## Learning Objectives

## After completing the topic, the student will be able to:

- Use a scientific notation, powers of ten, while writing numbers of very large and very small sizes compactly and memorize the SI prefixes of powers of ten.
- Scale the derived units by applying decimal multiplying factors and convert the magnitudes of units into different systems of units by using conversion factors.
- Classify the errors that occur during experiments, avoid and rectify the errors while doing an experiment.
- Cross check whether you are accurate or precise by using your experimental data.
- Measure the uncertainity in the experimental value.
- Round off the calculated value by using significant figures.
- Recognize the significance of physical constants such as Planck's constant (h), Boltzmann constant (k) etc.

The International System of Units, abbreviated as SI, was established in 1960 by the 11^{th} General Conference on Weights and Measures (CGPM) as the modern metric system of measurement.The core of the SI is the seven base units for the physical quantities length, mass, time, electric current, thermodynamic temperature,amount of substance, and luminous intensity. These base units are:

Base quantity | SI base unit | Symbol |
---|---|---|

Length | meter | m |

Mass | kilogram | kg |

Time | second | s |

Electric current | ampere | A |

Thermodynamic temperature | Kelvin | K |

Amount of substance | mole | mol |

Luminous intensity | candela | cd |

The above stated are the fundamental units of matter. There are certain derived units to measure all the macroscopic and microscopic properties of matter.

In chemistry, we come across many parameters like mass, volume, temperature, pressure, energy etc. All of them are expressed with their standard units. For example, mass is expressed in kilograms, volume in meter cube and so on, which are SI units. Along with SI units we can use metric units, which are milligrams for mass, milliliters for volume etc. So, in order to convert SI units to C.G.S. units or metric units we need a conversion factor. A conversion factor is a numerical factor, used to multiply or divide aquantity when converting from one system of units to another.

Let us now discuss the parameters, units and their conversion factors.

**Powers of ten:**

A scientific notation is needed while writing numbers of very large and very small sizes compactly. If the precision is not required this can be done by writing number and multiplied by a power of ten, sometimes written in the form **a × 10 ^{b}**.

Consider the number one thousand. Its numeral is "1000". It can be written as 1 × 10^{3}. "Powers of 10" is a very useful way of writing down large or small numbers. Instead of having lots of zeros, you show how many powers of 10 you need to make that many zeros.