Chemical Bonding and Structure

The melting point of CaS is higher than that of KCl. Which of the following are explanations for the observation?

I Ca²⁺ is more positively charged than K⁺.
II S²⁻ is more negatively charged than Cl⁻.
III The K⁺ ion is smaller than the Ca²⁺ ion.

Which statement about metals is not correct?

Two statements about the structure and properties of metals are given.

statement 1: Metals are malleable and have high melting points.
statement 2: Metals have mobile electrons in their structure.

Which statement is correct?

The table shows the sixth ionisation energies of four consecutive elements in the Periodic Table.

What is the formula of the fluoride of W?

Diazene has the molecular formula N₂H₂. Given that nitrogen and hydrogen show their usual numbers of bonds, which describes the shape and bond angle around each central atom? Each option gives the shape, then the bond angle.

Iodine and phosphorus each form a trifluoride. What are the shapes of these two molecules? Each option gives IF₃, then PF₃.

The valence shell electron pair repulsion (VSEPR) theory is used to predict the bond angles of molecules. Which bond angle is correctly predicted by VSEPR?

Which one of the following pairs of compounds shows the same shape and similar bond angles?

In which pair of molecules or ions do both species contain a bond angle of 107°?

When an iodine atom is covalently bonded to an electron-withdrawing group X, the electron density on the large iodine atom becomes uneven. The tip of the iodine atom directly opposite the X–I bond becomes very electron-deficient, while the region round the middle of the iodine atom is electron-rich. The electron-deficient region can attract an anion A⁻ without forming a covalent bond. What is the most likely X–I···A⁻ bond angle for this attraction? (··· shows the non-covalent attraction.)

The table identifies the shape and polarity of four molecules. Which row is correct?

The table shows the boiling points of some halogenoalkanes.

Which of the following correctly explains the difference in the boiling points?

1 The electronegativity difference between the halogen and carbon increases from C–Cl to C–I.
2 The strength of permanent dipole–permanent dipole attraction increases from C–Cl to C–I.
3 The strength of instantaneous dipole–induced dipole attraction increases from CH₃CH₂Cl to CH₃CH₂I.
4 The bond energy of the carbon–halogen bond decreases from C–Cl to C–I.

Which of the following substances consists of atoms or molecules held together only by instantaneous dipole–induced dipole forces of attraction?

Information about some hydrocarbons is given below.

Which statements help to explain the variation in boiling points of the hydrocarbons?

1 Presence of more hydrogen atoms results in stronger hydrogen bonding.
2 Presence of more covalent bonds results in more energy required to break them.
3 Greater surface area of contact results in stronger instantaneous dipole–induced dipole interactions.
4 Presence of more electrons results in stronger instantaneous dipole–induced dipole interactions.

Information about the properties of some compounds is given below.

Which statement about the hydrogen bonding in these compounds is correct?

The boiling point of water (100 °C) is greater than that of HF (20 °C). Which statement is a correct explanation of this?

The boiling points of H₂O, H₂S and H₂Se are different. Which statements are correct?

I H₂S has a lower boiling point than H₂Se because H₂S molecules have weaker permanent dipole–permanent dipole forces of attraction.
II H₂O molecules experience weaker temporary dipole–induced dipole forces of attraction than H₂Se molecules.
III H₂O molecules experience stronger permanent dipole–permanent dipole forces of attraction than H₂S molecules.

Use the table of densities and boiling points of five solvents.

Which pair of liquids can be separated by liquid–liquid extraction?

Which lattice structure is correctly described?

Silicon carbide is a shiny, hard and chemically inert material with a very high melting point. It can be used to sharpen knives and make crucibles. Which type of structure explains these properties?

Substances X, Y and Z are all solids. Some of their physical properties are given in the table.

What type of structure could each substance have? Each option gives X, Y and Z in that order.

Which row correctly describes the structure and bonding present in the solid lattice of the given substance?

Which property of X₂ increases down the group for X = Cl, Br or I?

Which statement about covalent bonds is true?

Consider these chlorine-containing species: ICl₂⁻, ClF₃, ClO₃⁻. Which statements about them are correct?

1 The bond angles increase in the order ClF₃, ClO₃⁻, ICl₂⁻.
2 Two of the three species have an overall dipole moment.
3 Only ClO₃⁻ is not planar.