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 = mv 2 /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

The normal distribution mean=

, 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 sample

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 Earth Fire Air

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-leadW-tungsten K-potassiumCu-copper Fe-ironHg-mercury Na-sodium Sn-tin

These non-metals are solids at room temperature: Arsenic-AsPhosphorous-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 compound X 100 Fe = 1.56 g S= g 2.47g % mass Fe = 1.56/2.47 x100 = 63.5%