User:Phaello/sandbox/Chemistry/Chemical Bonding

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Chemical Bonding

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Key points
  • Atoms can react with one another to form new substances called compounds
  • The resulting compound is both chemically and physically different from the parent atoms
  • e.g Sodium (a metal that starts burning on contact with water) and Chlorine (a poisonous gas) react to form NaCl – table salt that we consume
  • Sodium is a silver-coloured metal, Chlorine is a greenish gas – while NaCl compound is a white solid


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Key points
  • Chemical bonds form between atoms because electrons from the atoms interact
  • Most atoms become stable when they contain 8 electrons in the outermost shell
  • Atoms with fewer valence electrons than 8, bond together to share electrons to complete their valence shells
  • There are two main types of bonding – ionic bonding and covalent bonding

Ionic Bonding

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Key points
  • In ionic bonding electrons are transferred from one atom to another
  • The reacting atoms form irons
  • e.g. in the reaction of sodium and chlorine
  • The ions formed attract
  • An ionic bond is formed

Covalent Bonding

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Key points
  • Occurs when atoms share electrons
  • When two or more atoms share electrons
  • This occurs mainly with non-metals
  • The atoms share electrons in an attempt to complete their valence shells
  • For example hydrogen atoms – each has one electron on the valence shell -

  • They share each other's electrons to complete valence shells – and form H2 molecule
  • Chlorine – each has 7 valence electrons – they share each other's electron to complete valence shells – forming Cl2 molecule -

  • Hydrogen and Chlorine – H has 1 valence electron, Cl has 7 valence electrons – they each share one electron to complete their valence shells – forming HCl -
    Hydrogen chloride.png

  • Compounds with covalent bonding exist as true molecules – unlike ionic bonded compounds
  • For every pair of electrons shared between atoms a single covalent bond is formed
  • e.g. H and H bond is formed by sharing one electron from the 1st H atom, and another one from the 2nd H atom – so a pair of electrons is shared (one electron from each atom) – a single covalent bond is formed.
  • Some atoms can share many pairs
  • For example oxygen atoms need two electrons to complete their valence shells -
  • They share two pairs of electrons
  • Forming a double bond

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Key points
  • Carbon has 4 valence electrons while H has one
  • H needs to share one of its own electron with C also sharing one of its own
  • Each one of the H atoms forms a single covalent bond with Carbon – 4 covalent bonds

Polar and Non-polar Covalent Bonds

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Key points


  • Electronegativity is the ability of atoms to attract electrons towards themselves
  • Elements on the left hand side of the periodic table are less electronegative than those on the right
  • As you move across the period, from left to right, electronegativity increases
  • As you move down the group the electronegativity decreases

Periodic Table Showing Electronegativity values of elements

Electronegativity table.gif

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  1. Why does electronegativity of elements increase as you move across the period from left to right?
  2. Why does it decrease as you move down the group?

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Key points
  • H2, O2, N2, Cl2 are good examples of molecules with non-polar covalent bonds
  • Because in each molecule the atoms have the same electronegativity
  • A polar covalent bond is formed when bonding electrons are not shared equally
  • i.e. when there is a small difference in electronegativity of the bonding atoms
  • e.g. water molecule
My water molecule.png

  • The more electronegative atom (oxygen in the case of H2O) will pull shared electrons more towards itself, hence becoming slightly negative
  • The less electronegative atom (hydrogen atoms in the case of H2O) will be slightly positive because electrons are being pulled more towards the more electronegative atom

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How do electronegativity values of oxygen and hydrogen compare?

Refer to the following websites for more information