Germany Jahrgangsstufe 10 Chemistry

Chapters: 6

1. How chemists think and work

How chemists think and work

The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.

Orbitals, bonding and molecular shape

VSEPR Theory: Shapes of Molecules – VSEPR stands for Valence Shell Electron Pair Repulsion. The electron pairs around a central atom repel each other and move as far apart as possible. The number of pairs sets the basic arrangement: 2 linear, 3 trigonal planar, 4 tetrahedral, 5 trigonal bipyramidal, 6 octahedral. Lone pairs take more room than bond pairs (lp–lp > lp–bp > bp–bp), so they squeeze bond angles and change the shape we see, for example NH₃ (pyramidal, 107°) and H₂O (bent, 104.5°).

Polarity and intermolecular forces

Intermolecular Forces – Intermolecular forces are weak attractions BETWEEN molecules. From weakest to strongest (for similar-size molecules): London dispersion < dipole–dipole < hydrogen bond. Stronger forces mean higher melting and boiling points, higher viscosity and surface tension, and they decide what dissolves in what.

Acids, bases and proton transfer

Acids and Bases: Properties, Indicators and Reactions – An acid gives H⁺ ions in water and a base gives OH⁻ ions. Indicators show which one is present by a colour or smell change, and when H⁺ meets OH⁻ they make water, leaving a salt behind.

Redox reactions in aqueous solution

Redox Reactions: From Oxygen to Electron Transfer – Oxidation first meant adding oxygen or removing hydrogen. Reduction meant the opposite. Today we use a bigger idea: oxidation is losing electrons and reduction is gaining electrons. Both always happen together, so we call them redox reactions. A more active metal gives electrons to the ion of a less active metal.

Nucleophile-electrophile reactions: sugars and esters

Types of Organic Reactions and Their Mechanisms – Organic reactions are sorted by what happens to the molecule: substitution (one atom swaps for another), addition (atoms join across a double bond), elimination (a small molecule leaves and a double bond forms), condensation (two molecules join and lose water) and hydrolysis (water splits a molecule). The mechanism shows how electrons move: bonds break homolytically (radicals) or heterolytically (ions), and nucleophiles (electron-rich) attack electrophiles (electron-poor). Esters form from acids and alcohols in a reversible, acid-catalysed condensation and are split by hydrolysis.