Lecture 3 Units, Periodicity

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Lecture 3 - Units, Periodicity
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Length

• SI unit is the metre (m)
• will also use mm, cm, mm,nm, pm

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Mass

• SI unit is the kilogram (kg)
• also will use
• gram (g)
• milligram (mg)

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Time

• SI unit is the second (s)
• will also use
• millisecond (ms)

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Temperature

• SI unit is the Kelvin (K)
• will often use degrees Celcius (oC)
• K oC 273.15

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Temperature

• 25oC 298 K (standard temperature)
• 100oC 373 K
• 0 K -273 oC (absolute zero)

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Amount of Substance

• SI unit is the mole (mol)
• common uses include nanomoles (nmol), micromoles
  (mmol), etc.

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Derived Units

• Area m2
• Volume m3, cm3 (mL)
• Density kg/m3 g/mL
• (kg m-3) (g mL-1)

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Significant Figures

• 38.6 s (3 sig. figs.)
• 0.00386 s (3 sig. figs)
• 3.8600 s (3-5 sig figs)
• better to use scientific notation,
• e.g. 0.00386 3.86 x 10-3

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Significant Figures(multiplying and dividing)

• 2.5 doughnuts x 955 MJ/doughnut ? MJ
• 2.5 x 955 2,387.5
• thus, answer is 2,400 MJ (2-4 sig figs!)
• better yet, 2.4x103 MJ (2 sig figs.)

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Significant Figures(adding and subtracting)

• 1.6 beer 2.31 beers ? beers
• 1.6 2.31 3.91
• thus, answer is 3.9 beers (one digit to right of
  decimal)

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Using Units

• What mass of water is in this room?

60 kg
0.90 kg H2O
300 students x
x
student
kg
16,200 kg H2O 1.6 x 104 kg H2O
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Always estimate the answer

• diameter of an atom 10 9 m !
• number of atoms
• in the universe 10 - 45 !!

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The Chemical Elements

• Fundamental units of matter (to a chemist)
• Cannot be chemically changed to anything else
• 112 are known
• 109 are named

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Naming Elements

• One or two letter names
• First letter capitalized
• e.g. Na, not na
• I, not i

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History of the Periodic Table

• Early 1800s - John Dobereiner - Triads of
  elements e.g. Cl, Br, I
• 1864 - John Newlands - Octaves
• 1869 - Julius Meyer, Dimitri Mendeleev

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Mendeleevs Periodic Table (1872)
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Properties of Germanium

• Property Predicted Observed
• in 1871 in 1876
• Atomic Mass 72 72.3
• Density 5.5 g cm-3 5.47 Oxide
  Formula RO2 GeO2
• Chloride RCl4 GeCl4

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The Modern Periodic Table
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Group Characteristics

• 1A. Alkali metals
• (Li, Na, K, Rb, Cs)
• soft, shiny, low melting point metals
• metal H2O alkaline solution

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Group Characteristics

• 2A. Alkaline earth metals
• (Be, Mg, Ca, Sr, Ba, Ra)
• - lustrous, silvery, metals
• - reactive

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Group Characteristics

• 7A. Halogens
• (F, Cl, Br, I)
• corrosive, reactive non-metals

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Group Characteristics

• 8A. Noble gases
• (He, Ne, Ar, Kr, Xe, Rn)

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Group Characteristics

• 8A. Noble gases
• (He, Ne, Ar, Kr, Xe, Rn)
• low reactivities

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MAIN GROUP ELEMENTS
p-block
s-block
TRANSITION METALS
d-block
LANTHANIDES
ACTINIDES
f-block
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The zig-zag line
Non-Metals
Metals