Photosynthesis, Respiration, and Atomic Structure

PHOTOSYNTHESIS

water + carbon dioxide → glucose + oxygen

Photosynthesis Equation

6H₂O + 6CO₂ → C6H₁₂O6 + 6O₂

Factors Increasing Rate of Photosynthesis

Increasing temperature, Increasing light intensity, Increasing CO₂ concentration

Limiting Factor in Photosynthesis

Light intensity is the limiting factor if temperature is not.

Practical Method for Measuring Photosynthesis

Cut pondweed stem, put in inverted measuring cylinder filled with water, measure distance from light source.

Inverse Square Law

Distance x2 = light intensity ÷ 4

Uses of Glucose

Respiration, Making starch/fat to store energy, Making cellulose, Making amino acids for proteins.

AEROBIC RESPIRATION

glucose + oxygen → water + carbon dioxide

Anaerobic Respiration

glucose → lactic acid

Oxygen Debt

Occurs during intense exercise when lactic acid is broken down into glucose by the liver using oxygen.

Anaerobic Respiration in Plants

glucose → ethanol + carbon dioxide (aka fermentation)

METABOLISM

The sum of all chemical reactions in a cell/organism.

METALLIC BONDING

How metal atoms bond to each other forming a lattice of ions surrounded by a sea of delocalised electrons.

Conductivity of Metals

Metals are good conductors of electricity and heat due to free-moving electrons.

IONIC BONDING

How metals bond to non-metals by donating electrons to form ions.

Ionic Compounds

The charges of all ions in an ionic compound must add up to zero.

IONIC STRUCTURES

Ions are arranged in a lattice of repeating units of positive and negative ions forming a crystal.

Melting/Boiling Points of Ionic Compounds

Ionic substances have high melting/boiling points due to strong ionic bonds.

CATIONS

Positive ions.

ANIONS

Negative ions.

Conductivity of Ionic Compounds

Ionic compounds can conduct electricity when molten or in solution.

SALTS

Ionic compounds are also called salts, e.g., sodium chloride.

hydroxide ion

OH-

sulphate ion

SO²-

carbonate ion

CO3²-

nitrate ion

NO₂

ammonium ion

NH

covalent bonding

Atoms SHARE electrons to gain FULL OUTER SHELLS.

covalent bond

Every covalent bond consists of a PAIR OF SHARED ELECTRONS.

DOT & CROSS diagram

A representation of covalent bonding showing shared electrons.

structural formula

A diagram with a line representing each bond.

simple covalent structures

Molecules with a small number of atoms that have low boiling points due to WEAK INTERMOLECULAR FORCES.

allotropes of carbon

Structures made of the same element but arranged differently, resulting in giant molecules.

diamond

One of the hardest known substances due to very strong bonds.

silicon dioxide

Also known as 'silica', a giant covalent structure.

fullerenes

Molecules with high surface to volume ratio, useful for various applications.

graphite

Contains delocalised electrons and can conduct electricity.

Buckminster fullerene

C60, also known as 'Bucky Ball'.

atomic structure

The model of matter developed over time, including protons, neutrons, and electrons.

mass number

The sum of PROTONS and NEUTRONS in an atom.

atomic number

The number of PROTONS in an atom.

isotopes

Atoms of the same element with different numbers of neutrons.

nuclear decay equations

Equations describing the process where unstable nuclei emit radiation to become more stable.

Alpha Decay

Larger nuclei nucleus ejects a HELIUM NUCLEUS (2 protons + 2 neutrons).

Alpha Radiation

This is ALPHA RADIATION.

Beta Radiation

The high energy ELECTRON is BETA RADIATION.

Beta Decay

Smaller nuclei a NEUTRON decays into a PROTON ELECTRON.

Gamma Radiation

GAMMA RADIATION is a high energy EM wave that can be emitted by a nucleus, but this isn't due to decay; it's just due to a nucleus having excess energy.

Radioactivity

Radioactivity (or just 'activity') is the rate of decay in a sample of radioactive material.

Half-Life

The TIME it takes for the activity to halve; this is also true for NUMBER OF UNSTABLE NUCLEI LEFT, and also MASS.

Activity Unit

The unit of activity is Bq (Becquerel), which is essentially the same as c.p.s. (counts per second) detected.

Half-Life Example

The activity of a sample decreased from 96Bq to 12Bq in 12 months. What is its half-life?

Half-Life Calculation

12 months = 3 half-lives. It took 3 HALF-LIVES.

Ionising Power of Radiation

All three types of nuclear radiation IONISE other atoms, which can be dangerous for living things.

Background Radiation

e.g. cosmic rays, radon gas (rocks), nuclear weapons, medical equipment.

Alpha Radiation Characteristics

MASS: Helium nucleus (2p+2n), CHARGE: +2, IONISING POWER: high, PENETRATING ABILITY: low.

Beta Radiation Characteristics

MASS: 0, CHARGE: -1, IONISING POWER: medium, PENETRATING ABILITY: medium.

Gamma Radiation Characteristics

MASS: 0, CHARGE: 0, IONISING POWER: low, PENETRATING ABILITY: high.

Neutrons Ejection

NEUTRONS can also be ejected from nuclei under certain conditions.

Fission

FISSION is the splitting of a (heavier) nucleus (like Uranium-235) into two 'daughter' nuclei, releasing energy.

Fusion

FUSION is the joining together of two (lighter) nuclei (such as heavy hydrogen-2, also called deuterium, into helium), releasing energy.

Energy Conversion in Fission and Fusion

In both cases, the TOTAL MASS of particles DECREASES: mass has been converted to ENERGY.

Induced Fission

Fission is INDUCED by a nucleus absorbing a neutron, making it more unstable (U-236).

Chain Reaction

Fission releases up to 3 more neutrons - these go on to induce more fission.

Challenges of Fusion

This happens in the SUN, but it is proving difficult to harness the energy produced by fusion in the reactors being developed.