--- title: "Use the table to predict" subtitle: "Years 9 and 10 Chemistry · Atoms and the periodic table · Lesson 13" --- # Use the table to predict **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** When Mendeleev laid out the elements in 1869 he left gaps and said: an element will be found here, and it will behave like this. He was right. How could a table predict something nobody had seen? :::teacher-note **In one sentence:** Students use an element's position in the periodic table to predict its outer electrons, shells, reactivity and bonding, explain properties from atomic structure, and use the table as a predictive tool (AC9S10U06, node 4, an integration node). **Students should be able to say:** I can predict outer electrons and shells from group and period. I can predict reactivity and the ion an element forms. I can explain two properties with atomic structure. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **You are told only that an unfamiliar element sits in group 1, period 4. What can you predict?** ☐ Nothing: you must look it up ☐ It is an unreactive gas ☐ It has 4 outer electrons ☐ It is a metal with one outer electron, which is very reactive, losing that electron to form a 1+ ion My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** It has one outer electron (group 1), so it is an alkali metal that loses the electron easily, is very reactive and forms 1+ ions. Period 4 means four shells, so it is more reactive than the group 1 elements above it. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: predicting :::keep-together ### Outer electrons **An element is in period 3, group 16. How many outer electrons does it have?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 6 In groups 13 to 18 the group number minus 10 gives the outer electrons: 16 − 10 = 6 (sulfur). ::: :::keep-together ### Shells **The same element is in period 3. How many electron shells does it have?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 3 The period number is the number of shells. ::: :::keep-together ### Down a group **Which is more reactive, rubidium (group 1, period 5) or lithium (group 1, period 2)?** ☐ Lithium: it is smaller ☐ They are the same, because they are in the same group ☐ Rubidium: its outer electron is further from the nucleus and easier to lose ::: :::teacher-note **Answer:** Rubidium: its outer electron is further from the nucleus and easier to lose Down group 1 there are more shells, so the outer electron is further away, held less tightly and lost more easily. ::: :::keep-together ### Bonding **Chlorine (group 17) forms compounds with sodium (group 1). Predict the ions.** ☐ Na⁺ and Cl⁻: sodium gives up its one outer electron and chlorine gains one to fill its outer shell ☐ Na²⁺ and Cl²⁻ ☐ Na⁻ and Cl⁺ ::: :::teacher-note **Answer:** Na⁺ and Cl⁻: sodium gives up its one outer electron and chlorine gains one to fill its outer shell Group 1 loses 1 electron, group 17 gains 1, so they combine one to one: NaCl. ::: :::keep-together ### Noble gases **Why are the noble gases (group 18) almost unreactive?** ☐ They are too light to react ☐ They are gases, and gases don't react ☐ Their outer shells are full, so they have no need to gain, lose or share electrons ::: :::teacher-note **Answer:** Their outer shells are full, so they have no need to gain, lose or share electrons A full outer shell is stable. Atoms of other elements react to reach that arrangement. ::: :::typical ## Elaborate: a flame test :::keep-together **Sodium salts give a yellow flame and copper salts a green flame. What does this tell you about the atoms?** ☐ The colour comes from the flame, not the metal ☐ Electrons jump between shells with fixed energies and give out light of a colour set by each element ☐ All metals burn the same ::: :::teacher-note **Answer:** Electrons jump between shells with fixed energies and give out light of a colour set by each element When an electron falls from a higher to a lower shell it gives out light of one fixed colour. Each element has its own pattern, a fingerprint you can use to identify it. ::: ::: :::wider ## Elaborate: gaps in the table :::keep-together **Mendeleev left gaps and predicted the properties of the missing elements, such as the one later named germanium. Why was this good evidence for his table?** ☐ The table was copied from another scientist ☐ He had already found the elements ☐ The predictions came true when the elements were found, so the pattern in the table was real ::: :::teacher-note **Answer:** The predictions came true when the elements were found, so the pattern in the table was real A model that predicts something new, and is then confirmed, is more convincing than one that only fits what is already known. ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - The **group** gives the number of outer electrons; the **period** gives the number of shells. - Outer electrons decide reactivity and bonding: group 1 loses one electron, group 17 gains one, group 18 is stable. - Reactivity grows **down** group 1 and falls **down** group 17. - The table is a **predictive model**: Mendeleev's gaps predicted elements before anyone found them. ## Exit ticket :::keep-together **Predict the number of outer electrons and the ion formed by calcium, which is in group 2, period 4.** {{lines-3}} ::: :::teacher-note **Answer:** Two outer electrons; it loses them to form a Ca²⁺ ion. :::