Review for 8th Grade Chemistry unit

1. Chemistry Review
Chemical Building Blocks

2. As we review …
think about these questions
• How are matter and energy similar and how are
they different?
• How is the Periodic Table of the Elements used
to help us understand matter?
• How do physical and chemical changes affect
matter?
• How do we create models of something we can’t
see?
• Why do we create models in science?

3. Acid
• Any of a class of compounds that form
hydrogen ions when dissolved in
water
• Any of a class of compounds whose
aqueous solutions react with bases
and certain metals to form salts.
• Acids turn blue litmus paper red
• Acids have a pH of less than 7.
• Acids taste sour
• Acids conduct electricity in solution

4. Atom
• the smallest particle an ELEMENT can be
divided into …
and still be the same substance

5. Atom
Consists of a Nucleus (Protons (+) & Neutrons)
surrounded by Electrons (-)

6. Atomic Mass
• the average mass of the most common form
(isotope) of an element
• sometimes also called the Atomic Weight

7. Base
• Any of a class of compounds that form
hydroxyl ions (OH) when dissolved in
water
• Any of a class of compounds whose
aqueous (water-based) solutions
react with acids to form salts.
• Bases turn red litmus paper blue
• Bases have a pH greater than 7.
• Their aqueous solutions have a bitter
taste.
• Bases feel slippery
• Bases dissolve fats and oils

8. Boiling point & Melting point
• BOTH are characteristic properties of
matter which mark a transition from one
state (phase) of matter to another
• Boiling point – the temperature
in Celsius at which a substance
will boil. Marks the transition
from liquid state to gaseous
state, AKA condensation point
(gas  liquid)
• Melting point – the temperature in
degrees Celsius at which a substance will
melt. Marks the transition from solid state
to liquid state, AKA
freezing point (liquid  solid)

9. Chemical
• A chemical is any substance created by
chemistry.

10. Chemical [change]
• A chemical change produces a new substance
• Change takes place on a molecular level
• Cannot be reversed

11. Compound
• a substance made of two of more
different elements that are
CHEMICALLY combined
• Compounds are not changed by physical
changes … only chemical changes
• A compound has different
chemical properties to the
elements that formed it
Elements
• The elements are present
in FIXED ratios, never
random combinations
Compounds

12. Density
• Mass per unit volume.
Density = Mass ÷ Volume
• A measure of how close
together the molecules in a
particular substance are
packed
• Density determines whether
or not something will float
• If density > water, it will sink
• If density < water, it will float

13. Endothermic/ Exothermic
• Endothermic – a process or chemical reaction that is accompanied
by the absorption of heat
• Endothermic reactions take in energy from the surroundings
• Exothermic – a process or chemical reaction characterized by or
causing the liberation or release of heat
• Exothermic reactions transfer energy to the surroundings

14. Gas
• matter that can change shape and volume
(can expand or compress)
• Note: the concept of density applies to
gases also

15. Ion
• An atom or compound that carries an electric charge

16. Liquid
• matter that has a definite volume, but
takes the shape of the container holding it.

18. Mass
• the amount of matter in an object; a measure of the inertia
of an object
1,000 cm3 of water = 1,000 mL = 1 Liter

19. Matter
• any substance which has mass and occupies space.

20. Metal
• Any of a large group of chemical
elements, including
iron, gold, copper, lead, and magnesium, that
readily become cations
(+ ion) and form ionic bonds, having
relatively free valence electrons (electrons
in the outer shells)
• Metals are good conductors of electricity.
• Metals conduct heat well, and in solid form
are relatively malleable and ductile (can be
pressed/molded into different shapes) when
compared to other solids.
• They are usually shiny and opaque.
• All metals, except mercury, are solid at room
temperature.

21. Everything in blue is a metal

22. Mixture
• consists of two or more substances
that are NOT chemically bonded
• There are two kinds of mixtures
• Heterogeneous – the parts of
the mixture are not distributed
evenly
• Homogeneous – the parts of the
mixture are evenly distributed
• A solution is a very well-mixed
homogeneous mixture.
E.g. saltwater

23. Molecule
• the smallest unit a substance can be divided into and still
have the chemical properties and composition of the
substance. Examples: Oxygen (O2) and water (H2O)

24. Neutral
• Neither acid nor alkaline (pH = 7).
• Having no inherent or net charge
(like a neutron)

25. Non-metal
• an element that doesn’t have the characteristics of metal
including: ability to conduct heat or electricity, luster, or
flexibility. Everything in YELLOW is a non-metal.

26. Oxidation
• the process when oxygen combines with another
element, changing the appearance of the element.
• Oxidation is an example of a chemical change

27. Physical [change]
• A physical change is a type of change in which the
form or phase of matter is altered but one substance
is not transformed into another. Can be reversed.

28. Radioactive
• Description of an element that gives off energy
waves called radiation
• Radioactivity is the emission of radiation by
unstable atomic nuclei undergoing radioactive
decay

29. Reactivity
• the tendency of a substance to undergo
chemical reaction, either by itself or with
other materials, and to release energy.
Sodium reacting with water

30. Solid
• matter that has a definite shape and volume

31. Solubility
• the ability of a substance to dissolve
• Solubility is one of the characteristic properties
of matter
• A saturated solution cannot dissolve any more of
the solute

32. Solution
• A mixture in which particles of one or more substances
(the solute) are distributed uniformly throughout
another substance (the solvent), so that the mixture is
homogeneous at the molecular or ionic level
• A saturated solution cannot dissolve any more of the
solute

33. Volume
• The amount of space occupied by a three-
dimensional object or region of space.
Volumes are expressed in cubic units.

34. Weight
• the force that gravity exerts upon a body
• Warning: Chemists sometimes use the word weight
when they REALLY mean mass!

35. States (Phases) of Matter

36. Characteristic Properties of Matter
• Characteristic properties of matter
do not change
• A characteristic property (either a chemical
or a physical property) is so unique to a
particular substance that it is used to
identify the substance.
Examples:
• Density
• Melting/boiling point
• Solubility

38. Elements, Compounds, and Mixtures

39. Remember those questions …
• How are matter and energy similar and
how are they different?
• Matter is the stuff that everything is made of.
• Energy is a property of matter. Energy is what makes
matter do stuff.

40. The same amount of matter can have different
amounts of energy and so represent different states
of matter. For example, if you add energy to an ice
cube made of water, it becomes liquid water, and if
you add even more energy, it becomes steam. The
kind of matter and the amount of matter is the same
as in the original cube, but there is more energy.

41. Remember those questions …
• How is the Periodic Table of the Elements
used to help us understand matter?
The main purpose of any periodic table of the
elements is to help us understand the
relationships among the various elements.
• Elements in the same group have similar
reactive properties
• Elements in the same period gain a proton
and an electron from left to right.

42. Remember those questions …
• How do physical and chemical changes
affect matter?
Physical changes change the form or phase (state) of
matter, but not its chemical composition.
Example: melting ice changes water from its solid phase
to its liquid phase.
Chemical changes change the composition of matter;
changing the matter into a new substance with new
chemical properties.
Example: combining the elements sodium (Na) and
chlorine (Cl) forms NaCl, which is table salt.

43. Remember those questions …
• How do we create models of something we
can’t see?
We use a combination of observation and
inference. We experiment and do our best to
model what we can observe. Then we refine our
model to fit our latest understandings.

44. Remember those questions …
• Why do we create models in science?
Models are used when it is either impossible or
impractical to create experimental conditions in which
scientists can directly measure outcomes.
A scientific model is a way to represent
observations, phenomena, and physical processes in a
logical and objective way.
Examples: Using trail mix to model a mixture in
chemistry. Drawing a picture of an atom.

45. Now you know that …
• Everything in the universe is composed of matter and
energy.
• All kinds of matter can be identified based on their
physical and chemical properties.
• An atom is the basic unit of every element.
• All the matter in the universe is characterized in the
Periodic Table of the Elements
• Interactions between atoms cause chemical changes
that produce new substances with different chemical
properties.