Introduction to Chemistry - Measurement, Math and Matter

I. What is chemistry? the study of the structure and properties of matter

      What is matter?  all material - has mass, takes up space, exhibits the property of inertia, and can be changed by energy

II.  Studying Matter

      A.  Observations may be of two types;  Qualitative observations - general and usually expressed in words, express what we see, hear, feel, taste and smell;  Quantitative observations - more useful, measurements, expressed as numbers.

      B.  Inferences:  interpretations of observations

      C.  Properties:  unique characteristics

III.  Scientific Method

      A.  Observing

      B.  Hypothesis:  explanation of observations;  when can explain past and accurately predict future become theories

      C.  Experimentation

      D.  Analysis

      E.  Conclusion 

IV. Measurement and the Metric System

      A.  Measurement:  quantity compared with a standard;  measure to the unit of the instrument and estimate one unit beyond

      B.  Metric system:  system of measurements base on 10, SI is the international metric system

            1. length:  distance between two points - meter

            2. mass:  amount of matter - kilogram (this base unit is very large for chemistry, usually use the gram or smaller)

            3. time:  interval between two occurrences (1/86400 of a day) - second

            4. thermodynamic temperature:  average kinetic energy of the particles - Kelvin  (the size of one degree on the Kelvin scale equals the size of one degree on     the Celsius scale)

            5. amount of substance:  mole

     C.  Derived Units: combinations of 2 or more fundamental units, such as length, time, or mass

            1. speed = length ÷ time; such as km / hour  or  m / sec

            2. area = length . length; such as m2 or cm2

            3. volume = length . length . length; such as m3  or  dm3  or  cm3;  SI unit is m3, but this is too large so we use the dm3 - by definition  1dm3 equals 1 liter  (L)

            4. mass ÷ volume = density,  scientific measure of amount of matter in a specific space,  concentration of particles, changes with temperature;  D = g/V ;  units such as  g/cm3,  g/mL,

      D.  Metric system conversions:

            1. know prefix meanings  (Mega = 106, kilo = 103, hecto = 102, deka = 101, deci = 10–1, centi = 10–2, milli = 10–3,  micro = 10–6, nano = 10–9 - others are on the chart in your book)

            2. decide how many tens different the units are

            3. going from known to unknown, is the unit increment getting smaller or larger?

                  a. if the unit increment is getting smaller then the number must get larger – move the decimal to the right   (the exponent is moving to the right on a number line)

                  b. if the unit increment is getting larger then the number must get smaller – move the decimal to the left   (the exponent is moving to the left on a number line)

      E.  Accuracy:  (absolute error) - how close the measurement is to the actual dimensions or true value of what is being measured,  depends upon the quality of the instrument being used to obtain the measurement

      F.  Precision:  (uncertainty in measurement) - concerned with the reproducibility of the measurement,  how closely clustered are series of measurements, what can you measure to - the guess or estimation number

      G.  Percent Error:  how far from the "correct" answer is your experiment determined answer;    

V. Graphing - The most common graph used in chemistry is the "line" graph.

      A.  draw and label each axis

            1.  the data you will plot has two variables

                  a.  the independent variable is the quantity that is deliberately varied (you control its value in the experiment)

                  b.  the dependent variable changes  due to the variation of the independent variable (you measure this value)

            2.  the vertical component is dependent on the horizontal component

                  a.  a  vs  b  means the value of a is dependent upon the value of b and a is plotted on the vertical y-axis (called the ordinate) and b  is plotted on the horizontal x-axis (called the abscissa)

                  b.  b  vs  a  means the value of b is dependent upon the value of a and b is plotted on the y-axis and a  is plotted on the x-axis

            3.  label each axis with the appropriate variable and the units of measure (the quantity that is being measured and the unit it is being measured in)

      B.  select scales so that the range of data points fill, or nearly fill, the entire space allotted for the graph

            1.  the increments or subdivisions along the axis should be easy to interpret

            2.  the magnitude of the increments along the axis must be the equal along the axis  (but the magnitude of the x-axis increments do not have to equal the magnitude of the y-axis increments)

            3.  the intersection of the x-axis and the y-axis does not need to be at (0,0)

            4.  read the directions for the graph carefully to determine if any extrapolation (reading a graph beyond the limits of the experimentally determined data points) will need to be done and consider the extrapolation values when determining the magnitude of the the increments, the staring point and the ending point

      C.  plot the data points by locating the points with an x or a dot with a circle or triangle or square around the dot

      D.  draw the best smooth line through the data points

            1.  graphs drawn in math represent absolute numbers and each point falls on the curve being plotted; this is seldom the case in science where the data points represent experimental measurements and have uncertainty associated with them

            2.  the line does not have to be a straight line

            3.  the line does not need to pass through all or any of the data points - it represents the best averaging of all the data points

            4.  extrapolation of data extends the data and allows for additional interpretation and interpolation ( read from the graph between data points)

      E.  place a title on the graph that clearly states the purpose of the graph and includes the dependent variable and the independent variable

VI. Significant Digits -  exactness of a measurement

      A.  also called significant figures (sig figs); exactness of the measurement, includes all digits precisely measured plus a last estimated or rounded digit; good way to know where to round off a number

            Rules:   1. all nonzero digits are significant

                        2. a zero between two nonzero digits or between two significant zeroes is significant

                        3. a zero to the right of the decimal is significant if there is a nonzero digit somewhere to the left of it

                        4. all other zeroes are NOT significant, including spacing zeroes

      B.  Using significant digits in problems and  rounding off answers:

            1. adding or subtracting: the answer can have no more digits to the right of the decimal than the least number of digits to the right of the decimal in any of the numbers that are being added or subtracted

            2. multiplying or dividing: the answer can have no more significant digits than the least number of significant digits in any of the numbers that are being multiplied or divided

VII. Scientific Notation

      A.  An easier method to write a very large or a very small number; by expressing it as a decimal number multiplied by a power of 10;    M x 10n ;  where 0 < M < 10 and n = an integer   (there should be only one non-zero digit to the left of the decimal)

      B.  Remember every number can be written as itself  times 1 , and 1 = 100 ; and if there is no decimal written it assumed to be at the right side of the number.

      C.  To express a number in correct scientific notation form from a decimal number:

            1. place a decimal to the right of the first non-zero digit on the left

            2. multiply by 10

            3. count spaces the decimal has moved

            4. express the number of spaces as an exponent of the 10

                  a. if the decimal is moved to the right the exponent decreases from the "original"

                  b. if the decimal is moved to the left the exponent increases from the "original"

      D.  To express a number as a decimal number from the scientific notation form:  

            1. the exponent is the number of spaces the decimal must be moved

            2. move the decimal

                  a. if the exponent will increase to become 100,  move the decimal to the left                   

                  b. if the exponent will decrease to become 100,  move the decimal to the right

VIII. Classification of matter - four main groups;  how are they related;  how are they interchangeable

                                                                              matter

                                                                                    ¯                                                         

                 ¯                                                                                                                            ¯

            mixtures ------------------------ separate by physical means ------------------------> pure substances 

        combination of two or more substances where                                                                      definite or constant composition,

        each substance retains it's own properties,                                                                             distinct properties

        NOT constant composition                                                                                                                                                       

                  ¯                                                                                                                ¯                           

¯                                       ¯                                   ¯                                                                                ¯

heterogeneous              homogeneous               compound --------- separate by chemical means --------->element

"coarse"                                    "solution"                  two or more kinds of atoms                                   made of only one kind of

not uniform throughout              uniform throughout     combined in a definite ratio,                                   atom, cannot be broken

                                                                                                cannot be broken apart by                                     apart by ordinary    

                                                                                                physical means                                                         chemical means

 

        an atom is made of a single nucleus with a positively charged proton and a neutral neutron with negatively charged electrons surrounding the nucleus

 

IX. Formula - what does the formula of a compound show

      A.  it shows which elements are present, how many atoms of each element are present, how many total atoms are present, and the combining ratio of the atoms

      B.  which elements are present is shown by the symbol for each of the elements

      C.  the number of atoms of an element present is shown by the subscript, the subscript applies only to the element  it is beside; a subscript outside of parenthesis multiplies all elements and their subscripts that are on the inside the parenthesis

X. States of Matter - solid, liquid, gas;  gas vs. vapor -called a gas when in the gaseous state if it is normally a gas at room temperature, called a vapor when in the gaseous state if it is normally a solid or liquid at room temperature

XI. Changes of State - phase changes

      A.  solid–>liquid melting  

      B.  liquid–>solid freezing or crystallization  

      C.  liquid–>vapor or gas evaporation or boiling (is energy being continually added) 

      D.  vapor or gas –>liquid condensation

      E.  solid–>vapor sublimation

XII. Energy - measured in Joules and kiloJoules 

      A.  potential energy of position, stored energy  - found in chemical bonds; 

      B.  kinetic energy of motion, temperature measures average kinetic energy: 

      C.  physical changes, such as changes of state, and chemical changes are always accompanied by changes in energy

      D.  law of conservation of energy:  energy is neither created nor destroyed

XIII. Physical Properties

      A.  can be observed without a change in the chemical composition of the substance

      B.  intensive these do not depend upon how much is present (color, density, boiling and freezing points, malleability, ductility, conductivity of electricity and heat, crystalline shape, refractive index) - qualitative descriptions

      C.  extensive these depend upon how much is present (mass, volume, length, etc.) - quantitative descriptions 

IVX. Physical Changes

      A.  characteristic that can be observed without the substance changing in composition phase changes

      B.  dissolving;  filtration;  fractional crystallization;  fractional distillation;  size change

XV. Chemical Properties - how a substance will react or not react with another substance

XVI. Chemical Changes

      A.  a change in the chemical composition of a substance always producing a new substance with new and different properties 

      B.  evidence for chemical changes

            1.  change in temperature (either an increase or a decrease)

            2.  change in color

            3.  a gas is evolved (bubbling or fizzing is observed

            4.  a precipitate is formed

            5.  light is emitted