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Matter, Atoms, and Elements

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by

Colette Galivan

on 18 May 2014

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Transcript of Matter, Atoms, and Elements

Matter
The "stuff" that makes up all things.
Technical Definition of Matter: Anything that occupies space and has mass.
Atoms
The basic particles of Matter.
Aluminum foil is pure aluminum. If you tear a piece of aluminum foil into smaller and smaller pieces, until you (or a machine) cannot tear the aluminum any more, what you have left is
one atom
of aluminum. You cannot see an atom--it is that tiny.
Pure Substances--
Matter with a specific composition.
A pure substance can be an
element
, when composed of
one type of atom
.
Some elements are found as single atoms like carbon (
C
) and helium (
He
). Others occur naturally as molecules like oxygen and hydrogen (which we will cover in more depth later).
A pure substance also can be a
compound

when composed of two or more elements combined in a definite ratio. For example:
A
mixture
is a type of matter that consists of:
two or more substances that are
physically
mixed, not chemically combined.
two or more substances in different proportions.
substances that can be separated by
physical
methods.
In a

homogeneous mixture
:
the composition is uniform throughout.
the different parts of the mixture are
not visible
.
For Example: In a chocolate milkshake, you can't see the different parts of milk, ice cream, and chocolate syrup.
In a
heterogeneous mixture
,
the composition of the substances is not uniform.
the composition varies from one part of the mixture to another.
the different parts of the mixture are visible.
For Example: In an ice cream sundae, you can see the different parts of ice cream, hot fudge, nuts, and a cherry.
Identify each of the following as a pure substance or a mixture.
a. pasta and tomato sauce______________________
b. aluminum foil______________________________
c. helium____________________________________
d. air_______________________________________
Identify each of the following as a pure substance or a mixture.
a. pasta and tomato sauce______________________
b. aluminum foil______________________________
c. helium____________________________________
d. air_______________________________________
Identify each of the following as a heterogeneous or homogeneous mixture.
a. hot fudge sundae___________________________
b. shampoo__________________________________
c. sugar water________________________________
d. peach pie_________________________________
A chemical symbol is a one or two letter abbreviation for each element on the periodic table. It’s a “shorthand” notation.
A symbol may be comprised of a single capital letter (e.g. Carbon = C, Nitrogen = N) or two letters, a capital letter followed by a lower case letter (e.g. Iron = Fe, Magnesium = Mg).
Physical vs. Chemical Properties
Physical Properties are those characteristics of a material that depend only upon the material itself. These properties can be ascertained without changing the identity of the substance.
Chemical Properties are those characteristics of a material that relate to how the substance interacts. These properties change the identity of the substance.
In a physical change,
-the identity and composition of the substance do not change.
-the state can change or the material can be torn into smaller pieces.
In a chemical change,
-reacting substances form new substances with different compositions and properties.
-a chemical reaction takes place.
Go to www.ptable.com and look at the following sections of the periodic table:
Metals:
Solid at room temperature (except Hg--Mercury)
in a warm room (86F or warmer), Cs and Ga are liquids.
Lustrous (i.e. shiny)
Malleable & ductile (i.e. you can bend and shape them)
Named groups within the metals category:
-Transition Metals
-Alkali Metals
-Alkaline Earth Metals
Non-Metals:
At room temperature, 10 are gases, 2 are liquids, 5 are solids.
Solids and liquid have deep colors. Gases are colorless or pale in color.
Brittle
Poor conductors of heat & electricity
Named Groups within the nonmetals category:
-Halogens
-Noble Gases
Metalloids:
Located along the "zigzag" line: B, Si, As, Te, At, Ge, Sb
All are solids.
Most have a silvery appearance.
Brittle
Poor conductors of heat & electricity
Semi-conductors of electricity when “mixed.” This is important in solid state electronics for making chips where some areas do not conduct electricity and other areas do.

The atom is composed of three basic particles: protons, neutrons, and electrons. The following table shows the classification information for each particle.
The
atomic number
is specific for each element and appears above the symbol of an element in the periodic table. The atomic number is the same for all atoms of an element and is equal to the number of protons in an atom.
An atom of any element is electrically neutral—the net charge of an atom is zero. In order for this to be true, there has to be an equal number of protons and electrons.
The

mass number
represents the number of particles in the nucleus and is equal to the number of protons
plus
the number of neutrons.

Isotopes
are atoms of the same element that have different mass numbers. They have the same number of protons, but different numbers of neutrons.

A nuclear symbol represents a particular isotope of an element. It gives the mass number in the upper left corner and the atomic number in the lower left corner.
Atomic Mass:
To obtain a convenient mass to work with, chemists use the mass of an “average atom” of each element. Look at the periodic table. The number located under the element is the atomic mass. This is a “weighted” average of mass of all the naturally occurring isotopes of that element.
A sample of naturally occurring Magnesium is:
78.7% 24Mg
10.1% 25Mg
11.2% 26Mg
The atomic mass listed for magnesium is 24.305amu. Notice that the atomic mass is close to 24—that is because 24Mg is the most abundant isotope.
Valence electrons
-determine the chemical properties of the elements.
-are the electrons in the highest energy level (outer shell).
-are related to the group number of the element.
A compound would be something like that water molecule we saw earlier. Where there are two (or more, in many cases) elements put together to make a compound. Water has two elements--hydrogen and oxygen.
Water is a pure substance because the hydrogen and oxygen are always combined in the same exact way (ratio) where 2 hydrogens are connected to one oxygen.
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