Structure and Properties of Matter: Test Review

Key facts

Where marks get lost

• ×Calling an orbital an orbit. An orbit is a fixed path (Bohr's idea); an orbital is a three-dimensional region where the electron is likely to be found. (From Rutherford to the Quantum Atom)
• ×Forgetting to convert nanometres to metres before using $E=\frac{hc}{\lambda }$, which gives an answer off by a factor of a billion. (From Rutherford to the Quantum Atom)
• ×Reporting a negative photon energy. $\Delta E$ for the atom is negative when light is emitted, but the photon's energy is always the positive magnitude. (From Rutherford to the Quantum Atom)
• ×Thinking a bigger jump in $n$ always means a longer wavelength. Larger energy gaps give shorter wavelengths, so $n=2\to 1$ (ultraviolet) has a shorter wavelength than $n=3\to 2$ (red). (From Rutherford to the Quantum Atom)
• ×Saying the gold foil experiment showed electrons orbiting the nucleus. It showed a small, dense, positive nucleus; it gave no information about how electrons are arranged. (From Rutherford to the Quantum Atom)
• ×Filling 3d before 4s when writing a neutral atom's configuration. Follow the diagonal chart: 4s comes first. (Electron Configurations)
• ×Removing 3d electrons before 4s electrons when forming a transition-metal cation. Electrons leave from the highest shell first, so ${\text{Fe}}^{2+}$ is $[\text{Ar}]3d^6$, not $[\text{Ar}]4s^{2}3d^4$. (Electron Configurations)
• ×Pairing electrons in one p or d orbital while another orbital of the same subshell is still empty, which breaks Hund's rule and gives the wrong number of unpaired electrons. (Electron Configurations)
• ×Writing the aufbau prediction for chromium ($[\text{Ar}]4s^{2}3d^4$) or copper ($[\text{Ar}]4s^{2}3d^9$) instead of the actual ground states $[\text{Ar}]4s^{1}3d^5$ and $[\text{Ar}]4s^{1}3d^{10}$. (Electron Configurations)
• ×Using the wrong noble gas in the shorthand, such as $[\text{Ar}]$ for sodium. The bracket is always the noble gas at the end of the previous period. (Electron Configurations)
• ×Naming the electron-group arrangement instead of the molecular shape. Water has a tetrahedral arrangement of electron groups, but its shape is bent because lone pairs are not counted when naming the shape. (Molecular Shape and Polarity)
• ×Counting a double or triple bond as two or three electron groups. Every bond to one atom counts as a single group, so ${\text{CO}}_2$ has 2 groups, not 4. (Molecular Shape and Polarity)
• ×Forgetting lone pairs on the central atom in expanded-octet molecules, for example treating ${\text{XeF}}_4$ as tetrahedral instead of square planar. (Molecular Shape and Polarity)
• ×Placing the lone pair of ${\text{SF}}_4$ in an axial position. Lone pairs in a trigonal bipyramid go equatorial, which gives the seesaw shape. (Molecular Shape and Polarity)
• ×Deciding a molecule is polar just because it has polar bonds. ${\text{CCl}}_4$ and ${\text{CO}}_2$ have polar bonds but are nonpolar because their symmetrical shapes cancel the dipoles. (Molecular Shape and Polarity)
• ×Thinking that boiling water breaks the O–H bonds inside the molecules. Boiling overcomes the intermolecular forces between molecules; the molecules themselves stay intact. (Intermolecular Forces and Types of Solids)
• ×Saying any molecule containing hydrogen can hydrogen bond. The hydrogen must be bonded directly to N, O or F, so ${\text{CH}}_4$ and ${\text{CH}}_3{\text{OCH}}_3$ cannot hydrogen bond with themselves. (Intermolecular Forces and Types of Solids)
• ×Assuming hydrogen bonding always beats dispersion forces. Large nonpolar molecules such as octane can boil higher than water. (Intermolecular Forces and Types of Solids)
• ×Saying ionic solids conduct electricity. The ions are locked in place in the solid; an ionic compound conducts only when molten or dissolved. (Intermolecular Forces and Types of Solids)
• ×Classifying every nonmetal compound as molecular. Diamond, graphite, silicon, silicon dioxide and silicon carbide are covalent network solids with very high melting points. (Intermolecular Forces and Types of Solids)
• ×Reading IR peaks as pointing up. Spectra plot transmittance, so absorptions are dips (troughs) in the line. (Seeing Structure: Spectroscopy and Instrumental Analysis)
• ×Treating the tallest mass spectrum peak as the molar mass. The tallest is the base peak (often a stable fragment); the molar mass is given by the molecular ion, usually the highest-m/z peak. (Seeing Structure: Spectroscopy and Instrumental Analysis)
• ×Mistaking a chlorine M+2 peak for a second compound. Two peaks 2 units apart in a 3 : 1 ratio are the same molecule with chlorine-35 or chlorine-37. (Seeing Structure: Spectroscopy and Instrumental Analysis)
• ×Thinking IR light excites electrons to new energy levels. IR only makes bonds vibrate; electron transitions need visible or UV light. (Seeing Structure: Spectroscopy and Instrumental Analysis)
• ×Saying MRI uses X-rays or radioactivity. MRI uses a magnetic field and radio waves acting on hydrogen nuclei; CT scans are the ones that use X-rays. (Seeing Structure: Spectroscopy and Instrumental Analysis)

Practice test

25 questions from across the unit. Each one shows the lesson it comes from.

Endless drill

Fresh numbers every time, for the calculation questions in this unit.