Bonding and Structure Flashcards
What is the definition of ionic bonding?
Electrostatic attraction between a positive ion and a negative ion.
What is the definition of a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
What is a “lone pair”?
A pair of electrons in the outer shell not being used in a bond
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.
What is the “average bond enthalpy”
The average enthalpy change which takes place when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species.
Why do metals have a giant structure?
It is a continuous structure in three dimensions
What is the definition of metallic bonding?
The electrostatic attraction between positive metal ions and delocalised electrons
Why do metals have the following properties?
- High melting and boiling points
- Good conductors of electricity when solid or molten
- Insoluble in water or non-polar solvents
- Strong electrostatic attraction between metal ions and delocalised electrons requires a lot of energy to break
- Solid - Delocalised electrons can move and carry charge
Molten - Delocalised electrons and positive ions can move and carry charge - Strong electrostatic attractions between positive ions and delocalised electrons require a lot of energy to break, which is not available.
What do malleable and ductile mean?
Malleable - Can be easily bent into different shapes
Ductile - Can be drawn in to a wire
Why do ionic substances have the following properties?
- High melting and boiling points
- Non-conductors of electricity when solid
- Good electrical conductivity when molten or dissolved in water
- Often good solubility in water
- Brittle
- Strong electrostatic attraction between ions requires a lot of energy to overcome
- The ions are fixed in a lattice and so cannot move to carry charge
- The ions are no longer fixed and so can move to carry charge
- The oxygen atom in the water molecules is attracted to and surrounds the positive ions in the lattice , and the hydrogen atoms to the negative ions. This breaks down the lattice and dissolves the compound.
- The slight movement of a layer of ions brings the positive ions next to other positive ions, and negatives next to negatives. This causes repulsion and the structure breaks apart.
What are the key features of a giant covalent compound?
High boiling point - Strong covalent bonds require lots of energy
Do not conduct electricity as usually no mobile e-
Insoluble in non-polar solvents as strong covalent bonds require lots of energy
What are the key features of a simple molecular covalent compound?
Low boiling point - Intermolecular forces are weak
Does not conduct electricity - No free mobile e- or charged particles
Soluble in non-polar solvents - Solvent molecules form similar intermolecular bond; weak intermolecular forces do not require much energy to overcome
What 3 things does the Valence Shell Electron Pair Repulsion (VSEPR) theory state?
- Electron pairs repel each other
- They will adopt positions where they are separated by the largest possible angle
- Lone pairs repel more strongly than bonded pairs so the repulsion between lone pair- lone pair > Lone pair-bonded pair > Bonded pair - Bonded pair
How do London forces arise?
Electrons in molecules are constantly moving. At any instant, the distribution may not be symmetrical. This results in an instantaneous temporary dipole. This dipole induces dipoles in neighbouring molecules and leads to an attraction between neighbouring charges in the dipoles. These attractions between molecules are known as London forces.
What affects the strength of london forces?
- The more electrons in a molecule, the stronger the induced dipole
- The greater the contact area, the stronger induced dipoles can develop. Unbranched molecules have stronger London forces than branched ones.
