The Avogadro constant or (the Avogadro number earlier) is the number of elementary units in one mole of any substance. The Avogadro constant is denoted as N_A. It has the dimension of the reciprocal amount of substance (mol⁻¹). The approximate value of N_A is 6.022 × 10²³ mol⁻¹. This means one mole of any substance contains 6.022 × 10²³ elementary particles. The Avogadro constant is named after Italian scientist Amedeo Avogadro.

Accuracy refers to the closeness between the measured value and actual value of a quantity. While precision indicates closeness among the measured values of a quantity. Accuracy indicates how much the measured value agrees with actual value, and precision indicates how close the measured values agree among themselves. The results which are easily reproducible have good precision.

In chemistry, we may deal with different varieties of calculations. Sometimes, we may come across very large numbers like Avogadro’s constant (N_A = 6.022 × 10²³ mol⁻¹), or sometimes, with very small numbers like the diameter of hydrogen (120 pm). Many times, chemistry experiments involve the handling of large experimental data like vapour pressure data. So, there is a need for the right technique to manage numbers conveniently and maintain the accuracy of numbers. This is where the concept of significant figures arises.

To maintain consistency in SI units, the International System of Units has adopted specific rules and style conventions for writing SI units. General rules for writing SI units were first specified by the 9th CGPM in 1948. Later, various international bodies like ISO extended these rules. These rules are very important in scientific writing. Adherence to these rules is strictly recommended while submitting and reviewing a manuscript. The general guidelines are described below.

The SI stands for the International System of Units or Le Systeme International d’Unités (in French). It is the modern system of measurement. The article lists some of them.

The International System of Units or in short SI (in French Le Systeme International d’Unités) is the currently accepted system of measurement. It originated from France. The SI was established in 1960 by the 11 CGPM (General Conference on Weights and Measures or Conférence Générale des Poids et Mesures in French). The SI system is the updated version of the metric system. It is presently accepted worldwide; though, certain countries like the USA still follows traditional English units. The SI system includes the seven base units, names of 22 derived units, and a set of prefixes.

Everything around us, in the earth, and beyond earth is matter. Matter consists of atoms. Every type of atom is associated with an element. There are 118 elements known to us, and they are arranged in the modern periodic table. This article mentions some of the most abundant elements in different systems.

There are two ways in which we can classify properties of matter. Based on how properties are determined, they can be classified into two categories: physical properties and chemical properties. Based on the dependence of properties on the amount of a substance, we can classify them into intensive properties and extensive properties. The figure below explains the same.

Matter is anything which has mass and occupies space. Examples of matter are books, phones, laptops, water, juices, coffee, air, Earth, Moon, Sun, and anything which is composed of atoms. Based on physical characteristics, we can classify matter into two main categories: pure substances and mixtures. Mixtures can further divide into homogeneous and heterogeneous mixtures and pure substances into elements and compounds.

Matter is anything that possesses mass and occupies space. In other words, one which you can weigh and measure volume is matter. Matter includes everything which satisfies the above two conditions: mass and volume.

There are four classical or fundamental states of matter, viz. solid, liquid, gas, and plasma. The latter among the four is not common in comparison to the rest three.