Matter exists in three states - Solids, Liquids and Gases
Solids : A solid has a definite characteristic shape tends to resist deformation of its shape is relatively non compressible For example, diamond Solids can be classified as: Crystalline Amorphous
liquid : Has a definite volume no characteristic shape takes the shape of the container is fluid - is able to flow and change shape without separation is essentially non compressible .
Gas : has no definite volume or shape is fluid is very compressible. It takes the volume and shape of the vessel in which it is kept.
All the three states of matter are inter-convertible. When water is cooled to 0oC, it transforms into ice (solid). On heating, at 100oC, it begins to boil and gets converted into vapor (gas). On cooling, water vapor gradually converts back into water (liquid).
Elements compounds and mixture Element : A group of same type of atoms is known as an element . Compound : When two or more elements combine chemically with one another a compound is formed Mixture : A mixture is a material consisting of two or more kinds of matter each retaining its own characteristic properties .
Homogeneous Mixture : Solution is a homogeneous mixture of a solvent .
Heterogeneous Mixture : Physical states of components is different in heterogeneous mixture .
Difference between solute and solvent
Solutions Solution is defined as a homogeneous mixture of two or more chemical substances. The state of matter of a solution may be solid, liquid or gaseous. For example, common salt in water (liquid solution), air (gaseous solution), alloys (solid solution), etc. The components of a solution may be classified as: 1. Solute 2. Solvent
True Solutions A true solution is a homogeneous solution in which the solute particles have diameters less than 10-7cm. i.e., the solute particles are of molecular dimensions. The particles are invisible even under powerful microscopes. For example, sodium chloride in water is a true solution. Most ionic compounds form true solutions in water. Organic compounds like sugar and urea also form true solutions in water.
Suspensions Solutions A suspension is a heterogeneous mixture in which one or more components have a particle size greater than 10-5cm. Very often these particles are visible to the naked eye. For example, sand in water, sodium chloride in benzene, turmeric in water etc.
Colloids Solutions A colloid is a solution in which the particle size ranges between 10-7 and 10-5 cm. For example, milk, blood, honey, smoke, ink, gum, starch solution etc.
Atoms and Molecules . Atom : Atom is the smallest particle of an element, which may or may not have independent existence. It is made up of subatomic particles like electrons, protons and neutrons. Atoms of one type of element differ from those of the other due to different number of subatomic particles. Molecule : It is smallest particle (of an element or compound), which is capable of independent existence. Molecules are formed by combination of atoms.
Dalton's Atomic Theory John Dalton, a British school teacher, published his theory about atoms in the year 1808. His findings were based on experiments and also from laws of chemical combination.
Main assumptions or postulates of Dalton - All matter consists of indivisible particles called atoms. - Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements. - Atoms cannot be created or destroyed. - Atoms of different elements may combine with each other in a fixed, simple, whole number ratio to form compound atoms. - Atoms of same element can combine in more than one ratio to form two or more compounds. - Atoms are the smallest unit of matter that can take part in a chemical reaction.
Drawbacks of Dalton's atomic theory of matter
The indivisibility of an atom was proved wrong, for, an atom can be further subdivided into protons, neutrons and electrons. However an atom is the smallest particle, which takes part in chemical reactions.
-According to Dalton, the atoms of same element are similar in all respects. This is wrong because atoms of some elements vary in their mass and density. Such atoms of the same element having different masses are called isotopes. For example, chlorine has two isotopes having mass numbers 35 a.m.u and 37 a.m.u.
-Dalton also said atoms of different elements are different in all respects. This has been proved wrong in certain cases like argon and calcium atoms, which have the same atomic mass of 40. Such atoms of different elements that have the same atomic mass are called isobar. -According to Dalton atoms of different elements combine in simple whole number ratio to form compounds. This is not seen in complex organic compounds like sugar C12H22O11. -The theory completely fails to explain the existence of allotropes. The difference in properties of charcoal, graphite, diamond went unexplained in spite of being made up of same kind of atoms.
Merits of Dalton's atomic theory -It has enabled us to explain the laws of chemical combination. -Dalton was the first person to recognize a workable distinction between the ultimate particle of an element (atom) and that of a compound (molecule).
Mole Concept Since it is not possible to calculate the weight of particles individually, a collection of such particles called mole is taken for all practical purposes. Avogadro discovered that under standard conditions of temperature and pressure, (1atm and 273K) a sample of gas occupies a volume of 22.4 L.
-It was discovered that the number of atoms present in 12g of carbon is 6.023 x 1023 atoms. -This is referred to as Avogadro number. -A mole of a gas is the amount of a substance containing 6.023 x 1023 particles. -Avogadro's number is the number of atoms present in C12 isotope = 12g of C. -One mole of any gas at STP will have a volume of 22.4 L.