Download Rules For Significant Figures

Rules for Significant Figures
All non-zero digits (1-9) are significant.
Zeros between non-zero digits are significant. Ex: 3004 has 4 significant figs.
Zeros to the left of the first non-zero digit are not significant. Ex: 0.004 has 1 significant fig.
If a number ends in zeros to the right of the decimal point, those zeros are significant.
Ex: The number 40.0 has 3 significant figures
Multiplication and division, the result may have no more significant figures than the factor
with the fewest number of significant figures.
Example:
2.52
x
(3 sig figs)
(smallest)
1.003
(4 sig figs)
= 2.52756  recorded to 2.53
=
(3 sig. figs)
Adding and subtracting: Add or subtract the numbers. The final answer can contain only as
many decimal places as found in the measurement with the fewest number of decimal places.
Example: 134.052 m
+
1.23 m =
135.282  rounds to 135.28
(3 decimal places) (2 decimal places)
(2 decimal places)
________________________smallest_________________________________________
Density (mass unit/volume unit) = Mass (unit) ÷ Volume (unit)
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Specific heat (c) (units) = calories / (grams x C) or joules / (grams x C)
Heat released (cal or J) = mass (g) x Specific heat (choose one unit above) x temp change (ºC)
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Conversions: When converting units make sure the unit you are looking for is on top of the
conversion fraction and the unit given is on the bottom of the conversion fraction so the units
given can cancel.
1 dozen
Example:
132 pencils = ________ dozen
132 pencils x ---------------- = 11 dozen
12 pencils
Metric Conversions
Units
Length
(Decreasing
order)
Kilo:
0.001 Km
1m
Base unit:
Centi:
100 cm
1000
mm
Milli:
1,000,000 µm
Micro:
1,000,000,000 nm
Nano:
Mass
Volume
0.001 Kg
1g
100 cg
1000 mg
1,000,000 µg
1,000,000,000 ng
0.001 KL
1L
100 cL
1000 mL
1,000,000 µL
1,000,000,000
nL
3
1cm = 1 mL
When choosing the ratios from the table above, one part of the ratio goes on top of the fraction and the
other goes on the bottom. The ratio should be set up so that the top of the ratio should have the units that
you are looking for and the bottom should be the units that you start with.
Example:
2 mm = _______ cm
Get from chart above
100 cm
2 mm  ---------------- = 0.2 cm
1000 mm
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Lewis / Electron-dot diagrams
1. Write symbol of element
2. Place the correct number of dots around the symbol (The number of dots equals the
number of valance electrons or the group / roman number the element is in)
3. Spread out the dots before doubling up
●
Aluminum = Group III  ● Al ●
●●
Nitrogen = Group V  ● N ●
●
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Percent Error Formula
Percent error = [Measured value – Accepted value]  Accepted value x 100
Percent Composition
Percent composition = (Mass of element x subscript)  (mass of compound) x 100
Writing Formulas
Ionic Compounds: oppositely charged ions. A metal and nonmetal(s)
Binary Ionic Compounds
Criss-cross to arrive at subscripts
Ex:
Sodium nitride = Na+1 and N -3  Na3N
Ternary Ionic Compounds
Aluminum hydroxide = Al+3 and (OH-1)  switch numbers to get Al(OH)3
Binary Molecular (Covalent) Compounds:
Prefixes (see chart below) become subscripts: Ex: Trinitrogen pentabromide  N3Br5
Naming Compounds
Binary Ionic:
1. One metal and nonmetal
2. If metal is from transitional group must use roman number if not just name metal
3. Nonmetal drops ending and adds “ide”
Example: CaCl2
Calcium chloride
Example: Cr2S3
Chromium (IIII) sulfide (Roman number is found as other subscript)
Ternary Ionic Compounds
1. One metal and more than one nonmetal
2. If metal is from transitional group must use roman number if not just name
3. Nonmetal group gets name from polyatomic ion chart.
Example: Ca(NO3)2 Calcium nitrate
Example: Fe(OH)2
Iron (II) hydroxide (Roman number is found as other subscript)
Binary Molecular (Covalent) Compounds: Both negative charged ions. Both non-metals
(Use prefixes as subscripts)
1. Second nonmetal drops ending and adds “ide” Ex: N2O3 Dinitrogen trioxide
Prefix
Mon
Di
Tri
Tetra
Penta
Number of atoms
1
2
3
4
5
Prefix
Hexa
Hepta
Octa
Nona
Deca
Number of atoms
6
7
8
9
10
Drawing Bohr diagrams
1. The number of protons and neutrons are place in the nucleus.
2. The electrons are placed in energy levels according to the maximum occupancy.
(Fill each shell in numerical order until all electrons are used)
Energy Level Maximum number
of electrons
1
2
2
8
3
18
4
32
Ex:
18p+
22 n0
Argon #18
﴿
2e﴿
﴿
8e﴿
﴿
8e﴿
Temperature Conversions using formulas
1. To change Celsius to Fahrenheit: Take the given temperature and multiply by 1.80 then
press equal then add 32 then press equal.
2. To change Fahrenheit to Celsius: Take the given subtract 32 then press equal then multiply
the number by 0.56 then press equal.
3. To change Celsius to Kelvin: Add 273 to the given temperature
4. To change Kelvin to Celsius: Subtract 273 from the given temperature.
Types of Equations
Combination:
A + B  AB
Decomposition:
AB  A + B
Single Replacement:
A + BC  AC + B
A + BC  BA + C
Double Replacement:
(A is metal)
(A is a nonmetal)
AB + CD  AD + CB
Complete Combustion:
Incomplete Combustion:
AB + O2  CO2 + H2O
AB + O2  CO + H2O