struc & bond (2)

• How do you know if a substance is ionic or covalently bonded?

  A compound between a metal and non metal will have ionic bonds. A substance between two non metal atoms will be covalent bonds.
• What is an ion?


  A charged particle
• How are ions formed?


  By the loss or gain of electrons by atoms
• What is oxidation and reduction?

  OILRIG: Oxidation Is Loss of electrons Reduction Is Gain of electrons
• Do metal atoms form positive or negative ions?

  Metal atoms ALWAYS lose electrons to form positive ions
• Do non-metal atoms form positive or negative ions?

  Non-metal atoms gain electrons to form negative ions
• How can you use the periodic table to help you remember charges on ions?

  Look at the group number:

  Group 1 form +1 ions

  Group 2 = +2

  Group 3 = +3

  Group 4 = don't form ions

  Group 5 = -3

  Group 6 = -2

  Group 7 = -1

  Group 0 don't form ions
• How do ionic bonds form?

  Metal atoms lose electrons to form positive ions and these electrons are TRANSFERRED to non metal atoms which gain electrons to form negative ions.
• What is a lattice?

  A giant regular structure
• What is an ionic bond?

  The electrostatic force of attraction between oppositely charged ions (positive & negative ions attract) in a giant lattice.
• What are some of the properties of ionic compounds?

  Solids, brittle, high melting & boiling points, often soluble in water, only conduct when molten or dissolved.
• Why do ionic compounds have high melting and boiling points?

  The strong electrostatic forces between the oppositely charged ions take a lot of energy to break
• Draw a dot and cross diagram to show the formation of an ionic compound (NaCl) from the individual atoms.

  
• Why does MgO have a higher melting point than NaCl

  The ionic bond (attraction between oppositely charged ions) in MgO is stronger than in NaCl. This is because Mg is 2+ and O is 2- compared to Na which is 1+ and Cl which is 1-.
• What is a covalent bond?

  The electrostatic force of attraction between a shared pair of electrons and the two nuclei of the atoms forming the bond.
• How is a covalent bond formed?

  A pair of electrons is shared between two atoms
• Draw a dot and cross diagram of the bonding in hydrogen (H₂)

  
• Draw a dot and cross diagram of the bonding in ethene (C₂H₄)

  
• Draw a dot and cross diagram of the bonding in ammonia (NH₃)

  
• Draw a dot and cross diagram of the bonding in hydrogen chloride (HCl)

  
• Draw a dot and cross diagram of the bonding in methane (CH₄)

  
• What are the two types of covalent structures?

  Giant covalent and simple molecular structures
• What are the properties of simple molecular substances?

  Gases, liquids (with low boiling points) or solids (with low melting points), usually non conductors.
• Why do simple covalent compounds have low melting and boiling points?

  They have weak forces of attraction between their molecules that take little energy to overcome.
• What are the properties of giant covalent structures?

  Solids with very high melting and boiling points.
• Why do giant covalent structures have high melting points?

  To melt you need to break STRONG covalent bonds between the atoms which requires a lot of energy.
• What are some examples of giant covalent structures?

  Diamond, graphite (both forms of carbon), silicon dioxide (sand)
• What are some examples of simple molecular structures?

  water, ammonia, methane, oxygen, hydrogen, chlorine, ethene, nitrogen, carbon dioxide, hydrogen chloride, ethane (can you draw a dot and cross diagram for all of them?)
• Describe the structure of diamond and graphite.

  Diamond-each carbon atom forms 4 covalent bonds to other carbon atoms forming a rigid, giant 3D structure.

  Graphite-each carbon only forms 3 covalent bonds to other carbons, creating layers of hexagons between which there are delocalised electrons (one e- per carbon).
• Why is diamond used as a cutting tool and graphite as a lubricant?

  Diamond-rigid giant 3D structure makes it very hard (no planes of weakness)

  Graphite-contains layers held together by weak forces that slide over each other
• Describe the structure of a metal

  A giant lattice of positive metal ions (cations) surrounded by a sea of delocalised electrons
• Why do metals conduct electricity?

  They have delocalised electrons which can flow when an electric field is applied across it.
• What does malleable mean?

  Malleable means it can change shape (when a force is applied)
• Why are metals malleable?

  Layers of cations in a metal lattice can slide over each other when a force is applied. The layers of ions are held together by the delocalised electrons.
• What are delocalised electrons?


  Mobile (an move throughout the structure) electrons
• Draw the structure of a metal

  
• What is an electrical current?


  A flow of electrons
• Why do covalent compounds not conduct electricity?

  They have no mobile charges (electrons or ions). Graphite is an exception.
• Do ionic compounds conduct electricity?

  Yes, but only when molten or in solution. The ions are then free to move. In solid ions have fixed positions and can not move.
• Why does magnesium have a higher melting point than sodium?

  The metal bond (attraction between cations and electrons) in magnesium is stronger and takes more energy to break. This is because the ions have 2+ charge (1+ in Na) and there are twice as many delocalised electrons.