Web Based Learning Object
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Chemical Bonding and Periodicity - Part Two Level 3

Although there are only 92 naturally occurring elements, there are literally millions of chemical compounds that can be formed between them.

Given that most elements are not found free on Earth, but are combined in compounds, this argues that the chemical combination (or bonding) in these compounds leads to a state of higher stability than in the uncombined element. They are at equilibrium in a similar way to a mechanical system that has minimized its energy.

So what is the nature of this bonding, and how is it achieved? You should recall from your previous studies that bonds could be classified as either stronger, primary bonds or weaker, secondary bonds. Can you identify them and their characteristics?

periodic table

The drive to form chemical bonds is to achieve greater stability (i.e. the noble gas structure) with a consequent overall reduction in energy.

The three types of primary bond are the ionic, covalent and metallic bonds: two types of secondary bond are van der Waals and hydrogen bonds.

Ionic bonding involves the transfer of one or more electrons from one atom to another to form positively charged cations and negatively charged anions. The number of electrons transferred and the types of ions formed are governed by the valences of the atoms involved. Ionic bonds are electrostatic and non-directional. Ionic molecules don't exist - ionic solids consist of arrays of cations and anions (a superlattice) arranged so that a balance is achieved between electrostatic repulsion and attraction.

Covalent bonding involves the sharing between atoms of electrons in molecular orbitals. These can form single (two electrons), double (four electrons) or triple (six electrons) bonds, which are directed in space, and which produce discrete molecules. This can occur between atoms of the same element or between dissimilar atoms. An important example is the carbon-carbon bond, which can lead to linear or branched chains, two-dimensional networks (including rings) and three-dimensional arrays.

Metallic bonding involves the sharing of a "sea" of electrons amongst the atoms of the whole solid. It is a non-directional bond and has associated with it the high electrical and thermal conductivities characteristic of metals.

The "periodic" trends in physical properties of the elements are matched by similar trends in chemical behaviour


Assessment Help: Select the correct answer from the options given.

Question One: (access key 'q')

From the options below, select the item that does not apply to Covalent bonding.




 

Question Two: (access key 'w')

From the options below, select the item that does not apply to Ionic bonding.




 

Question Three: (access key 'e')

From the options below, select the item that does not apply to Metallic bonding.




 

Assessment Results: (access key 'm')







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