GCSE Double Award Science Chemistry Unit 1 Notes for CCEA Students

Atomic Structure Basics

Your atoms are made of three key particles that determine everything about an element. Protons (mass 1, charge +1) and neutrons (mass 1, charge 0) sit in the nucleus, whilst electrons (tiny mass, charge -1) whizz around in shells.

Here's what makes chemistry logical: atoms are always neutral because they have equal numbers of protons and electrons. The group number tells you how many electrons are in the outer shell, and the period number shows how many shells there are.

Isotopes are just atoms of the same element with different numbers of neutrons - same atomic number, different mass number. When calculating relative atomic mass (RAM), you multiply each isotope's mass by its percentage abundance, add them up, then divide by 100.

Quick Check: Sodium (Na) has the electron arrangement 2,8,1 - it's in Group 1, Period 3!

Ion Formation and Ionic Bonding

Creating ions is surprisingly straightforward - atoms simply gain or lose electrons to get a full outer shell. Metals lose electrons to become positive cations (like Na⁺), whilst non-metals gain electrons to become negative anions (like Cl⁻).

When you change a non-metal to an ion, its name changes to end in '-ide'. So chlorine becomes chloride, oxygen becomes oxide. Molecular ions contain more than one element, like sulfate (SO₄²⁻).

Ionic bonding happens when metals meet non-metals. Take sodium chloride: the sodium atom (2,8,1) loses one electron to become Na⁺ (2,8), and chlorine (2,8,7) gains that electron to become Cl⁻ (2,8,8). These oppositely charged ions are held together by strong electrostatic attractions.

Remember: Metals always form positive ions, non-metals always form negative ions!

Covalent Bonding Types

Covalent bonding occurs between non-metals that share electrons rather than transferring them. There are two main types you need to understand.

Simple molecular covalent substances like F₂ have weak Van der Waals forces between molecules. This means they have low melting and boiling points, don't conduct electricity (no charged particles), and are usually insoluble in water.

Giant covalent structures are different beasts entirely. Diamond has each carbon bonded to four others, making it incredibly hard with high melting points - perfect for cutting tools but can't conduct electricity. Graphite has each carbon bonded to three others with delocalised electrons, making it soft (good for pencils) but able to conduct electricity.

Graphene is just a single layer of graphite - it's thin, lightweight, transparent, and brilliant for batteries and solar cells because electrons can move freely.

Key Insight: The structure determines the properties - diamond's 4 bonds per carbon make it hard, graphite's 3 bonds with free electrons make it soft but conductive!

Structure Classification and Properties

Understanding how different structures behave helps you predict their properties. Molecular covalent substances like bromine have low melting points and poor conductivity. Giant ionic compounds like potassium chloride have high melting points and conduct when liquid but not solid.

Metallic structures like copper conduct electricity brilliantly and have high melting points. Giant covalent materials like graphite can vary - graphite conducts electricity due to delocalised electrons, but diamond doesn't.

Nanoparticles are incredibly tiny $1-100 nm$ with just a few hundred atoms. Their huge surface area to volume ratio makes them brilliant for things like sun cream - they're transparent on skin and spread easily. However, they can be toxic to cells and harmful to the environment.

Watch Out: The same element can have completely different properties depending on its structure - compare diamond and graphite!

Metallic Structure and Alloys

Picture metallic structure as positive metal ions arranged in a regular pattern, surrounded by a 'sea' of delocalised electrons. This electron sea is what makes metals so special.

Metallic bonding is the attraction between these positive ions and the delocalised electrons. This structure explains why metals are ductile (can be drawn into wires) and malleable (can be beaten into shape) - the electrons let ions slide over each other without breaking bonds.

Metals have high melting points because you need lots of energy to break those strong electrostatic attractions. They conduct electricity brilliantly because delocalised electrons are free to move and carry charge.

Alloys are mixtures of two or more elements (at least one metal) that keep metallic properties. They're often stronger than pure metals because different-sized atoms disrupt the regular structure.

Real World: Steel is an alloy of iron and carbon - it's much stronger than pure iron because carbon atoms prevent iron layers from sliding easily!

Chemical Analysis and Separation

A pure substance contains only one element or compound, not mixed with anything else. Pure substances have specific melting and boiling points that help identify them.

Formulations are carefully designed mixtures where each component is added in precise amounts to give the product specific properties - think paint, medicine, or alloys.

Understanding solubility is crucial: soluble solids dissolve in water, insoluble ones don't. The solute dissolves in the solvent to form a solution.

Separation techniques depend on the mixture type. Filtration separates insoluble solids from liquids - the liquid (filtrate) passes through filter paper whilst the solid (residue) stays behind. Evaporation recovers the solute from a solution by heating.

Lab Tip: Always use a pencil line for chromatography baselines - ink would dissolve and mess up your results!

Distillation and Chromatography

Simple distillation separates a liquid from a solution (like pure water from seawater). The solution is heated until the liquid evaporates, then it condenses in the Liebig condenser and collects as pure liquid.

Fractional distillation separates mixtures of liquids with different boiling points. The fractionating column is hotter at the bottom and cooler at the top, so different liquids condense at different heights.

Paper chromatography separates mixtures of soluble substances. Different substances move at different rates because some are more soluble in the solvent. The mobile phase is the solvent, the stationary phase is the paper.

Calculate Rf values using: Rf = distance moved by compound ÷ distance moved by solvent. This helps identify substances by comparing with known values.

Pro Tip: Always mark the solvent front immediately when you remove the chromatography paper - it disappears as the solvent evaporates!

Chemical Tests and Analysis

The Rf value helps identify substances in chromatography - substances with the same Rf value under the same conditions are likely the same compound.

Testing for water is simple: add white anhydrous copper sulfate, and it turns blue if water is present.

Flame tests identify metal ions by their characteristic colours. Clean a nichrome wire with concentrated HCl, dip it in the metal salt, then hold in a blue Bunsen flame. Potassium gives lilac, sodium gives yellow, lithium gives crimson, calcium gives brick red, and copper gives blue-green.

These tests are crucial for identifying unknown substances and checking purity. The colours are so distinctive that you can often identify metals instantly.

Safety First: Always wear safety goggles during flame tests - metal salts can spit and concentrated HCl is corrosive!

Chemical Formulas and Equations

Diatomic elements always exist as molecules of two atoms: I₂, H₂, N₂, Br₂, Cl₂, O₂, F₂. Remember: "I Have No Bright or Clever Friends."

Writing chemical formulas for compounds involves balancing charges. Cross-multiply the charges: Al³⁺ and NO₃⁻ gives Al(NO₃)₃, because you need three nitrate ions to balance one aluminium ion.

Chemical reactions rearrange atoms but never create or destroy them. This is why we can write balanced symbol equations - the same number of each type of atom must appear on both sides.

State symbols show the physical state: $s$ for solid, $l$ for liquid, $g$ for gas, and (aq) for aqueous solution (dissolved in water). Hazard symbols warn about dangers like corrosive, toxic, flammable, or explosive substances.

Balancing Tip: Start with the most complex molecule when balancing equations, then work through each element systematically!

Acids, Bases and pH

Hazard symbols are internationally recognised for safety. Toxic substances may cause death, flammable substances catch fire easily, explosive substances may explode, and corrosive substances burn living tissue.

Indicators change colour to show if something is acidic, alkaline, or neutral. Red litmus stays red in acid but turns blue in alkali. Blue litmus stays blue in alkali but turns red in acid. In neutral conditions, red litmus stays red and blue litmus stays blue.

The pH scale runs from 0-14: pH 0-2 is strong acid, pH 3-6 is weak acid, pH 7 is neutral, pH 8-11 is weak alkali, and pH 12-14 is strong alkali.

Acids dissolve in water to produce hydrogen ions (H⁺), whilst alkalis produce hydroxide ions (OH⁻). This is what makes them react together in neutralisation reactions.

Memory Aid: Acids = H⁺ ions, Alkalis = OH⁻ ions. When they meet, H⁺ + OH⁻ → H₂O (water)!