1.2 structure and bonding Flashcards
What is a covalent bond?
- atoms share pairs of electrons
- the bond is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons
What are polar covalent bonds?
-when the attraction of the atoms for the pair of bonding electrons is different giving rise to a dipole
What symbols can be used to represent the partial charges on atoms in a polar covalent bond?
- delta positive δ+
- delta negative δ-
What is an ionic bond?
the electrostatic attraction between positive and negative ions.
What is the structure of ionic substances?
lattice structures of oppositely charges ions
Explain the bonding continuum
- ionic bonding on one end
- pure covalent bonding is at the other end
- polar covalent bonding lies between these two extremes
What gives an indication of ionic character? and explain this.
the difference in electronegativities between bonded atoms
- 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
Explain how ionic bonds are formed
- The larger the electronegativity 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.
What physical properties should be used to deduce the type of bonding and structure in the compound
- state at room temperature
- melting point
- boiling point
- solubility
- electrical conductivity
What are London dispersion forces?
they are 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 London dispersion forces related to?
the number of electrons within an atom or molecule
What makes a molecule polar?
if it has a permanent dipole
-the spacial arrangement of polar covalent bonds can result in a molecule being polar
What are permanent dipole-dipole interactions?
- additional electrostatic forces of attraction between polar molecules.
- they are stronger than London dispersion forces for molecules with similar numbers of electrons
What are hydrogen bonds?
electrostatic forces of attraction between molecules that contain highly polar bonds between hydrogen and F, O,or N.
How is a hydrogen bond formed?
a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen. The bond created is highly polar
Order the Van Der waal forces from strongest to weakest
- hydrogen bonding
- permanent dipole-dipole
- London dispersion forces
What properties can be rationalised in terms of nature and strength of intermolecular forces?
- melting point
- boiling point
- viscosity
How can you make predictions on the strength of intermolecular forces?
by considering the polarity and the number of electrons present in molecules
compare the melting and boiling points of polar and non polar substances with a similar number of electrons
-polar are higher than non-polar
What properties are affected by hydrogen bonding?
- boiling points
- melting points
- viscosity
- solubility/miscibility in water
name 3 compounds that their abnormal boiling point is as a result of hydrogen bonding
- ammonia
- water
- hydrogen bonding
Explain the structure of ice
- hydrogen bonding between molecules
- results in an expanded structure
- the density of ice is therefore less than the density if water
Explain the like dissolves like rule
- ionic compounds and polar molecular compounds are soluble in polar substances
- non-polar molecular substances are soluble in non-polar solvents
- insoluble in the converse
what are two key features that can be used to predict the solubility of a compound?
- hydrogen bonding
- spacial arrangement of polar covalent bonds-result in permanent dipole
