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Allotropes of Carbon

Allotropes are different physical forms of the same element. All elements are made up uniquely of their own atoms and therefore any physical differences must be a consequence of how the atoms are joined together – their arrangement within the bulk structure.   Many elements exhibit allotropy as there are often various ways in which the atoms can be linked together into molecules and also different ways in which the molecules can be arranged to make larger structures. The two most common allotropes of carbon are diamond and graphite.   The crystal structure of diamond is an infinite three-dimensional array…

Acids and Bases

By the 1884 definition of Svante Arrhenius (Sweden), an acid is a material that can release a proton or hydrogen ion (H +) and base, or alkali, is a material that can donate a hydroxide ion (OH-). By the definition of both Thomas Lowry (England) and J.N. Brønsted (Denmark) working independently in 1923, an acid is a material that donates a proton and a base is a material that can accept a proton. When an acid and a base are placed together, they react to neutralize the acid and base properties, producing a salt.   Basically, if you’ve got something…

Laws of Chemical Combination

Chemical combination occurs in definite proportion by weight or by volume. Based on various experiments performed by different scientists, the laws of chemical combinations were formulated.   There are five laws of chemical combinations. The first four deal with combination of substances by weight and the fifth with combination of gases by volume.  

Bohr’s Model of an Atom

In 1913 Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. The motion of the electrons in the Rutherford model was unstable because, according to classical mechanics and electromagnetic theory, any charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus. To remedy the stability problem, Bohr modified the Rutherford model by requiring that the electrons move in orbits of fixed size and energy. The energy of an electron depends on the size of the orbit and is…


A mixture is a substance made by combining two or more different materials in such a way that no chemical reaction occurs. A mixture can usually be separated back into its original components.   Most natural substances are mixtures. eg:Graphite   A homogeneous mixture has the same uniform appearance and composition throughout. Many homogeneous mixtures are commonly referred to as solutions. A heterogeneous mixture consists of visibly different substances or phases. The three phases or states of matter are gas, liquid, and solid.  

Elements and Compounds

An element is a single type of atom, while a compound consists of two or more types of atoms. Elements cannot be further divided into smaller units without using large amounts of energy. Compounds, meanwhile, can often have their bonds broken using reasonable amounts of energy, such as heat from a fire. Examples of elements : gold, copper, carbon, and oxygen. Example of compound :Table salt, i.e., sodium chloride (NaCl), a compound that is composed of elements sodium (Na) and chlorine (Cl).  

Atoms and Molecules

Atoms are the smallest particle into which an element can be divided. Atoms can join together to form molecules, which in turn form most of the objects around you.   Atoms are composed of particles called protons, electrons and neutrons. Protons carry a positive electrical charge, electrons carry a negative electrical charge and neutrons carry no electrical charge at all. The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons ‘orbit’ the nucleus. A particular atom will have the same number of protons and electrons and most atoms have at least…

Interconversion of States of Matter

Another important physical property of matter is phase. The three most common phases of matter are solids, liquids, and gases. Water can exist in the solid, liquid, or gas phase.   Examples of phase changes include melting, freezing, condensation, evaporation, and sublimation. Melting occurs when a solid changes to a liquid. Freezing occurs when a liquid becomes a solid. Condensation involves a gas becoming a liquid. Evaporation involves a liquid becoming a gas and sublimation is the change of a solid directly to a gas. Phase changes require either the addition of heat energy (melting, evaporation, and sublimation) or subtraction…

States of Matter

Matter is anything made of atoms and molecules. Matter is anything that has mass and takes up space.   All matter exists as solids, liquids, or gases. These are called the states of matter. Matter can change from one state to another if heated or cooled. If ice (a solid) is heated it changes to water (a liquid). This change is called MELTING. If water is heated, it changes to steam (a gas). This change is called BOILING. The particles of ice, water, and steam are identical, but arranged differently.  

Thomson’s Model of an Atom

In 1897, J.J. Thomson discovered the electron, the first subatomic particle.   In 1904, Thomson proposed atomic model where electrons are embedded within spherically distributed, positive charge (so-called “plum pudding” model).Both the positive charge and the mass of the atom would be more or less uniformly distributed over its size.  

Chemical Reactions

In a chemical change, chemical reaction takes place and the substances undergo a change in their state. During chemical reactions, one substance reacts with another to form a new substance. The chemical composition of the new substance is different from that of the reacting species. Due to a chemical change, the chemical properties of matter also change. That means the product is entirely different from either of the reactants. Some chemical reactions may be either exothermic or endothermic in nature. In endothermic reactions, a substance absorbs energy in the form of heat and undergoes a chemical reaction. In exothermic reactions,…

Separation of Mixtures using Different Techniques

In chemistry, a mixture is a material system made up of two or more different substances which are mixed but are not combined chemically. Mixtures come in many forms and phases. Most of them can be separated, and the kind of separation method depends on the kind of mixture it is. Some common separation methods are: Simple distillation, fractional distillation, Separating funnel, centrifugation and Paper Chromatography. Simple distillation and fractional distillation are best for separating a solution of two miscible liquids. Fractional distillation is most suitable for separation of a mixture of two or more miscible liquids for which the…

Properties of Acids and Bases

The word acid comes from the Latin word acere, which means “sour.” All acids taste sour. Well known from ancient times were vinegar, sour milk and lemon juice. Acids produce hydrogen ion (H+) in solution and make a blue vegetable dye called litmus turn red. Upon chemically reacting with an active metal, acids will evolve hydrogen gas. Another common acid reaction some sources mention is that acids react with carbonates (and bicarbonates) to give carbon dioxide gas.   Bases are substances which will restore the original blue color of litmus after having been reddened by an acid. All bases taste…

Basic Laboratory Techniques

Laboratory experiment is an important part in chemistry which required a good observation and utilization of right laboratory technique. In a chemical laboratory we carry out some simple operations like bending or cutting a glass tube, boring a cork and studying the complex process of analyzing substances qualitatively and quantitatively.   This video explains some basic laboratory techniques.  

Purification of Impure Samples by Crystallization

Crystallization is a method of purifying a solid. There are two types of impurities: those more soluble in a given solvent than the main component and those less soluble. The crystallization process itself helps in the purification because as the crystals form, they select the correct molecules, which fit into the crystal lattice and ignore the wrong molecules. The solubility of the compound in the solvent used for crystallization is important. This is of course not a perfect process, but it does increase the purity of the final product.   This video explains how to prepare the crystals of (a)…

Detection of Elements: Lassaigne’s Test

The sodium fusion test, or Lassaigne’s test, is used in elemental analysis for the qualitative determination of the presence of foreign elements, namely halogens, nitrogen, and sulphur, in an organic compound. It was developed by J. L. Lassaigne. The compound is heated with sodium metal to convert the elements present in the organic compound into the water-soluble salts of sodium. Sodium is fused with the organic compound and then the fused mass is extracted with water. The extract is filtered and the filtrate is called sodium extract or Lassaigne’s extract. Nitrogen, if present in the compound, is converted into NaCN…

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