Chapter
#4 – Lecture Notes
SECTION #1 – ELEMENTS
An
element is a pure substance that cannot be separated into anything simpler by
physical or chemical means. A
pure substance is a substance that is made up of only one type of particle.
The particles of a pure substance are alike no matter where the
substance is found.
Each
element has a unique set of properties that allows you to identify it.
These properties do not depend on the amount of material present in the
sample.
There
are 92 natural elements, the rest are manmade.
Information about these elements can be found on the Periodic Table of
Elements. Elements are classified
into groups according to their shared properties.
There are 3 major categories of elements:
1) METALS – These are elements that are shiny, good conductors of thermal energy, and good conductors of electrical current. They are malleable and ductile.
2)
NONMETALS – These are elements that are dull, poor conductors of thermal
energy, and poor conductors of electrical current.
Solid nonmetals tend to be brittle and unmalleable.
The rest are liquids and gases.
3)
METALLOIDS – These elements are also called semi-conductors.
They have properties of both metals and nonmetals.
Most elements take part in chemical
changes fairly easily. This means
that few elements are found alone in nature.
They are usually found combined with other elements as compounds.
A compound is a pure substance made up of 2 or more elements that are
chemically combined. For a
compound to form, atoms from 2 or more elements must join together.
For this to happen, the elements must react and undergo a chemical
change. Compounds are not random combinations of elements.
When a compound forms, the elements join in a specific ratio according
to their masses.
Each compound has a unique set of properties that allows you to
distinguish it from other compounds. The
compound will have different properties than the elements that make it up.
Some compounds can be broken down into the elements that make it up through chemical changes. Other compounds undergo chemical changes to form simpler compounds. These compounds can then be broken down further into the elements that make it up through additional chemical changes. The only way to break down a compound is through chemical change.
All
mixtures share certain properties. A
mixture is a combination of 2 or more substances that are not chemically
combined. Since no chemical
change occurs, each substance in a mixture has the same chemical makeup it had
before the mixture formed. This
means each substance keeps its own identity.
Mixtures can be physically separated, unlike compounds that can only be
broken down chemically. The parts
of a mixture do not need to combine in a definite ratio.
A
solution is a mixture that appears to be a single substance, but is actually
composed of particles of 2 or more substances that are distributed evenly
throughout each other.
A)
There are 2 basic types of solutions:
1) HOMOGENEOUS – Which looks the same throughout. (Kool-Aid)
2) HETEROGENEOUS – Where you can see that it is made from more than one thing. (salad dressing)
B)
There are 2 parts to a solution:
1) THE SOLUTE – Which is the substance that dissolves.
Usually this is a solid.
2) THE SOLVENT –
Which is the substance that the solute dissolves into.
Usually this is a liquid.
The
process that forms a solution is called dissolving. If a substance is able to dissolve, it is said to be soluble.
If it doesn’t dissolve, it is said to be insoluble.
C)
There are 3 forms of solutions:
1) UNSATURATED – This form of solution has more solvent than solute. There is still room for more solute to dissolve.
2)
SATURATED – This form of solution is holding as much solute as it possibly can.
There are no empty spaces between the solvent’s particles for more
solute to dissolve.
3) SUPERSATURATED
– This form of solution is holding
more
dissolved solute than it should be able to at
a given
temperature. This is created by
increasing the temperature,
which
increases the motion of the solvent’s
particles, which
creates
more space between the solvent’s particles, which
allows more
solute to dissolve. Supersaturated
solutions are
very
unstable.
Solutions may also be made from solids and gases.
The particles in a solution are so small that they never settle or
filter out, and they do not scatter light.
The amount of particles in a solution is measured by its concentration.
If a solution is concentrated, it has a large amount of solute compared
to the solvent, and is very strong. If
a solution is dilute, it has a
small amount of solute compared to the solvent, and is weak.
D)
FACTORS THAT AFFECT SOLUBILITY AND R.O.S.
Solubility is the ability of a substance to dissolve. How fast this happens is called the ‘Rate of Solution’ or R.O.S.. There are 4 factors that affect R.O.S.:
1)
SIZE OF THE PARTICLE – The smaller the particle the faster it
dissolves.
2)
SURFACE AREA – Increasing the surface area increases the R.O.S..
3)
MIXING – Of any type increases the R.O.S..
4)
HEATING – Increasing the temperature increases the R.O.S. for solids and
liquids, but decreases the R.O.S. gases.
These mixtures have properties of both solutions and suspensions. The particles are dispersed throughout, but never settle out, cannot be separated by filtering, and they scatter light. The scattering of light by suspended particles is called the ‘Tyndall Effect’.
***REVIEW THE FOLLOWING***
The diagram and explanation of how something
dissolves.
The diagram and explanation of the Tyndall Effect.
The diagrams and explanation of the 3 forms of a solution.
The graph on the top of page 95 in your textbook.