Ch 1Some Basic Concepts of Chemistry — Class 11 Chemistry, concept-first.

Chemistry is the branch of science devoted to studying matter — everything that occupies space and has mass — along with its physical and chemical properties and the changes matter undergoes under dif…

Chemistry is traditionally divided into five branches, each covering a different slice of the subject. Organic chemistry studies the properties and reactions of carbon-containing compounds.

Matter is anything that occupies space and possesses mass — a fact already familiar from earlier study.

A pure substance has a definite, fixed chemical composition, and as a result it always shows the same set of properties no matter where the sample originally came from — distilled water and a pure met…

Matter is already known to exist in three familiar physical states — solid, liquid and gas — a topic taken up in much greater depth later in Unit 3 (Chapter 10).

Every kind of matter has its own set of characteristic properties, and these fall into two broad categories: physical properties and chemical properties.

Many properties of matter — mass, length, area, pressure, volume, time and so on — are quantitative, meaning they can be expressed as a number.

Mass and weight, though often used loosely as synonyms in everyday speech, are physically distinct: mass is an inherent property of matter, the measure of how much matter a body actually contains, and…

Elements combine with one another to form compounds, and — long before anyone actually knew what a molecular formula was — chemists worked out, purely through careful experimental weighing, a set of b…

The law of conservation of mass was established by the French scientist Antoine Lavoisier (1743-1794), often called the father of modern chemistry, through a careful series of combustion experiments —…

The law of definite proportions (also called the law of definite, or constant, composition) was established by the French chemist Joseph Proust, who compared two samples of cupric carbonate — one that…

The law of multiple proportions was proposed by John Dalton in 1803, based on the observation that two elements can sometimes combine with each other to form MORE than one distinct compound.

Gay-Lussac's law of gaseous volumes, put forward by Gay-Lussac in 1808, states that whenever gases combine with each other, or are produced, in a chemical reaction, they always do so in a simple ratio…

Avogadro's law, proposed by Amedeo Avogadro in 1811, states that equal volumes of any gas, measured at the same temperature and pressure, contain an equal number of molecules — regardless of what the…

In 1808, John Dalton published a work titled 'A New System of Chemical Philosophy', in which he set out a theory of matter that later came to be known as Dalton's atomic theory.

Having introduced the ideas of atoms and molecules, it is worth pausing to define precisely what is meant by 'atomic mass' and 'molecular mass'.

Every element has its own characteristic atomic mass, meaning the mass of a single atom of that element — a genuinely tiny quantity that is not practical to measure directly or to work with in grams (…

Most elements, as they actually occur in nature, exist not as a single, uniform kind of atom but as a mixture of two or more isotopes — atoms of the same element that carry different individual atomic…

The molecular mass of a substance is the mass of a single molecule of that substance, again expressed relative to the mass of one carbon-12 atom (i.e.

Some substances — sodium chloride is the standard example — do not actually exist as discrete, separate molecules at all.

Because even a very small, weighable amount of any substance contains an enormous number of atoms or molecules, chemists borrow the same idea behind everyday counting words like 'dozen' (12 items) or…

Since many chemical substances exist as gases, it is often much more practical to find how many moles of a gas are present by measuring its VOLUME rather than by weighing out its mass.