Many ancient scholars believed matter was composed of such
things as earth, water, air, and fire. Many believed matter could
be endlessly divided into smaller and smaller pieces.
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Section 4.1 Early Ideas About Matter Key Concepts Democritus
was the first person to propose the existence of atoms. According
to Democritus, atoms are solid, homogeneous, and indivisible.
Aristotle did not believe in the existence of atoms. John Daltons
atomic theory is based on numerous scientific experiments.
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J.J. Thomson's plum pudding model of the atom states that the
atom is a uniform, positively changed sphere containing
electrons.
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In 1911, Ernest Rutherford studied how positively charged alpha
particles interacted with solid matter. By aiming the particles at
a thin sheet of gold foil, Rutherford expected the paths of the
alpha particles to be only slightly altered by a collision with an
electron.
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Rutherford concluded that atoms are mostly empty space. Almost
all of the atom's positive charge and almost all of its mass is
contained in a dense region in the center of the atom called the
nucleus.nucleus Electrons are held within the atom by their
attraction to the positively charged nucleus.
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The repulsive force between the positively charged nucleus and
positive alpha particles caused the deflections.
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Rutherford refined the model to include positively charged
particles in the nucleus called protons.protons James Chadwick
received the Nobel Prize in 1935 for discovering the existence of
neutrons, neutral particles in the nucleus which accounts for the
remainder of an atoms mass.neutrons
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All atoms are made of three fundamental subatomic particles:
the electron, the proton, and the neutron. Atoms are spherically
shaped. Atoms are mostly empty space, and electrons travel around
the nucleus held by an attraction to the positively charged
nucleus.
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Symbols 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.
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Common Elements and Symbols
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Key to the Periodic Table 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 an atom of
that element has. For instance, hydrogen has 1 proton, so its
atomic number is 1. The atomic number is unique to that element. No
two elements have the same atomic number.
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Whats in a square? Different periodic tables can include
various bits of information, but usually: atomic number symbol
atomic mass number of valence electrons state of matter at room
temperature.
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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
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Atomic Mass Atomic Mass refers to the weight of the atom. It is
derived at by adding the number of protons with the number of
neutrons. H
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Atomic Mass and Isotopes 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. When written in this format, the top number is
the mass number and the bottom number would be the atomic number.
(because the atomic number does not change, it may not always be
included.)
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Section 4.3 How Atoms Differ Key Concepts The atomic number of
an atom is given by its number of protons. The mass number of an
atom is the sum of its neutrons and protons. atomic number = number
of protons = number of electrons mass number = atomic number +
number of neutrons Atoms of the same element with different numbers
of neutrons are called isotopes. The atomic mass of an element is a
weighted average of the masses of all of its naturally occurring
isotopes.
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Families Periods 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.
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.
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Alkali Metals The alkali family is found in the first column of
the periodic table. Atoms of the alkali metals have a single
electron in their outermost level, in other words, 1 valence
electron. They are shiny, have the consistency of clay, and are
easily cut with a knife.
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Alkaline Earth Metals They are never found uncombined in
nature. They have two valence electrons. Alkaline earth metals
include magnesium and calcium, among others.
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Transition Metals Transition Elements include those elements in
the B families. These are the metals you are probably most
familiar: copper, tin, zinc, iron, nickel, gold, and silver. They
are good conductors of heat and electricity.
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Boron Family The Boron Family is named after the first element
in the family. Atoms in this family have 3 valence electrons. This
family includes a metalloid (boron), and the rest are metals. This
family includes the most abundant metal in the earths crust
(aluminum).
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Carbon Family Atoms of this family have 4 valence electrons.
This family includes a non- metal (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.
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Nitrogen Family The nitrogen family is named after the element
that makes up 78% of our atmosphere. This family includes non-
metals, metalloids, and metals. Atoms in the nitrogen family have 5
valence electrons. They tend to share electrons when they bond.
Other elements in this family are phosphorus, arsenic, antimony,
and bismuth.
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Oxygen Family Atoms of this family have 6 valence electrons.
Most elements in this family share electrons when forming
compounds. Oxygen is the most abundant element in the earths crust.
It is extremely active and combines with almost all elements.
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Halogen Family The elements in this family are fluorine,
chlorine, bromine, iodine, and astatine. Halogens have 7 valence
electrons, which explains why they are the most active non-metals.
They are never found free in nature. Halogen atoms only need to
gain 1 electron to fill their outermost energy level. They react
with alkali metals to form salts.
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Noble Gases 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.
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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.
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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.
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Periodic Table: electron behavior The periodic table can be
classified by the behavior of their electrons
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Atomic Radius size of atom 1998 LOGAL z First Ionization Energy
Energy required to remove one e - from a neutral atom. 1998 LOGAL z
Melting/Boiling Point C. Other Properties
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Atomic Radius Decreases to the RIGHT and Increases as you go
DOWN D. Atomic Radius
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Electronegativity Trend Increases up and to the right.
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First Ionization Energy Increases UP and to the RIGHT E.
Ionization Energy
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Melting/Boiling Point Highest in the middle of a period. F.
Melting/Boiling Point
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Summary of Periodic Trends 1. Melting/Boiling Point 2. Atomic
Radius 2. Atomic Radius 3. Ionization Energy 3. Ionization Energy
4. Electron Affinity 4. Electron Affinity Note: direction of arrow
shows increase; arrows are color coded