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Study guide/worksheet BASIC CHEMISTRY– ref. ch 2 though not following exactly
1. The ELEMENTS and the Periodic Table -There is a Table in your text’s appendix. We will use it for
some data like atomic numbers and masses. We will discuss metals/nonmetals etc as in a chem class.
a. The “stuff” of the universe consists of “pure substances” called e________________. The
Periodical Table lists information about each of them. Most of these substances were created before
our solar system formed, from a massive star explosion - a supernova.
b. Cells consist mostly of H and O (bonded to make water molecules) as well as N and C.
Write their English names and their Atomic Number from the Periodical Table
HONC!
c. Our bodies need elements found as salts/electrolytes and minerals. Some of these elements have
symbols based on Latin words,- e,g,: Iron, Fe (ferrous), potassium___ and Sodium ____ .
Vitamins are molecules made of several elements, mostly carbon and hydrogen.
2. The structure of ATOMS:
- An atom is the smallest form of an element that still retains all the properties of that element (e.g.
melting point).
- Atoms are made of three kinds of subatomic particles:
name of particle:
** P
E
N
charge:
+
mass:
1 unit
~0 (1/1836)
where located within atoms?
Clustered in the center/atomic nucleus
** The PROTONS dictate each element’s properties and identity.
Elements differ because atoms have different ______________ of subatomic particles.
Choose: a) types b) sizes c) numbers d) charges
atomic mass = # protons + # neutrons
What about the electrons- don’t they have mass?
The Periodic Table lists the average mass for each element- that is why they are decimals.
When considering single atoms, round the average mass unless told otherwise.
Look at the Periodic Table to find the following information:
-> Which element has 17 protons per atom? _______
–> Which element in bones and teeth has an average atomic mass of 40 units? _______
–> Which other element’s average mass is 40? _______
-> Zinc: atomic #_______; average mass:_____; # protons:_____ ; # neutrons _______
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Simplified atom diagrams (we will not review orbitals nor Lewis dot structures)
Which atom is this?
Which atom is this?
-
o +o
o +o+
+o+ o
-
-
+o
o+
-
The big circle =
electron path =
zooming zone=
electron “shell” =
“energy shell”
-
Recall the rules about how many electrons can fit in the inner (first) shell: _______
How many can potentially fit in the second shell? ______ the 3rd shell? ________
Memorize this.

Another rule to recall: OPPOSITE CHARGES ATTRACT (conversely, “LIKE” CHARGES REPEL).
Ponder this rule with regard to atom structure: are the protons attracted to one another inside the
middle? ___________
What is also inside the center that may help this issue? ____________
It would seem the electrons would zoom into the center but they don’t. The explanations are deeper
than we can go into, but involve atomic forces and electron speed.
3. PRACTICE DRAWING SMALL ATOMS
Using the Periodic Table’s information in a similar manner as the Boron and Helium above, draw
simple atom diagrams with all their subatomic particles showing in their proper relative positions and
proper charges: (you don’t need starbursts around your electrons)
Step #1: PROTONS (p+) The element’s atomic # = # protons. Draw in atom’s center.
Step #2: ELECTRONS ( e-) Assume that the atom begins with an even #electrons as #protons. (The
atom may make changes but we will get to that later). Draw in shells properly (2 fit in inner shell, up
to 8 fit in 2nd shell)
Step #3: NEUTRONS (no)
a) Look up the average atomic mass in the Table.
b) It is usually a decimal so round it to the nearest whole number (if 0.5 go up).
c) Subtract the # protons from the mass to calculate the average # neutrons.
Draw them in the center.
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Lithium (#3 in the Table)
Beryllium (# 4 in the Table)
Fluorine (#9)
5. IONS Some atoms give away 1, 2 or even 3 electrons. Others gain 1 extra electron (but usually no
more than 1). When an atom does this, its OVERALL CHARGE is altered. Atoms with extra/fewer
electrons are called IONS. (Ref 2.7 though book is already presenting molecular bonds)
Why would an atom give electrons away or take one more electron? Answer: to create a full outer
electron shell.
Why create a full outer shell? Answer: because they are more stable that way.
If atoms gain electrons, they become (choose: positive or negative)_________
If atoms lose electrons, then become (choose: positive or negative) _________
If atoms become positive, you write it like this: K+ (potassium ion)
If atoms become negative, you write it like this: Cl- (chlorine ion)
 Look at the Lithium (Li) atom above. It was not ionized, but they often ionize. Do they lose or gain
electrons? ________ How would you write lithium using shorthand to show it had ionized?________
Look at the Periodic Table and find Lithium. Which element is in the same column right under it?
Look at Beryllium in the second column. What can Be do to have a full outer shell?
(All of the elements in the 2nd column do the same thing as Beryllium).
When Beryllium ionizes, how do you write the symbol: Be+ or Be-? (choose one)
Which column consists of atoms which usually take one extra electron? ____
Which column consists of atoms that already have full shells? _____
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5. ISOTOPES: (ref 2.3, 2.4) Atoms of the same element can have different numbers of neutrons.
They are all “isotopes” of that element. “iso” = same and “tope” is type.
If an atom has fewer neutrons than average, it is called a _________ isotope (choose light or heavy).
Some isotopes are unstable and can “decay” (rearrange or blow up), releasing r______________
energy and particles. You cannot hear or feel this energy but you can be damaged or even killed by it.
Special instruments are used to detect and measure the energy and particles. Can you List some
sources of dangerous radioisotopes?
One famous isotope, C-14, is used to date fossils and archeological artifacts.
Some radioisotopes are useful in medicine… know of any?
Critical thinking questions about atoms:
If the following event
happened…
… would the atom’s
charge differ?
If so, how?
… would the atom’s
mass differ? If so, is it
heavier or lighter?
… is the atom a
different kind of
element?
An atom somehow
magically* got an extra
proton
An atom somehow got
an extra neutron
An atom got an extra
electron
An atom lost one
electron
* (Note that proton numbers are not normally changed- only in nuclear reactions)
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6. MOLECULES
Definition: A molecule consists of one or more atoms or ions bonding.
A. Ionic bonds and ionic molecules: (ref 2.7)
Different kinds of ions will often stick together because opposite charges attract.
e.g. Hydrochloric acid, also called stomach acid: H+ Cl Name another very famous ionic pair: _____________ (hint: in most processed foods)
The attractions between ions are called “ionic bonds” and the bonds can be pretty strong- especially
when millions of ions are all bonding to one another. Some ions form crystals.
B. Covalently bonded molecules (2.6)
Some atoms share electrons with other atoms in an attempt to fill their missing spots in the outer
electron shells, thus forming covalent bonds.
co = together; valent refers to the empty places in the outer electron shells.
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Before we get into molecular diagrams, let’s draw atoms of the four most important elements of living
things: H, O, N, C. Use the Periodic Table information to draw the following atoms with the proper
number of electrons in their shells:
H
H needs
O needs
N needs
C needs
O
N
more electrons to fill its outer shell.
more electrons to fill its outer shell.
more electrons to fill its outer shell.
more electrons to fill its outer shell.
C
HONC
!
The smallest covalently bonded molecule in the universe is Hydrogen gas. Hydrogen gas can be
written as H2 which is its “molecular formula”. What does the “’2” mean?
Hydrogen gas can be written as H-H, its “molecular structure”. The line represents the covalent bond.
-> What is actually happening between the two Hydrogen atoms?
-> Why are they engaged in this activity? (what advantage is there?)
Molecular bonds can be measured in calories = the heat it takes to pull them apart.
C. Symbols, diagrams, and models of molecules with covalent bonds
This activity is most useful if you have access to molecular models. Do note that REAL atoms
are not dense spheres - they are mostly empty space and energy. Likewise what do real
covalent bonds consist of? _________________
You can make each molecule and then break it down to make the next molecule listed in the table. Or
if you have enough models you can make them all. The fewest # atoms you’d need to build all the
molecules in the following table are listed below:
- 6 Hydrogen atoms (each with 1 hole);
- 2 Oxygen atoms (each with 2 holes close to one another like nostrils);
- 2 Nitrogen atoms (each with 3 holes); (If the model has 4 holes, pretend there are 3)
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-
2 Carbon atoms (with 4 equi-distant holes).
7 sticks for single bonds and 4 bendable items for double and triple bonds (springs, curved
plastic).
When you draw the diagrams and build the models, ensure that ALL HOLES ARE FILLED.
Name:
Formula:
Structural diagram:
(optional pic: Ball/stick model)
Hydrogen
H2
fuel/gas
_________________________________________________________________
Water
__________________________________________________________________________________
Methane
CH4
__________________________________________________________________________________
Ammonia
NH3
_________________________________________________________________
oxygen
O2
_________________________________________________________________________________
carbon dioxide
CO2
_________________________________________________________________________________
nitrogen gas
N2
_________________________________________________________________________________
Ethanol
C2H5OH
(keep the O&H together)
__________________________________________________________________________________
Ethyne
C2H4
_________________________________________________________________________________________________________________________
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E. Vocabulary about molecules
1. A substance with two or more elements is a “compound”.
Examples: a glass of H2O. Dry ice is CO2.
2. “Organic molecules” contain both carbon and hydrogen atoms (and may have a few other atoms as
well). There are millions of kinds of organic molecules.
They include molecules like: ________________________________________
What is the smallest organic molecule? __________________
Aside: In foods and other crops like cotton, people use the word “organic” to mean something different
from what chemists mean by the word “organic”. What does “organic produce” mean at the grocery
store? ____________________________. This is ironic because most pesticides are organic
compounds!
3. Inorganic chemicals do NOT contain both carbon and hydrogen.
Is water (H2O) organic or inorganic?_____ What about ammonia, NH3? _____
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7. CHEMICAL REACTIONS (2.9)
When ions, atoms, and molecules interact and form new bond, lose electrons, etc. they are
undergoing “chemical reactions”
Though there may be many intermediate steps involved, a summary statement of the “before” and
the “after” can be expressed as follows:
Reactants (chemical inputs)
----
products (including wastes)
The arrow represents many things: time, catalysts like enzymes, necessary “helpers” like pigments,
electron “taxi” molecules, particular conditions like temperature, pressure, etc.
Sometimes people add other notes like “heat” along with the products.
Sometimes a chemical reaction is “balanced” so that all the atoms on the reactant side of the arrow
equal the atoms on the product side (i.e. every atom is accounted for).
 Write the balanced equation for an overall chemical reaction of your choice (e.g. of important
ones are photosynthesis or aerobic cellular respiration)
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8. WATER (2.10---)
A. Water has “polar covalent bonds”
When two different kinds of atoms form a covalent bond, the
electrons are likely to be attracted to one atom more than
another. If this effect is dramatic, the covalent bond is said to be
“polar” (charge lopsided).
Which atom is slightly negative in this dog diagram: Atom A or Atom B? ________
In biology, the most famous polar covalent bond is O-H.
Oxygen is EXTREMELY attractive to electrons, especially hydrogen’s
electrons. You can think of oxygen atoms
as electron “hogs” (a property called
electron-negative). Oink!
Water molecules have two polar covalent
bonds.
B. Water molecules are polar
For reasons we are not getting into, an oxygen atom has two bonding sites that fairly close to one
another. Thus when two H atoms bond to O to form a water molecule, the entire water molecule is
BENT like the letter “V”.
Where are most of the electrons: near the oxygen or near the hydrogens? _________
The whole water molecule is polar with a partially positive pole and a partially negative pole, like a
little magnet.
C. Water is attracted to anything charged (ionized) or polar (slightly charged):
Recall that opposite charges attract.
Because of water’s slight positive and negative charges, it is attracted to anything else with charges,
including other water molecules.
 The attraction between water molecules is a weak bond called ______________. (section 2.11)
(These bonds are not just between water molecules. These bonds can be between other kinds of
atoms too. They hold DNA together and a host of other examples.)
 What do you call the collective attraction between lots of water molecules?
C___________________
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 Draw several water molecules aligned with one another according to their charges and show little
dotted lines to indicate the weak fleeting H-bonds between the molecules:
The polarity of water allows it to dissolve ions such as salts and other minerals.
 Draw a Na+ ion being dissolved (surrounded) by some water molecules (aligning the water
molecules properly):
 What other properties of water are directly tied to cohesion and its attraction to anything with
ionic or partial charges (called “adhesion”, like water’s attraction to glass)
Oil and water do not mix
i.e. water is not attracted substances unless they have charge or polarity
1. When the atoms within a molecule (or region of a molecule) are sharing electrons evenly it’s
“nonpolar”. Examples: H-H O=O and CH4 (methane)
 what does methane’s molecular diagram look like?
In the next chapter we will focus on CARBON atoms and why carbon + hydrogen atoms, as found in
lipids, are nonpolar, and thus hydrophobic.
9. Introduction to acidity and alkalinity and the pH scale (2.14)
pH is written with a lowercase “p” and uppercase “H”.
It is not correct, but can be handy, to think of “pH” referring to “proportion H ions”.
Hydrogen ions are also written as H+ and called protons! (Remember this!)
 If you start with a whole H atom, what must happen to create an H ion?
 We write hydroxyl ions like OH- by convention, but which atom took the e-: O or H?
There are no units to the pH scale.
- Acidic solutions have more hydrogen ions (H+) per liter than hydroxyl ions (OH-);
- Neutral solutions have an equal number of H+ and OH-.
- Bases (alkalines) have more OH- ions per liter than H+ ions.
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The pH scale is a measurement of how many H+ are in the solution.
The pH value is really the number of decimal places as follows:
1. 0 grams of H+ /liter = pH 0. What solutions are this acidic?
0. 1 grams of H+ /liter = pH 1
0. 01 grams of H+ /liter = pH ___
0. 001 grams of H+/liter = pH ____ Name something this acidic:
0. 000,0001 grams of H+ = pH ____ This is considered neutral. The [H+] = [OH-].
0. 000,000,000,001 g H+/l = pH _____What solutions are this alkaline?
What is the highest the pH scale goes? pH __________
The pH scale is logarithmic. Thus tiny changes in pH mean big changes in reality. pH 6 is 100 x more
acidic than pH 8 because they are two pH units apart. How many times more acidic is pH 3 from pH 7?
 If saliva is measured to be pH 6.0, how many grams of H+ are there per liter? ____
 What is the pH of a substance with 0.0001 grams of H+ per liter? ______
 Why is pure water considered “neutral” when it has 0.0000001 g H+ per liter?
What are BUFFERS? And why essential to organisms?