The International System of Units (SI units)

The International System of Units (SI units)

The SI units has seven base units and all the other are derived from these seven base units and are called derived units

Base Physical quantity	Symbol	SI units
Length	l	Meter (m)
Mass	m	Kilogram(kg)
Time	t	Sec(s)
Temperature	T	Kelvin(K)
Electric current	I	Ampere(A)
Amount of Substance	N	Mole(M)
Luminous intensity	Iv	Candela(cd)

Speed, Volume, density can be derived from these base Units.Some Common Physical quantity and their derived units

Physical Quantity	Symbol	Name	Unit
Mass	m , M	kilogram	kg
Linear position Length, Distance Radius	x, r l, d R	meter	m
Time	t,	second	s
Area	A	-	m2
Volume	V	-	m3
Density		-	kg/m3
Linear velocity	v, u, c	-	m/s
Linear momentum	p	-	kg*m/s
Linear acceleration	a	-	m/s2
Force	F	newton	N=kg*m/s2
Impulse	I	-	N*s
Work Energy	W E	joule	J=N*m
Power	P	watt	W=J/s

SI Unit system allow the use of prefix to show multiples or sub multiple of units

Prefixes in SI system Multiple	Prefix	Symbol
10-12	pico	p
10-9	nano	n
10-6	micro	μ
10-3	milli	m
10-2	centi	c
10-1	deci	d
10	deca	da
102	hecto	h
103	kilo	k
106	mega	M
109	giga	G
1012	tera	T

Mass and Weight
Mass of a substance is the amount of matter present in it while weight is the Force exerted by gravity on an object. The mass of a substance is constant whereas its weight may vary from one place to another due to change in gravity. The mass of a substance can be determined very accurately by using an analytical balance

Volume-- it has the units of (length)³. So volume has units of m³ or cm³.A common unit, litre (L) is not an SI unit, is used for measurement of volume of liquids. 1 L = 1000 mL, 1000 cm³ = 1 dm³

1 cm3	1mL	1000 mm3
1 Litre	1000mL	1000 cm3
1 m3	106cm3	1000 L
1 dm3	1000 cm3	1 L

Density: Density of a substance is its amount of mass per unit volume.
SI unit of density = SI unit of mass/SI unit of volume
= kg/m³.
This unit is quite large and a chemist often expresses Density in g /cm³

Temperature--There are three common scales to measure temperature—°C (degree Celsius), °F (degree Fahrenheit) and K (kelvin). Here, K is the SI unit.
K = °C + 273.15
$F= \frac {9}{5} C + 32$
Note—Temperature below 0 °C (i.e. negative values) are possible in Celsius scale but in Kelvin scale, negative Temperature is not possible.




Also Read

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• Notes
  • Some Basic Concepts of Chemistry
  • Physical States of matter
  • Chemical Classification Of matter
  • The International System of Units (SI units)
  • Significant Figures
  • Laws of Chemical Combination
  • Atomic Mass
  • Molecular Mass
  • Mole Concept (Avogadro Constant) And Molar mass
  • Gram Atomic Mass
  • Gram Molecular Mass
  • Percentage composition
  • StioChiometry
  • Mole Fraction
  • Molarity Definition
  • Molality Definition
  • Normality Formula
• Questions
  • Some Basic Concepts of Chemistry MCQ
  • Mole Concepts Numericals

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