Chapter 1Introduction: Matter & MeasurementCHEMISTRY The Central Science

The Molecular Perspective of ChemistryMatter 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.As we see, molecules may consist of the same type of atoms or different types of atoms.

The Study of Chemistry

The Molecular Perspective of ChemistryThe Study of Chemistry

Why Study ChemistryChemistry is central to our understanding of other sciences.Chemistry is also encountered in everyday life.The Study of Chemistry

Matter can be a gas, a liquid, or a solid.These are the three states of matter.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 and MixturesAtoms 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).If more than one atom, element, or compound are found together, then the substance is a mixture.Classification of Matter

Pure Substances and Mixtures

Pure Substances and MixturesIf 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.Classification of Matter

Classification of Matter ElementsIf a pure substance cannot be decomposed into something else, then the substance is an element.There are approximately 117 elements known.Each element is given a unique chemical symbol (one or two letters).Elements are building blocks of matter.The earths crust consists of 5 main elements.The human body consists mostly of 3 main elements.

Elements

Classification of Matter

Classification of MatterElementsChemical 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).

Classification of MatterCompoundsMost 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 composition of a pure compound is always the same.

Classification of MatterCompoundsIf 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.

Classification of Matter MixturesHeterogeneous mixtures are not uniform throughout.Homogeneous mixtures are uniform throughout.Homogeneous mixtures are called solutions.

Properties of Matter Physical ChangesWhen 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.

Properties of Matter Chemical ChangesWhen 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.

Physical and Chemical ChangesProperties of Matter

Properties of MatterPhysical and Chemical ChangesIntensive 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.

Properties of MatterSeparation of MixturesMixtures 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.

Properties of MatterSeparation of MixturesHomogeneous 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

Properties of Matter Separation of MixturesChromatography 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.

Steps in the Scientific Method1.Observationsquantitativequalitative2.Formulating hypothesespossible explanation for the observation3.Performing experiments gathering new information to decide whether the hypothesis is valid

Outcomes Over the Long-TermTheory (Model)A set of tested hypotheses that give an overall explanation of some natural phenomenon.Natural LawThe same observation applies to many different systemsExample - Law of Conservation of Mass

Theory vs. Law

A theory (model) is an attempt to explain why it happens.

A law summarizes what happens

Units of MeasurementSI UnitsThere are two types of units:fundamental (or base) units;derived units.There are 7 base units in the SI system.

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

SI UnitsUnits of Measurement

Units of Measurement SI UnitsNote the SI unit for length is the meter (m) whereas the SI unit for mass is the kilogram (kg).1 kg weighs 2.2 lb. TemperatureThere are three temperature scales:Kelvin ScaleUsed in science.Same temperature increment as Celsius scale.Lowest temperature possible (absolute zero) is zero Kelvin. Absolute zero: 0 K = -273 oC.

TemperatureCelsius ScaleAlso used in science.Water freezes at 0 oC and boils at 100 oC.To convert: K = oC + 273Fahrenheit ScaleNot generally used in science.Water freezes at 32 oF and boils at 212 oF.To convert:

Units of Measurement

TemperatureUnits of Measurement

Units of MeasurementDerived UnitsDerived units are obtained from the 7 base SI units.Example:

Volume

Units of MeasurementThe 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.

VolumeUnits of Measurement

DensityUsed 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). Units of Measurement

Uncertainty in Measurement Uncertainty in MeasurementAll 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 AccuracyMeasurements that are close to the correct value are accurate.Measurements that are close to each other are precise.

Precision and AccuracyUncertainty in Measurement

Uncertainty in MeasurementSignificant FiguresThe 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

PAIf decimal is Present, start from left of number and count with the 1st non-zero to the right (0.025 = 2 Sig. Fig.)If decimal is Absent, start from right of number and count starting with the 1st non-zero to the left. (1050 = 3 Sig. Fig.)

Uncertainty in Measurement Significant FiguresNon-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 is an aid in problem solving that uses the units (dimensions) that are part of a measurement to help solve (analyze) a problem.Given units can be multiplied or divided to give the desired units. Conversion factors are used to manipulate units:Conversion Factor: A fraction whose numerator and denominator are the same quantity expressed in different units. 2.54 cm = 1in 1 in 2.54 cmDimensional Analysis

* The key is correctly using conversion factors to change one unit to another.Because the numerator and denominator of a conversion factor are EQUAL, multiplying any quantity by a conversion factor is equivalent to multiplying by 1, so the quantity is not changed.

Dimensional Analysis

1. Identify the Units of the given data. 2. Identify the Units of the unknown data. 3. Write down the given quantity and units. 4. Write down the unknown units. 5. Determine what conversion factors will convert from the given quantity to the unknown quantity. 6. Carry out calculations to get desired units.Dimensional Analysis

Given Unit X Desired Unit = Desired Unit Given Unit If an object is 8.50 in. long, how long is it in cm. ? 8.50 in x 2.54 cm = ? cm 1 in1.Dimensional Analysis1.2.3.4.5.

If an object is 8.50 in. long, how long is it in cm. ? (2.54 cm / in) 8.50 in x 2.54 cm = 21.6 cm 1 in

Dimensional Analysis6. Solve the problem

Using Two or More Conversion FactorsExample to convert length in meters to length in inches:Dimensional Analysis

Dimensional AnalysisUsing Two or More Conversion FactorsIn 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?

End of Chapter 1Introduction: Matter & Measurement