AP Chapter 2 Study Guide: Chemistry
(Rob Hamilton © 2011)
Teachers Note: The purpose of introducing you to college biology with a chapter of chemistry is NOT for you to learn a lot of chemistry. You will learn (or have learned) chemistry in chemistry. I have done quite well (my own opinion) in biology knowing very little chemistry. So if you are a bit confused over this or that, or uncomfortable with the pace…RELAX, a bit of chemistry is all you really need to know and it will lay the foundations for a richer understanding of biochemistry and biochemistry is the foundation of all modern biology. PLEASE DO NOT SLACK. This is a college course and you will have to come to class prepare!
Let’s start out with some simple definitions so we can communicate effectively. Pgs 30-32
1. What is anything that has mass and takes up space? ______
2. What is a substance that cannot be broken down into another substance by chemical
reactions? ______
This is, in fact, a biology course, so we are particularly interested in the atoms of elements that are found most frequently in living things. You will need to know these elements and use their symbols all year. So memorize them now and be done with it.
3. List the eight elements that are most abundant in living things and their symbols.
Element Symbol Element Symbol
1.______5. ______
2.______6. ______
3.______7.______
4.______8. ______
Some Biology I review. Pgs 33
4. List the subatomic particles, their location within the atom, their charges and their mass
Subatomic Particle Location Charge Mass
______
______
______
Our authors provide a somewhat convoluted description electron configuration and chemical bonding (pgs 37-42.) I will lead you through a series of exercises that should get us where we need to be. First let’s look at the periodic table………...
The periodic table provides information about the various elements:
* The Atomic Number determines the elements identity and is equal to the number of Protons
* All atoms are neutral in charge, therefore the number of Protons must be equal to the number of Electrons
* Protons weigh 1 Dalton, Neutrons weigh 1 Dalton, Electrons weigh 1/2000th of a Dalton, therefore, the number of Neutrons can be determined by subtracting the Atomic Number (Protons) from the Atomic Weight (Protons + Neutrons)
5. Use your periodic table to fill in the missing information for each element
Chemical Symbol / Atomic Number / Element Name / Atomic Weight / Number of Protons / Number of Electrons / Number of NeutronsHydrogen
6
Nitrogen
O
19.00
Na
Magnesium
Si
P
32.064
35.453
Now that you can determine the number of subatomic particles in an atom, we can use this information to construct illustrations of atoms (Bohr diagrams) which will enable us to make predictions about the number and type of bond(s) an element is capable of making.
6. One thing stands between us and this intellectual leap. While protons and neutrons are found in the nucleus, electrons orbit the nucleus at distances that are roughly equivalent to their potential energy
called ______with electrons with lower potential energy orbiting closer to
the nucleus.
7. Energy levels are represented symbolically by ______.
8. Study figure 2.9 on pg 36. What is the maximum number of electrons allowed in the first energy level? (The
one nearest the nucleus) ______.
9. What happens if an atom has more electrons than the first energy level can hold? ______
______
10. How many electrons are allowed in the second energy level? ______
11. What happens if an atom has more electrons than the 1st & 2nd energy levels can hold? ______
______
Our authors neglected to tell you that the 3rd energy level can hold 18 electrons and the 4th energy level can hold 32. The reason for this omission is probably due to the fact that heavy elements are not abundant in living things but it is still something that is nice to know.
12. Use your knowledge of electron shells and the periodic table to fill in the correct number of protons, neutron and electrons in the Bohr diagrams below and on the next page. Be sure to place the electrons in their correct energy level. Figure 2.9 on pg 36 will be useful to you
Hydrogen Helium Lithium
Beryllium Boron
Carbon
Nitrogen Oxygen Fluorine
Now that you are bored with Bohr diagrams, it is time to move on. So if you are feeling tired, WAKE UP! We are going to use the periodic table and Bohr diagrams to make an important point.
13. Find hydrogen, lithium and sodium on your periodic table. What do all three elements have in common?
______
14. Now examine the Bohr diagrams of hydrogen, lithium and sodium. What do hydrogen, lithium and sodium
atoms have in common? ______
______
15. Now predict how many electrons potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr) have in their
valence shell (outer energy level) ______
16. Now look at beryllium and magnesium in column 2, Family 2A. How many valence shell electrons do you
think they have? ______. Check your hypothesis with your Bohr diagrams.
Now let’s redundantly drive the point home……………………
17. What Family is boron in? ______Boron has how many valence electrons?______
What Family is carbon in? ______Carbon has how many valence electrons?______
What Family is nitrogen in? ______Nitrogen has how many valence electrons?______
What Family is oxygen in? ______Oxygen has how many valence electrons?______
What Family is fluorine in? ______Fluorine has how many valence electrons?______
So it turns out that the elements of the periodic table are not just arranged by their number of protons. They are placed in columns with other elements that contain the same number of valence electrons. Imagine that, there are actually human beings who seeking order in our chaotic world!! This brings us to the column on the far right. Helium, neon, argon, krypton, radon and xenon are the noble gases and they have an extraordinary property: they are stable and will not form compounds!!! So go back and actually read pgs 36-37 and answer the questions below.
18. What determines the chemical behavior of an atom? ______
19. Why are the nobel gases (far right column) reactive? ______
So all the other elements that do not have their valance shell filled with electrons are unstable and reactive and will form compounds!!!
20. Hydrogen has a single energy level. How many electrons are required to fill hydrogen’s valence shell (which
is also its first shell) and make it stable and unreactive? ______
21. Lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon have two energy levels. How many
electrons are required to fill their valence shells and make them stable and unreactive? ______
All elements with atomic numbers greater than 10 have 3 or more energy levels. While the 3rd energy level can hold up to 18 electrons and the 4th energy level can hold up to 32, if the 3rd or 4th or any other energy level is the outer energy level (valence shell), it will only hold 8 electrons. This is called the octet rule. Now read about the formation of compounds on pgs 38-42.
22. Atoms with unfilled valance shells will share, borrow or lose electrons in order to fill their valance shell and
become stable. What kind of chemical bond is formed when two atoms share electrons to become stable?
______bond
23. Two or more atoms held together by a covalent bond are called a ______
24. If atoms share two pairs of electrons it is called a ______
25. What is an atom’s valence? ______
Indicate the valence of the following elements: H _____, Li _____ Be_____, B _____, C _____, N _____,
O _____, F _____.
26. However, the sharing of electrons in a covalent bond is not always equal. Different atoms have different
levels of attraction for their electrons. The attraction of a particular kind of atom for its electrons is called its
______
The electronegativity of the elements is listed in the chart below. As a rule of thumb, electonegativities increase as you move from the lower left to the upper right.
H2.1 / He
0
Li
0.98 / Be
1.57 / B
2.04 / C
2.55 / N
3.04 / O
3.44 / F
3.98 / Ne
0
Na
0.93 / Mg
1.31 / Al
1.61 / Si
1.9 / P
2.19 / S
2.58 / Cl
3.16 / Ar
0
K
0.82 / Ca
1 / Sc
1.36 / Ti
1.54 / V
1.63 / Cr
1.66 / Mn
1.55 / Fe
1.83 / Co
1.88 / Ni
1.91 / Cu
1.9 / Zn
1.65 / Ga
1.81 / Ge
2.01 / As
2.18 / Se
2.55 / Br
2.96 / Kr
0
Rb
0.82 / Sr
0.95 / Y
1.22 / Zr
1.33 / Nb
1.6 / Mo
2.16 / Tc
1.9 / Ru
2.2 / Rh
2.28 / Pd
2.2 / Ag
1.93 / Cd
1.69 / In
1.78 / Sn
1.96 / Sb
2.05 / Te
2.1 / I
2.66 / Xe
2.6
Cs
0.79 / Ba
0.89 / La
1.1 / Hf
1.3 / Ta
1.5 / W
2.36 / Re
1.9 / Os
2.2 / Ir
2.2 / Pt
2.28 / Au
2.54 / Hg
2 / Tl
2.04 / Pb
2.33 / Bi
2.02 / Po
2 / At
2.2 / Rn
0
27. If two atoms are equally electronegative or if their difference in electronegativies is small (<1.0) then the
atoms will form ______bonds.
28. Conversely, if two atoms have electronegativites that are greater than 1, but not more than 1.67, they will not
share electrons equally and the electrons will be pulled towards the atom with the greater electonegativity.
This is called a ______bond.
An example of a polar covalent bond is water. Do the math.
29. The electronegativity of Oxygen is ______
The electronegativity of Hydrogen is ______
The difference in electronegativities is ______
Therefore, the electrons will be pulled towards the oxygen atom giving it a sight negative charge which is symbolized by the lower case Greek letter delta with a minas following: δ - Because the electrons spend more time around the oxygen, the hydrogen atoms have a slight positive charge which is symbolized by the lower case Greek letter delta with a plus following: δ +
30. In some cases, two atoms have electronegativities that are so unequal (>1.67) that the atom with the
greater electronegativity strips an electron away from the other atom. The bond that results is called
an ______bond. An example is table salt (NaCl)
31. The electronegativity of chlorine is ______
The electronegativity of sodium is ______
The difference in electronegativities is ______
32. When sodium loses an electron, it can no longer be an atom because it now has unequal numbers of protons
(11) and electrons (10). It is now called a ______and it has a positive charge.
33. When chlorine gains an electron, it now has 17 protons and 18 electrons and therefore has a negative charge.
It is now called a ______
Read pgs 40-43. Sometimes weak electrostatic attractions occur between two polar molecules like water or parts of very large molecules with polar portions. These attractions are extremely important in producing a molecule’s shape which, in turn, determines the molecule’s function!
Listen up, this appeared on last years AP exam!!! So a slight electrostatic charge of a molecule or a portion of another molecule or another portion of the same molecule is a hydrogen bond. Read pgs 42-43.
35. What occurs in a chemical reaction?______
______
36. What do we call the compounds that enter a chemical reaction? ______
37. What do we call the compounds that a produced in a chemical reaction? ______
38. What is wrong with this chemical reaction: H2 + O2 à H20? ______
______
39. What is wrong with this molecule? H-C=C-H ______
______