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1、O2 (O,F)9.3.2 homonuclear diatomic molecules The homonuclear diatomic molecules in the Second period Homonuclear diatomic moleculesMO energy levels of homonuclear diatomic molecules MO electron arrangements O2 has two unpaired electrons and is paramagnetic.KK(2S)2(*2S)2(2P)2(2PX)2(2PY)2(*2PX)1(*2PY)
2、1KK means that the k-shell is fully filled.The bonding(2S)2 and the anti bonding(*2S)2 offset each other and do not contribute to the bonding,which is named as non-bonding orbitals and non-bonding electrons.The actual contributions to bonding are as follows:(2PX)2 forms a bond in O2 molecule (2PY)2(
3、*2PY)1 and(2PY)2(*2PY)1 have the same spatial configuration and form a three electron bond.O2 molecule is composed of three bonds:one bond and two three electron bond Bond order=(6-2)/2=2:O O:Discussion:1.O2 presents paramagnetism.2.Peroxide ions are oxidized by chlorine gas and lose one-by-one elec
4、trons to obtain excited oxygen,which emits red light and becomes ground state oxygen.3.In fact,each“three electron bond”is only equivalent to half a bond,and two“three electron bond”is less than one normal bond,which is the reason why oxygen molecules are active and can react with many elements.The
5、measured bond lengths of O2+,O2,O2-and O22-are gradually longer,which can be explained by MO theory.Which of them has paramagnetism?Why?O2+KK(2S)2(*2S)2(2P)2(2PX)2(2PY)2(*2PX)1 O2 KK(2S)2(*2S)2(2P)2(2PX)2(2PY)2(*2PX)1(*2PY)1O2-KK(2S)2(*2S)2(2P)2(2PX)2(2PY)2(*2PX)2(*2PY)1O2 2-KK(2S)2(*2S)2(2P)2(2PX)2(2PY)2(*2PX)2(*2PY)2Bond order:O2+=2.5 ，O2=2，O2-=1.5，O2 2-=1Paramagnetism:O2+,O2,O2-Stability:O2+O2 O2-O2 2-Bond length:O2+O2 O2-O2 2Bond energy:O2+O2 O2-O2 2-