Chapter 1.3: Units of Measurement

Flashcards from Chapter 1.3 of Chemistry: The Molecular Nature of Matter and Change.

SI units

A unit composed of one or more of the base units of the Systeme International d’Unites, a revised form of the metric system

Base units

A unit that defines the standard for one of the seven physical quantities in SI; includes:

• Mass: kilogram (kg)

• Length: meter (m)

• Time: second (s)

• Temperature: kelvin (K)

• Amount of substance: mole (mol)

• Electric current: ampere (A)

• Luminous intensity: candela (cd)

Derived units

Combinations of the seven base units, such as speed (meters per second)

Kilogram (kg)

The SI unit for mass

• Is the only base unit whose name has a prefix

• Is constant opposed to weight, varying due to gravity

Weight

A variable measurement that depends on the local gravitational field of an object

Meter (m)

The SI unit for length

• The distance light travels in a vacuum in 1/299 792 458 sec

• 1.094 yards

• Used also for volume, when cubed

Cubic meter (m³)

The SI unit for volume, derived from the meter (m)

Liter (L)

The more common chemistry measurement for volume, non-SI

• Equivalent to 1 dm³

• Uses uppercase L

milliliter (mL)

The more common chemistry measurement for smaller volumes, non-SI

• Equivalent to 1 cm³

• Also uses uppercase L

Second (s)

The SI unit for time

• Based on an atomic standard: 9 192 631 770 oscillations of gaseous cesium atoms cooled to around 10^-6 K, measured by lasers

Kelvin (K)

The SI unit for temperature

• Differs from heat as just a measure of how hot or cold an object is and not the energy introduced

• No degree sign is used for this unit

• Uses the same size degree as Celsius, but is 273.15 degrees higher due to its zero point meaning absolute zero

Absolute zero

The temperature of 0 K or -273.15 degrees C, where all atoms cease movement

Celsius (C)

The metric unit for temperature; it sets water’s freezing point at 0 degrees and its boiling point at 100 degrees

Fahrenheit (F)

The English unit for temperature; it differs in zero point and degree size, with water freezing and boiling at 32 and 212 degrees respectively

• Thus, 180 of these represent 100 Celsius degrees, leading to a 9/5 ratio — one can add 32 to fully convert

• Converting back requires subtracting 32 first, then multiplying by 5/9

Temperature (T)

A measure of how hot or cold one object is relative to another

Heat

The energy that flows from an object with a higher temperature to an object with lower temperature

• This flows from your hand into ice, instead of “cold” flowing into your hand

Thermometer

A graduated tube containing a fluid that expands when heated

Mole (mol)

The SI unit for an amount of substance

Ampere (A)

The SI unit for electric current strength

Candela (cd)

The SI unit for luminous intensity

Decimal prefixes

Prefixes to multiply the base unit for very large or small quantities; includes:

• tera (T): 1 × 10¹²

• giga (G): 1 × 10⁹

• mega (M): 1 × 10⁶

• kilo (k): 1 × 10³

• hecto (h): 1 × 10²

• deka (da): 1 × 10¹

• base (one)

• deci (d): 1 × 10^-1

• centi (c): 1 × 10^-2

• milli (m): 1 × 10^-3

• micro (u): 1 × 10^-6

• nano (n): 1 × 10^-9

• pico (p): 1 × 10^-12

• femto (f): 1 × 10^-15

tera (T)

The SI prefix for 1 × 10¹²

giga (G)

The SI prefix for 1 × 10⁹

mega (M)

The SI prefix for 1 × 10⁶

kilo (k)

The SI prefix for 1 × 10³

hecto (h)

The SI prefix for 1 × 10²

deka (da)

The SI prefix for 1 × 10¹

deci (d)

The SI prefix for 1 × 10^-1

centi (c)

The SI prefix for 1 × 10^-2

milli (m)

The SI prefix for 1 × 10^-3

micro (u)

The SI prefix for 1 × 10^-6

nano (n)

The SI prefix for 1 × 10^-9

pico (p)

The SI prefix for 1 × 10^-12

femto (f)

The SI prefix for 1 × 10^-15