Unit 4 Measurement – Basic Units The International System of Units (SI) (1.10) Current definitions of the seven base SI units Review of exponential notation (Appendix A-1) Metric prefixes and their interconversion (1.10)

What is Chemistry? (Intro to Chapter 1) Matter – anything that occupies space and has a mass (1.8) Chemistry – the study of matter and its transformations (Introduction to Chapter 1)

The SI System (1.10) Adopted in 1960 – states standard units to be used in measurement of seven basic properties as given below. Physical Quantity Name of UnitSymbol of Unit Lengthmeterm Masskilogramkg Timeseconds TemperatureKelvinK Amount of substance molemol Electric currentAmpereA Luminous intensity candelacd

Current Definitions of the Seven SI Units Six have very well defined, though somewhat abstract, descriptions. For example, –second: The second is the duration of periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. –meter: The meter is the length of the path travelled by light in vacuum during a time interval of 1/ of a second. Definitions of the other four that have precise definitions may be found at The kilogram is the only one not precisely defined – see next slide.

The Kilogram The kilogram is called a prototype standard – there is one chunk of matter that is “the” kilogram as pictured.

States of Matter (1.9) Three common states of matter (plus a bonus): –Gas – takes shape of container, flows easily, compressible –Liquid – takes shape of container but with a flat top, flows easily, not very compressible –Solid – retains shape, does not flow appreciably, not very compressible –(A bonus state: plasma – a stream of charged particles – this is the stuff of plasma TV)

Review of Exponential Notation (Appendix A-1) Looking at the SI base units gives a strong sense that it is a metric-based system The metric system depends heavily on the ability to maneuver the decimal point in a number Some of the numbers we will see during the semester are incredibly large or incredibly small and we must have a system to write and work with these numbers without difficulty Thus there is a need to be conversant in exponential notation

Review of Exponential Notation (Appendix A-1) The concept of exponential notation is based on our base 10 number system: In the left column, where the numbers are greater than 1, the power on 10 is the number of decimal places to the right of the digit “1” In the right column, where the numbers are less than 1, the exponent on 10 is negative and is the number of decimal places from the original decimal place to that just after the digit “1"

Examples of Converting Between Standard Notation and Exponential Notation Consider the following conversions: m = x 10 4 m s = x kg = 3.80 x kg 9.87 x 10 4 L = L 5.12 x cm = cm

Metric Prefixes (1.10) Part of the beauty of the metric system is that interconversions are simply a matter of moving the decimal point. Metric prefixes are used to indicate the size of the unit. Some of the more common metric prefixes are given in the table below. PrefixExponential Expression Abbreviation tera T giga-10 9 G mega-10 6 M kilo-10 3 k Base Unit deci d centi c milli m micro μ nano n

Metric Conversions Notice in the table: –The difference in exponents between two prefixes gives the number of decimal places to be moved in a conversion –If the conversion is from a larger unit to a smaller unit (down the table), the decimal point is moved to the right –If the conversion is from a smaller unit to a larger unit (up the table), the decimal point is moved to the left –See examples on the next page PrefixExponentia l Expression Abbreviatio n tera T giga-10 9 G mega-10 6 M kilo-10 3 k Base Unit deci d centi c milli m micro μ nano n Move Left Move Right

Examples of Metric Conversion PrefixExponential Expression Abbreviation tera T giga-10 9 G mega-10 6 M kilo-10 3 k Base Unit deci d centi c milli m micro μ nano n m = 42.6 km (m to km is three decimal places, since going up the table move three decimal places to the left) km = cm (km to cm is five decimal places, since going down the table move five decimal places to the right) 350 mL = L (mL to L is three decimal places, since going up the table move three decimal places to the left) 4.52 x ds = 4.52 x cs (ds to cs is one decimal places, since going down the table move to the right making the exponent bigger by one)