Module 2 - Bonding and structure Flashcards
what is covalent bonding
A covalent bond involves the electrostatic attraction between nuclei of two atoms and the bonding electrons of their outer shells
what is dative covalent bonding
a covalent bond in which electrons shared in the bond orignate only from one atom involved in bond
properties of a covalent compound
low mp- weak intermolecular forces
cant conduct
can dissolve
what is a lone pair
electrons that arent shared in a covalent bond
bond pair meaning
electrons that are involved in a covalent bond
what is ionic bonding
elecctrostatic attraction between two oppositely charged ions
examples of ionic compounds
NaCl, MgO, AgCl
structure of an ionic compund
giant ionic lattice
properties of an ionic compound
high mp- lots of energy needed to break strong forces
high conductivity- free electrons can carry a charge when molten
soluble– water is a polar molecule
3 types of intermolecular forces
induced dipole dipole
permanent dipole dipole
hydrogen bonding
what are intermolecular forces
forces between molecules
explain induced dipole dipole forces
a temporary dipole arises due to instantaneous movements of electrons
the temporary dipole can induce a dipole in neighbouring molecules
the delta positive on one molecule are attracted to the delta negative on the neighbouring molecule and vice versa
what are permanent dipole dipole
exists in all polar molecules
forces are between 2 molecules that have a dipole
what is hydrogen bonding
only exist between a hydrogen bonded to either a N,O or F.
hydrogen is so delta pos polarised that it bonds to the lone pairs of these elements
anomalous properties of water
high melting and boiling point - string intermolecular forces of hydrogen bonding
high surface tension
molecules are tightly packed
why is ice less dense than water
h2o molecules in ice are arranged in an orderly pattern: open lattice with h2 bonds
h20 molecules in water are more closer together: lattice is collapsed
does BP increase or decrease down the boble agas group
increases, due to increase of number of electrons
increases strength of induced dipole dipole forces
Define electronegativity. (1)
The ability of an atom to attract the pair of electrons in a covalent bond.
Explain why the C–Cl bond is polar. (2)
- Chlorine has a higher electronegativity
OR
Carbon has a lower electronegativity
OR
Carbon and chlorine have different electronegativities - So chlorine becomes δ- and carbon becomes δ+
Although the C–Cl bond is polar, CCl4 is a non-polar molecule.
Explain why. (2)
- CCl4 is symmetrical /is tetrahedral
- So the dipoles cancel out
There are van der Waals forces between non-polar molecules.
Explain what causes these forces. (3)
- (Random) movement of electrons, creates a temporary dipole
- Induces a dipole in another molecule
- Temporary attraction between δ+ and δ- in different molecules
SF6 and SF3+ have different shapes and different bond angles.
Deduce the shape of SF6 and the shape of SF3+
State the bond angle in SF6 and the bond angle in SF3+
6 marks
- SF6 is octahedral
- SF6 bond angle is 90°
- SF6 all the bond pairs repel equally
- SF3+ is pyramidal
(Allow tetrahedral) - SF3+ bond angle is 103-107°
- SF3+ lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion
Suggest, in terms of the intermolecular forces for each compound, why CBr4 has a higher boiling point than CHBr3
1.CBr4 has van der Waals’ forces between molecules
2. CHBr3 has van der Waals’ forces and dipole-dipole intermolecular forces
3. The van der Waals’ between CBr4 molecules are stronger than the dipole-dipole and van der Waals’ forces between CHBr3, more electrons
Sodium fluoride contains sodium ions (Na+) and fluoride ions (F–).
Na+ and F– have the same electron configuration.
Explain why a fluoride ion is larger than a sodium ion. (2)
- Fluoride ion has (two) fewer protons/lower nuclear charge
- Weaker attraction between nucleus and (outer) electrons
Explain, in terms of structure and bonding, why the melting point of sodium fluoride is high.
- (Electrostatic) forces of attraction between oppositely charged ions/Na+ and F–
- Lots of energy needed to overcome/break forces
The ion H2F+ is formed when hydrogen fluoride gains a proton as shown in the equation
HF + H+ → H2F+
Name the type of bond formed when HF reacts with H+
Explain how this bond is formed.
- Type of Bond: Coordinate bond / dative (covalent) bond
- Explanation: A (lone) pair of electrons is donated from F
Propan-1-ol has a higher boiling point than the other two compounds because of hydrogen bonding.
Describe the hydrogen bonding in propan-1-ol.
- attraction between O lone pair
- and δ+ H of OH on another molecule
