General and Inorganic Chemistry
Introduction to Chemistry
What is Chemistry
Chemistry is the study of chemicals; how properties depend on composition. What substances are and how they change.
El Khemid - the transformation. Chemistry is about changing substances into others.
What chemicals? First metals then cosmetics, medicines, ceramics, glass making.
What did early chemists do?
Identify, classify, describe; Knowledge leads to curiosity.
Rather than learn all substances seek underlying patterns and theories that explain chemical behavior.
Apply scientific method.
Apply scientific method.
• Observation vs interpretation Observation - with statement of certainty is a fact
Laws - generalized observations
Hypothesis to explain observations - predictions
Experiment - Test hypothesis
Theory - tested hypothesis
Model- Combination of theories that form a general explanation of wide variety of phenomenon
A Delicate Balance
• Science is different from art in that scientific knowledge requires agreement; first of the facts and then of the theories.
• There is a delicate balance between what is known and what we think about what is known.
• This is the idea of provisional truth; we believe our hypotheses but maintain a healthy skepticism.
Serendipity
• "Chance favors the prepared mind”
• When asked “what did you think when you saw the bones of your hand on the screen in front of the cathode ray tube”? Roentgen replied “I did not think. I investigated.
How do we describe matter?
• Matter occupies space and has weight. (Actually Mass, weight is the affect of gravity on mass).
• Matter exists in three physical states.– Solid– Liquid– Gas
Properties of Matter
• Physical properties: Color, mp, bp, density, index of refraction. Observation of these do not change chemical composition.
• Chemical properties: Observation of these causes a chemical change; substances become other substances. Reactivity with acids to liberate carbons dioxide.
Physical properties
• Physical properties can be:
• Extensive i.e. depend on amount of substance like mass or volume
• Intensive i.e. independent of amount like temperature or pressure.
• Some properties are qualitative others are quantitative.
Quantitative properties.
• Measurements require a system of units
• SI- Systeme International
• Base units m, kg, s, K, mol
• Derived units: Joule, liter, pascal…
• Prefixes: mega, kilo, deci, centi, milli, micro, nano, pico
conversions
Energy
• Energy: ability to do work
• Kinetic = mv2/2
• Potential - chemical
• Conservation of energy. Heat and work transfer energy
Temperature: zeroeth law
• Heat is the flow of energy from a hot object to a cold object.
• Heat flows from regions of high temperature to regions of low temperature.
• Differentiate between heat which is energy flow and temperature which gives the direction of flow.
Accuracy and Precision • An Advil Tablet was "weighed" on a
digital laboratory balance 22 times with the following results
determination of mass
0
1
2
3
4
5
6
7
8
9
10
mass/g
fre
q
The normal distribution
mean= 0.4586
mean= 0.4586
, Standard deviation
The normal distribution
67%
95%
Significant Figures
Every sample of a pure substance has the same properties. In contrast the properties of mixtures
depend on the compostion of each sampleM atte r
S o lu tion s C o llo id s
H om og en eou s H eterog en eou s
M ixtu res
M eta ls
S o lid s L iq u id s G ases
N on -m eta ls
E lem en ts
M olecu la r Ion ic
C om p ou n d s
P u re S u b s tan ces
S u b s tan ces
Mixtures can be separated into their pure components
• Mixtures can be separated into their pure components by physical means– Filtration– Mechanical separation– Distilation– Dissolving– Chromatography
Elements &Compounds
• Elements can not be broken down into simpler substances
• Compounds can be chemically broken down into the elements of which they are composed.
• There are 108 elements known but 40 of these compose 99.9% of all substances.
• 10 elements compose 99% of the earth’s crust.
Ten elements compose 99% of the earth’s crust
Water
EarthFireAir
Three quarters of the elements are metals
Metals are:
•Malleable
•Ductile
•Lustrous
•Conductors
•heat
•electricity
The chemical symbols for some metals are not the same as the first letter of the English name for the element:
Pb-lead W-tungsten
K-potassium Cu-copper
Fe-iron Hg-mercury
Na-sodium
Sn-tin
These non-metals are solids at room temperature:
Arsenic-As Phosphorous-P Sulfur-S
Iodine-I Boron-B
Selenium-Se Carbon-C
The rest are gases
The Law of Constant Composition
The relative amounts of each element in a compound are always the same.
Mass percentage or percent composition
Mass of Element
Mass of compoundX 100
Fe = 1.56 g
S= 0.9007g
2.47g
% massFe = 1.56/2.47 x100 = 63.5%
