Ionic and covalent bonding: ions, radii and dative bonds

Folie 1

• Ionic bond is the electrostatic force of attraction between oppositely charged ions formed by electron transfer.
• Metal atoms lose electrons to form positive ions
• Non-metal ions gain electrons to form negative ions.
• Ionic bonding is stronger and melting points higher when the ions are smaller and/or have larger charges.
• E.g. MgO has a higher melting point than NaCl as the ions involved (Mg2+ and O2-) are smaller but have higher charges than those in NaCl (Na+, Cl-).
• All non-metals (except for the noble gases which do not form ions) form negatively charged ions which become larger down a group. For non-metals, trend of decreasing ionic radii= found across a period. negatively charged ions are almost always larger than positively charged ions.
• Groups 1 and 2 form positively charged ions which become larger down a group. Beginning in the d-block of the periodic table, the ionic radii of the cations do not significantly change across a period. However, the ionic radii do slightly decrease until group 12, after which the trend continues.

Folie 2

• Covalent bond is a shared pair of electrons.
• DATIVE COVALENT BONDING aka Co-ordinate bonding.
• DCBond forms when the shared pair of electrons in the covalent bond come from only one of the bonding atoms.
• Common examples: Nh4+, H3O+, NH3BF3
• The dative covalent bond acts like an ordinary covalent bond when thinking about shape so in NH4+ the shape is tetrahedral
• The arrow goes from the atom that is providing the lone pair to the atom that is deficient.

Folie 3

• Metallic Bonding
• A metallic bond is the electrostatic force of attraction between the positive metal ions and the delocalised electrons.
• 3 Main factors that affect the strength of the metallic bond:
• 1.) Number of protons/Strength of nuclear attraction. More protons, stronger the bond
• 2.)Number of delocalised electrons per atom. (outer shell electrons are delocalised) More delocalised electrons, stronger the bond..
• 3.)Size of the ion--Smaller the ion, stronger the bond.
• Example:
• Mg has stronger metallic bonding than Na and TFR higher MP.
• The metallic bonding gets stronger because there are more delocalised electrons in Mg. The Mg ion is also smaller and has one more proton. There is TFR a stronger electrostatic attraction between the positive metal ions and the delocalised electrons.

Folie 4

• Electro