PT Trends
Tells you the number of valence electrons
Groups
List the three different intermolecular forces.
Dispersion, dipole-dipole, hydrogen bonding
List the three intramolecular bonds.
Covalent, ionic and metallic.
VSEPR stands for ________.
Valence Shell Electron Pair Repulsion
Salt and hydrogen gas are the products.
Metals + acid
Increases as you go up a group and right across a period. Top right hand corner is the most ________.
Electronegativity (and ionisation energy)
Explain the differences between the three intermolecular forces.
Dispersion forces: exists everywhere
Dipole-dipole: is polar
Hydrogen bonds: is polar and is the strongest. Occurs between H-FON
Malleability and ductility
Metallic Bonding: Delocalised sea of electrons allow for charged particles (electrons) to move freely along oppositely charged ions without breaking/shattering.
Symmetrical and asymmetrical
Determines polarity.
Symmetrical = non-polar (even distribution of charges)
Asymmetrical = polar (uneven distribution of charges)
Metal hydroxides and hydrogen gas are produced. Metal hydroxides provide a pink colour when phenolphthalein is added to the solvent.
Metals + water
Increases down a group and to the left across a period. Bottom left hand corner has the strongest ________.
Metallic character/reactivity
Propan-1-ol has a higher boiling and melting point than propane.
They both have 3 carbons. Propan-1-ol has a -OH group present. The -OH is a polar covalent bond and hydrogen bonds are present.
Propane is a non-polar covalent bond and only dispersion forces are present.
Delocalised sea of electrons or charged particles can flow from a positive end to a negative end to produce current.
Electrical conductivity.
Covalent (none)
Ionic (molten/liquid state)
Metallic (always)
Why does methane (CH4) have a lower melting and boiling point compared to ethane (C2H6)?
Only dispersion forces present in both. Ethane is a larger molecule, therefore more energy will be required to break ethane apart. Hence, methane has a lower melting and boiling point compared to ethane.
Shape and polarity of ethanol (C2H5OH)
Tetrahedral (4 bonded pairs around our C)
Stays the same as you go down a group. Increases as you move across a period towards the right.
Core charge
Same molecule of similar mass and size. Molecule 1 is made up of -OH, and Molecule 2 contains a C=O group attached. Explain which molecule will have a higher boiling point.
Molecule 1: Hydrogen bonds (H-FON). Strongest intermolecular force.
Molecule 2: Dipole-dipole forces. Stronger than dispersion forces, but weaker than hydrogen bonds.
Molecule 1 has a stronger intermolecular force and will require more energy to break these bonds. Therefore, Molecule 1 will have a higher boiling point.
Ionic compounds.
Hard: strong electrostatic forces between oppositely charged ions. Strong force is required to disrupt the lattice.
Brittle: like-charged ions (eg. + and +) repel against each other.
Linear, bent, tetrahedral, trigonal planar, trigonal pyramidal
VSEPR theory - uses lone pairs (or unbonded pairs) of electrons to determine the shape of molecules.
Two reactants are mixed together to form two new products (ie. The cations have swapped anions to form new products).
Double displacement reactions
Elements such as chromium and copper have special electron configuration - they like to have half-filled subshells. Explain this property with reference to a PT trend.
Half-filled = stable.
Stable = high ionisation energies.
Noble gases are very stable (octet rule) so they have very high ionisation energies compared to the elements before them.
Butan-1-ol (4 carbons) has a -OH group and its melting point is -89.8 °C. Decane (10 carbons) only has C's and H's but its melting point is 174.1°C. Why?
Larger molecule = more dispersion forces. Even though butan-1-ol has a -OH group with hydrogen bonds present, decane is a much larger molecule and has a stronger force overall. Hence, decane (despite only have dispersion forces), will have a higher melting point than butan-1-ol.
Does not conduct electricity. Is often not soluble in water and has low melting and boiling points. Describe the bond and why this bond exists.
Covalent bonding. Neither atoms are stable by themselves so they compensate with each other by obeying the octet rule. Covalent bonds are formed via sharing electrons.
A customer hypothesises that by heating up food containing salt at a moderate temperature, the salt will degrade and thus not have the same health consequences. Comment on the customer’s hypothesis, referring to the properties of ionic compounds.
The customer’s hypothesis is likely incorrect.
This is because ionic compounds are usually highly heat resistant and have a high melting point because of the strength of the ionic bonds.
Therefore, exposing food to moderate heat would be insufficient to degrade the molecule, and it would therefore still have the same health effects.
List the properties of use from these ionic compounds.
a) Lining surface of engines: Magnesium oxide (MgO)
b) Human bones and teeth: Calcium phosphate (Ca3(PO4)2)
c) Electrolyte enabling current flow in cell batteries: Ammonium chloride (NH4Cl)
a) High melting point
b) Hardness
c) Electrical conductivity