Atomic structure
Calculate the relative molecular mass of propanol.
60.096 g/mol
Explain the difference between groups and periods.
A period is a horizontal row of elements in periodic table.
A group is a vertical column of elements with similar properties because they have the same electron configuration.
Give the definition of ionic bonding.
The strong electrostatic attraction between oppositely charged ions.
Draw the skeletal formula of the following compound: 3,3,4-trimethylheptane.
Correct drawing.
What is a molecular ion?
The positive ion formed, M+, when a molecule loses one electron during mass spectrometry.
Give the equation for the second ionisation energy of sodium. State symbols are not required.
Na+ (g) --> Na2+ (g) + e-
Name and identify the four different blocks of the periodic table.
Correct identification of s, p, d and f blocks.
Give the shape and bond angles present in the following molecule: PCl5
90*, 120*, 180*
Under the influence of UV light, how does the bond in a chlorine molecule break?
Homolytic bond breaking forming a free radical.
Name the four stages of mass spectrometry.
Ionisation, acceleration, deflection, detection.
Give the electron configuration for Zn2+.
1s2 2s2 2p6 3s2 3p6 3d10
or
[Ar] 3d10
How was the model of the atom adapted after the alpha particle scattering experiment?
The experiment showed that there must be a small positive nucleus in the centre of the atom, surrounded by empty space. Adapted Thomson's plum pudding model to Rutherford's nuclear model of the atom.
Give an example of a molecule that contains polar bonds but is not a polar molecule.
Any valid example.
What is the mechanism involved in the reaction between a halogen and an alkene? (two words)
electrophilic addition
What is the label on the horizontal axis in a mass spectrum?
mass-to-charge ratio (m/z)
How many orbitals and electrons are present in each subshell s, p, d and f?
s: 1 orbital - 2 electrons
p: 3 orbitals - 6 electrons
d: 5 orbitals - 10 electrons
f: 7 orbitals - 14 electrons
Explain the trend in melting temperature across a period referring to bonding and structure.
Melting temperature depends on structure and bonding. In metals, bonding is strong. The more electrons each atom contributes to delocalised electrons, the stronger the bonding.
Therefore, melting temperatures rise from Group 1 to Group 2 to Group 3. In Group 4, carbon and silicon have giant covalent structures with strong bonds. Melting temperature still high. After this, melting temperatures decrease as Group 5, 6, 7 and 0 form simple molecules with weak intermolecular forces thus low melting points.
Explain, using the image, why ice floats on water. Refer to the bonding and structure in water.
Hydrogen bonding holds the water molecules together in an open structure. Therefore, ice has a lower density than water and it floats on water.
Explain why iodoalkanes are more reactive than bromo- and chloroalkanes.
Weakest bond, bond strength is lowest:
C-Cl > C-Br > C-I
Which bond does a broad peak in an IR spectrum between wavenumbers 3000 to 3500 cm-1 correspond to?
O-H
Explain why the 4s subshell is filled before the 3d shell.
As the shells of electrons around the nuclei of atoms get further away, they become closer in energy. There is an overlap between the orbitals with highest energy in the third shell and lowest in fourth shell. Orbitals with lower energy are filled first, so 4s is filled before 3d.
The ionization energy of an atom is determined by three atomic properties. Name and explain these three.
- size of the positive nuclear charge: as the positive nuclear charge increases, its attraction for outermost electrons increases and this increases ionisation energy.
- distance of the outermost electrons from the nucleus: as the distance increases, the attraction of positive nucleus for negative electrons decreases and this reduces ionisation energy.
- shielding effect of electrons: electrons in inner shells repel the electrons in the outer shells. This reduces the pull of the nucleus on electrons in the outer shell. Increased shielding (more inner shells) reduces the ionisation energy.
Explain how this pictures shows the effect of three different types of intermolecular forces on boiling temperature.
H2O and NH3 have hydrogen bonds between the molecules. This is the strongest intermolecular force, hence boiling points are high.
As the period increases, the molecules become heavier and the London forces between molecules increase with increased weight (size). Hence, the general trend for all groups is an increase in boiling point.
The red line shows non-polar molecules whereas the green and blue line show polar molecules. These molecules have a dipole and there is dipole-dipole attraction. That is why the molecules on green and blue line have higher boiling points.
Draw a distillation set-up.
Correct drawing.
Explain what causes the 'peaks' (dips) in an infrared spectrum.
Most compounds absorb infrared radiation. Bonds vibrate in particular ways and absorb radiation at specific wavelengths, corresponding to these vibrations. This gives rise to 'peaks' in the spectrum.