# Teaching with atoms and bonding A companion to the Year 9 **Bonding & Compounds** worksheet and the 14-slide lesson. ## A manageable way to use it Try two short sittings. First, use slides 1–9 for atoms, electrons, bonds and formulas. Later, use slides 10–14 for properties, the flame-test questions and explaining ideas aloud. Let the learner attempt each orange question before you read the answer. Return to the worksheet after each matching section. The PDF contains the slides. The PowerPoint also contains speaker notes. Those notes appear below so you can read them while the learner sees the slides. ## Three things to try together 1. **Move a counter.** Draw sodium and chlorine labels. Give sodium one outer-electron counter and chlorine seven. Transfer sodium’s counter to chlorine, then add Na+ and Cl− charge labels. Ask what stayed unchanged: the number of protons. Explain that electric attraction between the ions is the bond. The counters are a model, not little balls following fixed paths. 2. **Share a pair.** Draw an O with two H labels beside it. Use six counters for oxygen and two differently marked counters for hydrogen. Put one counter from each atom into each shared pair. Leave two lone pairs on oxygen. Count eight actual valence electrons, then show how shared pairs count around both bonded atoms. 3. **Find the mistake.** Say, “Sodium becomes positive because it gains a proton.” Let the learner correct you. Try, “Every covalent substance has a low melting point,” and, “An ionic bond is the electron transfer.” Useful corrections: sodium loses an electron; covalent structures vary; the bond is attraction between opposite ions. For another interactive option, use [PhET Build an Atom](https://phet.colorado.edu/sims/html/build-an-atom/latest/build-an-atom_en.html) to explore how changing protons, neutrons or electrons affects identity, mass and charge. Use the atoms available in the simulation rather than assuming it can build every element. For bonding animation, the [ACS covalent-bonding lesson](https://www.acs.org/middleschoolchemistry/lessonplans/chapter4/lesson4.html) links to student animations for hydrogen and water. Its teacher summary video is aimed at teachers. ## Slide-by-slide explanation and answers ### 1. Atoms & bonding Say: We are going to connect three things: what is inside an atom, what happens to its outer electrons, and how that changes a material. Work through slides 1–9 first. Take a break, then cover 10–14. Stop at each orange question and let the learner explain in her own words. The model diagrams simplify real atoms. ### 2. Inside a sodium atom Say: An atom is the smallest unit of an element that keeps its chemical identity. Its nucleus contains positive protons and uncharged neutrons. Negative electrons occupy the space around it. Atomic number tells us the proton count. Mass number counts protons plus neutrons, not electrons. For this sodium-23 atom, 23 minus 11 gives 12 neutrons. A neutral atom has equal proton and electron counts. Ask: Why are there eleven electrons? Answer: Their negative charges balance eleven positive protons. ### 3. The outer electron matters Say: Put sodium’s eleven electrons into this shell model: two in the first shell, eight in the second and one in the third. Count them together. The one in the outermost occupied shell is its valence electron. Rings are a school model of energy levels, not literal tracks travelled by electrons. The 2,8,1 pattern is sodium’s configuration, not a rule saying every shell holds eight. Ask: Which electron would sodium usually lose when forming an ion? Answer: The single outer electron. ### 4. Valence electrons and valency Say: These words sound similar but answer different questions. Valence electrons are the outer electrons. Valency describes combining capacity. In these simple examples it corresponds to the number of electrons lost, gained or shared in bonding. Oxygen has six outer electrons and usually forms two covalent bonds. Sodium has one outer electron and usually loses one to form sodium plus. Sodium’s valency is one, while its usual ion charge is plus one. Chlorine has seven outer electrons but valency one. Some elements have more than one valency, especially transition metals. Ask: Is oxygen’s valency six? Answer: No, its usual valency here is two. ### 5. Why bonds form Say: Atoms have no plans or wishes. A stable bonded arrangement has lower energy than the same atoms separated. Electrical attractions help hold particles together, while repulsions also matter. Full outer shells are a useful pattern for many simple examples. Hydrogen fits two in its first shell. The octet rule uses eight for many other outer shells, but it has exceptions. The worksheet’s nitrogen dioxide is one exception, so do not use it as a first dot diagram. Ask: What is the physical force involved? Answer: Electrostatic attraction. ### 6. Ionic bonding Say: Sodium loses one electron. It still has eleven protons, but now only ten electrons, so its ion has a plus-one charge. Chlorine gains that electron and becomes a minus-one ion. Transfer makes ions. The ionic bond is the electrostatic attraction between opposite charges. In solid sodium chloride, many ions form a repeating lattice, rather than separate NaCl molecules. A dot’s colour only tracks its starting atom. All electrons are the same type of particle. Ask: Does sodium become a different element? Answer: No, its proton count stays eleven. ### 7. Covalent bonding Say: A covalent bond is a shared pair of electrons attracted to both bonded nuclei. In water, oxygen contributes six valence electrons and two hydrogens contribute one each. There are eight valence electrons in total. Four form two shared pairs. The other four form two lone pairs on oxygen. Count each shared pair around both atoms: each H counts two, and O counts eight. There are still only eight actual electrons in this valence diagram. The straight diagram shows electron bookkeeping, not water’s bent shape. Ask: How many shared pairs does water have? Answer: Two. ### 8. Sorting and naming the compounds Let the learner predict each row before reading it. For these introductory examples, metal plus non-metal suggests ionic; non-metal plus non-metal suggests covalent. KCl is potassium chloride and ionic. H2O is water and covalent. NO2 is nitrogen dioxide and covalent. FeCl3 is treated as ionic at this level and named iron(III) chloride. The Roman numeral gives the iron ion charge, not the number of iron atoms. CaCl2 is calcium chloride. CO is carbon monoxide. Molecular prefixes include mono for one, di for two and tri for three; mono is usually omitted on the first element. Chloride is the ion name; chlorine is the element name. NO2 has an odd electron count and is an octet exception; keep it for classification and naming here. ### 9. A formula must balance the charges Say: A compound is electrically neutral overall. One calcium ion has a plus-two charge. Each chloride ion has a minus-one charge. Two chlorides give minus two, which balances the calcium. The simplest ratio is one calcium to two chloride ions, so the formula is CaCl2. The small 2 counts chloride ions in the ratio. It does not mean chloride has a minus-two charge. Ionic formulas describe ratios in a lattice, rather than separate molecules. Ask: What formula balances Mg2+ and Cl−? Answer: MgCl2. Extension: Na+ and O2− give Na2O. ### 10. Structure explains properties Say: In an ionic lattice, strong attractions act between charged ions. In a simple molecular substance, covalent bonds hold atoms together within molecules, while weaker attractions often act between molecules. Melting a molecular substance usually overcomes attractions between molecules, not its covalent bonds. For ionic materials, mobile ions carry current when molten or dissolved; ions are fixed in the usual solid lattice. The worksheet gives broad patterns, not universal rules. Sugar dissolves despite being covalent. Diamond is a giant covalent structure with a high melting temperature, and graphite conducts. The molecular column does not describe every covalent material. ### 11. Properties explain uses Say: An electrolyte must carry charge through mobile ions. A suitable dissolved salt provides those ions. Battery chemistry determines which electrolyte works; this does not mean every salt suits every battery. A plastic wire coating, such as PVC, has very few mobile charge carriers, so it resists current and helps prevent shocks and short circuits. Plastic is a covalent polymer, made of long molecular chains. Its useful insulation does not depend on assuming that all covalent materials have low melting points. Ask her to use because in an answer. ### 12. A fair flame test Say: The independent variable is the metal salt being tested. The dependent variable is observed flame colour. Keep sample amount and flame conditions consistent. For a stronger comparison, use salts with the same anion and the same concentration. Improve validity by preventing contamination with a fresh splint or appropriately cleaned loop, so colour comes from the intended sample. Improve reliability by repeating each test and checking whether colours agree. Wear eye protection against splashes and tie back hair to reduce ignition risk. Follow the teacher’s laboratory procedure; this slide is revision, not a home practical. Ask: Does repeating a contaminated test fix validity? Answer: No. It may repeat the same error. ### 13. An extended answer needs “because” Worked comparison: Sodium chloride contains positive and negative ions in a repeating lattice. Paraffin wax is a mixture of covalent hydrocarbon molecules. Salt has a much higher melting point because strong attractions hold its ions together. Wax melts more easily because attractions between its molecules are weaker; this makes wax easy to mould into candles. Salt dissolves in water and supplies ions, which is useful when making brine. Wax is insoluble and repels water, useful for water-resistant coatings. Dissolved salt conducts because ions can move, so appropriate salt solutions can act as electrolytes. Wax is a poor conductor because it has no mobile ions or delocalised electrons, allowing uses in electrical insulation or protective potting. A material is chosen for a combination of properties, and practical insulation also needs suitable heat resistance. Ask the learner to write her own paragraph connecting arrangement, each property and a use. A high melting point alone does not explain every use of salt. ### 14. Can you teach it back? Keep the answers hidden in these notes. 1: Sodium-23 has 11 protons, 12 neutrons and 11 electrons when neutral. 2: Valence electrons occupy the outer shell; valency is combining capacity. Sodium has one of each in this example. 3: Ionic bonding is electrostatic attraction between oppositely charged ions. 4: Water has two shared pairs. 5: CaCl2 balances one Ca2+ with two Cl− ions. 6: Molten or dissolved salt has mobile ions that carry charge. If an answer is uncertain, return to that slide and have the learner draw or explain it. Praise the explanation process and let the learner correct the answer herself. ## A short narration script Use this as the opening of a narrated lesson, with the sodium, ionic and water diagrams on screen. Speak slowly and leave room to answer the questions. It is designed for a parent recording or a text-to-speech tool. It has not been turned into audio or video. Everything around us is made of atoms. Inside an atom is a tiny nucleus containing protons and neutrons. Protons have a positive charge. Neutrons have no electric charge. Electrons have a negative charge and occupy the space around the nucleus. Let’s look at sodium. Its atomic number is eleven, which means it has eleven protons. A neutral sodium atom also has eleven electrons. The sodium in your worksheet has a mass number of twenty-three. Subtract eleven from twenty-three, and you get twelve neutrons. In our shell model, sodium’s electrons are arranged two, eight, one. That single electron in the outside shell is a valence electron. Valence electrons are the outer electrons involved in bonding. Valency is a different idea. It describes how an atom combines with other atoms. Sodium usually loses one electron, so its valency here is one. Oxygen has six outer electrons, but it usually forms two covalent bonds. Its usual valency is two. Now watch sodium transfer its outer electron to chlorine. Sodium still has eleven positive protons, but only ten negative electrons. It becomes a positive ion. Chlorine gains the electron and becomes a negative ion. Opposite charges attract. That attraction is the ionic bond. In a salt crystal, many ions form a repeating lattice. Water shows another kind of bonding. Oxygen and hydrogen share electrons. Each shared pair makes one covalent bond. Water has two oxygen-to-hydrogen bonds, so it has two shared pairs. Each shared pair is attracted to both of the nuclei it joins. These arrangements help explain properties. In solid salt, ions cannot move freely. When salt melts or dissolves, the ions can move and carry electric current. Insulating plastic has very few mobile charge carriers, which makes it useful as a wire coating. Your turn. What is the difference between transferring an electron and sharing a pair? And why does sodium become positive when it loses a negative electron? ## Exploring more atoms, molecules and clouds The site adds eight neutral atoms and seven molecular examples. The molecule models distinguish single, double and triple bonds and count shared pairs. A line means one pair, so a double bond means two pairs and a triple bond means three pairs. O2 and N2 are molecular elements. H2O, CO2, CH4 and NH3 are molecular compounds. Sodium chloride is an ionic lattice, not a collection of separate molecules. Shell rings organise electrons by energy level. They do not show literal paths. A cloud shows a probability distribution. Each plotted dot represents one simulated position measurement on a separately prepared hydrogen atom. Adding dots improves the picture of the distribution; it does not add electrons. The hydrogen 1s pattern is spherical. One hydrogen 2p orbital has two lobes and a nodal plane. The two lobes belong to one orbital. These are isolated atomic states, not clouds calculated for the molecular models. Try 40 measurements, then 8,000. Ask what changed and what stayed the same. Next, rotate the 2p view to see how a three-dimensional pattern can look different from another direction. The cloud views use different display scales, so do not compare their drawn sizes. The site offers a device voice for reading the visible explanations aloud. This is labelled separately from any future ElevenLabs recording. ## Sources and model limits The supplied worksheet determines the scope. The lesson uses introductory shell and electron-pair models. Shell circles are not literal electron paths. The full-outer-shell rule has exceptions. Classification of FeCl3 follows the worksheet’s introductory ionic model. The properties table distinguishes simple molecular substances from the broader category of all covalent materials. 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