CIE A Level Chemistry复习笔记1.3.3 Electronegativity & Bonding

Electronegativity: Predicting Bond Formation

  • The differences in Pauling electronegativity values can be used to predict whether a bond is covalent or ionic in character

Electronegativity & covalent bonds

  • Single covalent bonds are formed by sharing a pair of electrons between two atoms
  • In diatomic molecules the electron density is shared equally between the two atoms
    • Eg. H2, Oand Cl2
  • Both atoms will have the same electronegativity value and have an equal attraction for the bonding pair of electrons leading to formation of a covalent bond
  • The equal distribution leads to a non-polar molecule

1.3-Chemical-Bonding-Covalent-Bonds-in-Diatomic-Molecules

The electronegativity values are equal resulting in the formation of a nonpolar covalent bond

Electronegativity & ionic bonds

  • When atoms of different electronegativities form a molecule, the shared electrons are not equally distributed in the bond
  • The more electronegative atom (the atom with the higher value on the Pauling scale) will draw the bonding pair of electrons towards itself
  • A molecule with partial charges forms as a result
  • The more electronegative atom will have a partial negative charge (delta negative, δ-)
  • The less electronegative atom will have a partial positive charge (delta positive, δ+)
  • This leads to a polar covalent molecule

1.3-Chemical-Bonding-Polar-Covalent-Bonds

The electronegativity values are not equal - polar bond forms

  • If there is a large difference in electronegativity of the two atoms in a molecule, the least electronegative atom’s electron will transfer to the other atom
  • This in turn leads to an ionic bond – one atom transfers its electron and the other gains that electron
    • The cation is a positively charged species which has lost (an) electron(s)
    • The anion is a negatively charged species which has gained (an) electron(s)

1.3-Chemical-Bonding-Ionic-Bonds_1

Large differences in electronegativity values lead to the formation of ionic bonds

Exam Tip

You can use the Pauling scale to decide whether a bond is polar or nonpolar:1.3-Chemical-Bonding-Table_4

 

 

 

 

 

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