Chemistry Review
Packet
For
AP Biology I
OBJECTIVES
Part 1: Elements, Atoms, and Atomic Structure
1a. Understand that living things are composed of the same materials as the rest of the universe.
There is no special living material. The main difference between living and nonliving is the
relative degrees of complexity.
1b. Understand that life is consistent with all of the principles of chemistry and physics.
2a. Name the six most abundant elements found in the human body.
2b. Define trace element and briefly explain why they are important. (Also give a specific example
of their importance.)
3. Describe the modern model of atomic structure.
4. Use the periodic table to determine the number of protons, neutrons and electrons in atoms of
any given element.
5. Distinguish between the isotopes of a given element.
6. Use the periodic table to predict electron configurations for atoms of any given element.
7. Identify the valence electrons in the electron configuration of an element.
8. Recognize that elements in the representative groups have the same valence electron
configuration.
9. Write Lewis-dot structures for atoms of any of the representative elements.
Part 2: Bonding
1. Name three factors, which influence the interactions between atoms resulting in compounds.
2. Given a chart of electronegativities, determine whether two atoms will form a bond that is
nonpolar covalent, polar covalent, or ionic.
3. Describe the formation of ionic bonds.
4. Describe the formation of covalent bonds using Lewis structures.
Part 3: Symbols, Formulas, and Equations
1. Recognize the symbols of the twenty-five elements commonly found in living organisms.
2. Interpret the information provided in the chemical formula of important biological molecules.
3. Interpret the information provided in a chemical equation.
• Identify the reactants and products.
• Interpret the meaning of the arrow(s) written between the reactants and products.
1
Introduction
The information and questions in this packet are designed to help you review the relevant
concepts and skills from chemistry that you will need to be successful in and understand much of
biology. It is very important that you also read Campbell’s Chapter 2: The Chemical Context of
Life and study to reach the objectives listed for Campbell Chapter 2 in the Syllabus and Study
Guide.
Part 1: Elements, Atoms, and Atomic Structure
1. Explain the following statement in your own words:
***
“Living things are made of the same materials as the rest of the universe.”
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
2. Name the six most abundant elements found in the human body.
The universe is composed of about 92 naturally occurring elements. In nature, most of these
elements are found in combination with one or more other elements. These combinations of
elements are called compounds. Twenty-five of the known chemical elements are commonly
found as part of compounds that make up living things. Eleven of these 25 elements are found in
significant amounts, while the remaining 14 are found only in trace amounts.
***
List the six elements found in greatest abundance in the human body in order from most to
least abundant. (Note: Use your text.)
______________________
______________________
______________________
______________________
______________________
______________________
***
Make up a mnemonic device to assist you in remembering these six elements in order from
most to least abundant. Write your mnemonic on the lines below.
____________________________________________________________________________
*** What is a trace element? Define the term:
____________________________________________________________________________
2
*** Describe several possible functions of trace elements (See Campbell Table 41.2, p. 852):
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
*** Using one of the examples above, explain why trace elements are important. In other words,
what are the consequences of deficiency?:
____________________________________________________________________________
3. Describe the modern model of atomic structure.
(NOTE: You may want to refer to pp. 34-39 and Figs. 2.4, 2.7, 2.8 and 2.9 in Campbell)
***
Complete this statement:
According to modern atomic theory, the atom
____________________________________________________________________________
____________________________________________________________________________
***
Atomic nuclei have a radius of about 1 x 10-13 cm and electrons move about the nucleus at
an average distance of about 1 x 10-8 cm. How many times larger is the sphere formed by the
electron?
cloud than the sphere formed by the nucleus? ______________________
***
If the nucleus were as large as a baseball (a radius of about 3.5 cm),
How far away (in cm) would the electrons be? _________________
How many miles would this be? ____________________________
3
4. Use the periodic table attached to the end of this packet to determine the number of protons,
neutrons, and electrons in atoms of any given element OR consult
http://www.webelements.com/webelements/scholar/index.html
The periodic table is used to organize a great deal of information about the elements. Among
the information presented for each element is the atomic number and the atomic mass. The
representation of the element carbon from the periodic table is shown below:
Atomic number
6
C
Element Symbol
Element Name
Carbon
12.0111
Atomic Mass
The nucleus of an atom is made up of a cluster of two kinds of particles called protons and
neutrons. Protons have a positive charge and neutrons have no charge, that is, they are neutral. A
cloud of negatively charged electrons surrounds the nucleus. The atomic number and the atomic
mass provide information about the number of protons and neutrons found in atoms of the element.
In the case of carbon, the atomic number indicates that there are 6 protons in the nucleus of carbon
atoms. The atomic mass is rounded off to the nearest whole number to give a mass number of 12.
The mass number indicates that there are twelve particles in the nucleus of the carbon atom.
Therefore, if there are 12 particles in the nucleus, and 6 of the 12 particles are protons (equal to the
atomic number), then the remaining 6 particles (12 - 6 = 6) are neutrons. The number of electrons
in an atom is equal to the number of protons. The negative charge of the electrons balances the
positive charge of the protons in the nucleus, thus the atom, as a whole, is neutral.
e-
ee-
e-
Atomic
Model
6 p+
6n
e-
4
e-
***
Find the number of protons, neutrons, and electrons in atoms of each of the following
elements (Carbon is done for you.):
Element
oxygen
Protons
__________
carbon
6
Neutrons
Electrons
__________
__________
6
6
hydrogen
__________
__________
__________
nitrogen
__________
__________
__________
phosphorus
__________
__________
__________
sulfur
__________
__________
__________
calcium
__________
__________
__________
potassium
__________
__________
__________
5. Distinguish between the isotopes of a given element.
The number of protons in the nucleus of an atom determines its identity. For example, all
carbon atoms have 6 protons (the atomic number, Z = 6). There are no exceptions. However,
not all atoms of the same element contain the same number of neutrons. For example, most
atoms of carbon contain 6 neutrons, but some contain seven neutrons and some contain 8
neutrons. These atoms, referred to respectively as carbon-12, carbon-13 and carbon-14, are
said to be isotopes of carbon. Isotopes are atoms of the same element that contain different
numbers of neutrons. The atomic number (Z) and the mass number (A) can be included in the
symbol of an element to distinguish between the isotopes of an element. For example, the most
common isotope of the element oxygen has Z = 8, and A = 16. The symbol for oxygen-16 can
be written
16
8
O
What would be the symbols for the three isotopes of carbon shown below?
C
C
C
5
***
Isotope
Complete the following table:
Atomic
Number
Mass
Number
#Protons
#Neutrons
#Electrons
14
N
7
________
________
7
________
15
N
________
________
________
________
________
31
P
________
31
________
________
15
32
P
________
________
________
________
________
32
S
16
________
16
________
________
35
S
________
________
________
________
________
6. Use the periodic table to predict the electron configuration for atoms of any given element.
The electron configuration of an atom shows the way in which the electrons in the atom occupy
the available orbitals in order of increasing energy. The electronic configuration for any atom
follows three principles:
A. Aufbau principle: In general, electrons occupy the lowest-energy orbitals available before
entering the higher-energy orbitals.
B. Hund’s rule: Equal-energy orbitals are each occupied by a single electron before the second
electron of opposite spin enters the orbital. For example, each of the three 2p orbitals will
hold a single electron before any of them receives a second electron.
C. Pauli exclusion principle: No two electrons can have the same four quantum numbers (i.e.,
no two electrons can have the same spin).
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The periodic table attached to the end of this packet will also provide assistance in
understanding and writing electron configurations OR consult
http://www.webelements.com/webelements/scholar/index.html
***
Write electron configurations for the following elements:
Element
Electron Configuration
oxygen
______________________________
carbon
______________________________
hydrogen
______________________________
nitrogen
______________________________
7. Given the electron configuration for atoms of an element, identify the valence electrons.
It is the electrons in the outermost (or highest) occupied energy level of an atom that are
usually involved in chemical bonding. These electrons in the outermost s and p orbitals are
referred to as valence electrons. The word “valence” derives from the Latin valere which means to
be strong. Historically, the term valence has been used in chemistry to refer to the capacity of an
element to combine with another, as measured by the number of hydrogen or chlorine atoms with
which one atom of the element will combine.
For example, the valence electrons of a carbon atom are those in the 2s and 2p orbitals since
those orbitals are in the highest occupied energy level.
1s22s22p1 p1 p0
valence
electrons
***
Identify the valence electrons of the following atoms:
S
1s22s22p63s23p4
______________________
Na
1s22s22p63s1
______________________
Cl
1s22s22p63s23p5
______________________
K
1s22s22p63s23p64s1
______________________
Ne
1s22s22p6
______________________
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8. Recognize that elements in the representative groups have the same valence electron
configuration.
Vertical columns of elements on the periodic table are known as families or groups. Elements
in the same group have the same number of valence electrons in their highest occupied energy
levels. Why do you suppose groups are also referred to as families?
The representative groups of elements are Groups 1, 2 and 13 – 18. These elements have
atoms whose differentiating electrons are in the s and p sublevels.
As an example, let’s look at Group 1 (IA). These are known as the Alkali Metals. Their electron
configurations (shown in order of sublevel filling) are written below. Do you see a pattern in the
number of valence electrons that atoms of each element have? (Valence electrons are underlined
and bolded.)
1s22s1
3Li
11Na
1s22s22p63s1
19K
1s22s22p63s23p64s1
37Rb
1s22s22p63s23p64s23d104p65s1
55Cs
1s22s22p63s23p64s23d104p65s24d105p66s1
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s1
How many valence electrons are found in elements of each of the following groups?
87Fr
***
Halogens (Group 17 or VIIA)
______________
Oxygen Family (Group 16 or VIA)
______________
Nitrogen Family (Group 15 or VA)
______________
Carbon Family (Group 14 or IVA)
______________
***
What influence does this similarity in atomic structure have on the properties of the
elements found in each of these groups?
____________________________________________________________________________
____________________________________________________________________________
8
9. Write Lewis-dot symbols for atoms of any of the representative elements.
A Lewis symbol is a form of notation that shows valence electrons and the possibilities for
bonding in an atom. The atomic symbol stands for the nucleus plus all the underlying occupied
energy levels. Valence electrons are represented individually by dots placed in an imaginary
square around the atomic symbol in a pairing pattern set by the aufbau principle and Hund’s rule.
That is, the electron dots representing the lower-energy s orbital electrons are paired first, while the
dots representing the higher, equal-energy p orbitals are paired only after each of the remaining
sides of the square has one.
For example the Lewis dot structure for atoms of the element phosphorus would be:
·P· ·
·
This structure shows only the 5 valence electrons of phosphorus atoms.
***
Write the Lewis dot symbol for Hydrogen.
Hydrogen (Group IA)
***
______________
Write the Lewis dot symbol for the first element in each of the following groups.
Halogens (Group VIIA)
______________
Oxygen Family (Group VIA)
_____________
Nitrogen Family (Group VA)
_____________
Carbon Family (Group IVA)
______________
Part 2: Bonding
1. Name three factors that influence the interactions between atoms resulting in compounds.
There are three factors that influence whether atoms of an element will interact with other
atoms to form a compound:
a. The tendency for electrons to occur in pairs.
b. The tendency of atoms to balance positive and negative charges. Atoms and molecules are
neutral.
c. The tendency of the outer shell, or energy level, of electrons to be full. This is the octet rule.
(An outermost shell electron configuration of s2 p6 is exceptionally stable.) Atoms that do
not have stable octets will gain, lose, or share electrons in order to achieve the s2 p6
configuration.
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2. Given a chart of electronegativities, determine whether two atoms will form a bond that is
nonpolar covalent, polar covalent, or ionic.
The attraction an atom has for the shared pair of electrons in a covalent bond is called the
atom’s electronegativity. The difference between the electronegativities of two atoms in a bond
can be used as a guide to determine the degree of electron sharing in the bond. As the difference
increases, the degree of sharing decreases. If the difference in electronegativities between the two
atoms is 0 the pair of bonding electrons is shared equally. The bond formed between these atoms is
called a nonpolar covalent bond. On the other hand, if the difference between electronegativities
is 1.7 or greater, electrons are transferred from one atom to the other. In such a case, the element of
greater electronegativity is said to exist as a negative ion, while the element of lesser
electronegativity exists as a positive ion. The electrostatic attraction between the two oppositely
charged ions is called an ionic bond.
Molecules that contain bonds with electronegativity differences between 0 and 1.7 are
considered to be covalent but with unequal sharing of electrons, that is they are polar covalent
bonds. In the HCl molecule, for example, chlorine has the greater electronegativity (3.0 in
comparison to 2.1 for hydrogen). The difference between the two electronegativities is 0.9. The
electrons are shared unequally. In such a case, the atom with the greater electronegativity takes on
a partial negative charge (between zero and 1-) as the shared pair of electrons spend more time
nearby. The other atom takes on a partial positive charge (less than 1+). The chart below will
enable you to predict the character of bonds between any two atoms that we may need to deal with
in biology.
δ+
δ–
Example:
H—Cl
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***
Predict the character of the bond between atoms of the following pairs of elements:
oxygen- nitrogen
_______________________
calcium-fluorine
_______________________
lithium-chlorine
_______________________
oxygen-oxygen
_______________________
3. Describe the formation of ionic bonds.
A simple example of ionic bonding occurs between the elements sodium and chlorine in the
compound NaCl. Sodium atoms lose (transfer) one electron to chlorine atoms, producing Na+ and
Cl- ions. Since it lost one electron, the sodium ion assumes an electron configuration similar to the
stable noble gas neon.
loss of 1eNa (1s 2s 2p 3s ) ---------> Na+ (1s22s22p6)
2
2
6
1
[Neon: 1s22s22p6]
Since the sodium ion now has an octet in its outermost shell, it is more stable than the sodium
atom. The electron that was lost by the sodium atom is transferred to a chlorine atom forming a
chloride ion with a stable octet also. Since it gained one electron, the chloride ion assumes an
electron configuration similar to that of the stable noble gas argon.
*** How is Na+ (1s22s22p6) similar to Neon: 1s22s22p6? How is it different?
____________________________________________________________________________
___________________________________________________________________________
-
gain of 1e
2 2
6 2
5
Cl (1s 2s 2p 3s 3p ) --------> Cl (1s22s22p63s23p6)
[Argon: 1s22s22p63s23p6]
*** How is Cl- (1s22s22p63s23p6) similar to Argon: 1s22s22p63s23p6? How is it different?
____________________________________________________________________________
____________________________________________________________________________
The sodium and chloride ions that are formed are held together, in an ionic bond. In other
words, they are held together by the mutual attraction of their opposite electrical charges.
11
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Part 3: Symbols, Formulas, and Equations
Chemists use chemical symbols, formulas, and equations when speaking and writing about
matter and the changes it undergoes. When possible, the symbol consists of a single letter, usually
the first letter of the name of the element. In cases where several elements have names that begin
with the same letter, two letters are used. For example, calcium (Ca), cobalt (Co), chromium (Cr),
and chlorine (Cl). No symbol contains more than two letters and the first letter is always
capitalized. Some symbols are abbreviations of the Latin names of the elements. Among the
twenty-five elements commonly found in the human body, only 5 of them have Latin names. These
are: potassium (K), sodium (Na), copper (Cu), iron (Fe), and tin (Sn).
A formula is a single symbol or a group of symbols which represents the composition of a
substance. The symbols in the formula identify the elements present in the substance. Subscripts
are used in the formulas to indicate the number of atoms in the compound, but only when more
than one atom of a given element is present. For example, the formula for water, H2O indicates that
each molecule contains two atoms of hydrogen and one atom of oxygen. Recall that the algebraic
sum of the positive oxidation numbers and the negative oxidation numbers of the atoms and ions
present in a compound must always be zero. Since the sum of the oxidation numbers is zero, a
compound is neutral, that is it has no net charge.
Atoms are the fundamental particles of the elements that enter into chemical changes.
Substances that take part in chemical changes are made up of atoms in the form of molecules or
ions (ions are atoms or groups of atoms that are electrically charged). Chemical changes involve
the regrouping of atoms or ions to form other substances. The chemical equation is the chemist’s
shorthand expression for describing a chemical change, and the symbols and formulas are used to
indicate the composition of the substances involved in the change. For example, the equation
2H2(g) + O2(g) → 2 H2O(l)
This formula states that 2 moles (or molecules) of hydrogen gas react with 1 mole (or
molecule) of oxygen gas to yield 2 moles (or molecules) of water which condenses as liquid. The
numbers written in front of the formulas are called coefficients and they indicate the number of
moles (or molecules) of the substance required as a reactant or formed as a product. The arrow
indicates the direction of the reaction and can be read as “produces,” “yields,” or “forms.” The
subscripted letters in parentheses indicate the state of matter. The following conventions are used:
(s) – indicates a solid
(l) – indicates a liquid
(g) or ↑ – indicates a gas
(aq) – indicates the substance is in aqueous solution
↓ – indicates that a solid precipitate forms in an aqueous solution
13
*** Interpret the information in the following chemical equations.
2Na(s) + 2H2O(l) →
2NaOH + H2↑
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
C6H12O6(aq) + 6O2 (aq) →
6H2O(l) +
6CO2 (aq)
____________________________________________________________________________
___________________________________________________________________________
____________________________________________________________________________
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