Teacher License – Science 2 Complete Review Guide 2026–2027

4. Across a period, left to right, atomic radius decreases and electronegativity increases. Down a group, atomic radius increases.
5. Electron configuration of iron (Z = 26): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, i.e. [Ar] 4s² 3d⁶.
6. An ionic bond transfers electrons between a metal and a nonmetal (NaCl). A covalent bond shares electrons between nonmetals (H₂O). A metallic bond is a sea of free electrons.
7. One mole contains 6.022 × 10²³ particles (Avogadro's number), and moles = mass ÷ molar mass.
8. To balance an equation, make the atoms of each element equal on both sides by changing coefficients only, never the subscripts in formulas. Example: 2H₂ + O₂ → 2H₂O.
9. Molarity M = moles of solute ÷ litres of solution. Example: 50.0 mL of 1.5 M NaOH holds 0.075 mol, i.e. 3.0 g (molar mass 40 g/mol).
10. A saturated solution cannot dissolve more solute at a given temperature, an unsaturated one can, and a supersaturated one holds more than the normal maximum and is unstable.
11. Reaction rate increases with higher concentration, temperature and surface area, and with a catalyst.
12. ΔH = enthalpy of products − enthalpy of reactants. ΔH is negative for exothermic reactions and positive for endothermic ones.
13. Arrhenius: an acid gives H⁺ and a base gives OH⁻. Brønsted-Lowry: an acid donates a proton and a base accepts one. Lewis: an acid accepts an electron pair and a base donates one (standard 6.5.18).
14. pH = −log[H⁺], and at 25 °C pH + pOH = 14. Example: 0.001 M HCl has pH = 3.
15. A free element has oxidation number 0; oxygen is usually −2 and hydrogen usually +1. The numbers in a neutral compound add up to zero (standard 6.5.19).
16. General formulas of hydrocarbons: alkanes CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂. Benzene, C₆H₆, is aromatic (standard 6.5.20).
17. Functional groups: alcohol –OH, aldehyde –CHO, ketone C=O within the chain, carboxylic acid –COOH, ester –COO–, amine –NH₂.
18. Fractional distillation separates crude oil by boiling point: gases and light fractions leave at the top of the tower and the heaviest (bitumen) at the bottom (standard 6.5.21).

Common mistakes in this chapter

• ✕ Atomic radius decreases across a period (left to right) and increases down a group. Reversing the two gives wrong answers on ordering questions.
• ✕ A hydrogen bond is not a covalent bond. It is an attraction between molecules in which H is bonded to F, O or N.
• ✕ Substances held together by weak van der Waals forces have low boiling points. Some students pick high because the bonds inside each molecule are strong.
• ✕ A catalyst lowers activation energy but does not change ΔH or the equilibrium position. An exothermic reaction has ΔH < 0.
• ✕ Diluting changes the volume and concentration but not the moles of solute, which is why M₁V₁ = M₂V₂ works.
• ✕ pH = −log[H⁺]. Each pH unit is a tenfold change in concentration, and the lower the pH, the more acidic the solution.
• ✕ Oxidation is loss of electrons (oxidation number increases) and reduction is gain. Oxidation occurs at the anode in every type of cell.
• ✕ In a galvanic cell the anode is negative and the cathode positive. In an electrolytic cell it is the reverse: anode positive, cathode negative.