EL - Bonding and structure *01 *02 Flashcards
what is ionic bonding?
when ions are stuck together by electrostatic attractions
ions are formed when electrons are transferred from one atom to another
overall charge zero
what are electrostatic attractions?
the forces that hold positive and negative ions together
- very strong
what is a giant ionic lattice
ionic crystals are giant lattices of ions
giant because made of the same unit over and over again
within the lattice, the ions with different charges attract each other and the ions with the same charge repel each other. the ions arrange themselves to maximise attractions and minimise repulsions
examples of a giant ionic lattice?
Sodium chloride
Na+ Cl-
Behaviour of ionic compounds
- conduct electricity when molten or dissolves - the ions are free to move so charge can move
- high melting points - giant ionuc lattices held together by strong electrostatic forces, it takes lots of energy to overcome these forces so melting point very high.
- often soluble in water - water molecules are polar, the water molecules pull the ions away from the lattice and cause it to dissolve
what is covalent bonding?
when atoms share electrons so they both have a full outer shell of electrons
both the +ve nuclei are attracted electrostatically to the shared electrons
what are simple covalent molecules?
substances made up of small molecules
properties of simple covalent molecules?
- fairly low melting point (no giant structure that needs to be broken down)
- don’t need to overcome covalent bonds that hold atoms together only the electrostatic forces between the molecules (these are weak) - don’t conduct electricity - no charge carriers
- usually insoluble in water (very slightly) - polar water molecules more attracted to each other than the molecular substance
what is dative covalent bonding?
when one atom donates both electrons to a bond
covalent bonding: exceptions to full outer rule
BF3 (B 6 electrons in outer shell, F 8 electrons in outer shell)
SF6 (S 12 electrons in outer shell, F 8 electrons)
what are giant covalent structures?
these structures have a huge network of covalently bonded atoms
the electrostatic forces holding the atoms together in these structures are much stronger than simple covalent molecules
examples of giant covalent structures
carbon and sillicon
giant covalent structures: carbon and silicon
each atom is bonded to its 4 neighbours in a tetrahedral arrangement
giant covalent structures: silicon dioxide (SiO2)
each atom bonded to 4 neighbouring atoms with oxygen atoms between each silicon atom
properties of giant covalent structures
- very high melting points - need to break lots of very strong bonds before the substance melts which takes a lot of energy
- extremely hard - very strong bonds all through lattice arrangement
- good thermal conductors - vibrations travel easily through lattice arrangement
- won’t dissolve - covalent bonds mean atoms are more attracted to their neighbours in the lattice than to solvent molecules (all insoluble in polar solvents shows they don’t contain ions)
- cant conduct electricity - no charged ions or free (graphite can)