Bonding & Structure Flashcards
What does it mean if there is a large difference in electronegativity between 2 elements
- the movement of bonding e- from the element of lower electronegativity to the element of higher electronegativity is complete
- results in formation of ions
ionic compounds form between
Metals and non-metals
What are ionic bonds
The electrostatic attraction between positive and negative ions
What do ionic compounds form
Lattice structures of oppositely charged ions
What are covalent bonds
A shared pair of electrons between atoms
What is the covalent bond a result of
2 positive nuclei being held together by their common attraction for the shared pair of electrons
What do pure covalent bonds form between
Atoms of identical electronegativity
When do polar covalent bonds form
When the atoms attraction for the pair of bonding e- are different
What does δ- indicate
The partial negative charge of an atom which causes a dipole
What does δ+ indicate
The partial positive charge of an atom which causes a dipole
What does the difference in electronegativities between bonded atoms show
Gives an indication of the ionic character
The larger the difference in electronegativities…
- the more polar the bond will be
- greater ionic character
What can we use to deduce the type of bonding and structure in the compound
Physical properties e.g. state at room temp, MP/BP, solubility and electrical conductivity.
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 (includes hydrogen bonding)
What are london dispersion forces
Forces of attraction that can operate between ALL atoms and molecules
What is the strength of london dispersion forces
Weaker than all other types of bonding
Why do london dispersion forces form
As a result of electrostatic attraction between temporary and induced dipoles
What is the strength of london dispersion forces related to
The number of electrons within an atom or molecule
What is a polar molecule
It has a permanent dipole
What else can make a molecule polar
The spatial arrangement of polar covalent bonds (3D symmetry)
What are permanent dipole - permanent dipole interactions
Additional electrostatic forces of attraction between polar molecules
What is the strength of permanent dipole - permanent dipole interactions compared to LDFS
Permanent dipole-permanent pole interactions are stronger than London dispersion forces
What is a hydrogen bond
Electrostatic forces of attraction between molecules that contain these highly polar bonds
What do highly polar bonds consist of
A hydrogen atom bonded to an atom of a strongly electronegative element (such as fluorine, oxygen or nitrogen)
Strength of hydrogen bonds
- Stronger than permanent dipole - permanent dipole interactions
- weaker than a covalent bond
How do we make predictions about the strength of the intermolecular forces
By considering the polarity and number of electrons present in molecules
The MP & BPs of polar substances are …
Higher than the MP & BPs of non-polar substances
What properties of substances are affected by hydrogen bonding
- boiling point
- melting point
- viscosity
- solubility in water
What are the irregular boiling points of ammonia, water and hydrogen fluoride a result of
Hydrogen bonding
What causes the density of ice to be less than water at low temperatures
Hydrogen bonding between molecules in ice results in an expanded structure
What are ionic compounds and polar molecules soluble in
Polar solvents e.g. water (like dissolves like)
What are ionic compounds and polar molecules insoluble in
Non-polar solvents
What are non-polar molecular substances soluble in
Non-polar solvents (like dissolves like)
What are non-polar molecular substances insoluble in
Polar solvents
What are the key features to consider when predicting the solubility of a compound
- presence of hydrogen bonding in molecules (O-H or N-H)
- spatial arrangement of polar covalent bonds
