Tiêu đề ALLEN Chemistry Module (1-6)Complete.pdf ✅

ALLEN Pre-Medical : Chemistry 3 Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-1\1.SOME BASIC CONCEPTS OF CHEMISTRY\01-THEORY.P65 E SOME BASIC CONCEPTS OF CHEMISTRY 1.0 INTRODUCTION Chemistry deals with the composition, structure and properties of matter. These aspects can be best described and understood in terms of basic constituents of matter: atoms and molecules. That is why chemistry is called the science of atoms and molecules. Can we see, weight and perceive these entities? Is it possible to count the number of atoms and molecules in a given mass of matter and have a quantitative relationship between the mass and number of these particles (atoms and molecules)? We will like to answer some of these questions in this Unit. We would further describe how physical properties of matter can be quantitatively described using numerical values with suitable units. MATTER PHYSICAL Solid Liquid Gas definite shape & volume no definite shape & volume definite volume but no definite shape CHEMICAL Pure Substances Mixtures fixed ratio of masses of constituents Elements Compounds Homogeneous Heterogeneous same composition throughout & components are indistinguishable. eg. gases, liquid solution, alloys, atmospheric air nearly homogeneous Consists of only one type of atoms Made of two or more atoms of different elements composition is not uniform. eg. sand & water, Classification of universe Universe is classified into two types i.e. matter and energy. (A) MATTER : The thing which occupy space and having mass which can be felt by our five senses is called matter. Matter is further classified into two categories : (I) Physical classification (II) Chemical classification PHYSICAL CLASSIFICATION It is based on physical state under ordinary conditions of temperature and pressure, so on the basis of two nature of forces matter can be classified into the following three ways : (a) Solid (b) Liquid (c) Gas (a) Solid : A substance is said to be solid if it possesses a definite volume and a definite shape. e.g. Sugar, Iron, Gold, Wood etc. (b) Liquid : A substance is said to be liquid if it possesses a definite volume but not definite shape. They take the shape of the vessel in which they are placed. e.g. Water, Milk, Oil, Mercury, Alcohol etc. (c) Gas : A substance is said to be gas if it neither possesses a definite volume nor a definite shape. This is because they completely occupy the whole vessel in which they are placed. e.g. Hydrogen(H2 ), Oxygen(O2 ), Carbon dioxide(CO2 ) etc.