Transcript balancing equations

Test #5
Review
Significant Figures
Define precision.
How detailed is your measurement.
Define accuracy.
How correct is your measurement.
Is it possible to be very precise and very inaccurate?
Yes.
You could, for example, measure your height to be
5.6224 meters.
Significant Figures
Which is more accurate, 2.3 meters or 2.321 meters?
Impossible to say. You don’t know the correct length.
How many sig figs in 2.00 grams?
three
How many sig figs in 1500 liters?
two
How many sig figs in 200.00 Newtons?
five
Unit Conversion
How many meters in 362 centimeters?
3.62 m
How grams in 4.5 kilograms?
4500 g
If 22.1 p equals 84 q, how many p are equal to 469 q?
120 p
(remember, only two sig figs)
What is the melting temperature?
100 degrees C
Once melting begins, how much energy is needed to finish?
60 calories
Phase Changes
Which phase has no definite volume or shape?
gas
Which has the higher temperature, melting or freezing?
It’s the same!
Changing from gas to liquid phase is called . . .
condensation.
Does a liquid absorb or give off energy when freezing?
Energy is given off.
Atomic History
Who discovered the nucleus?
Ernest Rutherford
Who discovered the electron?
J. J. Thomson
Who made the first periodic table of the elements?
Dmitri Mendeleev
What did the “gold foil” experiment discover?
the nucleus
Atomic Basics
What is the mass of the proton?
1 amu
Which force holds the nucleus together?
the strong force
Which force holds the electrons around the nucleus?
the electromagnetic force
Define mass number.
number of protons + number of neutrons
Atomic Basics
The identity of an element depends on the number of . . .
. . . protons
How many protons in one atom of iron?
26
How many neutrons in one atom of 19F?
10
How many electrons in a +1 ion of potassium?
18
Atomic Basics
How many valence electrons in one atom of sulfur?
6
What is an ion?
a charged atom
What is the most likely charge on an ion of sulfur?
-2
Add two neutrons to calcium-40. What’s the new element?
calcium-42
Table Trends
Which is more reactive, lithium or potassium?
potassium
Why?
Less force; it’s easier to remove an electron.
Which is more reactive, fluorine or bromine?
fluorine
Why?
It attracts electrons with greater force.
Table Trends
Which is larger, lithium or potassium?
potassium
Why?
more energy levels
Which is larger, fluorine or bromine?
bromine (For the same reason – more energy levels.)
Why do elements in the same family behave the same?
They all have the same number of valence electrons.
Chemical Formulas
Predict the formula for potassium sulfide.
K2S
Predict the formula for calcium iodide.
CaI2
Predict the formula for gallium oxide.
Ga2O3
Predict the formula for lithium sulfite.
Li2SO3
Chemical Bonds
Which bond would form between sodium and oxygen?
ionic
Which bond would form between nitrogen and oxygen?
covalent
What is the name of SiO2?
silicon dioxide
Which would be a better conductor, SiO2 or KCl?
Potassium chloride; it’s ionic.
Here are some other topics:
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electron orbitals
types of chemical reactions
balancing equations
energy of chemical reactions
reaction rates
acids & bases