Bonding Key phrases Flashcards
(25 cards)
Key Phrases about Giant covalent lattices and the 4 common giant covalent lattices.
Diamond, Graphite, silicon and silicon dioxide are the 4 common giant covalent lattices.
Key phrases - Giant covalent lattice contain many strong covalent bonds which causes their properties. Covalent bonds have a shared pair of electrons.
graphite has delocalised electrons and van der Waals forces between layers
Coordinate/Dative bond
Special type of covalent bond where both electrons come from one atom called a coordinate bond or dative bond
Key phrases around giant ionic lattices and how to spot them.
How to spot them: They’re either containing ammonium (NH4+) or a metal and at least one non-metal.
Giant ionic lattices/(ionic bonds) have strong electrostatic attraction between oppositely charged ions. Larger ions and lower charges have weaker attraction.
Key phrases around giant metallic lattices and how to spot them
How to spot them - These compounds are just metals on their own.
The atoms lose their outer electrons causing the molecule to have delocalised electrons (forming metal cations)
Key phrase - Giant metallic lattices have strong electrostatic attraction between delocalised electrons and positively charged ions. Larger ions and lower charges have weaker attraction.
Giant ionic lattices - Properties
Properties
Ionic compounds conduct electricity when melted or in solution, have high melting points and are the second strongest structure and second strongest bond.
Giant Metallic lattice - Properties
Properties
Metallic compounds conduct electricity, have high melting points, are ductile, malleable and are the third strongest structure and third strongest bond.
Define electronegativity
Electronegativity is the ability of an atom to attract a bonding pair of electrons in a covalent bond.
What effects electronegativity? How to spot electronegative elements at a level?
Electronegativity is affected by having a smaller atomic radius and larger number of protons.
The most electronegative element is F. N, O and then Cl and the next most electronegative. This can be used to help compare electronegativity.
Simple molecular compounds -description
Simple molecular compounds are the most common crystal structure for covalent molecules. They have bonds holding atoms together to make molecules. The molecules are held together as solids and liquids by forces between the molecules.
Define polar bonds and what causes them/cancels them out
Polar bonds are bonds that have a permanent uneven distribution of electron density caused by a large difference in electronegativity. Symmetrical molecules the electronegative elements pull in equal and opposite directions so cancel.
Hydrogen bonding - What is it? Key phrases around it? Where is it between? How is it represented in diagrams?
Misnamed – this is not a bond but is the strongest intermolecular force
Key Phrases:
The electrostatic attraction in a hydrogen bond is between the lone pair on the N/O/F and the ∂+ hydrogen on a different molecule attached to a N/O/F. This attraction is between molecules
This is represented as a dotted line.
Permanent Dipole-Dipole forces key phrases and what cases them.
This kind of intermolecular force is caused by the large difference in electronegativity between two elements in a covalent bond. It is the second strongest intermolecular force.
This creates a polar bond where one of the elements is usually one of N/O/F/Cl. This, more electronegative, element is ∂-. The other element is less electronegative, such as C, H or other elements further to the left of the periodic table. This less electronegative element is ∂+.
The attraction is between molecules, this time between the ∂+ atom in one molecule and the ∂- in the other molecule. This is shown with a dotted line.
van der Waals’ forces key phrases/description
Key description
It is caused by a random movement of electrons causing a temporary dipole in that molecule (with a small d+ and d-). This partial charge then causes electron density to be attracted/repelled in other nearby molecules which induces a dipole in them.
Van Der Waals’ forces are the weakest intermolecular force, but the larger the surface area of the electron cloud (or the larger the molecule) the stronger this intermolecular force is as the size of the partial charge will increase. This can mean for large molecules van der waal’s forces are stronger between molecules than other intermolecular forces
Scaffold for doing melting point comparisons
When asked questions about melting points it’s essential to identify the crystal structure of the materials being compared. You need to discuss the forces/bonds that hold them together. The list below is in order of melting point from highest to lowest.
Diamond, graphite, silicon and silicon dioxide are giant covalent lattices (macromolecular). Bonds break to melt this.
metal and a non-metal is a giant ionic lattice, Forces of attraction are overcome.
Metals (usually alone) are giant metallic lattices. Forces of attraction are overcome.
2 or more non-metals bonded together tend to be simple molecular. Forces of attraction are overcome between molecules (chose most relevant of the three intermolecular forces)
Define Lattice enthalpy of formation
Enthalpy change when one mole of a solid ionic compound is formed from into its constituent ions in the gas phase
Define Lattice enthalpy of dissociation
Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase
Define Enthalpy of vaporisation
Enthalpy change when one mole of a liquid is turned into a gas
Define Enthalpy of fusion
Enthalpy change when one mole of a solid is turned into a liquid
Golden rules for making born haber cycles
Make only one change at a time,
Start by making compounds gasesous atoms if you can,
Remove electrons from positive ion one mole at a time until the desired charge is reached,
Add electrons one mole at a time until the desired charge is reached.
What’s the equation to calculate enthalpy of solution from a Hess cycle?
enthalpy of solution = lattice enthalpy of dissociation + enthalpy of hydration
Calculating values from calorimetry?
List the values in the question
Convert the units
Find q from q=mc∆T
Find ∆H using ∆H=q/1000/n
Put in the sign
Scaffold for calculating values from born haber cycles
Identify each enthalpy change in the Born-Haber cycle and label them with symbols
Put in the data for each enthalpy change you’ve identified and make sure you’ve put in multipliers where needed. (all enthalpy definitions use one mole, bond dissociation enthalpy = 2xatomisation enthalpy)
Change the sign on any arrows in the cycle not moving in the same direction
Construct an equation by adding up all the enthalpies and making it equal zero
Rearrange equation to find unknown
Put numbers into your equation to solve
What is the perfect ionic model?
The perfect ionic model suggests that all ions are perfectly spherical and the charge is found in the centre (point charges)
Larger anions bonded to small cations tend to have more covalent character as smaller cations distorts (polarises) the electron density of the larger anion
The bigger the difference between the lattice enthalpy and the theoretical value the more covalent character. More covalent character the stronger the ionic bond.
What does the size of the lattice enthalpy of formation/dissociation tell you about the compound?
The larger in magnitude the value then the stronger the ionic bond is.
