Atomic bonds, energy and chemical reactions

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Atomic bonds, energy and chemical reactions
2013-03-24 02:56:37

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  1. What is the valence shell of an atom?
    The outer most shell of an atom.
  2. What is special about the noble gases, what is the octet rule?
    The octet rule states that any atom with more than one shell will try to achieve a valency of 8. The noble gases all have full valency, including helium with is single shell at a valency of 2.
  3. How do most atoms achieve a valency of 8?
    By forming molecules through chemical bonding. They give and take electrons (ionic) or they share them (covalence).
  4. What are ionic bonds?
    Bonds formed by 2 atoms without full valency giving and taking atoms. Because there is a give and take of electrons, the atoms become either positively or negatively charged, pulling them together. There is never pure ionic bonding, always some covalence.
  5. What are ions, cations and anions?
    • Ions are atoms where the number of protons does not match the number of electrons.
    • Cation: More protons, + charge
    • Anion: More electrons, - charge
  6. What are covalent bonds?
    Bonds where atoms share electrons in order to create full valency. The formation of a new, shared outer shell binds them and this bond tend to form between atoms at opposite ends of the table. It also creates polar bonds unless it is an elemental molecule.
  7. What are polar and non polar covalent bonds?
    In covalent bonds of different elements, their differing size means electrons will tend to spend more time on larger atoms, creating a charge difference between the atoms. This pulls them together, but also affects the way molecules interact with other molecules. Elemental molecules or molecules formed by atoms of similar size have little or no difference and are non polar.
  8. What are hydrogen bonds?
    Hydrogen bonds are bonds formed by the attraction of polar hydrogen atoms in a molecule. Surface tension in water is one example of this. They are relatively weak bonds.
  9. What are chemical reactions?
    • The process by which new chemical bonds are formed or existing chemical bonds are broken. They are affected by - 
    • SA-V ratio
    • temperature
    • concentration
    • surface area of medium
    • the medium substance itself
  10. What are endothermic and exothermic chemical reactions?
    Endothermic chemical reactions need heat to be performed. It results in absorptions of heat.

    Exothermic reactions produce heat and have a net gain of heat.
  11. What does the term metabolism refer to?
    The sum of all chemical reactions taking place in an organism.
  12. What are synthesis reactions?
    Reactions that involve the combination of atoms into molecules.
  13. What are decomposition reactions?
    Reactions that involve the breaking down of molecules into components.
  14. What are exchange reactions?
    Reactions that involve both synthesis and decomposition and thus can be thought of as molecules "exchanging" atoms.
  15. What are reversible reactions?
    Reactions that can occur in both directions.
  16. What is energy?
    A hard to define, intangible component of the universe that is required to do mechanical work. It can come in a variety of forms such as potential, chemical and kinetic energy. The law of conservation states that energy can be neither created nor destroyed and can only change form.
  17. What is potential energy?
    Energy stored in matter due to its position. For example a suspended item has potential energy because it has the potential to fall to the ground.
  18. What is chemical energy?
    Energy that is stored between the bonds of atoms. Chemical reactions absorb or give off energy (endogenic or exogenic).
  19. What is kinetic energy?
    Energy stored in an object due to its movement. For example a car converts chemical energy into kinetic energy when it accelerates and dissipates its energy through braking.
  20. What is chemical potential energy?
    Energy that can be stored or released during a chemical reaction.
  21. What is the activation energy of a chemical reaction?
    The level of a particular energy needed to catalyse a chemical reaction. E.g. a certain temperature is needed for chemical reactions to take place.
  22. What are enzymes? What is there function in the body?
    Enzymes are proteins that catalyse chemical reactions in the body, lowering the activation energy level required for them to take place.