Science Semester 1 Revision – Chemistry, Biology & Physics

A comprehensive set of flashcards covering key concepts from the Chemistry, Biology and Physics sections of the Semester 1 revision booklet.

What three sub-atomic particles are found in atoms and where are they located?

Protons and neutrons are in the nucleus, while electrons orbit the nucleus in shells.

Which two numbers appear in every square of the Periodic Table and what do they represent?

Atomic number = number of protons; Mass number = total number of protons + neutrons.

Why are atoms electrically neutral?

Because they contain equal numbers of positively-charged protons and negatively-charged electrons.

How many electrons can the first, second and third shells hold?

First shell 2, second shell 8, third shell 18 (but stable at 8 for main-group elements).

Define ‘isotope’.

Atoms of the same element with the same number of protons but different numbers of neutrons.

What does a period number tell you about an element?

How many electron shells are occupied.

What does a group number tell you about a main-group element?

The number of valence (outer-shell) electrons.

Which group of elements is the most chemically unreactive and why?

Group 18 (noble gases) because their valence shell is already full.

State the charges of the following polyatomic ions: ammonium, sulfate, carbonate, nitrate.

NH₄⁺ = +1, SO₄²⁻ = –2, CO₃²⁻ = –2, NO₃⁻ = –1.

What is formed when a metal atom loses electrons?

A positively charged ion (cation).

Describe an ionic bond.

The electrostatic attraction between oppositely charged ions (metal cation and non-metal anion).

Write the chemical formula for magnesium oxide using the criss-cross method.

MgO.

Write the name of the compound Al₂O₃.

Aluminium oxide.

What must be equal on both sides of a balanced chemical equation?

The number of atoms of each element.

Give the general word equation for complete combustion of a hydrocarbon.

Hydrocarbon + oxygen → carbon dioxide + water.

What two additional products can appear in incomplete combustion?

Carbon monoxide (CO) and/or soot (C).

State Collision Theory’s two requirements for a successful reaction.

Particles must collide with sufficient energy and in the correct orientation.

List four factors that increase the rate of reaction.

Higher temperature, higher concentration/pressure, greater surface area, presence of a catalyst.

How do catalysts speed up a reaction?

They provide an alternative reaction pathway with a lower activation energy without being consumed.

Define systematic error and give one way to detect it.

Consistent bias in measurements; detected by repeating the experiment with different equipment and comparing results.

Define random error and one way to reduce its effect.

Unpredictable variations in measurements; reduce by taking many trials and averaging.

Give the four general acid reaction types tested in the exam.

(I) Acid + metal → salt + H₂, (II) Acid + metal hydroxide → salt + H₂O, (III) Acid + metal oxide → salt + H₂O, (IV) Acid + metal carbonate → salt + H₂O + CO₂.

According to the Periodic Table, which group contains the most reactive metals?

Group 1, the alkali metals.

Provide the electron configuration of calcium (atomic number 20).

2, 8, 8, 2.

What ion (symbol and charge) is formed by sulfur?

S²⁻.

Name a metalloid element.

Examples: Silicon, arsenic, germanium, antimony (any one).

What does ‘biodiversity’ mean?

The variety of all living species, their genes and the ecosystems they form.

Differentiate between genetic and environmental variation.

Genetic variation is inherited through genes; environmental variation arises from external factors such as climate or diet.

Define ‘gene pool’.

All the alleles present in a population.

What is a mutation and why is it important in evolution?

A random change in DNA sequence; it introduces new alleles that can be acted on by natural selection.

Define adaptation.

A heritable feature that increases an organism’s chance of survival and reproduction in its environment.

State Darwin’s mechanism for evolution.

Natural selection—organisms with favourable traits survive and reproduce more, passing on those traits.

What is meant by ‘survival of the fittest’?

Individuals best suited to the environment are more likely to survive, reproduce and pass on their genes.

Give two examples of selection agents.

Predators, disease, competition, temperature, human hunting, etc. (any two).

Distinguish between convergent and divergent evolution.

Convergent: unrelated species evolve similar traits; Divergent: related species evolve different traits, leading to speciation.

What is speciation?

The formation of new species when populations become reproductively isolated and diverge genetically.

Name five lines of evidence supporting evolution.

Fossil record, biogeography, molecular (DNA) similarities, comparative anatomy, comparative embryology.

Define artificial selection and give an example.

Human-directed breeding for desired traits, e.g., domestication of dogs or selective breeding of crops.

Explain how geographic isolation can lead to divergent evolution.

Separated populations experience different environments and selection pressures, causing accumulation of genetic differences that can lead to new species.

Why are homologous structures evidence for common ancestry?

They have similar underlying anatomy despite different functions, indicating descent from a common ancestor.

Give an example of a homologous feature.

The forelimbs of humans, whales and bats.

What is the unit ‘light year’ a measure of?

The distance light travels in one year (~9.46 × 10¹² km).

State the speed of light in a vacuum.

3.0 × 10⁸ m s⁻¹ (or 300,000 km s⁻¹).

Write the formula that links velocity, frequency and wavelength of a wave.

v = f λ.

State Wien’s Law used in astronomy.

Temperature (K) = 3 × 10⁶ ÷ peak wavelength (nm).

Differentiate between apparent and absolute magnitude.

Apparent magnitude is how bright a star appears from Earth; absolute magnitude is how bright it would appear at 10 parsecs (≈33 ly).

Describe the life cycle stage that produces a neutron star.

The collapsed core left after a massive star explodes in a supernova.

Give two characteristics of the electromagnetic spectrum’s waves as frequency increases.

Wavelength decreases and energy increases.

Write the average speed equation.

v_avg = distance ÷ time (v = d/t).

Write the acceleration equation.

a = (final speed – initial speed) ÷ time (a = (v – u)/t).

State Newton’s First Law of motion.

An object remains at rest or moves with constant velocity unless acted on by an unbalanced external force.

Provide one everyday example of Newton’s First Law.

Passengers lurch forward when a car suddenly stops because their bodies tend to keep moving.

State Newton’s Second Law of motion.

The net force on an object equals its mass times its acceleration (F = ma).

If force is constant, how are mass and acceleration related?

They are inversely proportional; doubling mass halves acceleration.

State Newton’s Third Law of motion.

For every action there is an equal and opposite reaction.

Why does a gun recoil when fired? (Use Newton’s Third Law.)

The bullet is pushed forward while the gun experiences an equal and opposite backward force.

Define weight and give its formula.

Weight is the force of gravity on an object; W = m g.

Explain the difference between mass and weight.

Mass is the amount of matter and is constant; weight is gravitational force and varies with gravity.

What is the acceleration due to gravity near Earth’s surface?

Approximately 9.8 m s⁻² (often rounded to 10 m s⁻² in school problems).

Give the units for speed, acceleration and force in SI.

Speed: m s⁻¹, Acceleration: m s⁻², Force: newton (N).

Convert 55 km h⁻¹ to m s⁻¹.

≈15.3 m s⁻¹ (divide by 3.6).

What is meant by ‘uniform acceleration’?

Acceleration that is constant in magnitude and direction.

State the formula for average speed when initial and final speeds are known.

v_avg = (u + v)/2.

Calculate the force needed to accelerate a 5 kg trolley at 2 m s⁻².

F = ma = 5 × 2 = 10 N.

Define inertia.

An object’s resistance to changes in its state of motion.

Which has more inertia: a 200 kg motorbike or a 1000 kg car?

The 1000 kg car, because inertia increases with mass.

What two measurements are plotted on a distance-time graph?

Distance on the y-axis and time on the x-axis.

How is constant speed shown on a distance-time graph?

A straight line with positive slope.

State the relationship between slope of a distance-time graph and speed.

The slope equals speed (steeper = faster).

Describe what a horizontal line on a distance-time graph represents.

The object is stationary (zero speed).

Give the formula for calculating temperature in Kelvin.

T(K) = T(°C) + 273.

What is the Kelvin temperature equivalent of 35 °C?

308 K.

Outline one reason why scientific notation is useful in astronomy.

It allows very large distances or very small wavelengths to be expressed compactly and compared easily.

Write 6.5 × 10² in ordinary form.

650.

Express 345 000 000 000 in scientific notation.

3.45 × 10¹¹.

What is meant by absolute zero?

0 K, the theoretical temperature at which particles have minimum possible kinetic energy.

State the wave characteristic measured from crest to crest.

Wavelength.

What part of a wave indicates its energy?

Amplitude—the greater the amplitude, the more energy.

Calculate the speed of a wave with frequency 300 Hz and wavelength 0.5 m.

v = fλ = 300 × 0.5 = 150 m s⁻¹.

Using Wien’s Law, what is the peak wavelength of a star at 2000 K?

λ = 3 × 10⁶ / 2000 = 1500 nm.

Explain why chewing an aspirin tablet speeds up its reaction in the body (collision theory).

Chewing increases surface area, producing more frequent effective collisions with stomach acid, so the tablet dissolves faster.

What is a hydrocarbon?

A compound made solely of hydrogen and carbon atoms.

Name the products of an acid-metal carbonate reaction.

Salt, water, and carbon dioxide.

Give an example of artificial selection in agriculture.

Breeding wheat varieties with higher yield or disease resistance.

How do phylogenetic trees depict evolutionary relationships?

They show branching patterns indicating common ancestry and divergence over time.

What happens to an unfavourable allele over many generations?

Its frequency decreases because individuals carrying it are less likely to survive and reproduce.

Why are antibiotic-resistant bacteria an example of evolution by natural selection?

Resistant mutants survive antibiotic treatment, reproduce, and pass resistance genes to the next generation, increasing resistance frequency.

State two sources of acceleration data you could plot on a speed-time graph.

Time intervals (x-axis) and measured speed values (y-axis).

According to Newton’s Second Law, what happens to required force if both mass and desired acceleration double?

Force increases four-fold (F = ma).

What causes weightlessness experienced by astronauts in orbit?

They are in continuous free fall around Earth, experiencing no normal reaction force.

Explain why seatbelts reduce injury in a crash using Newton’s First Law.

They exert a force to decelerate passengers with the car, preventing them from continuing forward at the pre-crash speed.

How do airbags reduce force on passengers (Newton’s Second Law)?

They increase the stopping time, reducing deceleration and therefore force (F = ma).

Using Newton’s Third Law, describe the force pair when you push against a wall.

Your hand exerts a force on the wall; the wall exerts an equal and opposite force on your hand.

What happens to average molecular speed as temperature increases?

It increases, because kinetic energy of particles is proportional to temperature.

Define ‘apparent magnitude’.

A measure of a star’s brightness as observed from Earth.

Define ‘absolute magnitude’.

A measure of how bright a star would appear at a standard distance of 10 parsecs (≈33 ly).

Which factor, mass or velocity, affects momentum more for a given force?

Both equally (momentum p = mv), so changing either alters momentum proportionally.

Why is carbon monoxide dangerous in incomplete combustion?

It binds to haemoglobin more strongly than oxygen, reducing oxygen transport in blood.

What is meant by ‘controlled variable’ in an experiment?

A factor kept constant to ensure it does not influence the dependent variable.

Write the acid + metal hydroxide reaction for H₂SO₄ and NaOH (give salt).

H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O.