Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
CHEMISTRY REVIEW
I.
Atoms vs. Molecules
a. Atoms - the smallest piece of matter you can have that chemists can do
reactions with is an atom. Each element is defined by the number of protons
contained in its nucleus
b. Molecules - two or more atoms bonded together with a covalent bond (more on
that bond later) is called a molecule.
i. If all the atoms bonded together are of the same type (for example N2 or
O2, the molecule formed is still an element.
ii. If different types of atoms are bonded together, then the molecule
formed is a compound.
iii. Both elements and compounds are considered pure substances.
II.
Pure Substances vs. Mixtures
a. Matter can be classified in to two broad categories: pure substances and
mixtures.
i. Pure Substances
1. Elements - all the same type of atom.
2. Compounds - substances made from two or more different kinds
of atoms.
b. Mixtures are substances made by combining two or more different
materials in such a way that no chemical reaction occurs. No bonds
are broken and none are created in the mixture.
i. Homogeneous mixtures
1. Mixtures which are the same throughout with identical properties
everywhere in the mixture.
2. Not easily separated.
3. This type of mixture is often called a solution. A good example
would be sugar dissolved in water or some type of metal alloy
used in many bike frames. Homogeneous mixtures do NOT have
to be liquids!
ii. Heterogeneous mixtures
1. Mixtures which can have different properties when sampled from
different areas.
2. Heterogenous mixtures separate over a short period of time.
3. Examples of this would be sand mixed with water or peanuts
mixed with raisins, a tossed salad, or a mixed bag of M&M's candy
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
Test your knowledge. Read the following statements and identify the
“component in a living thing” as a solution, a mixture, a compound or an element
1. Blood consists of white blood cells, red blood cells, serum and can contain
varying amounts of amino acids and carbohydrates
2. You breathe in air. Air is composed on Nitrogen, Oxygen, Carbon Dioxide
and a few other gases.
3. A hormone is a type of protein or lipid that is created in your cells and that
travels in your blood.
4. When you are sick or undergo surgery, you may be given a fluid that
contains 9 g of salt mixed in 1 L of water (0.9% saline or normal saline). This
is a homogenous mixture.
5. Sometimes, after surgery or sometimes before surgery or a procedure, you
are not allowed to eat. To make sure that you still get carbohydrates so
that your body can make ATP, you are given a fluid that contains 50 g of
glucose/1000 ml of water. This mixture of glucose and water is
homogeneous.
6. Salt (NaCl) and Glucose (C6H12O6) are examples of this type of pure
compound.
7. Your body needs many ions. Ions include Mg++, Ca++, Cl-, K+. Are these
compounds or elements?
8. How many atoms are needed to have one particle of an element?
9. If two or three of the same type of atom are bonded together, are they still
considered an element?
10.Are bones mixtures or compounds?
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
IONIC AND COVALENT BONDS- Found in compounds
Two general types of bonds form during chemical reactions: ionic and covalent. Both types of
bonds will form compounds. However, ionic compounds can dissolve in water (they separate
into a positive and a negative ion).
Ionic bonds form when the outermost, or valence, electrons of one atom are donated or
received by a second atom. Because there are one or more additional electrons orbiting around
the receiving atom, the receiving atom now has a negative charge (more electrons than
protons. The donating atom now has less electrons than before, and so has less electrons than
protons and becomes a positively charged ion.
The resulting molecule has properties different from the original atoms. It is important to
remember that because of the unequal electron distribution around the reacting atoms, the
resulting ionic compounds have partial charges. This explains the fact that water can dissolve
any substance that has a partial charge on it. A typical example for an ionic bond is the joining
of a sodium atom, which donates an electron, to a chlorine atom, which accepts the electron,
to form sodium chloride, also known as table salt.
Elements that form ionic bonds that are found in the body are generally those in the first two
columns (these lose electrons) of the periodic table and those in the seventh “full column”
(these gain electrons). However, ionic bonds can also be formed between any metal (in the
first two columns) and a non-metal (which includes oxygen).
Covalent bonds occur when two or more atoms share their electrons. The electrons are not
donated/accepted; instead, they join their orbitals to create an electron cloud around all
participating atoms. When the electrons are shared evenly around all reacting nuclei, there is
no partial charge on the resulting molecule, as is the case when carbon covalently bonds with
itself.
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
1. In an ionic bond, are the electrons shared? ______________ If not, what does happen?
2. What determines whether an atom gains or loses an electron in the formation of an
ionic bond?
3. Can you put together two elements? Calcium oxide is a compound. Based on its name,
what two elements does this compound contain?
a. Based on the valance electrons present in calcium and oxygen how many atoms of
each element are found in calcium oxide? Explain how you figured out your answer.
b. Do you think this compound is covalently bound, or is it ionic?
4. Now tell me the formula for sodium chloride, again explain how you arrived at this
answer and identify whether you believe it contains ionic or covalent bonds.
5. Oxygen is diatomic (has two atoms) and has 6 valence electrons. How many covalent
bonds are there in an oxygen molecule.
6. When Cl gains an electron, the charge of its ion is __________________
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
POLAR COVALENT BONDS
https://www.youtube.com/watch?v=ASLUY2U1M-8
Some bonds are actually a blend of ionic and covalent bonds and have characteristics of both
types. Atoms with polar covalent bonds share their electrons (covalent characteristic) unevenly
(ionic characteristic), giving a slight positive (+) charge to one end of the molecule and a slight
negative (-) charge to the other end. Water is a polar covalent molecule because the electrons
spend more of their time around the oxygen atom because the oxygen atom has more protons
acting as electron-magnets. Because of this uneven sharing of electrons, the oxygen end of the
molecule has a slight negative charge, and the hydrogen end has a partial positive charge
because the electrons are spending more time orbiting around the oxygen atom. The overall
molecule has a partial positive and a partial negative end. Because water is polar, it dissolves
ionic compounds and even compounds that have a charge, but are not ionic.
1. For which Lab activity (Lab 4- Chemical Reactions) might this information be useful?
2. Based on what the above paragraph indicated, why might one powder have dissolved, and the
other did not?
3. If one of your powders seems to have “partially dissolved” and you know the solution is not
saturated (in other words, if I put more powder in , some would still dissolve), what might you
conclude about the ingredients in the powder? Do you think it is a pure substance, or could it
be a mixture. Provide evidence.
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
CHEMICAL REACTIONS IN LIVING SYSTEMS
Chemical reactions are important to all levels of biology.
A reaction requires reactants and products.
CO2 + H2O  C6H1 O6 + O2
Reactants
Products
starting material for a reaction. The products are the resulting changed atoms or molecules and
are always on the right side of the equation.
A chemical reaction occurs when reactants are joined together to create one or more products
that have different chemical properties than the original reactants.
https://www.youtube.com/watch?t=112&v=LG7pLufXAo
Models of exothermic and endothermic reactions.
Chemical reactions always involve an energy
change and a change in the configuration of the
valence electrons (bonds are broken and
reformed) Covalent bonds are formed with
electrons that are shared between two atoms
while ionic bonds occur when electrons are
donated.
QUESTIONS
1. Watch the youtube video on chemical reactions. Refer to results from 1a and 1b.
a. Which of your reactions was an exothermic reaction? How do you know?
b. Which of your reactions was an endothermic reaction? How do your know?
i. What is the “environment” for the second reaction (in what are you
measuring the temperature?
2. Do these reactions require much activation energy? What could you do to increase
both reactions, without changing the amount of reactants used?
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
ENZYMES AND CHEMICAL REACTIONS
https://www.youtube.com/watch?v=OttRV5ykP7A
https://www.pinterest.com/pin/58124651413032825/ (honors)
In most biological reactions, enzymes act as catalysts to increase the rate of a reaction. A
fundamental task of proteins is to act as enzymes—catalysts that increase the rate of virtually
all the chemical reactions within cells. Most biological reactions are catalyzed by proteins.
Without enzymes, most biochemical reactions are so slow that they would not occur under the
mild conditions of temperature and pressure that are compatible with life. Enzymes decrease
the energy barrier (activation energy
Enzymes accelerate the rates of such reactions by well over a million-fold, so reactions that
would take years in the absence of catalysis can occur in fractions of seconds if catalyzed by the
appropriate enzyme. Cells contain thousands of different enzymes, and their activities
determine which of the many possible chemical reactions actually take place within the cell
1. Why are enzymes important in living systems? Why is it important to lower the
activation energy (energy barrier) for reactions in living systems?
IN SUMMARY
In all cases, the driving force for any chemical reaction is a move toward greater stability of the
atoms. To increase stability, atoms tend to react so that they lower their energy. This means
that they seek to have a stable number of electrons in their outermost orbital. The stable
number means that the outermost energy level is either completely full or completely empty.
Atoms react to achieve this electron configuration by donating/accepting electrons (ionic) or
sharing them (covalent). Biomolecules that are considered organic molecules because they
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
contain the elements carbon, hydrogen AND oxygen and are covalently bonded.(they must
have ALL THREE ELEMENTS!)
FLUORESCENCE
https://www.youtube.com/watch?v=blv1KxYLhc0
The use of fluorescent molecules in biological research is the standard in many
applications, and their use is continually increasing due to their versatility, sensitivity
and quantitative capabilities. Molecular fluorescent probes are used to identify protein
location and, in the case of enzymes, to determine whether the protein is in an active
state.
Fluorescent molecules, also called fluorophores will glow when placed under an ultraviolet
light. The UV light is absorbed by an electron of
a fluorescent particle, which raises the energy
level of the electron to an excited state. It only
occurs for a few nanoseconds, and then the
electron returns back to its normal “stable”
position. The remaining energy is emitted as a
photon (light). The color of the light depends on
how much light is lost during the transfer. The
photon of light “given off” usually carries less
energy and therefore has a longer wavelength
than the excitation photon, so is almost always a
different color than the original light used to
generate the fluorescence.
Questions:
1. We use an ultraviolet (UV light) to make some substances “glow”(they emitted or gave
off light). While several substances emitted blue light, we saw a few other colors as
well.
a. What determines the color of the light that is given off by a substance?
b. Why doesn’t a substance emit ultraviolet light, if that is the energy that is
absorbed?
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
MIXTURES
Mixtures are absolutely everywhere you look. Most things in nature are mixtures. Look at
rocks, the ocean, or even the atmosphere. They are all mixtures, and mixtures are
about physical properties, not chemical ones. That statement means the individual molecules
enjoy being near each other, but their fundamental chemical structure does not change when
they enter the mixture. If the chemical structure changed, it would be called a reaction.
When you see distilled water (H2O), it's a pure substance. That means that there are only water
molecules in the liquid. A mixture would be a glass of water with other things dissolved inside,
like vitamin water. Each of the substances in that glass keeps its own chemical properties. So, if
you have some dissolved substances in water, you can boil off the water and still have those
dissolved substances left over. If you have some salt (NaCl) in water and then boil off the water,
the salt remains in the pan. The salt is left because it takes very high temperatures to melt salt
(even more to boil it).
Mixtures can be homogeneous or heterogeneous
Mixtures are Everywhere
There are an infinite number of mixtures.
Solutions are also mixtures, but all of the molecules are evenly spread out
through the system. They are called homogenous mixtures. A solution
may appear to be a single substance, but it is really just a physical mixture
of two or more substances that are distributed evenly amongst each other.
Examples of solutions are things like salt water, koolaid, cleaning supplies, gasoline,
steel, and air. Notice not all solutions have to be liquids.
If you put sand into a glass of water, it is also considered to be a mixture but is not
homogeneous. Use the flow chart below to differentiate matter into pure substances
(compounds and elements) and mixtures (heterogeneous or homogeneous).
In a mixture, each of the substances can be separated from the group in different physical ways
that include a magnet, distillation, centrifuge, and filtering. You can always get the sand out of
the water by filtering the water away. If you were busy, you could just leave the sand and water
mixture alone for a few minutes. Sometimes mixtures separate on their own. When you come
back, you will find that all of the sand has sunk to the bottom. Gravity was helping you with the
separation. Don't forget that a mixture can also be made of two liquids. Even something as
simple as oil and water is a mixture.
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Bio A/H. Please read over this review and answer questions. This is review of Middle School Topics.
Think about the mixtures you created in experiment 2. Identify whether each mixture was
homogeneous or heterogenous and what you observed that provides evidence for your
conclusion.
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