Structure and bonding

What is a covalent bond?

A bond formed when two positive nuclei are being held together by their electrostatic 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 these be used to indicate?(δ+, δ-)

The partial charges on atoms which give rise to a dipole

What does δ+ mean?

Slightly positive

What does δ- mean?

Slightly negative

What are Ionic bonds?

The electrostatic attraction between positive and negative ions

What do ionic compounds form?

Lattice structures of oppositely charged ions

What is the order of bonding in the bonding continuum from left to right and the electronegativitys?

The difference in electronegativities between bonded atoms gives?

an Indication of the ionic character

The larger the difference in electronegativity, The more ……?

Polar the bond will be

What will happen if the difference in electronegativity is large?

Then 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

Are compounds formed between metals and non metals always ionic?

Not always but often

Physical properties of a compound, such as ————, should be used to ….. in the compound?

• State at room temperature, melting point, boiling point, solubility and electrical conductivity

• Deduce the type of bonding and structure

Which type of elements and compounds condense and freeze at sufficiently low temperatures?

All molecular elements and compounds and monatomic elements

For all molecular elements and compounds and monatomic elements to be able to condense and freeze at sufficiently low temperatures, What must exist?

Attractive forces between the molecules or discrete atoms

Intermolecular forces acting between molecules are known as?

van der Waals forces

What are types of van der Waals forces?

Intermolecular forces, London dispersion forces and permanent dipole-permanent dipole interactions that include hydrogen bonding

What is the weakest van der Waals force?

London dispersion forces

What are London dispersion forces?

Forces of attraction that can operate between all atoms and molecules.

When are London dispersion forces formed?

They are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.

The strength of London dispersion forces is related to…..?

The number of electrons within an atom or molecule

An increased number of electrons leads to bigger temporary dipoles which causes …?

Larger London dispersion forces

A molecule is described as polar if it has a ..?

Permanent dipole

The spatial arrangement of polar covalent bonds can result in?

A molecule being polar

What are permanent dipole-permanent dipole interactions?

Additional electrostatic forces of attraction between polar molecules

Pd-pd interactions are stronger than LDFs for …..?

Molecules with similar numbers of electrons

Bonds consisting of a hydrogen atom bonded to an atom of _____ ___________ ________ such as …….? Are highly polar

• strongly electronegative element

• Fluorine, oxygen or nitrogen

What are hydrogen bonds?

Electrostatic forces of attraction between molecules that contain highly polar bonds

A hydrogen bond is stronger than other forms of _________ but weaker than a __________

• permanent dipole-permanent dipole interactions

• Covalent bond

The melting and boiling point of a substance depends on the …..?

strength of the intermolecular forces between its molecules

The mpt and bpts of polar substances are ______ than the mpt and bpts of non polar substances with similar numbers of electrons

Higher

Substances will tend to be most soluble in solvents with the …?

Same type of intermolecular forces as themselves

What statement can be said about solubility in terms of intermolecular forces to help you remember?

Like dissolves Like

Non polar substances tend to be soluble in?

non polar solvents

Polar substances and Ionic compounds tend to be soluble in

Polar solvents

Highly polar molecules can be strongly attracted to _______ or _______ __________ _____

• Positively

• Negatively

• Charged ions

To predict the solubility of a compound, key features to be considered are the:

• presence in molecules of O-H or N-H bonds, which implies hydrogen bonding

• spatial arrangement of polar covalent bonds, which could result in a molecule possessing a permanent dipole

What is viscosity ?

A measure of how thick a liquid is or how slow it is to move

Thick liquids have ___?

High viscosities

Runny liquids have …?

Lower viscosities

The stronger the intermolecular forces in a liquid are the ………?

Greater the viscosity

Substances with hydrogen bonding will tend to be _____ viscous than substances without hydrogen bonding

More

The inconsistency of the bpts of ammonia, water and hydrogen fluoride are a result of

Hydrogen bonding

Hydrogen bonding between molecules in ice results in?

an expanded structure that causes the density of ice to be less than that of water at low temperatures.