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Common Unit Prefixes
Prefix Symbol Factor Example
femto f 10 −15 1 femtosecond (fs) = 1 × 10 −15 s (0.000000000000001 s)
pico p 10 −12 1 picometer (pm) = 1 × 10 −12 m (0.000000000001 m)
nano n 10 −9 4 nanograms (ng) = 4 × 10 −9 g (0.000000004 g)
micro µ 10 −6 1 microliter (μL) = 1 × 10 −6 L (0.000001 L)
milli m 10 −3 2 millimoles (mmol) = 2 × 10 −3 mol (0.002 mol)
centi c 10 −2 7 centimeters (cm) = 7 × 10 −2 m (0.07 m)
deci d 10 −1 1 deciliter (dL) = 1 × 10 −1 L (0.1 L )
kilo k 10 3 1 kilometer (km) = 1 × 10 3 m (1000 m)
mega M 10 6 3 megahertz (MHz) = 3 × 10 6 Hz (3,000,000 Hz)
giga G 10 9 8 gigayears (Gyr) = 8 × 10 9 yr (8,000,000,000 Gyr)
tera T 10 12 5 terawatts (TW) = 5 × 10 12 W (5,000,000,000,000 W)

Si base units

The initial units of the metric system, which eventually evolved into the SI system, were established in France during the French Revolution. The original standards for the meter and the kilogram were adopted there in 1799 and eventually by other countries. This section introduces four of the SI base units commonly used in chemistry. Other SI units will be introduced in subsequent chapters.


The standard unit of length    in both the SI and original metric systems is the meter (m)    . A meter was originally specified as 1/10,000,000 of the distance from the North Pole to the equator. It is now defined as the distance light in a vacuum travels in 1/299,792,458 of a second. A meter is about 3 inches longer than a yard ( [link] ); one meter is about 39.37 inches or 1.094 yards. Longer distances are often reported in kilometers (1 km = 1000 m = 10 3 m), whereas shorter distances can be reported in centimeters (1 cm = 0.01 m = 10 −2 m) or millimeters (1 mm = 0.001 m = 10 −3 m).

One meter is slightly larger than a yard and one centimeter is less than half the size of one inch. 1 inch is equal to 2.54 cm. 1 m is equal to 1.094 yards which is equal to 39.36 inches.
The relative lengths of 1 m, 1 yd, 1 cm, and 1 in. are shown (not actual size), as well as comparisons of 2.54 cm and 1 in., and of 1 m and 1.094 yd.


The standard unit of mass in the SI system is the kilogram (kg)    . A kilogram was originally defined as the mass of a liter of water (a cube of water with an edge length of exactly 0.1 meter). It is now defined by a certain cylinder of platinum-iridium alloy, which is kept in France ( [link] ). Any object with the same mass as this cylinder is said to have a mass of 1 kilogram. One kilogram is about 2.2 pounds. The gram (g) is exactly equal to 1/1000 of the mass of the kilogram (10 −3 kg).

The photo shows a small metal cylinder on a stand. The cylinder is covered with 2 glass lids, with the smaller glass lid encased within the larger glass lid.
This replica prototype kilogram is housed at the National Institute of Standards and Technology (NIST) in Maryland. (credit: National Institutes of Standards and Technology)


Temperature is an intensive property. The SI unit of temperature is the kelvin (K)    . The IUPAC convention is to use kelvin (all lowercase) for the word, K (uppercase) for the unit symbol, and neither the word “degree” nor the degree symbol (°). The degree Celsius (°C)    is also allowed in the SI system, with both the word “degree” and the degree symbol used for Celsius measurements. Celsius degrees are the same magnitude as those of kelvin, but the two scales place their zeros in different places. Water freezes at 273.15 K (0 °C) and boils at 373.15 K (100 °C) by definition, and normal human body temperature is approximately 310 K (37 °C). The conversion between these two units and the Fahrenheit scale will be discussed later in this chapter.

Questions & Answers

what is matter
Arinze Reply
Matter is anything that occupied space
matter is anything that has mass and occupies space
matter is anything that has mass and volume.
matter is any thing that can that has mass
a plot of the atomic radius against atomic number shows a periodic variation with group 1elements occupying the peaks and group 4 the troughs.plot the graph
Ngoline Reply
what is the periodic table all about
Godstime Reply
it's about predicting the different types of matter around us and organizing them in an elegant way
what is boyle law
Daniel Reply
the law states that at a constant absolute temperature the volume of a fixed of a gas is inversely proportional to the pressure of the gas...
write short not on paper chromAtogphy
Ujunwa Reply
I am sorry, I don't understand the question. Are you referring to photospectometry, a machine that uses lightwaves to determine the chemical composition of a substance? Instead of the "coffee filter and solvent" method which is more crude, but simple enough to understand basic concepts.
what is esterification?
Darey Reply
Esterification is the general name for a chemical reaction in which two reactants (typically an alcohol and an acid) form an ester(-COOR) as the reaction product....
pls i dont know chemistry wat shall i do?
Please...what do you mean by you don't know chemistry..can you explain further
I am afraid you may end up injuring yourself working with these chemical processes with limited lab experience. Please be extremely careful. Research chem analysis, precedure and equipment.
Pls can I be enlighten about boys law on chemistry
how we Learn full periodic table
muhammad Reply
Hello guys am new here my name is Angel from Nigeria how are u guys doing?
Angel Reply
Gud am from Nigeria too my name is sav
explain the atomic orbital
Masti Reply
2nacl➡️2na+cl2 2.58.5g 22.4l
suvarthavani Reply
what is neclear energy
Moyosoreoluwa Reply
nuclear energy is the energy released during nuclear fission or fusion.especially when used to generate electricity
How many processes to break down CARBON DIOXIDE into carbon and oxygen
Prabhakar Reply
biology is my best subject
Oseni Reply
o really
biology quick chemistry ass
You're in the wrong place lmao
hi Guy
How are you guys
fine and u
were are you guys from?
l'm from Nigeria
please someone should ask question
like what
Am from malawi
I'm from Nigeria, my name is Vincent. what is the relationship between volume an temperature?
who is the father of chemistry?
hey guys I'm new to the conservation, my name is Vincent from Nigeria, how are you guys doing?
the relationship between volume and temperature is. volume is directly proportional to temperature
Antoine lavoisier
good evening everyone my name is Maryann
an acid is any substance which when dissolved in water produces hydrogen ion as its only positive ion
Ezemadu Reply
its just me or you guys also hate chemistry?
I partially hate it
there's some parts that I actually like to study
tell me about it
like radiation
physics have this too
good evening everyone my name is Maryann
Why acid is sour in taste. Please don't say naturally because there are a scientific reason in all natural thing
Prabhakar Reply
since it has a negatively charge nitrogen ions
sorry, positively hydrogen ions, which has a pH less than 7
Corrct, as the H+ ion concentration increases acidity increases.
because it's pH value is smaller than 7.
what is molecules
what is acid

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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