
good accuracy the physical and chemical
properties of the element. You can also predict
what other elements a particular element will react
with chemically.
Understanding the organization and plan of the
periodic table will help you obtain basic information
about each of the 118 known elements.
What’s in a square?
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Different periodic tables
can include various bits
of information, but
usually:
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atomic number
symbol
atomic mass
Key to the Periodic Table
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Elements are organized on
the table according to their
atomic number, usually
found near the top of the
square.
 The atomic number refers
to how many protons or
electrons an atom of that
element has.
 For instance, hydrogen
has 1 proton, so it’s
atomic number is 1.
 The atomic number is
unique to that element.
No two elements have
the same atomic number.
Symbols
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C
Cu
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Carbon
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Copper
All elements have their
own unique symbol.
It can consist of a single
capital letter, or a capital
letter and one or two
lower case letters.
Elements have their name
for a variety of reasons.
Some are named after
mythology, countries,
scientists or in Latin or
Greek.
Atomic Number
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Bohr Model of Hydrogen Atom
This refers to how
many protons or
electrons an atom
of that element
has.
No two elements,
have the same
number of protons.
Atomic Mass
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Atomic Mass refers
to the “weight” of
the atom.
It is derived at by
adding the number
of protons with the
number of
neutrons.
This is a helium atom. Its atomic mass is 4
(protons plus neutrons).
What is its atomic number?
Atomic Mass Unit (AMU)
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The unit of
measurement for
an atom is an AMU.
It stands for atomic
mass unit.
One AMU is equal
to the mass of one
proton.
Atomic Mass Unit (AMU)
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There are
6 X 1023 or
600,000,000,000,000,
000,000,000 amus in
one gram.
(Remember that
electrons are 2000
times smaller than
one amu).
Atomic Mass and Isotopes
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While most atoms have the same number of protons and
neutrons, some don’t.
Some atoms have more or less neutrons than protons.
These are called isotopes.
An atomic mass number with a decimal is the total of the
number of protons plus the average number of neutrons.
We write isotopes like this:
Uranium has 2 isotopes: Uranium – 238 & Uranium - 239
Mass #
Atomic #
238
U
92
239
92
U
Isotope Examples
List the protons, neutrons, electrons and the symbol
 Carbon – 12
 Carbon – 13
 Carbon – 14
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The # of neutrons may vary.
Isotopes have different mass numbers.
Isotopes of the same element are still chemically alike
because they have the same number of protons and
electrons.
Properties of Metals
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Metals are good conductors
of heat and electricity.
Metals are shiny.
Metals are ductile (can be
stretched into thin wires).
Metals are malleable (can be
pounded into thin sheets).
A chemical property of metal
is its reaction with water
which results in corrosion.
Properties of Non-Metals
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Sulfur
Non-metals are poor
conductors of heat and
electricity.
Non-metals are not
ductile or malleable.
Solid non-metals are
brittle and break easily.
They are dull (not
shiny).
Many non-metals are
gases.
Properties of Metalloids
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Silicon
Metalloids (metal-like)
have properties of both
metals and non-metals.
They are solids that can
be shiny or dull.
They conduct heat and
electricity better than nonmetals but not as well as
metals.
They are brittle and not
ductile
A Family is also called a Group.
based on their atomic numbers.
Groups or
Families
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Columns of elements are
called groups or families.
Elements in each family
have similar but not
identical properties.
For example, lithium (Li),
sodium (Na), potassium
(K), and other members of
family IA are all soft,
white, shiny metals.
All elements in a family
have the same number of
valence electrons.
Periods
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Each horizontal row of
elements is called a period.
The elements in a period
are not alike in properties.
In fact, the properties
change greatly across even
given row.
The first element in a
period is always an
extremely active solid. The
last element in a period, is
always an inactive gas.
The period tells us how
many orbitals the element
has.
Valence Electrons
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The number of valence
electrons an atom has
may also appear in a
square.
Valence electrons are the
electrons in the outer
energy level of an atom.
These are the electrons
that are transferred or
shared when atoms bond
together.
What does it mean to be
reactive?
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We will be describing elements according to their
reactivity.
Elements that are reactive bond easily with other elements
to make compounds.
Some elements are only found in nature bonded with
other elements.
What makes an element reactive?
 An incomplete valence electron level.
 All atoms (except hydrogen) want to have 8 electrons
in their very outermost energy level (This is called the
octet rule.)
 Atoms bond until this level is complete. Atoms with less
than 4 valence electrons lose them during bonding.
Atoms with 6, 7, or 8 valence electrons gain electrons
during bonding.
Elements that have either gained
or lost electrons are called ions.
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Positively charged: Cations
 Any atom that loses electrons to form
compounds are called cations. Cations
have a positive charge.
 Naming cations: Use the element name
followed by the word “ion”. Some Cations
have more than one charged form.
Table: Metal cations with more than one common charged form
Cation formula
Fe2+
systematic name
iron(II) ion
common name
ferrous ion
Fe3+
iron(III) ion
ferric ion
Cu1+
copper(I) ion
cuprous ion
Cu2+
copper(II) ion
cupric ion
Hg1+
mercury(I) ion
mercurous
ion
Hg2+
mercury(II) ion
mercuric ion
Pb2+
lead(II) ion
plumbous
ion
Pb4+
lead(IV) ion
plumbic ion
Sn2+
tin(II) ion
stannous ion
Sn4+
tin(IV) ion
stannic ion
Elements that have either gained
or lost electrons are called ions.
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Negatively charged: Anions
 Atoms that gain electrons to form
compounds are called anions. Anions
have a negative charge.
 Naming Anions: Drop the last few letters
of the element name and add “ide”.
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How can we determine the
charge of an ion?
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For some of the elements it is very easy.
Elements in groups 1, 2, 13, 14, 15, 16, & 17
will lose or gain electrons so they have the
same # as the nearest Noble Gas (group
18).
The transition metals (groups 3- 12) cannot
have their charges predicted in this way due
to many of them having isotopes. Their
charges must be predicted in other ways.
Noble Gases
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Noble Gases are colorless gases that are extremely un-reactive.
One important property of the noble gases is their inactivity. They are
inactive because their outermost energy level is full.
Because they do not readily combine with other elements to form
compounds, the noble gases are called inert.
The family of noble gases includes helium, neon, argon, krypton,
xenon, and radon.
All the noble gases are found in small amounts in the earth's
atmosphere.
Bohr’s Model of the Atom
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Bohr Model
Electrons orbit the
nucleus at a fixed
distance.
Each orbit is associated
with a definite energy
level.
Energy levels are quantized
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Electrons travel in orbits
around the nucleus
The farther the electron
is from the nucleus the
more energy it has.
Electron Dot Diagrams
• If you want to see how atoms of one element
will react, it is handy to have an easier way
to represent the atoms and the electrons in
their outer energy levels.
• You can do this with electron dot diagrams.
• An electron dot diagram is the symbol for
the element surrounded by as many dots as
there are electrons in its outer energy level.
How to Write Them
• The dots are written in pairs on four sides of
the element symbol.
• Start by writing one dot on the top of the
element symbol, then work your way around
adding dots to the right, bottom, and left.
How to Write Them
• Add a fifth dot to the top to make a pair.
Continue in this manner until you reach the
number of valence electrons the element
has or until there are eight dots to complete
the level.
Forming Compounds
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Sodium is an element.
Chlorine is an
element.
When sodium and
chlorine bond they
make the compound
sodium chloride,
commonly known as
table salt.
Compounds have different properties
than the elements that make them up.
Table salt has different properties than
sodium, an explosive metal, and chlorine,
a poisonous gas.
Forming Compounds
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A chemical bond is formed when valence
electrons of atoms interact and become
stable.
Ionic Compounds – substances composed of
cations and anions forming ionic bonds.
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Certain combinations of elements form ionic
bonds
groups 1, 2, and 3 metals with group
16 & 17 nonmetals.
Eg. Na+ + ClNaCl
Forming Compounds
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Covalent bond – A
bond formed when
atoms share 2 or more
pairs of electrons.
A neutral particle that is
composed of atoms
joined together by
covalent bonds is
called a molecule.
Eg. Diatomic molecules
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Molecules that contain two (“di”) atoms.
“The Magic 7” + Hydrogen – These
elements are never found by themselves in
nature, they are always in pairs. Mark them
on your periodic table.
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H, N, O, F, Cl, Br, I, At
These start at the element #7
They form the shape of a 7
Naming Formulas
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Binary Compounds – Contain 2 different
elements. The name usually ends in “ide”
Eg. sodium chloride.
When combining 2 ions, you need to create
a net charge of zero.
Eg. Ca2+ + ClCaCl2 (2 positives, 2
negatives = 0 charge)
Crossing Over Method
2+
Ca
+
2O
Ca2O2
(2’s cancel out) CaO = Calcium Oxide
2+
Mg
+
Cl
MgCl2
= Magnesium Chloride
Do Investigations Exercise on pg. 156-158 in text
Polyatomic Ions
Consists of 2 or more different non metals
like ammonium (NH4 = Nitrogen and 4
Hydrogen). See list on page 159.
Eg. NH4+ + OHNH4OH = Ammonium hydroxide
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Parentheses may be needed for polyatomic ions.
Fe3+ + OH-
Fe(OH)3 = Iron (III) hydroxide
Things to look for
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If cations have (), the number inside the () is
their charge. Not how many.
If anions end in -ide they are probably off the
periodic table (Monoatomic)
If anion ends in -ate or -ite it is polyatomic.
The positive piece always gets written first.
Hydrogen- it depends on where it’s at
If it is first, it is a metal – hydrogen ion
 If it is second, it’s a nonmetal - hydride
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