Summary of Sections 12.3 and

1 The hydrides of the typical elements can be classified as either salt-like (Group 

I and Group II except Be), macromolecular (Be and Al) or molecular (boron and Groups IV-VII/14-17.) Salt-like hydrides, which have the characteristics of ionic compounds, and macromolecular hydrides, react with water giving em aqueous or solid hydroxide. 

2 The highest molecular hydrides of Groups IV-VIII/14-18 have formulae EH, where x = S - N and N is the Mendeleev Group number. The shapes are correctly predicted by VSEPR theory. 

When aluminium is heated with tellurium, solid aluminium telluride, Al2Te3, is formed. If this is treated with chilled dilute hydrochloric acid, a gaseous hydride of tellurium with a revolting smell is evolved. What is the formula of the hydride, and what is the shape of the molecule  

These elemental states do not occur naturally. Fluorine, chlorine and bromine are found almost exclusively as solutions or minerals containing halide ions, X . Furthermore, most iodine is obtained from iodide solutions, but some occurs as iodates (e.g. NaI03) in, for example, the famous sodium nitrate deposits in the Atacama desert near the west coast of South America. In industry, the halogens are obtained primarily from halide ions. 

Orbital energy-level diagrams for homonuclear diatomic molecules with s and p 

1 Atomic orbitals must be of similar energy in order to combine to make molecular orbitals. 

2 n atomic orbitals combine to form n molecular orbitals. Thus from two s orbitals, one on each atom, two molecular orbitals can be made. From six 2p atomic orbitals (three on each atom) we can make six molecular orbitals. 

3 Each pair of 2p orbitals will combine to form two molecular orbitals, one bonding and one antibonding. 

5 The two orbitals formed from the 2pz atomic orbitals are unchanged by rotation through any angle about the molecular axis and are therefore o orbitals. 

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