2 Chapter 6 â¢ organising elements Organising elements

More documents

Recommendations

Info

Identifying patterns in the periodic table What you need: A3 sheet of paper, pens, highlighter pens 1 on an A3 sheet of paper, make a copy of the periodic table only up to element 20. Leave a gap for the block of transition metals. Ensure that the size of the box for each element will fit the information you will need to insert, as detailed below. (Chlorine has been completed for you as an example.) 2 use different colours to shade in the metals, the noble gases, hydrogen, the non-metals other than the noble gases and hydrogen, and the metalloids. Place a suitable key under your periodic table. 3 First, identify the elements that will not gain or lose electrons in a reaction because their uncharged atoms are already very stable. Beneath them, write: • already a stable structure • does not form an ion 4 Now identify the elements that will not gain or lose electrons in a reaction, because this would require them to gain or lose more than three electrons. Beneath them, write: • needs to gain or lose more than three electrons for a more stable structure • does not form an ion What do you know about electrons and properties? 1 Carefully examine the periodic table. 5 Finally, complete the box for each of the other elements listed, except for the metalloids and hydrogen, by stating how many electrons the element needs to gain or lose to achieve a more stable structure, and hence what charge its ion should have, like the example of chlorine. Information for chlorine: • Chlorine (Cl) • needs to gain one electron • charge on ion = –1 • What pattern(s) do you notice in your entries for the alkali metals? • What pattern(s) do you notice in your entries for the alkaline earth metals? • What pattern(s) apply to all the metals listed? • What pattern(s) do you notice in your entries for the halogens? • What pattern(s) do you notice in your entries for the group 16 elements? a Which elements are likely to form positively charged ions? b Which elements are likely to form negatively charged ions? c What does this tell you about the likely ionic bonding between elements? PRACTIVITY 6.1 2 How does the group in which an element is found in the periodic table quickly identify one or more of its properties? 3 Helium is placed in group 18 of the periodic table, even though it has only two electrons in the outer shell compared with the eight electrons that the other elements in this group have in their outer shell. Why is helium placed in this group? 4 Hydrogen is not placed in a group or period in the periodic table. Why is this? 5 What is the maximum number of electrons that can be gained or lost by an atom? Why? • What pattern(s) apply to the nonmetals, except for hydrogen and the noble gases? • in general, what do you expect to happen when a metal atom and a non-metal atom meet? Which groups of non-metals will not react in this way? Discuss. • predict what might happen if: a a potassium atom and a fluorine atom meet b a calcium atom and an oxygen atom meet • you can illustrate your predictions by drawing shell diagrams of the atoms and showing what happens in the reaction. • suggest why hydrogen and the metalloids were not considered in this activity. UNCORRECTED PAGE PROOFS Unit 7.3 • What are the risks of using chemicals? 23 CAS_SB10_TXT_06_1pp.indd 23 11/11/11 4:58 PM
SKILLS LAB 24 Ionic compounds Ionic compounds are those formed from the bonding of ions. Let’s consider sodium chloride, which is produced when sodium and chlorine meet and react. In this compound, the metal sodium is present in the form of positively charged ions (Na + ) and the non-metal chlorine is present as negatively charged ions (Cl – ). Notice that the: • metal is named first and its name is not changed • non-metal is named second and the end of its name is changed from -ine to -ide This follows a standard naming convention, as follows. • The positively charged ion (cation) in the compound is written first and keeps the name of the metal from which it was formed. • The negatively charged ion (anion) in the compound is written second. Replace the end of the name of the non-metal from which it formed with -ide. • Some transition metals can form more than one ion. In these cases, a Roman numeral is used to show the charge on the ion. For example, copper forms two ions: one with a 1+ charge and one with a 2+ charge. These ions are called copper (I) and copper (II) ions, respectively. The properties of ionic compounds Compounds that are held together by ionic bonds are called ionic compounds. As an ionic compound forms, the like charged ions repel each other and the oppositely charged ions attract each other. After all the pushing and pulling, the ions settle into alternating positions, as shown in Figure 6.32, because this is the most stable arrangement. The particles are held together by strong electrostatic forces of attraction between the positively charged ions. Because these forces bind the ions together, this is known as ionic bonding. A lot of energy is required to move the ions out of their positions because the electrostatic forces are so strong. This means that ionic compounds are hard to melt. At room temperature, they are in the form of hard, brittle crystals. The most commonly known example of an ionic compound is sodium chloride (table salt). Its melting point is 801°C. If you use a salt grinder at home, you will be aware of how hard and brittle salt crystals are. Chapter 6 • organising elements The names and formulas of some common examples of some ions are listed in Table 6.5. Table 6.5 Formulas of some common ions Cations Anions Name Formula Name Formula Lithium Li + Fluoride F − Sodium Na + Chloride Cl − Potassium K + Bromide Br − Magnesium Mg 2+ Iodide I − Calcium Ca 2+ Oxide O 2− Aluminium Al 3+ Sulfide S 2− Silver Ag + Nitride N 3− Zinc Zn 2+ Copper (II) Cu 2+ Iron (II) Fe 2+ Iron (III) Fe 3+ Polyatomic ions A number of ions are made up of more than one atom. These are termed polyatomic ions. Figure 6.33 shows some examples of polyatomic ions. These clusters of atoms have a charge because the total number of protons does not equal the total number of electrons present. For example, in the hydroxide ion, which is made up of two atoms (one each of oxygen and hydrogen), there are nine protons and ten electrons. This means the ion has an overall charge of 1–. Calcium carbonate, the main constituent of marble, is an example of an ionic compound that contains a polyatomic ion. Calcium carbonate contains calcium 2– ions, Ca 2+ , and carbonate ions, CO 3 . These ions must be present in the ratio 1:1 so that the total positive charge equals the total negative charge. The formula of calcium carbonate is CaCO 3 . Ammonium carbonate is used in smelling salts. It contains ammonium ions, NH 4+ , and 2– carbonate ions, CO 3 . In this case, the ions need to be present in the ratio 2:1. The formula of ammonium carbonate is (NH 4 )2CO 3 . UNCORRECTED PAGE PROOFS CAS_SB10_TXT_06_1pp.indd 24 11/11/11 4:58 PM
Page 1 and 2: 2 6 Chapter 6 • organising eleme
Page 3 and 4: 6.1 4 Why do we organise elements?
Page 5 and 6: 6 Some properties of Dobereiner’s
Page 7 and 8: 8 1894 William Ramsay, a Scottish c
Page 9 and 10: 10 Properties and structure 6.1 F
Page 11 and 12: 12 Grouping elements The two main t
Page 13 and 14: 14 • Many of the transition metal
Page 15 and 16: 16 What do you know about non-metal
Page 17 and 18: 6.3 18 How are properties linked to
Page 19 and 20: 20 Emission spectrum and electron s
Page 21: 22 EXPERIMENT 6.2 Conductivity of i
Page 25 and 26: 26 Table 6.6 gives the electrical c
Page 27 and 28: 28 Properties and structure 6.3 Ho
Page 29 and 30: 30 >>ZOOMING OUT
Page 31 and 32: 6 Properties and structure Element
Page 33 and 34: 34 Given the fact that so many coun

2 Chapter 6 â¢ organising elements Organising elements

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?

2 Chapter 6 â¢ organising elements Organising elements