Atoms, Compounds, and End of Unit Test
This end of unit test will cover the topics of breaking down compounds (electrolysis), atoms and
compounds, the Periodic Table of Elements, and some problems related to previous topics we
have looked at in Properties of Matter. As you read through this guide it should all make sense
to you and renew your memory of these topics.
Electrolysis is a method of using electricity to break apart the compound water. Using this
method we discovered that water is composed of two different gases. Hydrogen is a
transparent, odorless gas that explodes when brought in contact with a flaming splint. Oxygen
is a transparent, odorless gas that enhances combustion when brought in contact with a
glowing splint. These gases are produced in a ratio of 2:1 or two parts hydrogen for every one
part of oxygen. Water can be produced when you put two parts hydrogen and 1 part oxygen in
a container (syringe) and light it.
The atom is the basic unit of all matter. All matter in the universe is composed of atoms. All
atoms are made of sub atomic particles and these include: neutrons, protons, the nucleus, and
electrons. The neutron is a neutrally charge particle with a mass of 1 atomic mass unit (amu)
and is located within the nucleus of the atom. The proton is a positively charge particle with a
mass of 1 atomic mass unit (amu) and is located within the nucleus of the atom. The nucleus
contains the majority of the mass because it contains both the neutrons and the protons.
Electrons are negatively charged particles located within the electron cloud or within orbitals
surrounding the nucleus of an atom. Their mass is very small, 1/1800 of the mass of neutrons
or protons. Atoms can exist as neutrally charged or as charged atoms. A neutrally charged
atom has the same number of protons in the nucleus as electrons within the surrounding
electron cloud.
The atomic mass of an atom is determined by the number of neutrons and protons found
within the nucleus of the atom. For example, the element Carbon has 6 protons and 6 neutrons
in its nucleus and the atomic mass is 12 amu.
The atomic number of an atom is determined by the number of protons found within the
nucleus of the atom. For example, the element Carbon has 6 protons found within the nucleus
of this atom and its atomic number is 6.
Atoms have chemical names and element symbols. For example, Carbon has this as its
chemical name and the element symbol of C. Some element symbols are just the capitalized
first letter of its name, but others are not. For example Lead has an element symbol of Pb and
Gold has an element symbol of Au.
Elements are pure substances that cannot be broken down into other substances by chemical
or physical means: (except by a nuclear reaction). An example of an element would be
hydrogen gas.
Compounds are pure substances consisting of two or more elements combined. For example,
water consists of the elements hydrogen and oxygen combined.
The Periodic Table of Elements is a table that contains information about all of the known
elements. Each square on the table includes an element’s name, chemical symbol, atomic
number, and atomic mass. Some tables contain other information about the element.
Periodic means happening at regular intervals and the rows of the table are referred to as
Periods. Periodic law states that properties of elements change periodically with the elements
atomic number.
Vertical columns are called groups. Elements in the same group often have similar chemical
and physical properties. For this reason, a group is also called a family. An example of a group
would be the Noble Gases. These are non-reactive elements found within the far right group
on the periodic table.
In the Periodic Table of Elements, elements are classified as metals, metalloids, and nonmetals.
Metals have some properties such as being a solid at room temperature with the exception of
mercury. Metals look shiny to some degree and are good conductors of electric current. They
are ductile (can be drawn into thin wires) and malleable (flattened into sheets and bendable).
Metalloids have some properties of metals and some properties of non-metals. Non-metals
are mostly gases at room temperature and have properties that are opposite of the properties
of metals. They are mostly not shiny, poor conductors, and not malleable or ductile. Sulfur is an
example of a non-metal element.