Principles of Chemistry I: Matter and Its Properties

Chemistry

is the study of matter and the changes in matter.

Matter

is anything that occupies space and has mass.

Pure Substance

is a form of matter that has a definite composition and distinct properties.

Element

is a substance that cannot be separated into simpler substances by chemical means.

Atomic Element

is an element that exists as individual atoms.

Molecular Element

is an element that exists as molecules composed of two or more atoms of the same element.

Compound

is a substance composed of atoms of two or more elements chemically united in fixed proportions.

Covalent Compound

are substances that contain atoms of different types bonded together to form molecules.

Ionic Compound

are substances that contain ratios of ions of different elements.

Mixture

is a combination of two or more components, i.e. pure substances.

Homogeneous Mixture

is uniform throughout, e.g., salt water, milk, air.

Heterogeneous Mixture

is non-uniform, e.g., sand in water, oil in water.

Filtration

is a physical separation technique that uses particle size to separate different components.

Distillation

is a technique that uses differences in the boiling points of substances to separate a homogeneous mixture.

Evaporation

is used to separate out homogeneous mixtures where there is one or more dissolved solids.

Sublimation

is a physical separation technique where a solid changes directly into a gas.

Chromatography

is a physical separation technique that separates components based on their movement through a stationary phase.

Melting Point of Ammonia

is -77.7°C.

Boiling Point of Ammonia

is -33.3°C.

Number of Identified Elements

114 elements have been identified.

Examples of Covalent Compounds

H2O (water), NH3 (ammonia), SF6 (sulfur hexafluoride), C2H6O (ethyl alcohol), CH4 (methane).

Examples of Ionic Compounds

NaCl (sodium chloride), KOH (potassium hydroxide), MgO (magnesium oxide), CaBr2 (calcium bromide).

Separation by phase change

Occurs when mixed components have different vapor pressures.

Sublimation

Separates a mixture of solids, one of which sublimes from the solid state directly into a gas.

Dry Ice Sublimation

An example is the sublimation of dry ice, which is solid carbon dioxide (CO2).

Chromatography

This technique separates substances on the basis of differences in polarity or solubility in a solvent.

Mobile phase

The mobile phase in chromatography is either a liquid or gas.

Stationary phase

The stationary phase in chromatography is a solid like paper or silica gel.

Physical properties

Can be observed without changing the basic identity of the substance.

Chemical properties

Can only be observed when a substance is changed into another substance.

Intensive properties

Are independent of the amount of the substance that is present.

Extensive properties

Depend upon the amount of the substance present.

Chemical changes

A substance is transformed into a chemically different substance, i.e. the composition is changed.

Physical changes

Changes in matter that do not change the composition or identity of a substance.

Phase changes

A physical change in matter that involves a change in state.

Conditions for phase changes

Temperature and Pressure are important conditions to consider.

Measurements

All measured quantities have three pieces of information: the quantity or number, the unit, and the uncertainty in the measurement.

Système International d'Unités (SI Units)

There are seven base units from which other units of measurement are derived.

Length

Base unit is meter (m), which is slightly longer than a yard (0.9144 m).

Volume (V)

Derived from length cubed (l3).

Mass

Base unit is kg and is a measure of the amount of matter that something contains.

Weight

A measure of the pull of gravity on an object.

Temperature

Measure of 'hotness' or 'coldness' of an object.

Temperature Units

K (Kelvin) - SI unit, oC (degrees Celsius) - a common scientific unit, oF (degrees Fahrenheit) - not used in science.

Volume (m3)

1 m3 is a unit of measurement for volume.

Volume

A unit of measurement obtained by multiplication of appropriate base unit, i.e. l3.

SI unit for volume

Meter cubed (m3), but commonly used units are Liter (L) or milliLiter (mL).

Volume formula

Volume = l x l x l (l3), which is length cubed.

1 Liter (L)

1 L = 1 dm3.

1 milliLiter (mL)

1 mL = 1 cm3.

Scale of milli-

The prefix milli- means that there are 1000 mL in 1 L, thus, the equality 1000 mL = 1 L.

Common Measuring Devices for Volume

Pipettes can also be used to deliver variable volumes.

Mass (m)

Measure of the quantity of matter.

SI unit of mass

Kilogram (kg).

Kilogram to gram conversion

1 kg = 1000 g.

Weight

Force that gravity exerts on an object.

Mass vs. weight

Mass does not equal weight.

Weight of a 1 kg bar on Earth

2.2 lb.

Weight of a 1 kg bar on Moon

0.4 lb.

Temperature relationship (Kelvin and °C)

K = °C + 273.15.

Absolute zero

0 K (-273.15°C), the lowest possible attainable temperature.

Density (D) of Matter

Defined as the amount of mass contained in a unit volume of a substance.

Common units for density

g/mL or g/cm3.

Density of water at 25°C

D = 1.0 g/mL (or D = 1.0 g/cm3).

Density of 1 mL of water

D = 1.0 g/mL.

Density of 20 L of water

D = 1.0 g/mL.

Scientific Notation

How to convert numbers (n) into Scientific Notation (N x 10n).

Scientific Notation Rule #2

If n < 0; then move decimal to right.

Scientific Notation Rule #1

If n > 0; then move decimal to left.

Example of Scientific Notation

0.00000772 = 7.72 x 10-6.

Example of Scientific Notation

568.762 = 5.68762 x 102.

Adding and Subtracting Numbers in Scientific Notation

Write each quantity with the same exponent n and combine N1 and N2.

Multiplying Numbers in Scientific Notation

Multiply N1 and N2 and add exponents, n.

Dividing Numbers in Scientific Notation

Divide N1 and N2 and subtract exponents, n.

Inexact numbers

Obtained from measurements; values have some uncertainty and are subject to error.

Exact numbers

Not obtained from a measurement; values known exactly; infinitely precise.

Significant Figures (Sig. Figs.)

Digits that were measured (certain + uncertain).

Sig. Fig. Rule

All nonzero digits are significant.

Sig. Fig. Rule

Zeroes at the beginning of a number are never significant.

Significant Figures

Digits in a number that contribute to its precision.

Estimated Digit

The last digit in any measurement that is estimated and has error (+/- 1).

Precision

A measure of how closely individual measurements agree with each other.

Accuracy

A measure of how closely individual measurements agree with the correct value.

Dimensional Analysis

A method used to convert one quantity to another using conversion factors.

Conversion Factor

A ratio that expresses how many of one unit are equal to another unit.

Scientific Method

A systematic approach to studying matter involving observation, hypothesis, experimentation, and conclusion.

Hypothesis

A possible explanation of an observation that can be tested with an experiment.

Experiment

A procedure to test a hypothesis, law, or theory.

Conclusion

An interpretation of experimental results to determine the validity of a hypothesis.

Scientific Law

A summary of the connections between observations seen during experiments, often written as an equation.

Theory

A unifying principle that explains a body of facts and/or laws based on observations.

Significant Figures in Addition/Subtraction

Answers are rounded to keep the least number of significant figures to the right of the decimal.

Significant Figures in Multiplication/Division

Answers are rounded to keep the least number of total significant figures from the numbers used in the calculation.

Density

Mass per unit volume, commonly expressed as g/mL.

Molar Mass

The mass of one mole of a substance, expressed in grams.

Molar Concentration

The number of moles of solute per liter of solution.

Percent Error

A calculation used to determine the accuracy of a measurement.

Mean Deviation

A calculation used to determine the precision of a set of measurements.

Ruler A Measurement

Measures a length of 4.8 cm with two significant figures.

Ruler B Measurement

Measures a length of 4.85 cm with three significant figures.