--- marp: true theme: default html: true --- # Use the table to predict Years 9 and 10 Chemistry · Atoms and the periodic table --- ## Today **We are learning to** the periodic table is not a list to look up but a tool for prediction. An element's group gives its number of outer electrons, and so how reactive it is and what it bonds with; its period gives its number of shells. From the position alone you can predict whether an element is a metal, how it reacts and what its atom looks like. - 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. --- ## Why it matters > 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? --- 💬 Discussion ## Engage: predict **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 --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fchemistry-9-10%2Fpredict-from-table%2Fstep-2&code=widget%3A+atom%0Amode%3A+table%0Acolour%3A+outer%0A&fresh=1}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-9-10/predict-from-table/?full=step-2#step-2) --- ✅ Check ## What happened? * 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. --- ✅ Check ## Outer electrons **An element is in period 3, group 16. How many outer electrons does it have?** * Answer: 6 --- ✅ Check ## Shells **The same element is in period 3. How many electron shells does it have?** * Answer: 3 --- ✅ Check ## 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 * Answer: Rubidium: its outer electron is further from the nucleus and easier to lose --- ✅ Check ## 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⁺ * Answer: Na⁺ and Cl⁻: sodium gives up its one outer electron and chlorine gains one to fill its outer shell --- ✅ Check ## 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 * Answer: Their outer shells are full, so they have no need to gain, lose or share electrons --- ✅ Check ## Elaborate: a flame test **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 * Answer: Electrons jump between shells with fixed energies and give out light of a colour set by each element --- ✅ Check ## Elaborate: gaps in the table **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 * Answer: The predictions came true when the elements were found, so the pattern in the table was real --- ## 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. --- ✅ Check ## Exit ticket **Predict the number of outer electrons and the ion formed by calcium, which is in group 2, period 4.** * Two outer electrons; it loses them to form a Ca²⁺ ion.