Chemistry Paper 1: Essential Mind Maps

Acids, Bases and the pH Scale

Ever wondered why lemon juice stings cuts or why soap feels slippery? It's all about acids and bases. Acids have a pH less than 7 and release hydrogen ions $H+$ in water - think stomach acid (pH 2) or acid rain (pH 4). Bases have a pH greater than 7 and form hydroxide ions $OH-$ in water, like washing up liquid (pH 9) or bleach (pH 13).

The pH scale runs from 1-14 and measures hydrogen ion concentration. A pH of 7 is neutral (pure water), whilst anything below is acidic and anything above is alkaline. You can measure pH using indicators (chemical dyes that change colour) or a pH meter for more accurate results.

When acids and bases meet, they have a neutralisation reaction: acid + base → salt + water. For example, HCl + NaOH → NaCl + H2O. The key reaction is H+ + OH- → H2O, which is why the solution becomes neutral.

Quick Tip: Don't confuse acid strength (how much it breaks apart) with concentration (how much acid is in a given volume) - they're completely different things!

The Evolution of Atomic Theory

Your understanding of atoms has come a long way since ancient Greece! Democritus (500 BC) first suggested everything was made of tiny, unbreakable particles. Much later, John Dalton (1803) proposed atoms were solid spheres - different elements had different types of spheres.

JJ Thompson (1897) discovered electrons and created the plum pudding model - a positive ball with negative electrons dotted throughout. However, Ernest Rutherford's gold foil experiment (1909) changed everything when some particles bounced back, proving atoms had a dense, positive nucleus with electrons around it.

Niels Bohr (1913) refined this into the electron shell model, showing electrons orbit the nucleus in specific shells. Finally, James Chadwick discovered neutrons in the 1930s, completing our modern picture of atoms with protons and neutrons in the nucleus, and electrons in shells.

Remember: Each scientist built on previous work - science is about testing and improving ideas, not getting everything right first time!

Chemical Bonding - How Atoms Stick Together

Atoms bond in three main ways, and understanding these explains why materials behave so differently. Ionic bonding happens between metals and non-metals - metals lose electrons to become positive ions, non-metals gain them to become negative ions. The strong electrostatic attraction between oppositely charged ions creates the bond.

Covalent bonding occurs between non-metals that share electron pairs. This creates either small molecules (like water H₂O) with weak forces between molecules, or giant covalent structures like diamond and silicon dioxide. Diamond's incredibly hard because every carbon atom bonds to four others in a rigid 3D network.

Metallic bonding explains why metals conduct electricity and can be hammered into shape. Metal atoms release electrons into a "sea" of delocalised electrons, creating positive ions held together by attraction to these mobile electrons. The layers can slide over each other, making metals malleable.

Key Insight: The type of bonding determines a material's properties - ionic compounds have high melting points, small molecules are often gases, and metals conduct electricity.

Advanced Carbon Structures and Alloys

Carbon's versatility creates some amazing materials beyond diamond. Graphite has a layered structure where each carbon bonds to three others, leaving one electron delocalised. This makes graphite soft (layers slide easily) and electrically conductive - perfect for pencils and electrodes.

Graphene is essentially a single layer of graphite arranged in hexagons - it's incredibly strong, nearly transparent, and conducts heat and electricity brilliantly. Fullerenes are hollow carbon structures like cages, tubes, and balls. The most famous is buckminsterfullerene (C₆₀), which looks like a football and has potential uses in drug delivery and nanotechnology.

Metallic bonding also explains alloys - mixtures containing at least one metal. Steel (iron with carbon) is stronger than pure iron because the different-sized atoms disrupt the regular arrangement, preventing layers from sliding easily. This gives alloys improved properties like increased strength.

Polymers are large molecules made from repeating units held by strong covalent bonds. They're typically solid at room temperature, cheap to produce, and incredibly versatile - forming everything from plastic bottles to synthetic fibres.

Cool Fact: Fullerenes have an incredibly high strength-to-weight ratio, making them perfect for reinforcing materials in everything from tennis rackets to spacecraft!