Difference ionic and covalent bonds

In summary, the difference between ionic and covalent bonds is that in covalent bonds, electrons are shared between the bound nuclei, while in ionic bonds, two ions are held together by the electric force between them. However, in reality, the wave functions of electrons in both types of bonds are spread out around the nuclei. Bonds can exist anywhere between purely covalent and purely ionic, with the degree of sharing determining the type of bond. In quantum mechanics, a bond is considered ionic if the corresponding bonding orbital has a higher probability density around one nucleus than the other. While some textbooks may discuss the concept of an ionic bond, it is debatable whether it truly exists. Linus Pauling's book
  • #1
jostpuur
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According to chemistry books the ionic and covalent bonds are a different thing. In covalent bonds the electrons share the same space around the bound nuclei, while in ionic bonds two ions are bound by the electric force between the ions.

However, the truth is that the wave functions of the electrons are spread onto the surroundings of the both nuclei anyway, and I'm left unable to understand what the ionic bond is supposed to mean.
 
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  • #2
My understanding is that you never get bonds that are perfectly ionic.

Claude.
 
  • #3
It is a question of degree. Pure covalent bonds can only exist between identical atoms (such as a homonuclear diatomic molecule), while one could argue a long time whether pure ionic bonds can exist. [Edit: the other Claude was faster than me on this last point.]

For most molecules, a bond will be somewhere between covalent and ionic. When the sharing is more or less equal, then we call that a covalent bond; when it is very unequal, ionic. In QM (LCAO-MO), you would call a bond ionic if the corresponding bonding orbital leads to a much greater probability density of the electron around one nucleus than the other.
 
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  • #4
I've consulted several textbooks looking for 'quantum theory of the ionic bond' (let's say in CsF). Turned up nothing. So I'm assuming that the 'ionic bond' doesn't exist.

EDIT: Just saw post #3.
 
  • #5
You could have a look in Linus Pauling "The nature of the chemical bond"
Usually you can draw two potential energy curves, even for bonds between equal atoms.
One of the curves is predominantly ionic, the other one covalent.
At large distances, the ionic rises like 1/R and lies above the covalent one. In molecules which are
covalent at the equilibrium distance, the ionic curve lies always above the ionic one, in those molecules which are
predominantly ionic at equilibrium distances, the two curves nearly intersect at some larger distance.
There are pictures in Paulings book and good explanations.
 

Related to Difference ionic and covalent bonds

1. What is the main difference between ionic and covalent bonds?

The main difference between ionic and covalent bonds is the way in which they are formed. Ionic bonds are formed between a metal and a non-metal, where one atom donates an electron to the other to form a complete outer shell. Covalent bonds are formed between two non-metal atoms, where they share electrons to form a stable bond.

2. How do the properties of ionic and covalent compounds differ?

Due to the difference in bonding, ionic and covalent compounds have different properties. Ionic compounds tend to have higher melting and boiling points, are soluble in water, and conduct electricity when dissolved in water. Covalent compounds, on the other hand, have lower melting and boiling points, are insoluble in water, and do not conduct electricity.

3. Which type of bond is stronger, ionic or covalent?

The strength of a bond depends on the difference in electronegativity between the atoms involved. Generally, covalent bonds are stronger as the atoms involved have similar electronegativities and are able to share electrons more evenly. Ionic bonds, on the other hand, are weaker as there is a large difference in electronegativity and the bond is more easily broken.

4. Can ionic and covalent bonds exist together in a compound?

Yes, ionic and covalent bonds can coexist in a compound. This type of bond is called a polar covalent bond, where there is a partial transfer of electrons from one atom to another, resulting in a slight charge difference between the atoms. An example of this is HCl, where the hydrogen atom has a partial positive charge and the chlorine atom has a partial negative charge.

5. How do you determine if a bond is ionic or covalent?

The electronegativity difference between the atoms involved is used to determine if a bond is ionic or covalent. If the difference is greater than 1.7, the bond is considered ionic. If the difference is less than 1.7, the bond is considered polar covalent. If the difference is less than 0.5, the bond is considered non-polar covalent.

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