Bonding and structure- bonding
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What is meant by the term ionic bond?
The electrostatic attraction between positively and negatively charged ions
What is meant by the term covalent bond?
The electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What is a molecule?
A small group of atoms bonded together by covalent bonds
What are lone pairs?
A pair of electrons in the outer shell NOT used in conding
What is a dative covalent bond?
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
Why do metals have high melting and boiling points?
• Strong electrostatic attraction between metal cations and delocalised electrons • Requires a lot of energy to break
Why are metals good electrical conductors when solid?
-Delocalised electrons can move and carry charge
Why are metals good electrical conductors when molten?
-Delocalised electrons and metal cations can move and carry charge
Why are metals insoluble in water?
• strong electrostatic attraction between metal cations and delocalised electrons which require a lot of energy to break • This energy is not avaliable
Why do the melting points of metals increase in order from sodium, magnesium, aluminium?
• the charge on the metal ion increases from 1+, to 2 +, to 3+ -the no. delocalised electrons per ion increases -this results in a stronger electrostatic attraction between metal ions and delocalised electrons -more energy is necessary to break them
Out of sodium, magnesium, and aluminium which would you expect to be the best conductor of electricity and why?
Aluminium • greatest no. delocalised electrons per metal ion • greatest capacity for carrying charge
How does the model of metallic bonding explain why metals are ductile and malleable?
-layers of ions can slide over each other easily
What metals are present in the following alloys? i) Brass ii) Stainless steel
i) Zinc and Copper ii) Iron and Chromium
How does an alloy make a metal harder?
• Each metal ion is a slightly different size - So layers of ions do not slide over each other so easily
What does ductile mean?
Able to be drawn into a wire
Define ion
A positively or negatively charged atom or (covalently bonded) group of atoms where the number of protons differs from the number of electrons
Define giant ionic lattice
A 3D structure of charged ions bonded together by strong ionic bonds
Define simple molecular lattice
A 3D structure of molecules bonded together by weak intermolecular forces
Define giant covalent lattice
A 3D structure of atoms bonded together by strong covalent bonds
Define giant metallic lattice
A 3D structure of positive ions and delocalised electrons held together by strong metallic bonds
Why do ionic substances have high melting and boiling points?
• strong electrostatic attractions between anions and cations • require a lot of energy to overcome
Why are ionic substances non-conductors of electricity when solid?
• the ions are fixed in the lattice - so cannot move and carry charge
Why are ionic substances good electrical conductors when in solution or molten?
• the ions are no longer fixed in the lattice - and so are free to move and carry charge
Why do ionic substances generally have good solubility in water?
• oxygen atoms in water are attracted to and surround the positive ions • hydrogen atoms in water are attracted to and surround the negative ions • this results in the breaking down of the ionic lattice and the compound dissolving