Chapter 6 Materials made of molecules

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1 hapter 6 Materials made of molecules Section 6.1 roperties of non-metallic substances 6.1 Key questions 1 Non-metallic elements: 2 and Br 2 as they consist of only one type of atom. Non-metallic compounds: N 2 as it consists of more than one type of atom (nitrogen and oxygen. 2 A molecule is a discrete group of atoms of known formula, bonded together. 3 a Non-metals do not conduct electricity because they do not contain free-moving charged particles (neither delocalised electrons nor ions. b Non-metals have low melting and boiling temperatures because they have weak intermolecular bonds between molecules. 4 a True. Methane is formed from two types of non-metal atoms (carbon and hydrogen. b alse. Methane contains 5 atoms (1 carbon and 4 hydrogen atoms. c True. There are 5 atoms per molecule and so 4 molecules will have 20 atoms. d alse. Bonds in the molecule are intramolecular bonds. 5 When sugar turns to a liquid, it is melting; the intermolecular bonds are broken. When the liquid turns black and a gas is produced, the intramolecular bonds are broken, allowing new substances to be produced. Section 6.2 ovalent bonding Worked example: Try yourself ELETRN DT DIAGRAMS Draw an electron dot diagram of the molecule formed from nitrogen and hydrogen atoms. Thinking Write the electronic configuration of the atoms in the molecule. Determine how many electrons each atom requires for a stable outer shell. Draw an electron dot diagram of the likely molecule, ensuring that each atom has a stable outer shell. Electrons not involved in bonding will be in non-bonding (lone pairs. Working N electronic configuration: 2,5 electronic configuration: 1 N requires 3 electrons requires 1 electrons Draw an electron dot diagram of the molecule. N 6.2 Key questions 1 a ydrogen requires 1 electron to complete its outer shell, so it forms a single covalent bond. b 3. Nitrogen requires 3 electrons to complete its outer shell, so it forms a triple covalent bond. c 2. xygen requires 2 electrons to complete its outer shell, so it forms a double covalent bond. d 1. luorine requires 1 electron to complete its outer shell, so it forms a single covalent bond.

2 2 fluorine ( 2 hydrogen fluoride ( water ( 2 tetrachloromethane ( 4 phosphine ( 3 butane ( 4 10 carbon dioxide( 2 3 a 1 b 2 c 3 d 4 e 1 f 0 4 To complete its outer shell, the oxygen atom uses two of its outer-shell electrons to form two single bonds or a double bond with suitable non-metal atoms. The remaining four electrons in the outer shell are not required for bonding, as the outer shell is now complete, and they arrange themselves as two lone pairs around the oxygen atom. 5 a 4 b NBr 3 c Si 2 d e 3 6 a Ball-and-stick model b Electron dot diagram c Space-filling model

3 ATER 6 REVIEW 6.1 RERTIES NN-METALLI SUBSTANES 1 The strength of the intermolecular bonds in pure hydrochloric acid (hydrogen chloride must be relatively weak. Since the pure hydrochloric acid exists as a gas at room temperature, it must have a low boiling temperature, which indicates that not much energy is required to break the intermolecular bonds between molecules. 2 Non-metallic substances do not conduct electricity. 3 Intramolecular bonds are the forces that hold the atoms within a molecule together. In carbon dioxide molecules they are the bonds between the carbon atoms and the oxygen atoms. Intermolecular bonds are the forces between one molecule and its neighbouring molecules. It is the intermolecular bonds that are broken when carbon dioxide sublimes. 4 a Space-filling model b Valence structure c Ball-and-stick model d Electron dot diagram 6.2 VALENT BNDING 5 D. Each hydrogen atom has one electron only. If two atoms share an electron each they both obtain a complete outer shell. A single covalent bond is formed. 6 a 6. Each nitrogen atom shares three electrons with the other nitrogen atom. b 3. Each nitrogen atom shares three electrons with the other nitrogen atom, so three bonding pairs are formed, which is equal to a triple covalent bond. c Each nitrogen atom has two non-bonding electrons, making a total of four when both atoms are counted. 7 B. To have a formula XY 4, atom X must require four more outer-shell electrons and atom Y must require one. The likely molecule is 4 as carbon has four outer-shell electrons and hydrogen requires one more. xygen has 6 valence electrons and needs to form 2 covalent bonds. ydrogen has one valence electron and needs to form one bond. or 4, each hydrogen would need to form a single covalent bond, giving a total of 4, but oxygen only needs to form 2, so this option is incorrect. Bromine has 7 valence electrons. Each bromine needs to form a single covalent bond, giving a total of 4, but hydrogen only needs to form one bond, so this option is incorrect. arbon has 4 outer-shell electrons and needs to form 4 bonds. xygen has 6 valence electrons and needs to form 2 covalent bonds, to have a total of 8, but carbon only needs to form 4, so this option is incorrect. 8 Atom X requires 2 electrons to form a stable outer shell. Each atom of element Y can share 1 electron. Therefore the molecular formula will be XY 2. 9 Neon will not form bonds to other atoms as it has a stable outer shell. 10 a 0 b 1 c 3 d 4 N 11 The diagrams of each molecule below show the number of electron pairs. a 2 bonding electrons, 6 non-bonding electrons Br b 4 bonding electrons, 4 non-bonding electrons

4 c 8 bonding electrons, 24 non-bonding electrons d 14 bonding electrons, 0 non-bonding electrons e 6 bonding electrons, 20 non-bonding electrons f 4 bonding electrons, 16 non-bonding electrons g 8 bonding electrons h 4 bonding electrons, 4 non-bonding electrons S 12 a The bonds are similar in that they all involve the sharing of electron pairs between two atoms; that is, they are covalent bonds. b They differ in the number of electron pairs shared: one pair (fluorine, two pairs (oxygen and three pairs (nitrogen. 13 a b In a single bond there are two electrons that are shared between the atoms, whereas in a double bond there are four electrons. The net attraction is stronger and more energy is needed to break the double bond than the single bond. c xygen has six outer-shell electrons and completes its outer shell by forming two single covalent bonds or a double bond with another non-metal. There is no need for the oxygen to form a triple bond or three single covalent bonds as this exceeds its requirement of two electrons to complete its outer shell.

5 NNETING TE MAIN IDEAS 14 Metallic: Ag, u; ionic: u 2, as; molecular: N 3,, 2 Ag and u are both metals. This can be determined from general knowledge, their position in the periodic table or from their electronic configuration. u 2 and as are both formed from a combination of a metal and non-metal(s. This is characteristic of ionic compounds. N 3,, 2 are compounds made from non-metals. They are composed of small molecules. 15 a True. arbon dioxide is formed from two types of non-metal atoms (carbon and oxygen. b True. arbon dioxide contains 3 atoms (1 carbon and 2 oxygen atoms. c alse. There are 2 oxygen atoms per molecule and so 33 molecules will have 66 oxygen atoms. d True. Bonds in the molecule are intramolecular bonds. e alse. There are 2 double covalent bonds in a molecule of carbon dioxide. f True. Each oxygen atom has 2 lone pairs of electrons. As there are 2 oxygen atoms, there are 4 lone pairs of electrons in a molecule of carbon dioxide.