Topic 2 - STRUCTURE AND BONDING
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What are the 3 types of chemical bond?
• Ionic • Covalent • Metallic
What are the 4 types of structure?
• Simple molecular • Giant covalent lattice • Giant ionic lattice • Giant metallic lattice
What is the definition of a metal?
Something that forms positive ions
What is the definition of ionic bonding?
The electrostatic attraction between oppositely charged ions in all directions (metal/non metal)
What affects the strength of the electrostatic forces in ionic compounds?
The electrostatic forces will be stronger when: - The ion is smaller - The magnitude of charge is greater
Why does NaF have a high melting point?
• Giant ionic lattice structure • Many strong electrostatic forces in all directions] • Which require lots of energy to break
Would you expect CaF2 or NaF to have a higher melting point? Why?
• Ca 2+ has a higher magnitude of charge but a bigger ionic radius • Na + has a smaller charge and a smaller ionic radius • Hence CaF2 has a higher melting point
Why can’t solid ionic substances conduct electricity?
The ions are in fixed positions, hence cannot move
In what form can ionic substances conduct electricity?
Molten/aqueous ionic substances - Ions are free to move
What is the definition of metallic bonding?
The electrostatic attraction between positively charged metal ions and delocalised electrons
Why do metallic substances have high melting points?
A large amount of energy is required to separate the particles
Why are metallic substances insoluble in water?
There are no interactions with the water molecules
What is the definition of covalent bonding?
The electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What are lone pairs?
Electron pairs that aren’t shared - ie. electrons that are not involved in a bond
What is the octet rule, and why is it sometimes broken?
• 8 outer electrons is the most stable configuration • However, sometimes the atom has less than 4 electrons to share • Eg BF3 (Boron only has 3 electrons to share)
How many electrons do sulphur, chlorine and phosphorous all have the ability to accommodate in their valence shell?
18
What is the definition of double covalent bonds?
The electrostatic attraction between 2 shared pairs of electrons and the nuclei of the bonded atoms
What is the definition of triple covalent bonds?
The electrostatic attraction between 3 pairs of electrons and the nuclei of the the bonded atoms
What is the definition of dative bonding?
A dative bond is a covalent bond where only one of the bonded atoms donates both electrons being shared
Give an example of dative bonding
Boron trifluoride
Why is X-ray diffraction useful?
It allows bond lengths and spacing between ions or structures of crystals to be investigated
How is covalent bond strength determined by average bond enthalpy?
• Single bonds are longer than double bonds, which are longer than triple bonds • Large atoms form longer bonds as bonding pair of electrons is more shielded from the nucleus • Shorter the bond, the stronger the bond enthalpy
What substances have monoatomic structures?
• Group 8 elements • Made of atoms
What substances have simple molecular structures?
• Most non-metal elements (except group 8) • Most non-metal compounds (- Molecules)