Chapter 4 Section 1
Introduction to Atoms
1. Scientists once thought atoms
were the smallest particles of
matter.
2. In modern terms, an atom is the
smallest particle of an element.
3. Atomic theory grew as a series
of models that developed from
experimental evidence.
4. As more evidence was
collected, the theory and models
were revised.
5. In 1887, J.J. Thompson did
experiments that led to the
discovery of the electron,
negatively charged particles in
atoms.
6. In 1911, Ernest Rutherford and
his team did experiments that led
to the discovery of the nucleus—
the tiny, positively charged center
of an atom.
7. In Rutherford’s model, the
nucleus contained protons,
positively charged particles.
8. In 1913, Niels Bohr described
electrons has having only certain
amounts of energy and moving in
specific orbits around the nucleus.
9. By the 1920’s, the model of the
atoms described electrons as
moving in a cloudlike region
around the nucleus.
10. It also suggested that an
electron moved in certain regions
depending on its energy level, or
specific amount of energy.
11. To this model was later added
the neutron, a particle having no
charge and found in the nucleus.
12. The modern model describes
an atom as consisting of a nucleus
that contains protons and
neutrons, surrounded by a
cloudlike region of moving
electrons.
13. Protons and neutrons are about
equal in mass.
14. Electrons are much smaller.
15. It takes about 2,000 electrons
to equal the mass of one proton.
16. Electrons, however, take up
much more space in the atom than
does the nucleus.
17. Atoms are so small they are
measured in atomic mass units
(amu).
18. A proton or neutrons has a
mass of one amu.
19. Every atom of an element has
the same number of protons.
20. This unique number is called
the atomic number.
21. It is equal to the number of
protons in the nucleus of the
atom.
22. Although all atoms of an
element have the same atomic
number, they may have different
numbers of neutrons.
23. Isotopes are atoms with the
same number of protons and a
different number of neutrons.
24. An isotope is identified by its
mass number, which is the sum of
the protons and neutrons in the
nucleus of that atom.
25. Although isotopes have
different mass numbers, they
react the same way chemically.
Chapter 4 Section 2 Notes
Organizing Elements
1. In 1869, the Russian scientist
Dmitri Mendeleev discovered a
set of patterns in the properties of
the elements.
2. He noticed that a pattern of
properties appeared when he
arranged the elements in order of
increasing atomic mass.
3. The atomic mass of an element
is the average mass of all the
isotopes of that element.
4. After protons were discovered,
elements were arranged according
to atomic number.
5. The properties of an element
can be predicted from its location
in the periodic table.
6. Each horizontal row is called a
period.
7. From left to right across a
period, the properties of elements
change in a predictable pattern.
8. The elements in columns are
called a group, or family.
9. The groups are numbered from
Group 1 on the left to Group 18
on the right.
10. Elements in each group have
similar characteristics.
11. The modern periodic table
contains over 100 squares, one for
each element.
12. Each square includes the
element’s atomic number,
chemical symbol, name and
atomic mass.
13. The chemical symbol for an
element usually consists of one or
two letters, such as Fe, the
chemical symbol for iron.
14. Stars consist of matter in the
form of plasma, a gas-like
mixture of free electrons and
atomic nuclei.
15. Elements are created when the
extreme high pressure inside the
stars forces atomic nuclei to
collide.
16. The process is called nuclear
fusion.
17. Nuclear fusion, which occurs in
stars on a huge scale, combines
smaller nuclei into larger nuclei,
creating heavier elements.
18. In small stars, such as the sun,
isotopes of hydrogen fuse,
forming helium.
19. Over time, fusion reactions
produce beryllium, carbon, and
other elements up to oxygen.
20. In larger stars, elements up to
iron can be produced.
21. The heaviest elements are
produced when the most massive
stars explode in an event called a
supernova.
Chapter 4 Section 3 Notes
Metals
1. Most of the elements are
metals.
2. Chemists classify an element as
a metal based on physical
properties.
3. The physical properties of
metals include shininess,
malleability, ductility, and
conductivity.
4. A malleable material can be
hammered or rolled into flat
sheets and other shapes.
5. A ductile material can be
pulled out, or drawn, into a long
wire.
6. Conductivity is the ability of an
object to transfer heat or
electricity to another object.
7. Many metals are good
conductors.
8. Several metals are also
magnetic. They are attracted to
magnets and can be made into
magnets.
9. Most metals are solid at room
temperature.
10. The ease and speed with which
an element combines with other
elements and compounds is called
its reactivity.
11. Metal usually react by losing
electrons to other atoms.
12. Some metals react with oxygen
in the air, forming metal oxides,
or rust. This process is called
corrosion.
13. The metals in a group or family
have similar properties.
14. Family properties change as
you move across the periodic
table.
15. The metals in group 1 are the
alkali metals. They are so
reactive they are never found
uncombined in nature.
16. Group 2 of the periodic table
contains the alkaline earth metals.
17. While not as reactive as the
alkali metals, they are so reactive
that they cannot be found
uncombined in nature.
18. The elements in groups 3
through 12 are called the
transition metals. They form a
bridge between the very reactive
metals on the left and the less
reactive metals and other
elements on the right.
19. Groups 13 through 15 of the
periodic table include metals,
nonmetals, and metalloids. The
metals in these groups are not
nearly as reactive as those on the
left side of the table.
20. The elements placed below the
main part of the periodic table are
called the lanthanides and the
actinides.
21. Lanthanides are mixed with
more common metals to make
alloys.
22. Many of the actinides are
synthetic elements.
23. Elements that follow uranium
are made—or synthesized—when
nuclear particles are forced to
crash into one another.
24. Some synthetic elements are
made in nuclear reactors.
Powerful machines called particle
accelerators make synthetic
elements with atomic numbers
above 95.
Chapter 4 Section 4 Notes
Nonmetals and Metalloids
1. Nonmetals are elements that
lack most of the properties of
metals.
2. Most nonmetals are poor
conductors of electricity and heat
and are reactive with other
elements.
3. Solid nonmetals are dull and
brittle.
4. Nonmetals usually have lower
densities than metals, and are
poor conductors of heat and
electricity.
5. Except for Group 18, most
nonmetals readily form
compounds with other elements.
6. Many metals and nonmetals
react with each other.
7. Because atoms of nonmetals
usually gain electrons, electrons
move from metal atoms to
nonmetal atoms.
8. Nonmetals can form
compounds with other nonmetals
by sharing electrons.
9. The elements in Group 14, the
carbon family, can gain, lose, or
share four electrons when
reacting with other elements.
10. Carbon is the only nonmetal
element in the group. Carbon
plays an important role in the
chemistry of life.
11. Group 15 is also known as the
nitrogen family.
12. The two nonmetals in the group
are nitrogen and phosphorus.
13. These nonmetals usually gain
or share three electrons when
reacting with other elements.
14. Nitrogen is an element that
occurs in nature as a molecule
formed from two nitrogen atoms
bonded together.
15. A molecule that is made up of
two atoms is a diatomic molecule.
16. The elements in Group 16, the
oxygen family, include three
nonmetals—oxygen, sulfur, and
selenium.
17. Atoms of these elements
typically gain or share two
electrons in a reaction.
18. The oxygen you breathe is O2
and ozone is O3.
19. The elements in Group 17 are
known as the halogens.
20. All but one of the halogens is
nonmetals.
21. A halogen atom typically gains
or shares one electron when it
reacts.
22. In their elemental form, all of
these elements are very reactive.
23. The elements in Group 18, the
noble gases, do not ordinarily
form compounds. That is because
the atoms of these elements do
not gain, lose, or share electrons.
24. Hydrogen has the simplest and
smallest atoms. Its atoms contain
one proton and one electron.
25. Some hydrogen atoms also
contain neutrons.
26. Because hydrogen’s chemical
properties are so different from
the other elements, it cannot be
grouped into a family.
27. On the boarder between metals
and nonmetals are seven elements
called metalloids.
28. The metalloids have some of
the characteristics of metals and
some of the characteristics of
nonmetals.
29. The most useful property of the
metalloids is their varying ability
to conduct electricity.
30. Some metalloids are used to
make semiconductors.
31. Semiconductors are substances
that under some conditions carry
electricity, and under other
conditions cannot carry
electricity.
32. Semiconductors are used to
make computer chips, transistors,
and lasers.
Section 5 Notes
Radioactive Elements
1. Remember that atoms with the
same number of protons and
different numbers of neutrons
are called isotopes.
2. Some isotopes are unstable.
3. In a process called radioactive
decay, the atomic nuclei of
unstable isotopes release fastmoving particles and energy.
4. In 1896, the French scientist
Henri Becquerel discovered the
effects of radioactive decay
5.
6.
7.
8.
while studying a mineral
containing uranium.
Becquerel presented his finding
to Marie Curie and her husband,
Pierre.
The Curries concluded that a
reaction was taking place with
the uranium nuclei.
Radioactivity is the name that
Marie gave to this spontaneous
emission of radiation by an
unstable atomic nucleus.
Natural radioactive decay can
produce alpha particles, beta
particles, and gamma rays.
9. The particles and energy
produced during radioactive
decay are forms of nuclear
radiation.
10.An alpha particle consists of
two protons and two neutrons
and is positively charged.
11.It is the same as a helium
nucleus.
12.Alpha radiation can cause an
injury much like a bad burn.
13.A beta particle is a fast-moving
electron given off by a nucleus
during radioactive decay.
14.Beta particles can travel into the
body and cause cell damage.
15.Alpha and beta decay are
almost always accompanied by
gamma radiation.
16.Gamma radiation is high-energy
waves.
17.Gamma rays can pass right
through the human body,
causing severe cell damage.
18.The decay of radioactive
isotopes makes them useful in
many ways.
19.Uses include tracing the steps of
chemical reactions and
industrial processes, and
diagnosing and treating
diseases.
20.These uses are possible because
radioactive isotopes give off
detectable radiation.
21.Tracers are radioactive isotopes
that can be followed through the
steps of a chemical reaction or
an industrial process.
22.Tracers may be used by
biologists studying plants,
engineers surveying flaws in
metal, and doctors detecting
medical problems.
23.In addition, the radiation given
off by certain radioactive
isotopes can be used to destroy
unhealthy cells in the body,
such as those in cancer tumors.