Trends in the Periodic Table and Bonding Bonding Continuum

Ionic Bonds Ionic bonds are formed between atoms with a large difference in electronegativities. They are often (though not always) between metals and non-metals. For example, in potassium bromide, the difference in electronegativities is so large that potassium will lose an electron and form a positive ion. Bromine gains this electron and forms a negative ion. The ionic bond is the electrostatic force of attraction between a positive and negative ion.

transfer of an electron K Reacting Elements: e- Br 2,8,8,1 2,8,7 Electron Arrangement: gains 1e- During Reaction: loses 1e- transfer of an electron K Br + - Ions Formed: New Electron Arrangement: 2,8,8 2,8,8

The electrostatic force of attraction between the oppositely charged ions is called the ionic bond K + Br - Ionic compounds form a LATTICE STRUCTURE. Millions of oppositely charged ions are held together in a very stable arrangement.

Bonding Continuum We can place each of the types of intermolecular bond in one continuous series based on how much ionic character the bond displays. This is governed by the difference in electronegativities between the two atoms. Increasing ionic character

Pure Covalent Bonding H A pure covalent bond has no ionic character at all. The electronegativities of both atoms are identical and the bonding electrons are evenly shared between both atoms. H e Increasing ionic character 2.2 Electronegativities e H Increasing ionic character

Polar Covalent Bonding A polar covalent bond has some ionic character. There is a small difference between the electronegativities of both atoms and the bonding electrons are pulled more closely to the more electronegative atom. δ- δ+ P Cl e 2.2 3.0 Electronegativities e P Cl δ- δ+ e H Increasing ionic character Increasing ionic character

Ionic Bond There is no sharing of the electrons and oppositely charged ions are formed. An ionic bond exists when the difference in electronegativities is so great that the movement of the bonding electrons between the two atoms is complete. Li + F - Li F + - e 1.0 4.0 Electronegativities e P Cl δ- δ+ e H Li F + - Increasing ionic character Increasing ionic character

Bonding Continuum Pure Covalent Bond Polar Covalent Bond Ionic Bond To judge the type of bonding in any particular compound it is more important to look at the properties it exhibits rather than simply the names of the elements involved. e P Cl δ- δ+ e H Li F + - Increasing ionic character