welcome to the world of chemistry. the language of chemistry chemical elements -chemical elements -...
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Welcome to the World of Chemistry
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The Language of ChemistryThe Language of Chemistry• CHEMICAL ELEMENTS -
– pure substances that cannot be decomposed by ordinary means to other substances.
SodiumBromine
Aluminum
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The Language of ChemistryThe Language of Chemistry
• The elements, their names, and symbols are given on the PERIODIC TABLE
• How many elements are there?
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The Periodic Table
Dmitri Mendeleev (1834 - 1907)
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Glenn Seaborg
(1912-1999 )• Discovered 8
new elements.• Only living
person for whom an element was named.
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Copper atoms on silica surface.
See CD-ROM Screen 1.4
• An atom is the smallest particle of an element that has the chemical properties of the element.
Distance across = 1.8 nanometer (1.8 x 10-9 m)
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An atom consists of a • nucleus
–(of protons and neutrons) • electrons in space about the nucleus.
The Atom
Electron cloud
Nucleus
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The red compound is composed of• nickel (Ni) (silver)• carbon (C) (black)• hydrogen (H) (white) • oxygen (O) (red)• nitrogen (N) (blue)
The red compound is composed of• nickel (Ni) (silver)• carbon (C) (black)• hydrogen (H) (white) • oxygen (O) (red)• nitrogen (N) (blue)
CHEMICAL COMPOUNDS are composed of atoms and so can be decomposed to those atoms.
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A MOLECULE is the smallest unit of a compound that retains the chemical characteristics of the compound.Composition of molecules is given by a MOLECULAR FORMULA
H2O C8H10N4O2 - caffeine
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The Nature of MatterThe Nature of Matter
Chemists are interested in the nature of matter and how this is related to its atoms and molecules.
Gold Mercury
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Graphite — layer structure of carbon atoms reflects physical properties.
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Chemistry & Matter
• We can explore the MACROSCOPIC world — what we can see —
• to understand the PARTICULATE worlds we cannot see.
• We write SYMBOLS to describe these worlds.
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A Chemist’s View of Water
H2O (gas, liquid, solid)
MacroscopicMacroscopic
SymbolicSymbolicParticulateParticulate
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A Chemist’s
View
2 H2(g) + O2 (g) --> 2 H2O(g)
MacroscopicMacroscopic
SymbolicSymbolicParticulateParticulate
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Kinetic Nature of MatterKinetic Nature of MatterMatter consists of atoms and molecules
in motion.
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STATES OF MATTERSTATES OF MATTER• SOLIDS — have rigid shape, fixed
volume. External shape can reflect the atomic and molecular arrangement.–Reasonably well understood.
• LIQUIDS — have no fixed shape and may not fill a container completely. –Not well understood.
• GASES — expand to fill their container. –Good theoretical understanding.
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Physical Properties
What are some physical properties?
• color• melting and boiling
point• odor
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Physical ChangesSome physical changes
would be• boiling of a liquid• melting of a solid• dissolving a solid in a
liquid to give a homogeneous mixture — a SOLUTION.
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DENSITY - an important and useful physical property
Density mass (g)volume (cm3)
Density mass (g)volume (cm3)
Mercury
13.6 g/cm3 21.5 g/cm3
Aluminum
2.7 g/cm3
Platinum
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Relative Densities of the Elements
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Problem A piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3).
Density mass (g)volume (cm3)
Density mass (g)volume (cm3)
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Strategy1. Get dimensions in common units.
2. Calculate volume in cubic centimeters.
3. Calculate the density.
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SOLUTION1. Get dimensions in common units.
2. Calculate volume in cubic centimeters.
3. Calculate the density.
0.95 mm • 1cm
10 mm = 0.095 cm
57.54 g
6.4 cm3 = 9.0 g / cm3
(9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3
Note only 2 significant figures in the answer!
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PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds?
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds?
Solve the problem using DIMENSIONAL ANALYSIS.
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Strategy1. Use density to calc. mass (g)
from volume.2. Convert mass (g) to mass (lb)
Need to know conversion factor= 454 g / 1 lb
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg?PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg?
First, note that 1 cm3 = 1 mL
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1. Convert volume to mass
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg?PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg?
95 cm3 • 13.6 g
cm3 = 1.3 x 103 g
1.3 x 103 g • 1 lb
454 g = 2.8 lb
2. Convert mass (g) to mass (lb)
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There’s more? Observations!
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Chemical Properties and Chemical Change
• Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules.
• Burning hydrogen (H2) in oxygen (O2) gives H2O.
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Types of Observations and Measurements
• We make QUALITATIVE observations of reactions — changes in color and physical state.
• We also make QUANTITATIVE MEASUREMENTS, which involve numbers.
• Use SI units — based on the metric system
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UNITS OF MEASUREMENT
Use SI units — based on the metric system
Length
Mass
Time
Temperature
Meter, m
Kilogram, kg
Seconds, s
Celsius degrees, ˚Ckelvins, K
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Units of Length
• 1 kilometer (km) = ? meters (m)
• 1 meter (m) = ? centimeters (cm)
• 1 centimeter (cm) = ? millimeter (mm)
• 1 nanometer (nm) = 1.0 x 10-9 meter
O—H distance =9.4 x 10-11 m9.4 x 10-9 cm0.094 nm
O—H distance =9.4 x 10-11 m9.4 x 10-9 cm0.094 nm
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Temperature Scales• Fahrenheit• Celsius• Kelvin
Anders Celsius1701-1744
Lord Kelvin(William Thomson)1824-1907
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Temperature Scales
Notice that 1 kelvin degree = 1 degree Celsius
Boiling point of water
Freezing point of water
Celsius
100 ˚C
0 ˚C
100˚C
Kelvin
373 K
273 K
100 K
Fahrenheit
32 ˚F
212 ˚F
180˚F
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Temperature Scales
100 oF38 oC311 K
oF oC K
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Calculations Using Temperature
• Generally require temp’s in kelvins
•T (K) = t (˚C) + 273.15• Body temp = 37 ˚C + 273 = 310 K
• Liquid nitrogen = -196 ˚C + 273 = 77 K
• Generally require temp’s in kelvins
•T (K) = t (˚C) + 273.15• Body temp = 37 ˚C + 273 = 310 K
• Liquid nitrogen = -196 ˚C + 273 = 77 K