South 중학교 2학년 Science 2
Chapters: 8
1. Properties of matter
Characteristic properties of substances · Pure substances and mixtures · Separating mixtures
- Properties of Matter – Matter is anything that has mass and takes up space. Some properties, like mass and volume, depend on how much you have. Others, called characteristic properties, are the same for any amount of a pure substance and help identify it: density (mass ÷ volume), melting point, boiling point and solubility. In a physical change (melting, boiling, dissolving) no new substance forms and the total mass stays the same. In a chemical change a new substance forms. Particles are close in solids and liquids and far apart in gases, which is why gases have very low density; moving particles also explain diffusion and Brownian motion.
- Mixtures and Their Separation – A mixture has two or more substances mixed without any fixed ratio, and each keeps its own properties. Homogeneous mixtures (solutions) look the same everywhere; heterogeneous ones do not. By particle size we get solutions (< 1 nm), colloids (1–1000 nm) and suspensions (> 1000 nm). Colloids scatter light (Tyndall effect). Concentration tells how much solute is in a solution. We separate mixtures by using a difference in their parts: evaporation, crystallisation, distillation, chromatography, sublimation, centrifugation and coagulation.
2. Changes in the geosphere
Earth system and layers of the Earth · Rock-forming minerals and their uses · Rock types and the rock cycle · Weathering and soil formation · Continental drift and plate boundaries
- Interior of the Earth: Earthquake Waves, Layers and Volcanoes – Nobody can dig to the centre of the Earth, so we learn about the inside from direct sources (mine rocks, deep drilling, lava) and indirect sources (heat and pressure with depth, meteors, gravity, magnetism and, above all, earthquake waves). P-waves travel through solids and liquids; S-waves only through solids. Where the waves do not arrive, we get shadow zones, which prove the outer core is liquid. Earthquakes are measured by magnitude (Richter) and intensity (Mercalli). The Earth has a thin crust, a thick mantle with a soft asthenosphere, a liquid outer core and a solid inner core. Magma that reaches the surface builds volcanoes; magma that cools inside forms intrusive landforms like batholiths, sills and dykes.
- Rocks and Minerals – A mineral is a natural, non-living solid with a fixed chemical make-up and a regular crystal shape, like quartz or halite. A rock is a mixture of one or more minerals. Rocks are of three types: igneous (from cooled magma or lava), sedimentary (from layers of pressed bits) and metamorphic (changed by heat and pressure). The rock cycle slowly turns each type into the others over millions of years.
3. Light and waves
Reflection and refraction; how we see · Images in mirrors and lenses · Colour and mixing light · Waves and properties of sound
- Light and Colour: Mixing, Seeing and Energy of Light – White light is a mix of colours (red to violet). Lights add: red + green + blue make white (additive mixing, used by screens). Paints take away: cyan + magenta + yellow make near-black (subtractive mixing). An object has a colour because it reflects some colours and absorbs the rest. Eyes use three kinds of cone cells. Light colour tells its energy: E = hf, blue photons carry more energy than red.
- Sound – Sound is made by vibrating objects. It travels through a medium (air, water, solids) as a longitudinal wave: particles move back and forth, making crowded parts (compressions) and spread-out parts (rarefactions). Frequency (Hz) sets the pitch, amplitude sets the loudness, and speed v = f × λ. Sound cannot travel in vacuum. Humans hear 20 Hz to 20,000 Hz; below is infrasound, above is ultrasound. Reflected sound gives echoes, used and controlled in buildings.
4. Composition of matter
Elements, compounds and formulas · Protons, neutrons, electrons · The periodic table and similar elements · Atoms, molecules and ions
- Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
- Structure of the Atom – An atom has a tiny, heavy, positive nucleus made of protons and neutrons. Electrons move around it in fixed shells K, L, M, N. The number of protons (Z) tells the element; protons + neutrons give the mass number (A). Outer electrons decide valency. Isotopes share Z; isobars share A.
- Periodic Classification of Elements – Scientists sorted elements so that similar ones sit together. Döbereiner made triads, Newlands found that every 8th element repeats (octaves), Mendeleev arranged elements by atomic mass and left gaps for unknown ones. Moseley showed that atomic number is the real key. Modern periodic law: the properties of elements are a periodic function of their atomic numbers. The modern table has 7 periods and 18 groups. Elements with Z > 100 get temporary IUPAC names built from digit roots (nil, un, bi, tri, quad, pent, hex, sept, oct, enn) plus -ium.
5. Plants and energy
Photosynthesis and its conditions · Plant respiration vs photosynthesis · Storing and using photosynthesis products
- Life Processes and Photosynthesis – Life processes are the jobs every living body must keep doing to stay alive: nutrition, respiration, transport and excretion. Green plants do nutrition by photosynthesis: using sunlight and chlorophyll, they turn carbon dioxide and water into glucose and give out oxygen.
- Respiration: Aerobic, Anaerobic and the Human Lungs – Respiration is the breakdown of food, usually glucose, inside cells to release energy, stored as ATP. With oxygen (aerobic) glucose is fully broken into carbon dioxide and water and gives much energy; without oxygen (anaerobic) it gives little energy and makes ethanol (yeast) or lactic acid (muscles). Our lungs bring oxygen to the blood through millions of alveoli.
6. Animals and energy
Digestive system and enzymes · Circulatory system and blood flow · Respiratory system and breathing model · Excretory system · Cellular respiration links all systems
- Human Digestive System and Heterotrophic Nutrition – Heterotrophs take ready-made food from other living things. Humans are holozoic: we eat whole food and break it down in a long tube, the alimentary canal. Teeth, saliva, stomach acid, enzymes, bile and pancreatic juice cut big food molecules into small ones that villi in the small intestine absorb into blood.
- Transportation in Humans: Heart, Blood Vessels, Blood and Lymph – The heart is a four-chambered muscular pump. Blood passes through it twice in one full round: once to the lungs to pick up oxygen, and once to the rest of the body. This is double circulation. Arteries carry blood away from the heart, veins bring it back and capillaries do the exchange. Blood (plasma, RBCs, WBCs, platelets) and lymph together carry food, gases, hormones and wastes.
- Respiration: Aerobic, Anaerobic and the Human Lungs – Respiration is the breakdown of food, usually glucose, inside cells to release energy, stored as ATP. With oxygen (aerobic) glucose is fully broken into carbon dioxide and water and gives much energy; without oxygen (anaerobic) it gives little energy and makes ethanol (yeast) or lactic acid (muscles). Our lungs bring oxygen to the blood through millions of alveoli.
7. Electricity and magnetism
Static electricity and induction · Current, voltage and resistance · Series/parallel resistors and electric power · Force on a current-carrying coil
- Static Electricity – Rubbing two different materials moves electrons from one to the other. The one that gains electrons becomes negative; the one that loses them becomes positive. Charge is never made or destroyed, only moved. Like charges repel and unlike charges attract. A charged object can pull a neutral one by induction. Earthing lets extra charge flow safely away.
- Ohm's Law – At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V = I × R. R is the resistance, measured in ohms (Ω); 1 Ω = 1 V/1 A. The V–I graph of an ohmic conductor is a straight line through the origin.
- Force on a Current-Carrying Conductor, Motor and Induction – A wire carrying current inside a magnetic field feels a push. The push is biggest when the wire is at 90° to the field and zero when it is parallel. Fleming's left-hand rule gives its direction. A motor uses this push to spin a coil; a generator does the reverse and makes current by moving a coil or magnet.
8. Stars and the universe
Distance, brightness and colour of stars · Our galaxy, nebulae and clusters · The expanding universe · Space exploration and its impact
- Stars: Colour, Brightness, Distance and the H-R Diagram – A star is a huge ball of hot gas that shines by nuclear fusion. Its colour shows its surface temperature: red stars are cool, blue stars are hot (Wien's law: λmax × T = 2.9 × 10⁻³ m K). Stars are sorted into spectral classes O B A F G K M, hottest to coolest. How bright a star looks (apparent magnitude) depends on its real power (luminosity) and its distance, because light weakens as 1/d². Nearby distances are found by parallax: d (pc) = 1/p (arcsec). Luminosity depends on size and temperature (L = 4πR²σT⁴). The H-R diagram plots luminosity against temperature and shows the main sequence, giants and white dwarfs.
- Stars and Galaxies: From Starlight to the Big Bang – Everything we know about stars comes from their light. Splitting starlight into a spectrum shows dark lines that tell us which elements a star has; the colour tells us its temperature (blue = hot, red = cool) and stars are sorted into classes O B A F G K M. The H-R diagram plots true brightness against temperature: most stars, including the Sun, lie on the main sequence, with giants top right and white dwarfs bottom left. A star is born in a nebula and its mass decides its life: a Sun-like star becomes a red giant and then a white dwarf; a star of more than about 8 solar masses becomes a supergiant, explodes as a supernova and leaves a neutron star or black hole. Stars gather in galaxies, which are spiral, elliptical or irregular. Distances are huge, so we use the astronomical unit, the light-year and the parsec. Galaxies are moving apart, faster when farther (Hubble's law), which together with the cosmic microwave background supports the Big Bang about 13.8 billion years ago.
- Cosmology: The Expanding Universe and the Big Bang – Cosmology is the study of the whole universe: its structure, history and future. Galaxies gather in groups, clusters and filaments around huge voids. Distant galaxies are moving away from us, faster the farther they are (Hubble's law, v = H₀d), because space itself is expanding. Running the expansion backwards leads to a hot, dense beginning about 13.8 billion years ago, the Big Bang. The main evidence is redshift, the cosmic microwave background and the amounts of hydrogen and helium. Most of the universe is dark matter and dark energy.
- Space Exploration – Space exploration means sending rockets, satellites, probes and people beyond Earth's air. Rockets rise by pushing gas down (action–reaction). At about 7.9 km/s sideways a craft keeps falling around Earth in orbit; at 11.2 km/s it escapes. Since 1957 space has been a place of rivalry and cooperation, and it gives us weather forecasts, navigation, communication and new science.