The diagram shows a carbon dioxide molecule released when an acid reacts with limestone in a school greenhouse. Carbon dioxide is a simple molecular compoun...

The diagram shows a carbon dioxide molecule released when an acid reacts with limestone in a school greenhouse. Carbon dioxide is a simple molecular compound. The student compares its properties with diamond, another substance made only from carbon. Table 1 gives the melting points and electrical conductivity of the two substances. The gas is collected over water before it is tested with limewater.

(a) Name the element in the centre of Fig. 1. [1]
(b) Describe the difference in melting point shown in Table 1. [1]
(c) Explain why carbon dioxide has a low melting point. [2]
(d) What type of structure does diamond have? [1]

Table 1 records the boiling points of substances stored in a laboratory chemicals cupboard. Ethanol is a covalent compound used to clean equipment. Sodium chloride is an ionic compound. Helium is a noble gas. Fig. 1 is a particle diagram for ethanol, showing separate molecules rather than a continuous lattice. A teacher asks students to use the evidence before heating any samples.

(a) Name the substance in Table 1 with the lowest boiling point. [1]
(b) Use Table 1 to calculate the difference between the boiling points of ethanol and helium. [1]
(c) Explain why sodium chloride has a much higher boiling point than ethanol. [2]
(d) What does Fig. 1 show about the structure of ethanol? [1]