Bonding

• Charged particles called ions are created when electrons are transferred in ionic bonding.
• Covalent bonds form between two non-metals by sharing electrons in order to achieve a full outer shell.
• Multiple electron pairs can be shared to produce multiple covalent bonds.
• Dot and cross diagrams can be used to represent shared electron pairs in covalent bonds.
• Dative or coordinate bonds form when both electrons in the shared pair are supplied from a single atom, indicated by an arrow.
• Ammonia (NH3) can form a dative bond with a H+ ion to produce an ammonium ion (NH4+).
• Dative bonds are treated as standard covalent bonds and react in the same way.
• Metallic bonding involves a lattice of positively charged ions surrounded by a 'sea' of delocalised electrons.
• Metallic bonding results in a strong electrostatic force of attraction.
• The greater the charge on the positive ion, the stronger the attractive force as more electrons are released into the 'sea'.
• Ions that are larger in size produce a weaker attraction due to their greater atomic radius.
• Physical properties of a substance include the boiling point, melting point, solubility, and conductivity.
• The type of bonding and the crystal structure of the compound determine the physical properties.
• Substances with an ionic crystal structure have a high melting and boiling point due to the strong electrostatic forces holding the ionic lattice together.
• Ionic substances can conduct electricity when molten or in solution.
• Ionic substances conduct electricity when the ions separate and are free to move, carrying an electrical current.
• Ionic substances are often brittle and can break apart when the layers of alternating charges are distorted.
• Metallic substances conduct electricity due to the movement of delocalized electrons.
• Metallic substances are malleable as the layers of positive ions can slide over one another.
• Metallic substances have high melting points and are usually solid at room temperature, with mercury being the only exception.
• Simple molecular substances consist of covalently bonded molecules held together with weak van der Waals forces.
• Simple molecular substances have low melting and boiling points.
• Water has a simple molecular structure but has a high boiling point due to the presence of hydrogen bonding.
• Simple molecular substances are poor conductors.
• Macromolecular substances have a covalently bonded giant lattice structure with multiple strong covalent bonds.
• Macromolecular substances have a very high melting point.
• Macromolecular substances are rigid.
• Diamond is a macromolecular structure made up of carbon atoms, each bonded to four further carbon atoms, making it one of the hardest and strongest materials known.
• Graphite is another macromolecular structure made up of carbon atoms, where each carbon atom is bonded to three others in flat sheets, allowing for the release of free electrons and conductivity.
• The shape of a molecule is determined by the number of electron pairs around the central atom, with lone pairs providing additional repulsive forces that can change the bond angle.
• For every lone pair present, the bond angle between covalent bonds is reduced by 2.5 degrees.
• The number of electron pairs determines the shape of a molecule.
• Bonding pairs indicate the basic shape, while lone pairs indicate additional repulsion.
• Common molecule shapes include linear, V-shaped, trigonal planar, triangular pyramid, tetrahedral, trigonal bipyramid, and octahedral.
• Bond polarity refers to the uneven distribution of negative charge around a covalent bond.
• Electronegativity is the power of an atom to attract negative charge towards itself within a covalent bond.
• Electronegativity increases along a period as atomic radius decreases and decreases down a group as shielding increases.
• Permanent Dipole: If two atoms with different electronegativities are bonded, a polar bond forms where the more electronegative atom draws more negative charge towards itself, creating a ∂- region and a ∂+ region.
• Example of a polar molecule with a permanent dipole: Hydrogen fluoride.
• Polar molecules with a permanent dipole can align to form a lattice of molecules similar to an ionic lattice.