1.2 Structure And Bonding Flashcards
What do atoms do in a covalent bond?
Share pairs of electrons
What is the covalent bond a result of?
2 positive nuclei being held together by their common attraction for the shared pair of electrons.
When are polar covalent bonds formed?
When the attraction of the atoms for the pair of bonding electrons is different
What can be used to indicate the partial charges on atoms?
Delta positive (δ+) and delta negative (δ-) notation - this gives a rise to a dipole
What is an ionic bond?
The electrostatic force of attraction between positive and negative ions.
How is an ionic compound structured?
They form lattice structures of oppositely charged ions
What is the positioning of pure covalent bonding, ionic bonding and polar covalent bonding on a bonding continuum?
Pure covalent bonding and ionic bonding can be considered as opposite ends of a bonding continuum, with polar covalent bonding lying between these two extremes.
What gives an indication of the ionic character?
The difference in electronegativity between bonded atoms.
The larger the difference in electronegativities…
The more polar the bond will be.
If the difference in electronegativities is large, what happens to the movement of bonding electrons?
The movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete, resulting in the formation of ions.
When are compounds often ionic?
When the bond is formed between metals and non-metals.
What are van der waals forces?
Intermolecular forces acting between molecules
What are the different types of van der waals forces?
London dispersion forces
Permanent dipole - permanent dipole interactions
hydrogen bonding
What are London dispersion forces?
-Forces of attraction that can operate between all atoms and molecules.
-These forces are much weaker than all other types of bonding.
How are LDFs formed?
As a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.
What is the strength of LDFs related to?
The number of electrons within an atom or molecule
When is a molecule described as polar
If it has a permanent dipole
What are pd-pd interactions?
Additional electrostatic forces of attraction between polar molecules.
Which is stronger? - pd-dp interactions or LDFs
pd-pd interactions are stronger than LDFs for molecules with similar numbers of electrons.
What bonds are highly polar?
Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen.
What are hydrogen bonds?
Electrostatic forces of attraction between molecules that contain these highly polar bonds.
What is the solubility of non-polar molecular substances?
Tend to be soluble in non-polar solvents and insoluble in polar solvents.
How strong are hydrogen bonds?
A hydrogen bond is stronger than other forms of pd-pd interactions but weaker than a covalent bond.
What features must be considered to predict the solubility of a compound?
-Presence in molecules of O-H or N-H bonds, which implies hydrogen bonding.
-Spatial arrangements of polar covalent bonds, which could result in a molecule possessing a permanent dipole.
The anomalous boiling points of what are a result of hydrogen bonding?
Ammonia, water and hydrogen fluoride.
What is the solubility of ionic compounds and polar molecular compounds?
They tend to be soluble in polar solvents like water, and insoluble in non-polar solvents.
Boiling points, melting points, viscosity and solubility/miscibility in water are properties of…
substances that are affected by hydrogen bonding
What are the melting point and boiling points of polar vs non-polar substances?
The mp and bp of polar substances are higher than the mp and bp of non-polar substances with similar numbers of electrons.
What can melting points, boiling points, and viscosity be rationalised in terms of?
The nature and strength of the intermolecular forces that exist between molecules
