CHEMISTRY

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• Chemistry is the physical science that deals with the composition, structure, and properties of substances and also the transformations that these substances undergo.
• Chemistry encompasses the entire material universe and is central to the understanding of other sciences.
• Decomposition Reaction is a type of chemical reaction where a more complex substance is broken down into two or more simpler substances.
• Endothermic Reaction is a chemical reaction that absorbs energy.
• Composition Reaction, also known as synthesis or combination reaction, is a type of chemical reaction where a more complex substance is broken down into two or more simpler substances.
• Single Replacement Reaction is a type of chemical reaction in which a less reactive element is displaced from a compound by a more reactive element.
• Exothermic Reaction is a chemical reaction that releases energy.
• Double Displacement reaction is a type of reaction wherein cations of two compounds switch anions to form new products.
• Branches of Chemistry include Organic chemistry, Inorganic chemistry, Analytical Chemistry, and Physical Chemistry.
• Matter in science is a general term applied to anything that has the property of occupying space and the attributes of gravity and inertia.
• Plasma is the collection of charged gaseous particles containing nearly equal numbers of negative and positive ions, is sometimes called the fourth state of matter.
• Solid is characterized by resistance to any change in shape, caused by a strong attraction between the molecules of which it is composed.
• Liquids have sufficient molecular attraction to resist forces tending to change their volume.
• Gas molecules are widely dispersed and move freely, offers no resistance to change of shape and little resistance to change of volume.
• Physical Change is characterized by a change in the phase or state of a substance, with some physical properties of the substance altered, but its chemical composition remains unchanged.
• Chemical change is characterized by a change in composition of its molecules, with the properties of the original substance lost, and new substances with new properties produced.
• Given the electronic configuration, one can determine its position in the periodic table.
• Valence electrons are electrons found in the highest energy level of the electron cloud.
• Isotopes are atoms of the same element having the same number of protons but different numbers of neutrons.
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• Atomic number equals to the number of proton in an electron.
• The term isotope defines atoms that have the same number of protons but a different number of neutrons, making them atoms of the same element that have different masses.
• Atomic Weight is the average weight (more correctly, the mass) of an atom of an element, taking into account the masses of all its isotopes and the percentage of their occurrence in nature.
• The electron configuration of an atom is the arrangement of the atom's electrons with respect to its nucleus.
• An electron may occupy a certain energy level (n).
• The energy level corresponds to the period of the periodic table (1-7) while the number of valence electrons corresponds to the group number of that element.
• An atom of an element is denoted by a X b where X corresponds to the nucleus of the atom (name of the atom, e.g.C), is the mass number and b, the atomic number.
• Element Number of Protons Number of electrons Number of neutrons Atomic number Mass number Carbon 6 6 6 6 12.
• An orbital is generally visualized as a cloud with a specified size and shape determined, in general, by the energy level of the electron.
• Mass Number is the total number of protons and neutrons in a nucleus.
• Neutron has nearly the same mass as the proton, but the neutron has no electric charge.
• Ca(OH)2 = 40 + 2(16) + 1(2) = 74 g/mol H2O = 1(2) + 16 = 18 g/mol mole Ca(OH)2 = 35 g / (74 g/mol) = 0.473 moles moles of H2O = 42 g/ (18 g/mol) = 2.333 mole moles of solution = 0.473 + 2.333 = 2.803 moles mole fraction of Ca(OH) 2 = 0.473 moles 2.806 moles = 0.17.
• Mole Fraction is the ratio of the number of moles of solute in a given mole of solution.
• Pv = Vsolute / Vsolution x 100%
• Molarity expresses the amount of solute in moles per liter of solution.
• The mole fraction of 35 g of calcium hydroxide dissolved in 42 grams of water can be determined by determining the moles of solute and solvent from their molecular weight.