Units of Measurement

  • International Systems of Units(SI)- this system of measurement has its base units derived from the metric system.


  • It has 7 base units and they are Volume(L), Mass(g/Kg), Time(S), amount(Mole/mol), Temperature(Candelas/d).


  • Prefixes are used to modify base units to show a change in magnitude to the varying quantities. They include:


  • Nano = 10^-9 

  • Centi = 10^-2

  • Micro = 10^-6

  • Mili = 10^-3

  • Kilo = 10^3

  • Mega = 10^6


  • Scientific notation: used to indicate very small or large numbers. The base power is multiplied by a power of 10. For small numbers the exponent is negative but is positive for a big number.


  • Since data can’t be more precise as you go, significant figures are used to represent all the known values in a measurement + a final estimated number.


  • There are no repeating numbers in chemical measurements. The rules for using significant figures are :


  1. All non zeros are significant into ( 1 to 9 )

  2. Numbers with a decimal place, leading zeros or insignificant but all others are significant. 

  3. Numbers without a decimal place, trailing zeros are insignificant but others are significant. 


  • The first and second rules are the most important ones because most chemical measurements have a decimal place.Significant figures only apply to measurements.