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ANSWER KEY:
Don’t forget: you can use a notecard with whatever you want on it. And don’t write any extra
information on your periodic table.
Questions to help you prepare.
1. What is a scientific law?
A law is a rule or principle that describes a phenomenon. It tells us how things work. It can be shown
in experiment easily and can predict what will happen in a situation.
2. What is a scientific theory?
A theory is an explanation of a phenomenon. It answers why something happens the way it does. It is
based on evidence and can be used to predict what will happen in a situation.
3. What is a hypothesis?
A hypothesis is an educated guess and is based on whatever knowledge the person making it has
access to. It tries to predict what will happen in a situation but until the situation happens, it isn’t
known if its right or wrong.
4. How does a scientific theory differ from a hypothesis?
Theories are developed after lots of experimenting is done and results are put together. Hypothesis
guides the experiment but could be right or wrong.
5. Can you change a hypothesis? Explain.
Sure – if you have new information that makes you want to say something else will happen, then
change your hypothesis.
6. Can you change a scientific theory? Explain.
Yes. Theories are based on evidence, so if there is new evidence that says something different, the
theory must be changed.
7. Make a list of the base SI units and what it is they measure.
Meter measures length, seconds measure time, kelvin measures temperature, kilogram measures
mass, ampere measures current, candela measures light intensity, and moles measure amount.
8. Describe the steps of the scientific method.
Question: What do you want to know?
Hypothesis: What do you think the answer is?
Experiment: How will you find out if you are right? The independent and dependent variables are part
of this step (not separate) and guide your experiment.
Observation: What did you find out in the experiment?
Conclusion: Was your hypothesis right or wrong?
9. What is the difference between the independent and dependent variable?
The independent variable is the one that you change.
The dependent variable is the one that you observe/measure to see how it is affected by what you did.
10. What is the difference between qualitative and quantitative observations?
Qualitative observations are those that use words to describe something. For example, the pen is blue.
Quantitative observations are those that use math to describe something. For example, there are 5
pens.
11. What does SI stand for and why are SI units used?
International system of units. They are used so that scientist around the world can communicate their
results to each other.
12. Explain how to find the number of significant figures in a measurement or answer.
Any number that is not zero IS significant.
Zeros that are to the left of the other numbers are NEVER significant (even if they are on the right of
the decimal)
Zeros that are to the right of the other numbers are significant ONLY if there is a decimal somewhere in
the number.
Zeros between other numbers are always significant.
13. How do you decide how many figures to record in an answer when multiplying or dividing?
When you multiply or divide, count the total number of significant figures in the numbers you are
working with. The one with the least wins, and that’s how many sig figs should be in the answer.
Round it so that when you count its sig figs it has the right number.
14. How do you decide how many figures to record in an answer when adding or subtracting?
When you add or subtract, count the number of significant figures AFTER THE DECIMAL in the numbers
you are working with. The one with the least wins, and that’s how many sig figs should be after the
decimal in the answer. Round it so that when you count its sig figs it has the right number.
15. What is matter?
Anything that has mass and takes up space (whether you can see it or not doesn’t matter)
16. How do you determine what elements and how many atoms of each are in a compound?
In the chemical formula there are letters and numbers. Capital letters start the symbol of each
element, so count up the capital letters to determine how many there are. The subscript numbers
(small and low) show how many atoms of that element it takes to make the compound. If there is no
number, then there is only one of that atom.
17. What are the two types of pure substances?
Elements and compounds (pure substances have fixed compositions, elements have to have all the
same atoms, and compounds have to have all the same molecules)
18. What’s the difference between an element and a compound?
An element is single atoms all the same type. A compound is different atoms chemical combined that
have different properties than when they are apart.
19. What is the difference between a heterogeneous mixture and a homogeneous mixture?
Hetero means different – the parts of a heterogeneous mixture are different and usually can be seen.
Two samples might have different amounts of the different parts of the mixture.
Homo means same – the parts of a homogeneous mixture look the same and can’t be distinguished.
Two samples will look the same.
20. What’s the difference between a pure substance and a mixture?
Pure substances have fixed compositions, all the samples are EXACTLY the same.
Mixtures can have a changing composition, all samples might have the same parts but not in the same
proportions. (some people put more sugar in their kool-aid than others, some people put more
chocolate chips in their chocolate chip cookies…)
21. What’s the equation to find density?
m
Density = mass ÷ volume
d=
V
22. What’s the difference between chemical and physical property?
Chemical properties are those that require changing the composition of the substance to measure.
When you are done finding out its chemical properties, you’ll have something new.
Physical properties are those that don’t require changing the composition. It might be different in
shape or size, but its still the same thing when you are done measuring.
23. What’s the difference between intensive and extensive properties?
Intensive properties are those that don’t depend on how much of the substance you have, for example
– boiling point: it doesn’t matter how much water you have, it all boils at 212 oF.
Extensive properties do depend on how much you have. If you have a bigger elephant, it will have
more mass. (They are all grey though, so color is an intensive property)
24. What’s the difference between properties and changes?
Properties are things that you measure, changes are things that happen. (chemical changes and
chemical properties are sometimes hard to distinguish, because a chemical change happens when you
measure a chemical property).
25. What’s the difference between a chemical change and a physical change?
Chemical changes result in new substances. Physical changes don’t.
26. What clues are there that a chemical change happened?
Clues to know there is something new: bubbling/fizzing/producing a gas (when you aren’t boiling it),
color change, change in smell, change in temperature (when you aren’t heating it up), producing sound
or light,
27. Describe the three main states of matter.
Solid: has a definite shape and a definite volume, particles are close together, move a little but are
fixed in place.
Liquid: has a changing shape, but definite volume, particles are fairly close, move easily around each
other, but stay together.
Gas: has changing shape and volume, particles are far apart and move quickly without any connection
to the other particles.
28. What is the law of conservation of mass?
Conservation of mass says that the total amount of mass must remain constant. However much you
had to begin with has to be there in the end. You can’t create mass and you can’t destroy mass, but
you can change where it is and what it looks like.
29. What is an atom?
The smallest part of an element that still has the same properties. It’s the building block of all matter –
everything is made up of atoms.
30. What is a subatomic particle? What subatomic particles are there?
Subatomic particles are the pieces of an atom (smaller than an atom, they make up the atom). There
are three – protons, neutrons, and electrons.
31. What is the mass and charge of each piece of the atom?
Protons are positive and have a mass of 1 amu. Neutrons are neutral and have a mass of 1 amu.
Electrons are negative and have a mass of nearly 0 amu.
32. What does an atom look like?
We can’t see atoms because they are so small, but we know that they have a nucleus in the middle
with protons and neutrons in it and an area around the nucleus where the electrons are called the
electron cloud.
33. What are the different areas of the atom? Describe their charge. (typo in the question, oops)
There is a nucleus and an electron cloud. Since the nucleus holds protons and neutrons, it has positive
and neutral parts to it, so its positive. The electron cloud has negative parts, so its negative.
Altogether, the atom is neutral (positives and negatives balance out)
34. Where are the different pieces found in the atom?
Protons are in the nucleus
Neutrons are in the nucleus
Electrons are not in the nucleus, they are in the electron cloud
35. What is the atomic number?
Atomic number is the number of protons in an atom, it identifies the atom.
36. What does the atomic number tell you?
It tells you how many protons are in the nucleus and it tells you which atom you have.
37. How do you find the atomic number?
If you know what element you are talking about, look it up in the periodic table.
If you don’t, count up the protons.
38. How do you identify an atom?
The atomic number or number of protons identifies the atom. If you change the number of protons
(and so the atomic number), you’ll have a different element.
39. How do you find the number of electrons?
In a neutral atom (one that has no charge), the number of electrons is the same as the number of
protons (so that all the positives and negatives cancel out)
40. What is mass number?
The number of protons plus neutrons. (the number of things in the nucleus)
41. What does the mass number tell you?
The mass number tells you how many protons and neutrons are in the nucleus (but it doesn’t tell you
which are protons and which are neutrons)
42. Do all atoms of an element have the same mass number?
No, they can have different mass numbers, but they have to have the same atomic number.
43. What is an isotope? What do different isotopes of an element have in common?
An isotope is an atom with a different amount of neutrons in its nucleus. All atoms of an element have
the same atomic number but different isotopes have different mass numbers.
44. How do you identify what isotope you have?
Isotopes are identified by their mass number. You write the name with the mass number like Carbon14 or Oxygen-18.
45. What is the difference between atomic mass and mass number?
Atomic mass is the mass of the element as compared to a carbon-12 atom. The mass number is the
number of protons and neutrons.
46. How is the atomic mass found?
Atomic mass is found by taking a weighted average of the mass numbers of the isotopes.
47. Show an example of finding the average atomic mass.
Lets say you have an element with three isotopes – one has a mass number of 11, 43.567% of that
element is this isotope. A second isotope makes up 52.019% and has a mass number of 12. A third
isotope makes up the rest, 4.414% and has a mass number of 13. To find its atomic mass:
1. Change the % abundance to decimal form43.567  .43567
52.019  .52019
4.414  .04414
2. Multiple the abundance by the mass number (don’t round until the end)
.43567 x 11 = 4.79237
.52019 x 12 = 6.24228
.04414 x 13 = .57382
3. Add the answers to get the atomic mass (round, match your sig figs to the % abundance sig figs)
4.79237 + 6.24228 + .57382 = 11.60847  11.608 amu
48. How do you find the number of protons?
The number of protons is the atomic number.
49. How do you find the number of electrons?
In a neutral atom, it’s the same as the number of protons, the atomic number.
50. How do you find the number of neutrons?
The mass number includes protons and neutrons, take out the protons and you’ll have neutrons left.
That is, mass number – atomic number = neutrons.
51. Show three examples of finding protons, neutrons, and electrons.
1. Oxygen with an atomic number of 8 and a mass number of 17
a. 8 protons, 8 electrons, 9 neutrons.
2. Nitrogen with an atomic number of 7 and a mass number of 14
a. 7 protons, 7 electrons, 7 neutrons.
3. Uranium with an atomic number of 91 and a mass number of 238
a. 91 protons, 91 electrons, 147 neutrons.
52. What is the Bohr model of the atom? How are electrons arranged in this model?
The Bohr model has protons and neutrons in the nucleus and electrons around the outside. The Bohr
model has them in rings of exactly the right amount of energy. Only so many electrons can be in each
ring. More can be in the rings as you move out from the nucleus.
53. What is the quantum mechanical model (also called the modern model) of the atom?
The quantum mechanical model accounts for the fact that we can’t really know where the electrons
are (because if we did, we just moved them, funny isn’t it?) So the electrons are in orbitals which show
where the electron is most likely to be.
54. How are electrons arranged in the modern model?
Electrons fill orbitals in a prescribed manner similar to the Bohr model, by energy level.
55. What is the same from Bohr’s model to the modern model?
Nucleus in the middle with the protons and neutrons, electrons in energy levels.
56. What is different between Bohr’s model and the modern model?
Electrons aren’t in rings around the nucleus like in the Bohr model but instead stay in regions called
orbitals.
57. What is an orbital?
An orbital is a shape within an energy level that shows where an electron could be around a nucleus in
an atom.
58. What are the 4 orbitals?
s, p, d, f. The first energy level only has s. The second has s and p, the third has s, p, and d, etc.
59. What is each orbital shaped like?
s is a ball, p is like a bow tie. d is like 2 bowties together, f is like 4 bowties together. (plus some other
weird shapes…)
60. How many different versions of each orbital are there?
There is only 1 s. There are 3 p oribitals, 5 d orbitals, and 7 f orbitals.
61. How many electrons can be in each orbital shape? How many electrons in each orbital total?
2 electrons go in each orientation.
s has one orientation so it can hold 2 electrons.
p has three orientations that hold 2 each, so 6 electrons total.
d has five orientations that hold 2 each, so 10 electrons total.
f has seven orientations that hold 2 each, so 14 electrons total.
62. What does the aufbau principle say about electrons in orbitals?
Aufbau says electrons go into orbitals in a particular order, lowest energy first.
63. What does the Pauli Exclusion principle say about electrons in orbitals?
Paulli says electrons repel and so they wont go into the same orientation until all orientations have 1
electron. (Electrons exclude the others)
64. What does Hund’s rule say about electrons in orbitals?
Hund’s rule says that no two electrons can have the same set of quantum numbers, so in one orbital
orientation, one has an up spin and the other has a down spin. (even though they aren’t really
spinning)
65. What is an electron configuration?
Electron configurations show how electrons fill orbitals in energy levels.
66. What is an orbital diagram?
An orbital diagram shows the orientations as boxes for each energy level and orbital shape. Arrows
pointing up and down go into the boxes to show where the electrons are.
67. How do you fill out an orbital diagram?
You follow the 3 rules above. Start at the lowest energy, work your way up.
s will have one box, p will have 3, d will have 5, f will
have 7 boxes. 2 electrons per box, one up and one down, don’t put them together in an orbital until all
the boxes have one.
68. What is electron configuration notation?
Electron configuration notation lists the energy levels and orbitals with the number of electrons in
them. After you make an orbital diagram, its really easy, just write down the orbital and count up your
arrows. If you don’t have an orbital diagram, just make sure your numbers add up to the right amount
of electrons. (You figure out how many electrons to put in there by looking at the atoms atomic
number).
69. How do you write an electron configuration in electron configuration notation?
The longest one ever is: ununoctium with 118 electrons.
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f146d107p6
These represent the highest numbers possible. If you have less electrons, you add up as you go and
stop when you have enough. Write a smaller number on the last one if you need less than it has.