Chemistry

• Chemistry is the physical science that deals with the composition, structure, and properties of substances and also the transformations that these substances undergo
• Branches of Chemistry


  • Organic chemistry
  • Inorganic chemistry
  • Analytical Chemistry
  • Physical Chemistry
• Matter


  Anything that has the property of occupying space and the attributes of gravity and inertia
• States of Matter


  • Plasma
  • Solid
  • Liquid
  • Gas
• Physical Change


  Change in the phase or state of a substance, but its chemical composition remains unchanged
• Chemical Change


  Change in composition of its molecules, the properties of the original substance are lost, and new substances with new properties are produced
• Phase transitions occur when the temperature and/or pressure of a sample of matter is adjusted, and matter shifts between its three states: solid, liquid, and gas

  
• Element


  A substance that cannot be broken down into simpler substances by ordinary means
• Compound


  A substance in which two or more elements are joined by chemical bonds, can be created or broken down by means of a reaction but not by mechanical or physical techniques
• Atom


  The smallest unit of an element that has the properties of the element
• Molecule


  The smallest unit of a compound or the form of an element in which atoms bind together that has the properties of the compound or element
• Sub-atomic Particles


  • Nucleus
  • Electrons
  • Proton
  • Neutron
• Mass Number


  The total number of protons and neutrons in a nucleus
• Atomic Number


  The number of protons in an atom
• Isotopes


  Atoms of the same element having the same number of protons but different numbers of neutrons
• Atomic Weight


  The average weight (mass) of an atom of an element, taking into account the masses of all its isotopes and the percentage of their occurrence in nature
• An atom of an element is denoted by aXb where X corresponds to the nucleus of the atom (name of the atom, e.g.C), a is the mass number and b, the atomic number
• Electron Configuration


  The arrangement of an atom's electrons with respect to its nucleus
• Valence electrons are electrons found in the highest energy level of the electron cloud
• Elements that do not have a noble-gas configuration (a stable configuration) try to attain such a configuration by entering into chemical reactions
• Stable molecules are formed when atoms combine so as to have outer shells holding eight electrons
• Ionic Bonds


  In the ionic model, electrons are transferred from one atom to another to achieve noble gas configuration
• Ionic bond


  Formed when electrons are transferred from one atom to another to achieve noble gas configuration. The atom giving up the electrons becomes positively charged (cation), while the atom accepting the electrons becomes negatively charged (anion).
• Ionic bonds


  • Formed when elements in Group IA to IIA (except hydrogen) combine with elements in group VIA to VIIA of the periodic table
  • Ionic solids form crystals
  • Cations and anions in crystals are arranged in a repeated fixed manner (crystal structure)

  
• Covalent bond


  Formed when sharing of available outer electrons of the atoms occur. There is no electron transfer in covalent bonding. There can be multiple covalent bonds between two atoms, including double or triple bonds.
• Chemical reaction


  Involves the breakage and reformation of chemical bonds of molecules to form different substances. Can be expressed through equations with reactants on the left and products on the right, connected by an arrow or double arrows.
• Types of chemical reactions

  • Composition (synthesis or combination) reaction
  • Decomposition reaction
  • Single replacement reaction
  • Double displacement reaction
• Composition (synthesis or combination) reaction

  A more complex substance is broken down into two or more simpler substances. General form: A + X → AX
• Composition reactions


  • 2H2 + O2 → 2H2O
  • Fe + S → FeS
• Decomposition reaction


  A more complex substance is broken down into two or more simpler substances. General form: AX → A + X
• Types of decomposition reactions

  • Decomposition of a metallic carbonate
  • Decomposition of a metallic hydroxide
  • Decomposition of a metallic chlorate
  • Decomposition of some acids
  • Decomposition of metallic oxides

  
• Decomposition reactions


  • CaCO3 → CaO + CO2
• Single replacement reaction


  A less reactive element is displaced from a compound by a more reactive element. General form: A + BX → AX + B
• Types of single replacement reactions

  • Replacement of a less active metal from a compound by a more active metal
  • Replacement of a less active nonmetal from a compound by more active non-metal
  • Replacement of hydrogen from water by metals
  • Replacement of hydrogen from an acid by a more reactive metal
• Double displacement reaction


  Cations of two compounds switch anions to form new products. General form: AX + BY → AY + BX
• Double displacement reaction


  • NaOH + HCl → NaCl + H2O
• Exothermic reaction


  A chemical reaction that releases energy, often in the form of heat or light
• Endothermic reaction


  A chemical reaction that absorbs energy
• Factors affecting rate of chemical reaction

  • Nature of reactants
  • Temperature
  • Concentration of reactants
  • Surface area
  • Presence of catalyst
• The laws of chemical combination were formulated in the early 19th century and were the result of the first use of quantitative measurement in chemistry.