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Objective List names and symbols of common elements. Describe the present model of
the atom. Describe how electrons are
arranged in an atom. Objective Identify quarks as particles
of matter that make up protons and neutrons. Explain how particle
accelera-tors are used to study particles within
atoms. Objective Compute the atomic mass and
mass number of an atom. Identify and describe
isotopes of common elements. Interpret the average atomic
mass of an element. Objective Describe the periodic table
of elements and use it to find info about an
element. Distin- guish between a group and a
period. Use the periodic table to
classify an element as a metal, nonmetal,
metalloid. |
Section 1 – Structure of the
Atom An abbreviated way to write
the name of an element is called a
. Chemical symbols consist of
one capital letter or a capital letter plus one or two small letters. Some of the symbols come from the
elements Latin name. The symbol for chlorine
is
. The idea of atoms began more
than 2400 years ago with the Greeks.
Atoms consist of a positively charged center or core that is called
the
. The nucleus is
surrounded by negatively charged particles called
. The electrons move around the
nucleus. The two major kinds
of particles in the nucleus are
and
. The mass of a proton
is about the same as that of a neutron. The mass of an electron is very,
very small. Proton
Positive charge
Electron
Negative charge
Neutron
No Charge The identity of an element is
determined by the number of
. The
of an atom is the number of protons in its
nucleus. Every atom of the same
element has the same number of protons. The number of electrons in a
neutral atom is equal to the number of protons. We use models to help us
understand something we can’t see directly, usually because it is too
large or small. As more
information is collected, scientists change their
models. One of the earliest models of
an atom was called the Bohr model.
Niels Bohr (1913) pictured the atom as having a central nucleus
with electrons moving around it in well-defined paths, or orbits. There were models by Dalton,
Thomson, and Rutherford that Bohr built his model
on. In 1926, scientists developed
a better model of the atom.
In this model, the electrons moved about in a region called an
. This cloud surrounds
the nucleus. Because an electron’s mass is
so small, no one can tell exactly where it is as it moves in the
atom. All anyone can tell you
is where it probably is.
According to present atomic theory, the location of an
in an atom is best represented by a probability
cloud. Within the electron cloud,
electrons are at various distances from the nucleus. Electrons closest to the nucleus
have low energy. Electrons
farther away from the nucleus have higher energy. Each energy level of an atom has a
maximum number of
it can hold. Energy Level of an
Atom
# of Electrons 1 2 2 8 3 18 4 32 Section 2 – Smaller Particles
of Matter Protons and neutrons are made
of even smaller particles called
. Right now, we know of 6
different quarks. Each proton
and neutron contains 3 quarks. To bust an atom up into the
quarks, a particle accelerator is used. Inside the particle accelerator,
protons are bombarded with other protons to produce the
quarks. One particle accelerator, the
Tevatron, is located at Fermilab in Batavia,
Illinois. Section 3 – Masses of
Atoms The mass of an atom is very
small. Even using grams to
measure them wouldn’t be small enough. The unit of measurement for atoms
is the atomic mass unit (amu).
A proton or neutron has a mass of 1 amu. The atomic mass is defined as 1/12
the mass of a carbon atom containing 6 protons and 6
neutrons. The sum of the number of
protons and the number of neutrons in an atom is the
.
Protons + neutrons=Mass number # of neutrons= Mass number – Atomic
number Ex.- A certain atom has 26
protons, 26 electrons, and 30 neutrons. Its mass number
is
. Not all atoms of an element
have the same number of neutrons.
Atoms of the same element that have different numbers of neutrons
are called
. Ex.- Two isotopes of carbon
are Carbon 12 and Carbon 14.
These isotopes differ from one another by 2
. Because of the existence
of
, the atomic masses of the elements are not whole value
number.p.279, Table 10-4. Because most elements have
more than one isotope, each element is given an
. It is the weighted
average of the mass numbers of all the isotopes that occur in nature for a
particular element. Complete the following
table. The atomic number of
hydrogen is 1.
Concept Map for
Atom
Atom Electron
Nucleus
Cloud
Mass Number
Electrons
Protons
Neutrons
Atomic # Negative charge
Pos. Charge
No charge
Section 4 – The Periodic
Table The word periodic means
repeated in a pattern. An
example would be a calendar. In the late 1800’s, Dimitri
Mendeleev searched for a way to organize the elements. When he arranged all the elements
known at the time(26) in order of increasing atomic mass, he found a
pattern. Because the pattern
was repeated, it could be considered periodic. We call this arrangement a
of elements. Although Mendeleev’s periodic
table was good, it needed some changes. In 1913, Henry G.J. Moseley
arranged the elements based on their properties and atomic numbers instead
of atomic masses. In a periodic table, the
vertical columns are called
or
. The groups are numbered
1-18. Elements in each group
have similar properties. The
number of electrons in the outer energy level determine the chemical
properties of the element.
These outer electrons are so important that a special way to
represent them has been developed.
A
uses
the symbol of the element and dots to represent the electrons in the outer
energy level. Ex. :Ne: The
elements in Group 18 are known as noble gases. They have a very stable electron
arrangement. Some of the later elements in
the periodic table are made by man or are called
synthetic. The horizontal rows of
elements in the periodic table are called
. On the table, there
is a stair-step line. All
elements to the left of the line, except hydrogen, are metals. Most metals have the common
properties of being solids, shiny, and good conductors of heat and
electricity. Metals also have
3 or less electrons in the outer energy level. The elements to the right of
the stair-step line on the periodic table are classified as
. Most nonmetals are gases that
do not conduct heat and electricity well. They also have between 4 and 8
electrons in their outermost energy level. The elements next to the
stair-step line are
because they have properties of metals and
nonmetals. The elements in groups 3
through 12 are called transition elements. As you move from left to
right in a row across the periodic table, metallic properties
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