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The Atom, the
Elements, & the
Periodic Table
Democritus (460-370 BC)
Proposed that matter was made of small particles
he called atoms. In Greek this means indivisible
or cannot be divided. He believed different atoms
would vary in size and would be in constant motion.
Extremely small
particles in motion
John Dalton (1766-1844)
Published the atomic theory:
1. Elements made of atoms.
2. Atoms of the same element are identical.
3. Atoms of different elements have different properties.
4. Atoms DON’T CHANGE, but can be combined and
rearranged with other atoms.
5. Compounds are formed when atoms of more than one
element combine in specific ratios.
Joseph John Thomson (1856-1940)
Identified the electron, which carries a negative
charge. He thought that electrons were embedded
in the atom like blueberries in a muffin.
Atom as
solid object
Atom as
solid object with
a positive center and
electrons embedded
in the atom
2
Ernest Rutherford (1871-1937)
Used high speed lightweight atoms called
alpha particles to bombard very thin gold foil.
Most of these alpha particles passed through
the gold foil. The fact that these particles went
through the foil lead to his theory that atoms
have mostly empty space.
Alpha particles
went through
spaces.
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Neils Bohr (1885-1962)
Described the electrons moving
around the nucleus in fixed orbits.
Each orbit has a set amount of energy.
We use this model for a basic
understanding of the atom’s structure.
However, more recent research has shown that
electrons move around the nucleus in waves rather
than elliptical orbits. Electrons are better represented
as an “electron cloud.”
James Chadwick (1891-1974)
Solved the problem of “missing mass” in the atom by
discovering the neutron.
Electrons move so fast
that scientists prefer the
atom model where
electrons are represented
by a cloud.
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3
Basic Structure of an Atom
Proton
Positive Charge
Neutron
1 AMU
1 AMU
++
1 AMU
1 AMU
No Charge
Electron
Negative Charge
4
Atomic Number
• This refers to how
many protons an atom
of that element has.
• No two elements,
have the same number
of protons.
Wave Model
Atomic Mass
• Atomic Mass = the
“weight” of the atom.
• Number of protons
plus 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)
• The unit of
measurement for an
atom is an AMU.
• One AMU = the mass
of one proton.
Atomic Mass Unit (AMU)
• 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).
Element Name
Beryllium
Atomic Number
4
(# of protons and electrons)
Element Symbol
Atomic Mass
(Average mass of all the isotopes of
that element)
Be
9.01
+
+
++
9
What are the numbers of protons, electrons and neutrons
in a Nitrogen-14 atom?
Nitrogen-14
Nitrogen
7
14 is the mass number.
Mass number = #p + #n
N
14.01
#p = 7 (atomic number)
#e= 7 (equal to the
number of protons)
#n = 7 (mass # - # p)
10
What are the numbers of protons, electrons and neutrons
in a potassium-39 atom ( remember 39 is the mass number)?
Potassium
19
K
P = 19
E = 19
N = 20
39.098
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What are the numbers of protons, electrons and neutrons
in a chlorine-36 atom?
Chlorine
17
Cl
P = 17
E = 17
N = 18
35.4
12
Energy Levels of Electrons
• Energy level Maximum # of electrons
•1
2
•2
8
•3
18
•4
32
•5
50
Atoms of a given element with different numbers of
neutrons.
All isotopes will have the same atomic
number but different mass numbers.
Mass number = #p + #n
1
Hydrogen
Shown below are three isotopes of
hydrogen. The letter after the name
tells you the mass number. The most
common isotope of hydrogen is
Hydrogen-1.
H
1.01
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Hydrogen-1
Hydrogen-2
Hydrogen-3
14
• The mass of an element is the mass of the element
compared to an isotope of carbon, Carbon 12.
– Carbon 12 is assigned an atomic mass of 12.00 g.
– 12.00 is one atomic mass unit
• The number of protons and neutrons in an atom is its
mass number.
• Atomic numbers are whole numbers
• Mass numbers are whole numbers
• The atomic mass is not a whole number.
Periodic Table of Elements
Patterns in the Elements
• Dmitri Mendeleev noticed a pattern in the
properties of the elements when he arranged
the elements in order of increasing atomic
mass.
• He is credited for developing the first
periodic table.
• Mendeleev left blank
spaces in his table when
the properties of the
elements above and
below did not seem to
match. The existence of
unknown elements was
predicted by Mendeleev
on the basis of the blank
spaces. When the
unknown elements were
discovered, it was found
that Mendeleev had
closely predicted the
properties of the elements
as well as their discovery.
• The Periodic Law
– Similar physical and chemical properties recur
periodically when the elements are listed in order of
increasing atomic number.
– Chemical Symbols
• There are about a dozen common elements that have
single capitalized letter for their symbol
• The rest, that have permanent names have two letters.
– the first is capitalized and the second is lower case.
• Some elements have symbols from their Latin names.
• Ten of the elements have symbols from their Latin or
German names.
• Introduction
– The periodic table is made up of rows of elements and
columns.
– An element is identified by its chemical symbol.
– The number above the symbol is the atomic number
– The number below the symbol is the rounded atomic
weight of the element.
– A row is called a period
– A column is called a group or family
Other information
• Many periodic tables include a zig-zag line
that separates the metals from the nonmetals. The metals are to the left of the
line, the non-metals to the right.
Properties of Metals
• Physical properties include:
– Malleable – ability to be hammered or rolled
into flat sheets or other shapes.
– Ductile – ability to be pulled out or drawn into
a wire.
– Good Conductors – of heat & electricity
Other Properties of (some) Metals
•
•
•
•
•
Shiny appearance / metallic luster
Solids
High density
Magnetic
React with other elements by LOOSING
electrons.
• Corrosion
Properties of Non-Metals
• Lack the properties of metals (opposites)
• Poor conductors
• Brittle (not malleable or ductile)
– Non-metals will generally break, crumble or
powder when hit with a hammer.
Other properties of Non-Metals
•
•
•
•
•
Dull appearance
Gases
Low density
Characteristic color
React with other elements by GAINING
OR SHARING electrons.
Properties of Metalloids
• 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 ductile and
malleable.
• Semi-conductors – computer
chips, transistors, lasers
Silicon
Organization
• The properties of an
element can be
predicted based on the
location within the
periodic table.
• Periods – horizontal
rows
– Indicates the number
of shells
Organization
• Groups
– Indicates the number of
valence electrons
– Shows how reactive an
element is.
• Groups/families share
similar characteristics
or properties
Valence Electrons
• 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.
Families
• 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
• 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.
Hydrogen
• The hydrogen square sits atop Family AI, but
it is not a member of that family. Hydrogen is
in a class of its own.
• It has one valence electron in its one and only
energy level.
• It’s a gas at room temperature.
• Hydrogen only needs 2 electrons to fill up its
valence shell.
Alkali Metals
• The alkali family is group 1.
• Atoms of the alkali metals have
1 valence electron that they
lose when forming bonds.
• They are shiny, have the
consistency of clay, and are
easily cut with a knife.
Alkali Metals
• They are the most
reactive metals.
• They react violently
with water.
• Alkali metals are
never found as free
elements in nature.
They are always
bonded with another
element.
What does it mean to be reactive?
• 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 rule of octet.)
– Atoms bond until this level is complete. Atoms with few valence
electrons lose them during bonding. Atoms with 6, 7, or 8 valence
electrons gain electrons during bonding.
5
Alkaline Earth Metals
• The alkaline earth family is group 2.
• They have two valence electrons that they lose when
forming bonds.
• They are never found uncombined in nature and very
reactive.
• Alkaline earth metals include magnesium and calcium,
among others.
Transition Metals
• Transition Elements include those
elements in families 3-12.
• Transition elements valence
electrons vary, but many have
1 or 2 valence electrons, which
they lose when they form bonds
with other atoms. Some transition
elements can lose electrons in their
next-to-outermost level.
• They are good conductors of heat
and electricity.
Transition Metals
• The compounds of transition metals are usually brightly
colored and are often used to color paints.
• These are the metals you are probably most familiar:
copper, tin, zinc, iron, nickel, gold, and silver.
Boron Family
• The Boron Family is family 13.
• Atoms in this family have 3
valence electrons that are
typically shared when forming
bonds.
• This family includes a metalloid
(boron), and the rest are metals.
• This family includes the most
abundant metal in the earth’s
crust (aluminum).
Carbon Family
• The Carbon family is family 14.
• There are 4 valence electrons
that are typically shared when
forming bonds..
• This family includes a nonmetal (carbon), metalloids, and
metals.
• The element carbon is called the
“basis of life.” There is an entire
branch of chemistry devoted to
carbon compounds called
organic chemistry.
Nitrogen Family
• The nitrogen family is family 15,
named after the element that
makes up 78% of our
atmosphere.
• Atoms in the nitrogen family
have 5 valence electrons. They
tend to share electrons when
they bond.
• This family includes non-metals,
metalloids, and metals.
• Other elements in this family are
phosphorus, arsenic, antimony,
and bismuth.
Oxygen Family
• Oxygen family is family
16.
• Atoms of this family have
6 valence electrons. They
tend to share or gain
electrons when they bond.
• Oxygen is the most
abundant element in the
earth’s crust. It is
extremely active and
combines with almost all
elements.
Halogen Family
• Halogen family is family
17.
• Halogens have 7 valence
electrons, and will gain
an electron when forming
bonds.
• This explains why they
are the most active nonmetals. They are never
found free in nature.
•They react with alkali metals
to form salts.
•The elements in this family are
fluorine, chlorine, bromine,
iodine, and astatine.
Inert Gases
• Noble Gases are family 18.
• One important property of the noble gases is their inactivity. They are
inactive because their outermost energy level is full, with 8 valence
electrons.
• They are colorless gases that are extremely un-reactive.
• 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.
Rare Earth Elements
• The thirty rare earth
elements are composed of
the lanthanide and actinide
series.
• One element of the
lanthanide series and most
of the elements in the
actinide series are called
trans-uranium, which means
synthetic or man-made.