the study of chemistry

The Molecular Perspective of Chemistry Matter is the physical material of the universe. Matter is made up of relatively few elements. On the microscopic level, matter consists of atoms and

molecules. Atoms combine to form molecules. Molecules may consist of the same type of atoms or

different types of atoms.

The Study of Chemistry

The Molecular Perspective of Chemistry

Why Study Chemistry• Chemistry is central to our understanding of other

sciences.• Chemistry is also encountered in everyday life.• It is the basis behind many medications

• “Form defines Function”

The Study of ChemistryThe Study of Chemistry

States of Matter Matter can be a gas, a liquid, or a solid. Gases have no fixed shape or volume. Gases can be compressed to form liquids. Liquids have no shape, but they do have a volume. Solids are rigid and have a definite shape and volume.

Classification of Matter

Pure Substances Atoms and Compounds

Atoms consist only of one type of element. Molecules can consist of more than one type of element.

Molecules can have only one type of atom (an element). Molecules can have more than one type of atom (a compound).

Pure substances are The same throughout Have a set ratio

Mixtures-

Two types

Solutions


Pure Substances and Mixtures If matter is not uniform throughout, then it is a

heterogeneous mixture. If matter is uniform throughout, it is homogeneous. If homogeneous matter can be separated by physical

means, then the matter is a mixture. If homogeneous matter cannot be separated by physical

means, then the matter is a pure substance. If a pure substance can be decomposed into something

else, then the substance is a compound.


Pure Substances and Mixtures

Elements• If a pure substance cannot be decomposed into

something else, then the substance is an element.• There are 114 elements known.• Each element is given a unique chemical symbol (one or

two letters).• Elements are building blocks of matter.• The earth’s crust consists of 5 main elements.• The human body consists mostly of 3 main elements.


• If a pure substance cannot be decomposed into something else, then the substance is an element.

• There are 114 elements known.• Each element is given a unique chemical symbol (one or

two letters).•Chemical symbols with one letter have that letter capitalized (e.g., H, B, C, N, etc.)

•Chemical symbols with two letters have only the first letter capitalized (e.g., He, Be).

• Elements are building blocks of matter.• The earth’s crust consists of 5 main elements.• The human body consists mostly of 3 main elements.

ELEMENTS

Elements

Classification of MatterClassification of Matter

Compounds• Most elements interact to form compounds.• The proportions of elements in compounds are the same

irrespective of how the compound was formed.• Law of Constant Composition (or Law of Definite

Proportions):– the ratio by mass of the elements in a chemical compound is always the

same, regardless of the source of the compound.

– The law of constant composition can be used to distinguish between compounds and mixtures of elements:

– Compounds have a constant composition; mixtures do not.

– Water is always 88.8% O and 11.2% H by weight regardless of its source.

–Brass is an example of a mixture of two elements: copper and zinc. It can contain as little as 10%, or as much as 45%, zinc.


Compounds• If water is decomposed, then there will always be twice

as much hydrogen gas formed as oxygen gas.• Pure substances that cannot be decomposed are elements.


Mixtures• Heterogeneous mixtures are not uniform throughout.• Homogeneous mixtures are uniform throughout.• Homogeneous mixtures are called solutions.


Physical and Chemical Changes When a substance undergoes a physical change, its

physical appearance changes. Ice melts: a solid is converted into a liquid.

Physical changes do not result in a change of composition.

When a substance changes its composition, it undergoes a chemical change: When pure hydrogen and pure oxygen react completely, they

form pure water. In the flask containing water, there is no oxygen or hydrogen left over.

Properties of MatterProperties of Matter

Physical and Chemical Changes


Physical and Chemical Changes Intensive physical properties do not depend on how

much of the substance is present. Examples: density, temperature, and melting point.

Extensive physical properties depend on the amount of substance present. Examples: mass, volume, pressure.


Separation of Mixtures Mixtures can be separated if their physical properties are

different. Solids can be separated from liquids by means of

filtration. The solid is collected in filter paper, and the solution,

called the filtrate, passes through the filter paper and is collected in a flask.


Separation of Mixtures Homogeneous liquid mixtures can be separated by

distillation. Distillation requires the different liquids to have different

boiling points. In essence, each component of the mixture is boiled and

collected. The lowest boiling fraction is collected first.


Separation of Mixtures

Separation of Mixtures Chromatography can be used to separate mixtures that

have different abilities to adhere to solid surfaces. The greater the affinity the component has for the

surface (paper) the slower it moves. The greater affinity the component has for the liquid, the

faster it moves. Chromatography can be used to separate the different

colors of inks in a pen.


SI Units There are two types of units:

fundamental (or base) units; derived units.

There are 7 base units in the SI system.

Units of MeasurementUnits of Measurement

Powers of ten are used for convenience with smaller or larger units in the SI system.


SI Units


SI Units Note the SI unit for length is the meter (m) whereas the SI

unit for mass is the kilogram (kg). 1 kg weighs 2.2046 lb.

TemperatureThere are three temperature scales: Kelvin Scale

Used in science. Same temperature increment as Celsius scale. Lowest temperature possible (absolute zero) is zero Kelvin. Absolute zero: 0 K = 273.15 oC.


Temperature Celsius Scale

Also used in science. Water freezes at 0 oC and boils at 100 oC. To convert: K = oC + 273.15.

Fahrenheit Scale Not generally used in science. Water freezes at 32 oF and boils at 212 oF. To convert:


32-F95

C 32C59

F

Temperature


Derived Units Derived units are obtained from the 7 base SI units. Example:


m/ssecondsmeters

timeof unitsdistance of units

velocityof Units

Volume


The units for volume are given by (units of length)3. SI unit for volume is 1 m3.

We usually use 1 mL = 1 cm3.

Other volume units: 1 L = 1 dm3 = 1000 cm3 =

1000 mL.

Volume


Density Used to characterize substances. Defined as mass divided by volume:

Units: g/cm3. Originally based on mass (the density was defined as

the mass of 1.00 g of pure water).


volumemass

Density

Uncertainty in Measurement All scientific measures are subject to error. These errors are reflected in the number of figures reported

for the measurement. These errors are also reflected in the observation that two

successive measures of the same quantity are different.

Precision and Accuracy Measurements that are close to the “correct” value are

accurate. Measurements that are close to each other are precise.

Uncertainty in MeasurementUncertainty in Measurement

Precision and Accuracy


Significant Figures The number of digits reported in a measurement reflect

the accuracy of the measurement and the precision of the measuring device.

All the figures known with certainty plus one extra figure are called significant figures.

In any calculation, the results are reported to the fewest significant figures (for multiplication and division) or fewest decimal places (addition and subtraction).


Significant Figures Non-zero numbers are always significant. Zeros between non-zero numbers are always significant. Zeros before the first non-zero digit are not significant.

(Example: 0.0003 has one significant figure.) Zeros at the end of the number after a decimal place are

significant. Zeros at the end of a number before a decimal place are

ambiguous (e.g. 10,300 g).


Dimensional Analysis Method of calculation utilizing a knowledge of units. Given units can be multiplied or divided to give the

desired units. Conversion factors are used to manipulate units: Desired unit = given unit (conversion factor) The conversion factors are simple ratios:

Dimensional AnalysisDimensional Analysis

unitgiven unit desired

factor Conversion

Using Two or More Conversion Factors Example to convert length in meters to length in inches:


cm 2.54

in 1m

cm 100m ofnumber in ofNumber

in cm conversion

cm m conversionm ofnumber in ofNumber

Using Two or More Conversion Factors In dimensional analysis always ask three questions: What data are we given? What quantity do we need? What conversion factors are available to take us from

what we are given to what we need?


the study of chemistry

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