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Bonding
3.1 Ionic bonding: • strong, depends on the size of the positive ions the
smaller the ion the less shielding occurs so there’s a
Occurs between a metal and a non-metal through the greater electrostatic attraction, which requires more
donation of the outer shell electrons so that both can energy to be overcome. Also depends on the charge of
have a full outer shell, results in the formation of the ion, the greater the charge the larger the electrostatic
positive and negative ions. attraction and the more e- that are delocalised.
The bond is held together through the electrostatic • Malleable
attraction between the oppositely • High melting point due to giant strong structures, no
charged ions, creating individual bonds to break so more energy required,
a lattice structure increasing the melting point.
PROPERTIES-
• solid at room temperature
• high melting point due to giant structure, must 3.4 Electronegativity
overcome the electrostatic attraction between ions
• conduct electricity when molton or in solution, Electronegativity: the power of an atom to attract the
ions are free to carry charge electron density in a covalent bond towards itself.
• Brittle and snap easily, when hit two ions of the Depends on nuclear charge, the distance from nucleus and
same charge can come into contact, creating the amount of shielding.
repulsion that’s easier to overcome to break the Going across a period-electronegativity increases, the
lattice nucleus charge increases with he same amount of
shielding but the atoms become smaller.
3.2 Covalent Bonding: Polarity: the difference in electron density across a bond,
creating a slightly positive and a slightly negative atom.
Between two non-metals through the sharing of The same atoms in a bond will have the same
electrons so both receive electrons and form a complete electronegativity. Different atoms create a polar bond, the
outer shell. Held together by the electrostatic attraction bigger the difference in electronegativity, the more polar
of the positively charged nucleus and the negatively the bond.
charged electrons that have been donated.
Double covalent bonds occur when two pairs of electrons
are shared.
3.5 Intermolecular forces:
PROPERTIES-
H
·
H
• molecular structures have low X
Van dear waals, these are very weak electrostatic Strength
• melting points as it’s attraction
attractions between all atoms and molecules caused
• is between the molecules in the bond,
by the uneven distribution of electron density.This
• needs less energy to overcome.
creates a temporary dipole causing the attraction.
• Poor conductors, they’re neutrally charged
When there are more van der waals they become
stronger and so lead to larger melting points. Eg.
Co-ordinate bonding: when a single atom gives both the
Giant structures / hydrocarbon chains
electrons to create the same bond, represented as an
arrow following direction of donation. An atom must
Dipole-Dipole, requires a polar bond that hasn’t been
have a lone pair of electrons in it’s outer shell.
cancelled out, molecules that have dipoles will attract
each other through a strong electrostatic attraction.
3.3 Metallic Bonding:
Hydrogen, occurs when you have a very
occurs between metals only, the outer shell of the metal electronegative atom eg. F, O, N and the atom has a
atoms merge to produce a sea of delocalised electrons lone pair of electrons. This means the elctron density
containing the lattice of positively charged metal ions. is pulled towards F/O/N and leaves H electron
The number of delocalised electrons depend on the deficient.This allows the lone pair of another molecule
number of electrons in the atom’s outer shell, this to attract the H creating a strong electrostatic
creates a giant structure. attraction.
PROPERTIES-
When water is a liquid H bonds break and reform when the
• conduct heat, as heat energy is transferred it
water molecules move. As ice, the water molecules cannot
increases kinetic energy of electrons/ions to vibrate
move so the H bonds hold a fixed position. This makes the
more.
molecules less closely packed than the water molecules and
so ice is less dense than water.
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