Transcript Radiation

PHYSICAL SCIENCE
What You Need to Know
Describe that matter is made of minute
particles called atoms and atoms are
comprised of even smaller components.
Explain the structure and properties of
atoms.
• Atoms are made of three basic
particles: protons (+), electrons (-),
and neutrons (0). Atoms of the same
element have the same number of
protons (atomic number). Protons
and neutrons make up the nucleus of
atoms, where electrons are outside
that nucleus. The reason the electron
keeps traveling around the nucleus is
the electric attraction between the
electron (-) and the proton (+).
Isotopes
• Atoms of the same element may have
different numbers of neutrons (which are
neutral in charge). This causes different
masses (atomic mass) BUT has no effect
on charge.
• For example, all carbon atoms have 6
protons (atomic number is 6). The
number of electrons depends on the
charge and the number of neutrons
depends on the atomic mass. C-14 has 6
protons and 8 neutrons.
Ions
• Each atom has the same number of
electrons as protons IF neutral; they
have more electrons than protons if
negative; and they have more
protons than electrons if positive.
Protons are +, electrons are -.
Charged atoms
are called ions.
Periodic Table
• Atoms are listed in order by atomic
number. Elements form “families”
where the elements in a family (a
vertical column on the table) have
similar properties. Some of these
properties are similarities in electron
patterns, similarities in physical
properties, and similarities in
chemical properties.
Explain how atoms react with each other
to form other substances and how
molecules react with each other or other
atoms to form even different substances.
• Atoms can “bond” to other atoms or molecules to form new
substances with different properties. Hydrogen and
oxygen, for instance, react to form water, a very different
substance. During these reactions, nothing is gained or
lost (conservation of matter).
• Equations showing reactions are “balanced.” For example,
2H2 + O2 = 2 H2O. There are 4 H atoms on left and right
and 2 O atoms on left and right.
• Reactions involve sharing of electrons or trading of
electrons.
• pH is used to tell if substances are acids (pH less than 7),
bases (pH greater than 7), or neutral (pH = 7).
Chemical Reactions
• In some reactions, an ionic bond is formed. An IONIC
BOND is a bond that holds together a positively charged
ion and a negatively charged ion. One atom loses an
electron to another atom, And, as everyone knows,
opposites attract.
In table salt, for example, an electron from a sodium atom
is transferred to a chlorine atom, forming Na+ and Cl-.
Because the ions have opposite charges, they are
attracted to each other. Ionic bonds form most often
between elements on opposite sides of the periodic table
(metals and non-metals) and result in the formation of ions.
Ionically bonded substances are held together with very
strong bonds; this means that these substances are hard
to melt, hard to boil, and hard to separate back into the
elements which made up the compound.
• It is possible for more than one electron to be taken away
from another atom, as in barium chloride (BaCl2, a
substance used in medicinal preparations). In barium
chloride, two chlorine atoms each take one electron away
from barium, leaving the barium ion Ba+2.
Chemical Reactions
• In some reactions, neither element is “strong” enough to
take electrons from the other SO, the atoms share
electrons. This is called a covalent bond. Covalent bonds
most often form between similar types of elements (nonmetals with other non-metals, etc). This type of bond
results in the formation of molecules. Covalently bonded
substances are held together with weaker bonds (generally
speaking) than ionic substances, which makes them easier
to boil, easier to melt, and easier to break back down into
the original elements that made up the compound.
• In both these reactions, as in all chemical reactions, the
number of protons and neutrons in each atom remains the
same. This also means that the atoms do not change their
identities. For instance, when sodium loses one electron to
chlorine to make salt, sodium is still sodium because it still
has 11 protons and that is true only for the element
sodium. The number of protons establishes the identity of
the element.
Describe the identifiable physical properties of
substances. Explain how changes in these
properties can occur without changing the
chemical nature of the substance.
• Substances are often classified by their properties. They
have physical properties (based on appearance, such as
color, melting point, etc) and chemical properties (based
on how they react and with what they react).
• Physical properties are color, MP, BP, conductivity,
hardness, density (mass divided by volume), etc. If you
investigate a substance’s physical properties, you do not
change the substance.
• Chemical properties are ability to burn, inability to react,
etc. If you investigate a substance’s chemical properties,
you turn it into a new substance (or would, if it reacted).
• The ability to conduct heat and electricity is a physical
property that depends on the substance’s electrons being
able to move from place to place (most often found in
metals).
Explain the movement of objects by
applying Newton’s three laws of motion.
• Motion depends on the observer and
where they are in relation to the moving
object and can be described in terms of
position, speed, velocity, acceleration,
and time.
• Friction often affects motion, sometimes
in a good way and sometimes in a bad
way. Friction is a force that opposes the
motion of an object when the object is in
contact with another object or surface.
What causes friction? How is friction bad
and good?
Newton’s Three Laws of
Motion
• An object at rest stays at rest or an object
in motion stays in motion unless acted on
by an unbalanced force. (First law or Law
of Inertia)
• If a force acts on an object, the affect on
that object’s motion depends on its mass
and the amount of force or F = m a.
(Second law)
• For every action force, there is an equal
and opposite reaction force.
(Third law)
Examples of Newton’s Laws
• Seat belts are used to provide safety for
passengers whose motion is governed by
Newton's laws. The seat belt provides the
unbalanced force which brings you from a state
of motion to a state of rest safely.
• Picture a big car and a small car. The bigger car
obviously has more mass than the small car. If
you give them the same force (the same push or
pull), won’t the big car move (accelerate) less?
• An unfortunate bug strikes the windshield of a
bus. The bug hit the windshield and the
windshield hit the bug. Which of the two forces is
greater: the force on the bug or
the force on the bus?
Friction
• The strength of a frictional force depends on the
nature of the surfaces that are in contact and the
force pushing them together.
• When friction affects a moving object, it turns the
object’s kinetic energy, or energy of motion, into
heat. People welcome the heat caused by
friction when rubbing their hands together to stay
warm. Frictional heat is not so welcome when it
damages machine parts, such as car brakes.
• Objects moving through a fluid, like air or water,
experience fluid friction, or drag.
• Teflon creates very little friction because it is so
smooth. Teflon, along with Velcro and many
other things, was developed as a result of our
explorations in space.
Demonstrate that energy can be
considered to be either kinetic (motion)
or potential (stored).
• Kinetic energy can be calculated as
KE = ½ m v 2. More mass and/or
more velocity means more KE.
• Potential energy can be calculated
as PE = m g h. More mass and/or
more height means more PE.
• Give examples of objects with either
kinetic or potential energy.
Conservation of Energy
Explain how energy may change form or be
redistributed but the total quantity of energy is
conserved.
• Thermal energy is the motion of atoms
and molecules. The more energy and
higher temperature, the faster the atoms
and molecules move.
• Reactions are either endothermic or
exothermic.
• In reactions, not only are elements the
same (left and right), the total energy is
the same (left and right). Energy can
change form but there is no more or no
less of it after it changes form. (Look at
totals for the skier.)
Nuclear Reactions
• Radioactive substances decay naturally
(remember from Earth science) and give off
small particles and energy.
• Nuclear reactions involve LOTS of energy (very
exothermic). This is because some mass is lost
and turned into energy. Total mass and energy is
the same, before and after. Unlike chemical
reactions, the nucleus of the atom DOES change
(in chemical reactions, only electrons are
involved). Fission is when an atom splits into
smaller ones; fusion is when smaller atoms
become one larger atom , like H into He in stars
(remember from Earth science).
Transfer of Thermal Energy
There are three ways thermal energy can be
transferred:
• Radiation - Radiation is the transfer of heat energy
by electromagnetic radiation and can occur through
mostly empty space. If you have stood in front of a
fireplace or near a campfire, you have felt the heat
transfer known as radiation.
• Conduction - Conduction is the transfer of heat
energy from one substance to another or within a
substance. These substances must be in direct
contact with each other and heat flows through the
materials by the collision of particles.
• Convection - Convection is the transfer of heat
energy in a fluid. This type of heating is most
commonly seen in the kitchen when you see liquid
boiling. Convection is how heat is transferred within
the liquid mantle which helps move the Earth’s
plates.
Demonstrate that waves (e.g., sound, seismic,
water and light) have energy and waves can
transfer energy when they interact with matter.
• Electromagnetic radiation is a form of
energy. There are many types as shown
in this diagram:
• Visible light is a part of this, and like all
electromagnetic waves, can travel
through empty space.
Wave Properties
Waves can sometimes:
• Bend around corners (diffract), like sound
• Reflect off surfaces
• Refract through new substances
(the bending is due to the change in speed)
• Interact with each other in other ways.
Trace the historical development of
scientific theories and ideas, and
describe emerging issues in the
study of physical sciences.
• The theory of atoms was only completely
developed in the last 100 years after
beginning with the Greeks, centuries ago.
• Einstein did a lot of work with changing
our ideas of energy and matter.
• Newton and Galileo changed the thinking
of people about forces and motion.
• Look at the changes in energy of many
types, nanotechnology, plastics,
computers, and other new technologies.