2. Atoms, elements and compounds
A section of Chemistry, 0620
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This question is about ionic and covalent compounds. Sodium reacts with oxygen to form the ionic compound sodium oxide. The electronic configurations of an atom of sodium and an atom of oxygen are shown in Fig.3.1. oxygen atom sodium atom O Na Ions are formed by the transfer of electrons from sodium atoms to oxygen atoms. Complete the dot-and-cross diagrams in Fig.3.2 to show the electronic configuration of one sodium ion and one oxide ion. Show the charges on the ions. O Na oxide ion sodium ion  Write the formula of sodium oxide. Carbon dioxide, CO2, is a covalent compound. Complete the dot-and-cross diagram in to show the electronic configuration in a molecule of carbon dioxide. Show outer shell electrons only. C O O  The melting points of sodium oxide and carbon dioxide are shown in Table3.1. Table 3.1 melting point / °C sodium oxide carbon dioxide –78 Explain, in terms of bonding, why sodium oxide has a high melting point. Carbondioxide has a low melting point. State the general term for the weak forces that cause carbondioxide to have a low melting point. 
0620_s23_qp_41
THEORY
2023
Paper 4, Variant 1
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Magnesium forms ionic compounds. Magnesium reacts with fluorine to form the ionic compound magnesium fluoride. The electronic configurations of an atom of magnesium and an atom of fluorine are shown in Fig.3.1. fluorine atom magnesium atom F Mg Ions are formed by the transfer of electrons from magnesium atoms to fluorine atoms. Complete the dot-and-cross diagrams in Fig.3.2 to show the electronic configurations of one magnesium ion and one fluoride ion. Show the charges on the ions. F Mg fluoride ion magnesium ion  Deduce the formula of magnesiumfluoride. When solid magnesiumfluoride is dissolved in water it forms a solution that conducts electricity. State one other change that can be made to solid magnesiumfluoride to allow it to conduct electricity. Silicontetrachloride, SiCl 4, and silicon(oxide, SiO2, are covalent compounds. Complete the dot-and-cross diagram in Fig. 3.3 to show the electronic configuration in a molecule of silicontetrachloride. Show outer shell electrons only. Si Cl Cl Cl Cl  The melting points of silicontetrachloride and silicon(oxide are shown in Table3.1. Table 3.1 melting point / °C silicon tetrachloride –69 silicon(oxide Silicon tetrachloride has a low melting point because it has weak forces of attraction between particles. Name the type of particles that are held together by these weak forces of attraction. Explain, in terms of structure and bonding, why silicon(oxide has a high melting point. 
0620_s23_qp_43
THEORY
2023
Paper 4, Variant 3
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