Electricity, Chemical Bonding and Evolution

MYP Unit Framework

Key Concept: CHANGE Related Concepts: Energy. Interaction. Evidence. Global Context: Scientific and Technical Innovation (How do scientific theories EXPLAIN change in matter, energy, and life?) Statement of Inquiry: At every scale — from the ELECTRON to the ECOSYSTEM — scientific models reveal that CHANGE is governed by UNDERLYING PRINCIPLES that are elegant, universal, and supported by evidence.

Inquiry Questions

Type	Question
Factual	What is Ohm's Law? What is an ionic bond? What is natural selection?
Conceptual	Why do different materials conduct electricity differently? Why do atoms FORM bonds — and what determines the TYPE of bond? What is the EVIDENCE for evolution?
Debatable	Is evolution a 'theory' or a 'fact'? Can science and religion COEXIST — or are they fundamentally incompatible? Should we use electricity from fossil fuels even though it contributes to climate change?

1. Electricity — The Flow of Charge

Electric Current (I) — Flow of electrons. Measured in AMPERES (A).

Potential Difference (V) — Energy per unit charge. Measured in VOLTS (V).

Ohm's Law: V = IR

'Voltage = Current × Resistance. For a GIVEN resistance, doubling the voltage DOUBLES the current — like water flowing through a pipe: higher pressure = more flow.'

Resistance (R) — Measured in OHMS (Ω)

R = ρL/A. Resistance INCREASES with LENGTH. DECREASES with cross-sectional AREA. ρ (resistivity) depends on the MATERIAL. 'Copper has LOW resistivity — good conductor. Rubber has HIGH resistivity — good insulator.'

Series and Parallel Circuits

	Series	Parallel
Current (I)	SAME everywhere	DIVIDES at junctions
Voltage (V)	DIVIDES across components	SAME across each branch
Resistance (R)	R_total = R₁+R₂+R₃	1/R_total = 1/R₁+1/R₂+1/R₃

Electrical Power: P = VI = I²R = V²/R.

Unit: Watt (W). Energy consumed: E = Pt (kilowatt-hours). 'Your electricity bill charges per kWh. A 1000W heater running for 1 hour consumes 1 kWh.'

2. Chemical Bonding — Why Atoms Stick Together

Why Do Atoms Bond?

Atoms bond to ACHIEVE A STABLE ELECTRON CONFIGURATION — usually an OCTET (8 electrons) in the outermost shell. 'The NOBLE GASES (Group 18) already have an octet. They are UNREACTIVE. Every other atom is, in some sense, TRYING to become a noble gas.'

Ionic Bonding — Electron TRANSFER

Metal (loses e⁻ → cation +) + Non-metal (gains e⁻ → anion −). Electrostatic attraction between OPPOSITELY charged ions. 'NaCl: Na loses 1 e⁻ → Na⁺. Cl gains 1 e⁻ → Cl⁻. They attract — IONIC BOND. The crystal lattice is a REGULAR, repeating 3D structure — which explains why ionic compounds are BRITTLE (layers shift, like charges repel).'

Two non-metals SHARE electrons. 'Each atom "counts" the shared electrons as part of its octet. Single bond: share 1 pair. Double: share 2 pairs. Triple: share 3 pairs.'

Metallic Bonding — 'Sea of Electrons'

Metal atoms in a lattice. Outer electrons are DELOCALISED — they move FREELY throughout the structure. 'This "sea" of electrons explains why metals: conduct electricity (electrons move freely). Are MALLEABLE and DUCTILE (layers slide — electrons flow around).'

Bonding and Properties

Bond Type	MP/BP	Conducts Electricity?	Examples
Ionic	HIGH	When MOLTEN or DISSOLVED	NaCl, MgO
Covalent (simple molecular)	LOW	NO	H₂O, CO₂, CH₄
Covalent (giant)	VERY HIGH	NO (except graphite)	Diamond, SiO₂
Metallic	HIGH	YES (solid or liquid)	Cu, Fe, Al

3. Evolution — Darwin's Dangerous Idea

Before Darwin

The dominant belief: species were CREATED, unchanging, by God. The Earth was ~6,000 years old (Biblical chronology).

Darwin's Observations (HMS Beagle, 1831–1836)

FINCHES on the Galápagos Islands: Each island had finches with DIFFERENT BEAK SHAPES — adapted to the specific FOOD available on that island. 'One original finch species arrived. Over millions of years, it DIVERSIFIED into many species — each adapted to a different ecological niche.'
FOSSILS of extinct species resembled LIVING species in the same region.

Natural Selection — The Mechanism

VARIATION: Individuals in a population VARY.
OVERPRODUCTION: More offspring are born than can survive.
STRUGGLE FOR EXISTENCE: Resources are limited. Competition.
SURVIVAL OF THE FITTEST: Individuals with ADVANTAGEOUS traits are more likely to survive and reproduce.
INHERITANCE: Those advantageous traits are PASSED ON. 'Over GENERATIONS: the advantageous traits become MORE COMMON. The population EVOLVES.'

Evidence for Evolution

Type	Example
Fossil Record	Transitional fossils. Archaeopteryx (dinosaur → bird).
Comparative Anatomy	Homologous structures — same BONE STRUCTURE in human hand, whale flipper, bat wing. 'Same underlying structure = common ancestor.'
DNA/Genetics	All life uses the SAME genetic code (DNA → RNA → Protein). Humans share ~98% of DNA with chimpanzees.
Biogeography	Species on ISLANDS resemble nearest CONTINENT (not identical — evolved separately).

Common Misconceptions

'Evolution is "just a theory."' → 'In science, a THEORY is a WELL-TESTED EXPLANATION supported by a VAST BODY OF EVIDENCE. Evolution is as well-established as the theory of gravity.'
'Humans evolved from chimpanzees.' → 'Humans and chimpanzees share a COMMON ANCESTOR. We did not evolve FROM chimps. We are COUSINS — not parent and child.'

Your Summative Assessment

Task: 'The Science and Society Symposium' Prepare a presentation on ONE of the following: (a) How should we generate ELECTRICITY — balancing energy needs with climate concerns? (b) How does the EVIDENCE for evolution challenge or coexist with religious belief? Use SCIENTIFIC EVIDENCE. Acknowledge MULTIPLE PERSPECTIVES. Argue YOUR position.