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Dative Covalent Bonds  (Co-ordinate Bonding)

Dative Covalent Bonds (Co-ordinate Bonding)

  • In a standard covalent bond there are a pair of electrons shared between two atoms where each atom donates one electron
  • In a dative covalent bond there is a pair of electrons shared between two atoms however donated by one atom providing both electrons
  • In a coordinate/dative covalent bond:
    • The atom that accepts the electron pair is an atom that does not have a filled outer main level of electrons (electron deficient atom)
    • Atom that is donating the electrons has a pair of electrons that not being used in a bond (lone pair)
  • They are represented by an arrow which points towards the atom that is accepting the electron pair
  • This is only to show how the bond is made

e.g.

  • All co-ordinate bonds have exactly the same strength and length as ordinary covalent bonds between the same pair of atoms
Metallic

Metallic

  • Metallic bonding is the bonding of metal atom to another metal atom
  • Unless a non-metal atom is present, a metal atom cannot donate electrons
  • The outer electrons of all metals are delocalised
  • Metals are a lattice of positively charged ions that are in a ‘sea’ of electrons

    Properties of Metallic Bonding

  • Good conductors of electricity (the delocalised electrons can move throughout the structure, therefore the electrons from the negative side of a terminal can join the electron sea at the one end (e.g. in a wire) whilst simultaneously a different electron can leave the wire at the positive terminal
  • Good conductor of heat
  • Metals have great strength as a result of the charge on the ions, a greater charge means the number of delocalised electrons is greater too. The stronger electrostatic attraction between the positive ions and the electrons. As well as the size of the ions, the smaller the ion, the closer the electrons are to the positive nuclei and thus the bond is stronger
  • Metals are malleable and ductile, as after a small distortion, each metal ion is exactly in the same environment as before, and therefore the shape is retained
  • Metals have a high melting point as a result of their large structure. There is a strong attraction between the metal ions and the delocalised sea of electrons.
  • Covalent

    Covalent

    • Covalent forms between pairs of non-metal atoms
    • Non-metal atoms need to receive electrons to fill the spaces in their outer shell
    • The atoms share some of their outer electrons so that each atom has a stable noble gas arrangement

      Structure of Covalent Bonds

      Atoms with covalent bonds are held together through electrostatic attraction between the nuclei and the shared electrons

      e.g. In a hydrogen molecule (H2), the two protons are held together by the pair of electrons.

      Forming Covalent Molecules

    • a group of covalently bonded atoms is called a molecule
    • in the example of Chlorine (Cl), which exists as a gas and therefore is a molecule Cl2
    • Chlorine has 8 electrons (in the orbitals [Ne] 2s2 2p5), the 2 atoms share one pair of electrons and therefore produces a stable noble gas.
    • The molecule has no charge as there are no electrons have been transferred from one atom too the other
    • Double Covalent Bonds

    • In a double bond, 4 electrons are shared
    • Double covalent bonds are presented as: =
    • They are present in alkenes and molecules such as O(O=O)
    • Properties of Covalent Bonds

    • Low melting points (the intermolecular covalent bond although strong, the intramolecular forces are weak)
    • Poor conductors of electricity (as each molecule has no overall charge)
    • Co-ordinate (dative) Bonding

    • A standard covalent bond is the sharing of a pair of electrons. Usually, one electrons comes from one atom, and one from the other
    • In co-ordinate bonding, the electron pair is provided by only the one atom
    • The atom that accepts the electron pair is the atom which has an incomplete outer main level of electrons. (or electron deficient)
    • The atom that is donating the electrons has a pair of electrons that is not being used in the bonds, called a lone pair
    • Co-ordinate bonds are represented as an arrow, where the arrow points towards the atom which is accepting the electron pair.
    • A Co-ordinate bond is equal in strength and bond length to a regular covalent bond

    Ionic

    Ionic

    • Ionic bonding is the bonding of ions that are held together through electrostatic attraction
    • Ionic bonding occurs between metals and non-metals
    • Electrons are transferred from the metal atom to the non-metal atom
    • Ions are formed when one or more electrons are transferred from one atom to another
    • The simplest ions are single atoms which have either lost of gained electrons which therefore have a full outer shell.
    • Electrostatic attraction holds positive and negative ions together. The result is a very strong bond.

    Forming ionic compounds

    • The ionic compounds are made up positively charged part and a negatively charged part
    • The overall charge of any compound is zero
    • All negative charges in the compound must balance the positive charge

    e.g. Na + Cl– -> NaCl (0 overall charge)

    Properties of Ionically Bonded Compounds

    • Always solids at room temperature
    • Giant structure
    • High melting point (in order to melt an ionic compound energy must be supplied to break up the lattice ions)
    • Conducts electricity well in dissolved in a solution or melted (as the ions that carry an electrical current are free to move in the liquid state but are not free in a solid state)
    • Brittle and shatter easily (the large lattice of alternating positive and negative ions, a physical collision of the material may cause these layers to move and have 2 positive ions touching which therefore repel)