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Electrons and bonding (Covalent bonding (• Covalent bonding is the…
Electrons and bonding
Electron structure
Electrons and shells
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• An atomic orbital is a region around the nucleus which can hold up to two electrons with opposite spin (high probability of finding an electron in that region)
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Filling of orbitals
• As the 3d subshell is higher energy than the 4s subshell, the 4s subshell fills before the 3d subshell
• Electrons are –ve charged, and the opposite spins of electrons in orbitals helps to counteract the repulsion due to their charges (spin shown with opposite arrows)
• Within a subshell, orbitals have same energy
• One electron occupies each orbital before pairing starts – this prevents any repulsion between paired electrons until no further orbital available at the same energy level
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• Short hand notation uses the previous noble gas in square brackets eg. [He], then the remaining subshells
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Ionic bonding
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• The ionic lattice must be broken down, then the water molecules must attract and surround the ions
• Solubility of an ionic compound therefore depends on the relative strengths of the attractions within the giant ionic lattice and the attractions between the ions and water molecules
Covalent bonding
• Covalent bonding is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
• Covalent bond attraction is localised – acting solely between the shared pair of electrons and the nuclei of the 2 bonded atoms
• A covalent bond is the overlap of atomic orbitals each containing one electron to give a shared pair of electrons
• Boron has 3 outer electrons, and can form 3 covalent bonds which then gives it 6 electrons, which is considered a full shell
• A dative covalent bond or coordinate bond is a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only
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• Average bond enthalpy serves as a measure of the covalent bond strength – the larger the value the stronger the bond