
Dative Covalent Bonds (Co-ordinate Bonding)
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e.g.
Properties of Metallic Bonding
Structure of Covalent Bonds
Atoms with covalent bonds are held together through electrostatic attraction between the nuclei and the shared electrons
e.g. In a hydrogen molecule (H2), the two protons are held together by the pair of electrons.
Forming Covalent Molecules
Double Covalent Bonds
Properties of Covalent Bonds
Co-ordinate (dative) Bonding
Forming ionic compounds
e.g. Na+ + Cl– -> NaCl (0 overall charge)
Properties of Ionically Bonded Compounds
Determining the Shapes of molecules:
The shape of the molecule can be found using the VSEPR model:
e.g. CH3–
C
C = +4
+4 + 3 (hydrogens) = 7
Negative ( – ) charge, therefore -1
7 -1 = 6
number of electron pairs
6 /2 = 3
As CH3— has 3 bonding groups according to VESPR, and has no lone pairs, it is a Trigonal Planar.
Forming Van der Waals
Polarity is the unequal sharing of electrons between 2 atoms which are covalently bonded together
Non-Polar
Non-polar molecules are ones that form between 2 non-metals which have the same electronegativity
Covalent bonds in diatomic gases (e.g. O2) are non-polar as the atoms have an equal electronegativity and therefore the electrons are equally attracted to both nuclei
Some elements such as carbon and hydrogen have similar electronegativities and so the bonds between them are non-polar
Polar
Polar molecules between 2 non-metal atoms that have a different electronegativity to one another and therefore have an unequal sharing of electron pairs
If charge is distributed unevenly over a whole molecule, the molecule will have a permanent dipole
Molecules with a permanent dipole are known as polar molecules
In simple molecules, the one polar bond means the charge is distributed evenly across the whole molecule
In complex molecules, several polar bonds may be present. The shape of the molecule will therefore be decided on whether or not there is an overall permanent dipole. If the polar bonds are arranged symmetrically so that the dipoles cancel each other out, then the molecule does not have a permanent dipole and is non-polar.
If all of the polar bonds point in the same direction and do not cancel each other out. The resulting charge will be arranged unevenly across the entire molecule, resulting in a polar molecule
The movement of electrons to the more electronegative atom can be displayed using an arrow: