Chem mid term

• What is a covalent bond?


  A pair of electrons is shared between two non-metal atoms.
• how do covalent bonds form?


  Atoms share electrons with each other to get a full outer shell. They only share electrons in their outer shells and both atoms involved in the bond end up with one extra electron in their outer shell. It makes it very stable.
• why are covalent bonds strong


  the positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces
• What does a covalent bond result in?


  the formation of molecules
• What is typical size of a simple molecules?


  10 to the -10m
• What is the formation of simple molecular - hyrdrogen (H2)?

  The hydrogen atoms share one pair (2 electrons in total) of electrons to form one covalent bond

  
• what is the formation of simple molecular - hydrogen chloride (HCl)?


  Similar to hydrogen - both needs one electron to complete outer shell so they share one pair of electrons.

  
• What is the formation of simple molecular - methane (CH4)?


  Carbon needs four electrons to complete its outer shell so it forms 4 separate covalent bonds with hydrogen with has 1 electron on each outer shell.

  
• What is the formation of simple molecular - water (H2O)?


  Oxygen atoms needs 2 electrons to complete its shell. The oxygen shares electrons with 2 hydrogen atoms to form 2 single covalent bonds.

  
• what is the formation of simple molecular - oxygen (O2)?


  Oxygen needs 2 more electrons to complete its outer shell. Two pairs of oxygen electrons are shared between another pair of oxygen electrons - it is known as a double covalent bond.

  
• what is the formation of simple molecular biology - carbon dioxide (CO2)?


  Carbon needs 4 more electrons to complete its outer shell and oxygen needs 2 more. Carbon atoms share two pairs 1 / 3 1.3 Covalent bonding Study online at https://quizlet.com/_cw1uqe - carbon dioxide (CO2) of electrons with two oxygen atoms to form two double covalent bonds.

  
• What are the properties of simple molecules?:


  : Does not conduct electricity - there are no ions or free electrons so there's nothing to carry electrical charge.

  
  

  Low melting and boiling points (mostly liquids or gases at room temperature) - although atoms within small molecules form very strong covalent bonds with each other. The forces of attraction between the intermolecular forces are very weak so it doesn't take much energy to break.

  
  

  as the molecules get bigger so does the melting and boiling point
• What are graphite and diamond?


  They are different forms of carbon and they are examples of giant covalent substances
• What is the structure of diamond?:


  Each carbon atom forms four covalent bonds with other carbon atoms. It is a rigid structure making it hard and has a high melting because the covalent bonds take a lot of energy to overcome. it doesn't conduct electricity because it has no free electrons or ions.

  
• What is the structure of graphite?


  Each carbon atom forms three covalent bonds which creates sheets of carbon atoms arranged into hexagons. Hexagons held together by weak intermolecular forces so they're free to move over each other. Makes graphite soft and slippery and has high melting point and can conduct electricity (has one free electron).

  
• What is diamond used for?:


  cutting tools - rigid structure from many strong covalent bonds which makes diamond very hard
• What is graphite used for?


  Lubricating - weak intermolecular forces so they're free to move over each other and to make electrodes as it can conduct electricity
• what are the properties of graphene?:


  A sheet of carbon atoms joined together in hexagons. A single layer of graphite and the sheet is just one atom thick (2d) . Network of covalent bonds is very strong and light so can be added to composite materials to improve their strength without adding weight. Contains delocalised electrons so can conduct electricity.

  
• what are the properties of buckminsterfullerene (C60):


  Buckminsterfullerene has got molecular formula C60 and forms a hollow sphere containing 20 hexagons and 12 pentagons. A stable molecule that forms soft brownish-black crystal.

  
• what is a polymer?


  A long chain of covalently bonded carbon atoms that are formed when lots of small molecules called monomers join together. Eg. Poly(ethene).
• what are the physical properties of ions?


  High melting and boiling points - large amount of energy to break strong ionic bonding. Ionic compounds conduct electricity when molten or dissolved in water - ions can move and carry charge. Most are soluble in water and form aqueous solutions
• What are the physical properties of giant covalent structures


  Very high melting and boiling points, most insoluble in water and most do not conduct electricity but some do (graphite)
• Physical properties of metallic structures


  High melting and boiling points, hard, strong, high density, good conductors and malleable and ductile