Atomic Structure and Models

The Structure of the Atom

• Atoms are extremely small and cannot be seen without powerful microscopes.
• The word 'atom' originates from a Greek term meaning 'cannot be split'.
• Atoms of the same element are identical, but different elements have different atoms.
• Atoms consist of sub-atomic particles: protons, neutrons, and electrons.
• Protons and neutrons are located in the center of the atom, forming the nucleus.
• Electrons move around the nucleus.
• Protons and neutrons have significantly more mass than electrons; electrons have almost no mass.
• Protons and neutrons have approximately the same mass.
• Protons possess a positive electrical charge, while neutrons have no electrical charge.
• Electrons have a negative electrical charge.
• Atoms mainly consist of empty space.
• Electrostatic attraction between positive protons and negative electrons holds atoms together.

Development of the Atomic Model

• J.J. Thomson discovered the electron in the late 1890s.
• Thomson's model, known as the 'plum pudding model', proposed that electrons were scattered throughout the atom.
• Ernest Rutherford discovered the proton in 1909 and the nucleus in 1911.
• In Rutherford's gold foil experiment, most particles passed through, but some were deflected, leading to the idea of a dense, central nucleus and mostly empty space.
• James Chadwick proved the existence of neutrons in 1932.
• Scientists collaborate and undergo peer review to validate discoveries.

Purity

• A pure element consists of identical atoms.
• Gold purity is measured in carats, with 24 carat being pure gold.
• 18 carat gold contains 18 parts gold and 6 parts other metals, meaning 75% pure gold.
• Silver purity is marked with parts per thousand, e.g., 925 silver is 92.5% pure silver.
• Diamonds are made of carbon atoms. Pure diamonds are colorless and translucent.
• Impurities cause diamonds to have different colors such as nitrogen for yellow, boron for blue, nitrogen/nickel/hydrogen for green.

Seawater and Pure Products

• Seawater contains water and various salts like sodium chloride.
• Evaporation of seawater produces salt, but it is not pure sodium chloride, as it contains other salts.
• To obtain pure sodium chloride, other salts must be removed.
• Salts are compounds made from acids, e.g., sodium chloride from hydrochloric acid.
• Pure products are essential, especially in medicines, to avoid harmful impurities.
• Some reactions have multiple products that need separation to produce a pure product.

Weather and Climate

• Weather is the state of the atmosphere at a specific time, changing rapidly.
• Climate refers to the average weather conditions of a place over a long period, typically more than 30 years.
• Factors affecting weather include temperature, humidity, cloudiness, precipitation, visibility, and wind.
• Climate is mainly affected by temperature and precipitation.
• Meteorology is the study of weather while climatology is the study of climate.

Climate Zones

• Polar: very cold and dry all year
• Temperate: cold winters and mild summers
• Arid: hot and dry all year
• Tropical: hot and wet all year
• Mediterranean: mild winters and hot, dry summers
• Mountains/tundra/taiga: very cold all year

Climate and Ice Ages

• The earth's climate cycles between glacial and interglacial periods.
• A glacial period is when much of the Earth is frozen.
• An interglacial period is the warmer period between glacial periods.
• Over the last 450000 years earth’s climate has cycled or swung between glacial and interglacial periods.
• Ice ages are longer periods when the Earth experiences cold periods, with glacials and interglacials.
• Evidence of past ice ages includes boulders in unexpected locations and scratches on rock surfaces.
• Scientists use pollen from peat bogs to determine past climates and the deeper the peat, the older it is.

Atmosphere and Climate

• The atmosphere is a layer of gas above the Earth's surface.
• The early atmosphere, formed by volcanic activity, contained mainly carbon dioxide, methane, ammonia, and water vapor.
• Today's atmosphere contains mainly nitrogen and oxygen.
• Micro-organisms and plants have changed the earth’s atmosphere as plants use carbon dioxide to produce food and release oxygen.
• Carbon is recycled when organisms die and rot; fossil fuels and limestone formation also lock up carbon.
• Human burning fossil fuels releases locked up carbon dioxide, leading to increased atmosphere carbon dioxide levels.
• Deforestation reduces carbon dioxide use, increasing atmospheric levels as well.
• Calcium carbonate in limestone releases carbon dioxide when used to make building materials.
• Increased carbon dioxide and other gases acts like a blanket around the Earth, this is an analogy for the greenhouse effect.

Reducing Global Warming

• Renewable resources, like wind, tidal, and solar power, do not deplete and reduce global warming.
• Non-renewable resources, like coal, petroleum, and and natural gas, cannot be replaced after use.
• Renewable resources such as wind turbines, tidal energy, solar electricity can be used to generate electricity.
• Bioplastics are biodegradable materials from renewable sources like vegetable oils or sawdust unlike conventional plastics from petroleum.