Some Basic Concepts of Chemistry - Chapter Summary

Chemistry deals with the composition, structure and properties of matter.
Anything that has mass and occupies space is called matter.
Matter mainly exists in three forms - solid, liquid and gaseous forms. These forms are inter convertible by changing the temperature and pressure.

SOLID <----> LIQUID <----> GAS

• Solids have a definite volume and definite shape. The particles are closely attached and there is not much freedom of movement.
• Liquids does not have a definite shape but have a definite volume. The particles are not so close and there is a freedom of movement.
• Gases neither have definite shape nor have a definite volume. The particles are situated as far as they can and are able to move freely. 

BASIC CLASSIFICATION OF MATTER

Mixtures - are the combination of two or more atoms which are combined in a ratio

• If the ratio is uniform throughout the mixture, then it is a homogeneous mixture
• If the ratio is not uniform throughout the mixture, then it is a heterogeneous mixture

Pure Substances - consist of either one type of atoms or the combination of them in a fixed ratio.

• If only one type of atom is present in it, then it is called an element
• If more than one type is present, it is called a compound

Molecules are are the combination of two or more atoms

Physical Properties can be measured or identified without changing the composition of the substance.

Chemical Properties occur due to a chemical change on the constituents.

Mass: It is the amount of matter present in a substance. It is independent of location.

Weight: It is the amount of force excerted on an object by gravity. It changes according to the change in gravitational force.

Volume: It is the amount of space occupied by an object.

LAWS OF CHEMICAL COMBINATION

1. Law of Conservation of Mass (Antonie Lavoisier) - Mass can neither be created nor be destroyed.
2. Law of Definite Proportions (Joseph Proust) - A given compound always contains the same elements in the same proportion by mass.
3. Law of Multiple Proportions (John Dalton) - When two or more elements combine to form more than one compound, a fixed mass of one compound to  a different mass of other always brings simple whole number ratios.
4. Gay Lussac's Law - When gases combine or are produced in a chemical reaction, they do so in a simple ratio provided all gases are in the same temperature and pressure.
5. Avogadro's Law - Equal Volumes of gases at the same temperature and pressure should contain equal number of molecules.

DALTON'S ATOMIC THEORY

1. Matter consist of indivisible atoms
2. All atoms of a given element have identical properties including identical mass. Atoms of different elements differ in mass.
3. Compounds are formed when atoms of different elements combine in a fixed ratio.
4. Atoms are neither created or are destroyed in a chemical reaction.

Atomic Mass - It is defined as the mass equal to 1/12th the mass of a Carbon-12 atom. It is represented by 'amu' (atomic mass unit) or 'u' (unified mass).

1 amu or 1 u = 1.66056 x 10-24 

Average Atomic Mass - It is atomic mass of elements or compounds having isotopes. It is the sum of the product of the Relative Abundance and Atomic mass of the Isotopes.

Molecular Mass - It is the sum of the atomic mass of the elements present in the molecule. Eg: CH4 - (1 X 12) + (4 X 1) = 16 amu

Formula Mass - It is used for measuring the molecular mass of the entities which does not exist in solid form. Eg: NaCl

Avogadro Number - It is the amount of atoms or molecules present in one mole of a substance. Avogadro Number(NA) = 6.023 X 1023

Molar Mass - Mass of one mole of a substance.

Percentage Composition - It is the Percentage of an element present in a compound. 

Empirical Formula - It represents the simplest whole number ratio of various atoms present in a compound. It is calculated in following steps:

1. Convert the given amount to grams
2. Calculate the number of moles for each element
3. Divide the rest of the moles with the smallest one among them
4. Write the ratio with respect to elements

Molecular Formula - It gives the exact number of various atoms in a given compound. It is calculated by:

1. Divide "Molar Mass" with "Empirical Formula"
2. Multiply the value with each element

Limiting Reagent - It is the reactant which gets consumed and thus influence the amount of product formed.

Mole Fraction of A = number of moles of A/(number of moles of A + number of moles of B)

Mole Fraction of B = number of moles of B/(number of moles of A + number of moles of B)

Molarity: 

Molality: