Metallic bonding
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Define metallic bonding.
Metallic bonding is the electrostatic attraction between positive metal ions and delocalised electrons. These delocalised electrons are free to move throughout the metallic lattice, contributing to the metal's conductivity.
Describe the structure of a typical metallic lattice.
A metallic lattice consists of a regular arrangement of positive metal ions surrounded by a 'sea' of delocalised electrons. These electrons are not associated with any single atom.
How does the charge and radius of a metal ion affect the strength of metallic bonding?
Higher charge density (higher charge and/or smaller ionic radius) leads to stronger electrostatic attraction between the metal ions and delocalised electrons, thus stronger metallic bonding.
Define covalent bonding.
Covalent bonding is the electrostatic attraction between the nuclei of two atoms and a shared pair of electrons. These shared electrons are attracted to both positive nuclei, holding the atoms together.
Draw a dot-and-cross diagram to show the covalent bonding in a molecule of oxygen, O2.
O2 contains a double covalent bond with each oxygen atom sharing two electrons, so that each oxygen atom achieves a stable octet of electrons in its outer shell.
Explain how elements in Period 3 can expand their octet.
Period 3 elements, such as sulfur and phosphorus, can expand their octet because they have available d-orbitals that can accommodate additional electrons, allowing them to form more than four covalent bonds. Examples include SF6 and PCl5.
Define coordinate (dative covalent) bonding.
Coordinate bonding occurs when one atom provides both electrons for the shared pair in the covalent bond. The resulting bond is essentially the same as a normal covalent bond, but its formation differs.
Describe the formation of the ammonium ion (NH4+) using a coordinate bond.
Ammonia (NH3) donates its lone pair of electrons to a proton (H+) to form NH4+. The bond between the nitrogen and the newly attached hydrogen is a coordinate bond, as both electrons originate from the nitrogen atom.
Describe the bonding in aluminium chloride dimer (Al2Cl6).
Aluminium chloride exists as a dimer (Al2Cl6) where each aluminium atom forms coordinate bonds with chlorine atoms on the other AlCl3 unit to achieve a more stable electron configuration. Thus each Aluminum has 4 bonds.
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