9.The Periodic Table. The periodic table is a way of organising all of the elements in the universe. It gives us the following information:

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1 9.The Periodic Table The periodic table is a way of organising all of the elements in the universe. It gives us the following information: Periods Groups Electrons and Valency Metal and Non-Metals Read CC pp for background on the development of the periodic table.

2 1.The Period of a particular element tells us how many shells of electrons that an element of the atom has. These shells are sometimes called energy levels. The period is given by the number down the side of the Periodic table. Give the periods of the following elements: Period Number of energy levels of electrons Mg B Ca 2. The Group that a particular element finds itself in gives the number of electrons that it has in the outer shell ( valence electrons) The group is indicated by the number across the top of the table: I-VII and 0 The number of valence electrons tells us about the reactivity of the element. Give the groups of the following elements: Group Number of valence electrons Na Al O Ar

3 3.Electrons and Valency The valency is the number of electrons that must be gained, lost or shared to achieve a full outer shell and stability. The period and the group help us the work out the electronic configuration and the valency of the element. Complete the following table: Electronic configuration Valency Li K S C NB. You should be able to work out the electronic configuration of the first 20 elements (up to Ca). 4.Metal and Non-Metals In general, the metals are on the left hand side of the Periodic Table, and the nonmetals on the right. There is a step like divide. Elements close to the divide can behave as metals or nonmetals. They are called semi-metals or metalloids. Metallic character: Metals lose electrons to form positive ions They react with oxygen to form basic oxides Metals react with non-metals to for ionic compounds egs. K Ca Al Fe Fe

4 Non-Metallic Character: Non metals can do 2 things to achieve stability. They can... (a)gain electrons to form negative ions and achieve the noble gas electronic configuration. Eg. Cl O Br N OR... (a)share electrons to form covalent bonds. NB. Metallic character DECREASES as you go across the period (as the group number increases). eg. Period 3 Na Mg Al Si P S Cl Ar Define the elements above.

5 Draw a dot and cross diagram for the following covalent compounds: Carbon dioxide Ammonia Ethene Hydrogen Chloride CC Read pp Answer Q1-7

6 Group 1: The Alkali Metals List their symbols: Properties: they are soft they have a low density. What evidence do we have of this? they are silvery and shiny when cut but quickly tarnish. Why? They have a low melting and boiling point. The melting point decreases down the group. Why? They are very reactive. NB. The reactivity of group 1 metals INCREASES down the group (K>Na>Li) Why?

7 Group 1 metals with water All of the metals react vigorously when placed in water. Li: EQN: Observations: Na: EQN: Observations: K: EQN: Observations: Important: 1. In all cases, the resulting solution is alkaline. Why? 2. All of these reactions are exothermic. How can you tell? 3. Group 1 metals are excellent REDUCING agents. Why? CC P169 Q1-6

8 ! Group 2: The Alkaline Earth Metals List their symbols going down the group: These metals show similar trends to Group 1 metals, for the same reasons: Reactivity: INCREASES down the group as the valence electrons are less tightly held and easier to lose. Mpt. decreases down the group as the larger atoms attract each other less strongly. In the same period, group 1 metals are more reactive than group 2 metals, eg. Na>Mg (Period 3). Group 7: The Halogens List their symbols: Halogens exist as diatomic molecules: Draw an Iodine molecule NB. It is important to get clear the difference between a halogen and a halide, eg. Chlorine and chloride. Diagram:

9 Fill in the following table: Halogen Formula Common Isotopes State and Appearance (at room temp.) Reactivity of the Halogens Reactivity DECREASES down the group. The smaller the atom, the greater its capacity for pulling an electron from another species. Diagram: In terms of reactivity: F>Cl>Br>I Melting and boiling point The LARGER the diatomic molecule, the greater the intermolecular forces, and the harder it is to melt and boil the halogen. Diagram: These forces are called Van der Waals forces.

10 Displacement reactions of the halogens The general rule: Any halogen (in its molecular form) will displace a halide ion from below it in Group 7 from a solution of one of its salts. i.e. Chlorine displaces bromides and iodides, bromine displaces iodides. 1. Chlorine with Potassium Bromide solution EQN: Ionic EQN: What would you observe in this reaction? Which of the species... Has been oxidised? Has been reduced? Is the oxidising agent? 2. Chlorine with Potassium Iodide solution EQN: Ionic EQN:

11 What would you observe in this reaction? Which of the species... Has been oxidised? Has been reduced? Is the oxidising agent? 3. Bromine with Potassium Iodide solution EQN: Ionic EQN: What would you observe in this reaction? Which of the species... Has been oxidised? Has been reduced? Is the oxidising agent? Notes of the Halogens: 1. We can show the presence of Iodine using starch solution, which turns BLUE- BLACK if the test is positive.

12 2. Iodine is used as an antiseptic, and has an antiseptic smell. Why? 3. The halogens are also soluble in organic solvents (tetrachloromethane, hexane,...). Bromine gives a brown solution and iodine a pink solution. CC P171 Q1-6 AV Patterns of reactivity Patterns of behaviour

13 The Transition Elements List the 10 metals in the first transition series: Sc,... Characteristics of the transition metals: They form coloured compounds Transition metals make good catalysts The have a variable valency, and are often involved in REDOX reactions. Egs: They tend to be hard, dense, high melting point metals. They are relatively unreactive They are used to make alloys Demos: 1.Coloured compounds 2.Preparing chlorine gas Which chemicals do we use? What is the oxidising agent in this reaction?

14 3. Preparing oxygen: Mn as a catalyst EQN: 4. Oxidising Fe(II) with Chlorine Observations: Write an ionic equation for the reaction between Iron(II)Sulphate and Chlorine gas: Indicate the REDOX involved. CC P175 Q1-5 AV EXPT: Displacement reactions of the halogens.

15 Group 0: The Noble Gases List them: He who adores the perfect and unchangable and scorns the corruptible and ignoble will prefer the nobel gases, by far, to all other elements. For they never vary, never waver, never pander to the other elements like hoi polloi offering cheap wares in the marketplace. They are incorruptible and ideal. Sam Kean These gases exist in the atmosphere in trace amounts. Characteristics: They are colourless, monotomic, gaseous non-metals Unreactive - they have a full outer shell Density increases down the groups as the atoms become more massive. The uses of the noble gases depend on their unreactivity, low density or how they behave when they come into contact with electricity: Uses: CC P173 Q1-5 AV. End of unit exam questions. p Q6,7

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