4/5. Chemical bonding/Structure and properties of metals

• What is an element?


  An element is a pure substance that cannot be broken down into 2 or more simpler substances by chemical methods
• What is a compound?


  A compound is a pure substance made up of two or more different elements chemically combined in a fixed ratio
• What are mixtures?

  Mixtures are physically combined and do not have a fixed ratio
• What are the characteristics of elements?

  FORMATION

  • Most elements are naturally occurring

  MELTING AND BOILING POINTS

  • Fixed
• What are the characteristics of compounds?

  CONSISTS OF

  • Two or more elements chemically combined in a fixed ratio

  FORMATION

  • From a chemical reaction

  RATIO OF ITS CONSTITUENTS

  • Fixed ratio

  PROPERTIES

  • Has different properties from its constituent elements

  MELTING AND BOILING POINT

  • Fixed
• What are the characteristics of mixtures?

  CONSISTS OF

  • Two or more elements and/or compounds that are physically combined

  FORMATION

  • Usually from physical mixing

  RATIO OF ITS CONSTITUENTS

  • No fixed ratio

  PROPERTIES

  • Usually has similar properties to its constituent substances

  MELTING AND BOILING POINT

  • Melt and boil over a range of temperatures
• Why do atoms lose, gain or share electrons?

  To achieve a stable noble gas electronic configuration
• How are ionic compounds formed?


  When electrons are transferred from a metal atom to a non-metal atom
• What is the charge of an ionic compound?

  They have no net charge and are electrically neutral
• What are the characteristics of ionic compounds?

  1. High melting and boiling points
  2. Most are soluble in water but insoluble in organic compounds
  3. Conducts electricity in molten or aqueous state, but not in solid state
  4. Hard
  5. Brittle
• Why do ionic compounds have high melting and boiling points?


  They have a giant ionic lattice structure with strong electrostatic forces of attraction between oppositely charged ions. As such, a large amount of energy is required to overcome these forces of attraction.
• THINK: Why does MgO have a higher melting and boiling point than NaCl?


  Mg2+ and o2- have higher charges than Na+ and Cl-. As such, the electrostatic forces of attraction between Mg2+ and O2- are stronger than that between Na+ and Cl-. Thus, more energy is absorbed to overcome the stronger forces of attraction in MgO than NaCl
• Why are most ionic compounds soluble in water?

  Water molecules are attracted to the ions which break up the lattice structure and separate the ions to allow them to move apart. There is an attraction between the ions and water molecules, causing the ions to separate
• What are examples of ionic compounds that are insoluble in water?

  Silver chloride, barium sulfate
• Why can't ionic compounds conduct electricity in solid state?

  Oppositely charged ions are held in fixed positions by strong electrostatic forces of attraction in the giant lattice structure. As such, there are no mobile electrons to act as mobile charge carriers. Thus, no electricity can be conducted.
• Why can ionic compounds conduct electricity in molten and aqueous state?

  The electrostatic forces of attraction has been overcome. The ions are free to move and can act as mobile charge carriers. These moving ions will carry electric current.
• Why are ionic compounds hard?

  They have strong electrostatic forces of attraction between oppositely charged ions, causing the ions to resist motion
• Why are ionic compounds brittle?


  When a force is applied, the layers of ions slide over each other. Strong repulsive forces between the like charges causes the lattice structure to shatter
• How are covalent bonds formed?

  When atoms share electrons to attain a stable noble gas electronic configuration
• What is formed during covalent bonding?

  No charged particle is formed, and they form molecules (H2, CO2)
• THINK!

  
• What are the 3 types of covalent bonds?

  1. Simple covalent
  2. Giant covalent
  3. Macromolecules
• What are the characteristics of simple covalent molecules?

  • Countable numbers of atoms in a fixed ratio

  STRUCTURE

  • Simple molecular structure

  BONDING

  • Small and discrete molecules are held together by weak intermolecular forces of attraction
  • Atoms within the molecule are held together by strong covalent bonds
• What is the structure and bonding of simple covalent molecules?

  STRUCTURE

  • Simple molecular structure

  BONDING

  • Small and discrete molecules are held together by weak intermolecular forces of attraction
  • Atoms within the molecule are held together by strong covalent bonds
  • Countable numbers of atoms in a fixed ratio
• What are the properties of simple covalent molecules?

  • Low melting and boiling point
  • Most are insoluble in water but soluble in organic compounds
  • Most cannot conduct electricity in any state
• Why do simple covalent molecules have low boiling and melting points?

  Simple covalent molecules have weak intermolecular forces of attraction between them. Thus, only a small amount of energy is absorbed to overcome these forces of attraction
• Why are most simple covalent molecules insoluble in water but soluble in organic compounds? [DONT NEED KNOW]

  simple covalent molecules are insoluble in water because of the polarity mismatch, but they are soluble in organic compounds because both the molecules and the solvents are typically nonpolar, allowing them to interact and dissolve together.
• Why do most simple covalent molecules not conduct electricity, regardless of state?

  There are no mobile electrons to act as mobile charge carriers. Thus, no electricity can be conducted.
• What is the structure and bonding of giant covalent molecules?

  STRUCTURE

  • Giant covalent structure

  BONDING

  • Practically uncountable number of atoms
  • Network of atoms held together by many strong covalent bonds extended through the structure
• What are the 3 types of giant covalent structures?

  Diamond, graphite, silicon dioxide
• What is the structure and bonding of diamond?

  Diamond has a network of carbon atoms arranged in a tetrahedral arrangement, where each carbon atom forms strong covalent bonds with 4 other carbon atoms
• What is the structure and bonding of silicon dioxide?

  It has a network of silicon and oxygen atoms in a tetrahedral arrangement, where each silicon atoms form covalent bonds with 4 oxygen atoms and each oxygen atom forms 2 covalent bonds with 2 silicon atoms by strong covalent bonds
• What are the properties of diamond and silicon dioxide?

  • Hard
  • High melting and boiling points
  • Insoluble in water and organic solvents
  • Don't conduct electricity (insulator)
• Why is diamond and silicon dioxide hard?

  Large amount of force must be exerted to break many strong covalent bonds present throughout the network of atoms
• Why do diamond and silicon dioxide have high melting and boiling points?


  Large amount of energy must be absorbed to break many strong covalent bonds present throughout the network of atoms
• Why does diamond and silicon dioxide not conduct electricity?

  They are insulators because all valence electrons in each atom are used for covalent bonding. Thus, no mobile charged electrons can act as mobile charge carriers that can move in the structure to conduct

  electricity. Thus, no electricity is conducted
• What is the use of diamond?

  Drill bits and jewellery
• What is the use of silicon dioxide?


  Sand and quartz in watches
• What is the structure and bonding of graphite?

  It has a layered structure of hexagonal ring of carbon atoms, where each carbon atom forms strong covalent bonds with 3 other carbon atoms. There is weak intermolecular forces between the layers.
• What are the properties of graphite?


  1. Soft and slippery
  2. High melting and boiling points
  3. Insoluble in water and organic solvents
  4. Conducts electricity