1.2 Structure and bonding Flashcards
Covalent bond
In a covalent bond, atoms share pairs of electrons. The covalent bond is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons.
Polar covalent bonds
Polar covalent bonds are formed when the attraction of the atoms for the pair of bonding electrons is different. Delta positive and delta negative notation can be used to indicate the partial charges on atoms, which give rise to a dipole
Ionic formulae
Written giving the simplest ratio of each type of ion in the substance
Ionic bonds
The electrostatic attraction between positive and negative ions. Ionic compounds form lattice structures of oppositely charged ions
Ionic character
The difference in electronegativities between bonded atoms gives an indication of the ionic character. The larger the difference, the more polar the bond will be. If the difference 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
Van der Waals forces
London dispersion forces, permanent dipole-permanent dipole interactions that include hydrogen bonding.
London dispersion forces
Forces of attractions that can operate between all atoms and molecules. These forces are much weaker than all other types of bonding. They are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules
Permanent dipole interactions
Additional electrostatic forces of attraction between polar molecules.
Stronger than LDFs for molecules with similar numbers of electrons
Hydrogen bonds
Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar. Hydrogen bonds are electrostatic forces of attraction between molecules that contain these highly polar bonds. A hydrogen bond is stronger than other forms of permanent dipole-permanent dipole interaction but weaker than a covalent bond
Hydrogen bonding between molecules in ice
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.
Ionic and polar molecular compounds solubility
Ionic compounds and polar molecular compounds tend to be soluble in polar solvents such as water, and insoluble in non-polar solvents.
Non-polar molecular substances solubility
Non-polar molecular substances tend to be soluble in non-polar solvents and insoluble in polar solvents.
Features to be considered when predicting solubility
- 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
