2. Bonding, Structure and Properties of Matter

• How ions form


  1. Electrons are transferred between atoms to achieve a full outer shell

  2. This makes them more stable
• Sodium atom


  • Has one electron in its outer shell, so the easiest way it can achieve a full outer shell is by losing 1 electron
  • Once it has lost the electron, it becomes an ion
• Oxygen atom


  • Has six outer electrons, so it needs to gain two electrons to achieve a full outer shell
  • The extra electrons have made the atom turn into a negative ion with a charge of -2
• You can predict what type of ion an atom will form by knowing the group of the element
• Ionic bonding


  • Occurs between a metal and a non-metal
  • Involves the transfer of electrons from a metal atom to a non-metal atom
  • The metal atom loses electrons to become a positively charged ion, while the non-metal atom gains those electrons to become a negatively charged ion
  • These ions are then strongly attracted to each other by electrostatic forces, creating an ionic bond
• Dot and cross diagrams


  • Represent the arrangement of electrons in atoms or ions where each electron is symbolised by a dot or a cross
  • These diagrams show which atom the electrons originally came from
• Lithium fluoride


  • Lithium has one outer shell electron, and Fluorine has seven
  • The best way for both atoms to get a full outer shell is for Lithium to transfer one electron to Fluorine
  • This gives both atoms a full outer shell and stability
  • As Lithium loses one electron it gets a +1 charge and Fluorine gains one electron it gets a -1 charge
  • Both ions are oppositely charged and they have electrostatic forces of attraction holding them together, forming an ionic bond
  • The Li+ and F- join to give the final formula for Lithium Fluoride as LiF
• Lithium oxide


  • Lithium has one outer shell electron, but Oxygen has six
  • This time Lithium needs to lose one electron, but Oxygen needs to gain two
  • This means you would need another Lithium atom to provide a second electron to Oxygen
  • Now they are stable with full outer shells
  • The Li+ and O2- join to give the final formula for Lithium Oxide as LiO
• Ionic compounds


  • Metals and non-metals that combine with ionic bonding form ionic compounds
  • Ionic compounds are known for their giant ionic lattice structure
  • This regular lattice consists of a 3D arrangement where ions are held together by strong electrostatic forces of attraction in all directions
• Key properties of ionic compounds


  • High melting and boiling points due to strong electrostatic forces of attraction between the oppositely charged ions
  • Electrical conductivity when molten or aqueous as the ions are free to move and can carry a charge
  • No electrical conductivity when solid as the ions are fixed and cannot move
  • Many can dissolve in water, allowing the ions to separate and move freely
• There are many different ways to represent the structure of ionic compounds, each type of diagram has their own advantages and disadvantages
• Determining the formula of an ionic compound


  1. Use dot and cross diagrams or 3D diagrams to identify the ratio of ions

  2. Balance the charges of ions to ensure the overall charge of the compound is zero
• Covalent bonding


  • Occurs between non-metals
  • Involves atoms sharing pairs of electrons so that the atoms can achieve a full outer shell and become stable
  • The positively charged nuclei are attracted to the shared pairs of electrons by electrostatic forces
• Dot and cross diagrams for covalent bonding


  • Only need to show the outer shell
  • Represent atoms sharing electrons by having overlapping shells where the shared electrons are drawn
• Displayed formula


  Simplified diagrams that use lines to represent covalent bonds
• There are 3D models that can help visualise the spatial arrangement of atoms and bonds in a molecule, offering insight into its structure
• To determine the molecular formula of a compound, count the number of each type of atom present in the molecule using any representation
• Types of substance made out of covalent bonds


  • Simple molecular substances
  • Giant covalent substances
  • Polymers
• Simple molecular substances


  • Consist of small molecules formed by covalent bonds
  • Not large networks but small groups of atoms bonded together
• Properties of simple molecular substances


  • Covalent bonds between atoms are strong and need a lot of energy to overcome
  • Intermolecular forces between molecules are weak and do not need a lot of energy to overcome
  • This gives them low melting and boiling points, so they are usually liquids or gases at room temperature
  • The larger the molecule, the stronger the intermolecular forces
  • Do not contain charged particles that are free to move, so they generally do not conduct electricity
• Polymers


  • Long chains of repeating units known as monomers
  • Atoms within the chains are held together by covalent bonds, creating large molecules with unique properties
  • The long chained molecules have very strong intermolecular forces which require a lot of energy to overcome, resulting in high melting and boiling points
• Giant covalent structures


  • Structures where atoms are bonded in a large network of covalent bonds
  • Every single atom is bonded to another with strong covalent bonds
  • They have high melting and boiling points because a large amount of energy is required to break the strong covalent bonds in the network
• Examples of allotropes of carbon


  • Diamond
  • Graphite
  • Graphene
  • Fullerenes
  • Carbon nanotubes
• Diamond


  • Formed from carbon atoms each sharing four covalent bonds in a rigid, three-dimensional structure
  • Very hard, with a high melting point due to the large network of covalent bonds
  • Does not conduct electricity as it has no free moving electrons or ions
• Graphite


  • Composed of layered structures of hexagonal rings, with each carbon atom bonded to three other atoms with covalent bonds
  • The fourth electron that is not used for bonding is delocalised, making graphite a good conductor of electricity
  • Soft, and used as a lubricant due to weak forces between layers, causing the layers to slide over one another
• Graphene


  • A single layer of graphite, and is strong and light
  • A good conductor of heat and electricity due to its delocalised electrons, so is used in electronics and composite materials
• Fullerenes


  • Molecules with hollow shapes, such as spheres or tubes
  • The structure is based on hexagonal rings of carbon atoms but may also contain rings with five or seven carbon atoms
  • Can encapsulate other molecules and are used in drug delivery and as industrial catalysts
  • Buckminsterfullerene is a spherical fullerene with a formula of C60
• Carbon nanotubes


  • Cylindrical fullerenes with very high length to diameter ratios
  • Their properties make them useful for nanotechnology, electronics and materials
  • Good conductors of heat and electricity as they have delocalised electrons, meaning they can be used in electronics and nanotechnology
  • Have a very high tensile strength without much mass, meaning they are useful for certain materials, such as the ones used in tennis rackets
• Metallic bonding


  • Occurs between metals
  • The outer shell electrons are delocalised and free to move, creating a sea of delocalised electrons
  • Within the sea of electrons, there are positive metal ions arranged in a regular pattern in a giant structure
  • The electrostatic attraction between the positive metal ions and the sea of delocalised electrons are the metallic bonds which hold the structure together
• Properties of metals


  • High melting points due to strong electrostatic forces of attraction between positive metal ions and the sea of delocalised electrons
  • Good conductivity of electricity as the delocalised electrons can carry an electrical charge through the structure
  • Good conductivity of heat as energy is transferred well by the delocalised electrons
  • Malleable, meaning they can be bent or shaped without breaking, due to the layers of atoms that can slide over each other
• Alloys


  • Mixtures of different metals
  • Harder materials than pure metals because the different sizes of atoms distort the layers of atoms, making it more difficult for them to slide over each other
• States of matter


  • Materials can exist in three states: solid, liquid, and gas
  • These states can be represented using a simple model that explains the behaviour of particles in different states
• Delocalised electrons


  Carry an electrical charge through the metal's structure
• Metals


  • Good conductivity of thermal energy
  • Delocalised electrons transfer energy well
• Malleable


  Can be bent or shaped without breaking, due to the layers of atoms that can slide over each other
• Pure metals are too soft for many uses, so are turned into alloys which are more useful
• Alloys


  • Mixtures of different metals
  • Harder materials than pure metals because the different sizes of atoms distort the layers of atoms, making it more difficult for them to slide over each other
• States of matter


  • Solid
  • Liquid
  • Gas
• Simple model


  Explains the behaviour of particles in different states using the model of small, inelastic spheres
• The simple model does not show the actual forces between particles, so there is no way of knowing how strong they are