Modern inorganic chemistry

STRUCTURE AND BONDING 55

Figure 2,7, Charge-cloud oj hydrogen atom

Now the combination of two hydrogen atoms to give a hydrogen
molecule can be visualised as in Figure 2.8.
In elements of Periods 2 and 3 the four orbitals are of two kinds;
the first two electrons go into a spherically symmetrical orbital—an
s orbital with a shape like that shown in Figure 2.7—and the next
six electrons into three p orbitals each of which has a roughly "double-
pear' shape, like those shown unshaded in each half of Figure 2. JO.

H -h H —•* H : H

• • • •

• 
  
  
  
  • 
    
    
    
    • 
      
      
      
      • He-I ike
      
      
      
      
    
    
    
    
  
  
  
  

,-'+ ' " + /•*'.:+• '+ + '*

Figure 2.8, The two orbitals overlap giving a covalent bond and the twv electrons are
now in a molecular orbital, (If the two nuclei could be pushed together completely, the
result would be analogous to a helium atom, but with no neutrons in the nucleus.}

When elements in Period 2 form covalent bonds, the 2s and 2p
orbitals can be mixed or hybridised to form new, hybrid orbitals
each of which has, effectively, a 'single-pear' shape, well suited
for overlap with the orbital of another atom. Taking carbon as an
example the four orbitals 2s,2p,2p,2p can all be mixed to form four
new hybrid orbitals (called s/?^3 because they are formed from one s
and three p); these new orbitals appear as in Figure 2.9, i.e. they

Figure 2.9. Orbitals of carbon in methane