Kalpana's education tech

Valence: valence (or) valency of an element was defined as the combining power Of an element with respect to hydrogen, oxygen or indirectly any other element through hydrogen and oxygen.          Valence of an element with respect to hydrogen is the number of hydrogen atoms with which one atom of that element chemically combines.valence of an element with respect to oxygen is twice the number of oxygen atoms with which one atom of that element combines.        For example one atom of 'na' chemically combines with one atom of 'H' to give NaH. Therefore,the valence of Na is 1. One atom of 'Ca' combines with one atom of 'O' to give CaO. So the valency of Ca is 2.   In general,the valence of an element with respect to hydrogen is it's traditional group number.if the element is in the group V or above,it's valence is 8- group number.for example, chlorine valence is 8-7=1. Generally every period Starts with valence '1' ends with '0'. Va...

Atomic radius of an element may be defined as the distance from the centre of the nucleus of the atom to its outer most shell  Atomic radius of an element is not possible to measure in its isolated state.this is because it is not possible to determine the location of the electron that surrounds the nucleus.however,we can measure the distance between the nuclei of adjacent atoms in a solid.from this we can estimate the size of the atom by assigning half of this distance to the radius of each atom.this method is best suited to elements such as the metals that exist in the solid state.more than 75 percent of the elements are metals and atomic radii of metals are called metallic radii. Another way of estimating the size of an atom is to measure the distance between the two atoms in covalent molecules. The size of a chlorine atom is estimated by measuring the length of the covalent bond between two chlorine atoms in a cl2 molecule. Half of this distance is taken as atomic radius which i...

johan newlands was a British chemist.newlands (1865) found that when elements were arranged in the ascending order of their atomic weights they appeared to fall into seven groups . each group contained elements with similar chemical properties .based on these observations, newlands proposed the law of octaves. The law of octaves states that when elements are arranged in the ascending order of their atomic weights they fall into a pattern in which their properties repeat at regular intervals.every eighth element starting from a given element resembles in it's properties are to be present along a horizontal row. New lands was the first to assign atomic numbers to the elements . unfortunately his work was neither accepted by his seniors nor by the journal of the chemical society, which rejected it's publication . In Newlands table of elements ,if we start with hydrogen and move down and then start at the top the eighth element is fluorine and next eighth element is chl...

Exchange of gases is a common life process in all living organisms,but it is not same in all . single celled organisms ameoba or multicellular organisms like hydra & planarians obtain oxygen & expel carbon dioxide directly from the body by the process of diffusion. In other multicellular animals special organs are evolved . animals either terrestrial or aquatic are adopted to different types of respiration and possess different types of respiratory organs mostly depending on the habitat in which they live. Body size, availability of water and the type of their circulatory system are some of the reasons for the animals to develop different types of respiratory organs. There is tracheal respiratory system in insects like cockroach, grasshopper etc... Tracheal respiratory system consists of series of tubes called trachea .this is divided into fine branches called tracheols which carry air directly to the cells in the tissues. Some aquatic animals like fishes have developed special...

1. Baking powder is a mixture of baking soda & a mild edible acid such as tartaric acid.when baking powder is heated or mixed in water,the following reaction takes place. Nahco3+CO2+h2o+ sodium salt of acid. Carbon dioxide produced during the reaction causes bread or cake to rise making them soft & spongy . 2.sodium hydrogen carbonate is also an ingredient in antacids.being alkaline,it neutralizes excess acid in the stomach & provides relief. 3.it is also used as soda - acid in figure extinguishers. 4.it acids as mild antiseptic