Chemistry - an illustrated guide to science (794128), страница 2
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How and how far itcollapses depends on the size of thestar.Time1 The fate of a star thesize of our sun2 Fate of a larger star● A starhgTimeijkthe size of our Sun burnshydrogen into helium until thehydrogen is exhausted and the corebegins to collapse. This results innuclear fu sion reactions in a shellaround the core. The outer shell heatsup and expands to produce a redgian t.● Ultimately, as its nuclear reactionssubside, a red giant cools andcontracts. Its core becomes a verysmall, dense hot remnant, a whitedwarf.2 Fate of a larger star3 Fate of a massive starTimelma hydrogen is converted to heliumb planetary system evolvesc hydrogen runs out and helium is convertedto carbond star cools to form a red giante carbonf star evolves to form a white dwarfg hydrogen is converted to helium and carbon,and eventually ironh hydrogen runs out, and star undergoesgravitational collapseni The collapsed star suddenly expands rapidly,creating a supernova explosionj creates many different elementsk the core of the dead star becomes a neutronstarl hydrogen converted to many differentelementsm hydrogen runs out, and the star collapses toform a black holen black holewith an initial mass 10 times thatof our Sun go further in the nuclearfusion process until the core is mostlycarbon.
The fusion of carbon intolarger nuclei releases a massiveamount of energy. The result is a hugeexplosion in which the outer layers ofthe star are blasted out into space.This is called a su pern ova.● After the explosion, the remainingmaterial contracts, and the corecollapses into an extraordinary denseobject composed only of neutrons—a neutron star.3 Fate of a massive star● Starswith an initial mass of 30 timesour Sun undergo a different fatealtogether.
The gravitational field ofsuch stars is so powerful that materialcannot escape from them. As nuclearreactions subside, all matter is pulledinto the core, forming a black hole.© Diagram Visual Information Ltd.● Stars10ATOMIC STRUCTUREKey wordsammoniafissionheliumhydrogenmethaneThe solar system1 Birth of the solar system3 Inner planetsMercury1 Birth of the solar system● Thesolar system is thought to haveformed about 4.6 billion years ago as aresult of nuclear fission in the Sun.● A nebula (cloud) of gases and dustthat resulted from the explosion.flattened into a disk with a highconcentration of matter at the center.2 Formation of the innerand outer planetsthe Sun, where the temperaturewas high, volatile substances could notcondense, so the inner planets(Mercury, Venus, Earth, and Mars) aredominated by rock and metal. Theyare smaller and more dense than thosefarther from the Sun.● In the colder, outer areas of the disk,substances like am m on ia andm ethan e condensed, while hydrogenand heliu m remained gaseous.
In thisregion, the planets formed (Jupiter,Saturn, Uranus, and Neptune) weregas giants.fgMarscba● Near3 Inner planetsplanets consist of a light shellsurrounding a dense core of metallicelements.● Mercury, the planet closest to the Sun,has a proportionately larger core thanMars, the inner planet farthest fromthe Sun.hfghiilight shelldense corelight shelldense core4 Outer planetsUranus andNeptunekja hydrogen and heliumb heavier elementsc lighter elements● Innerlj diameter = 2 or 3 that of the Earthk solid water, methane, and ammonial liquid water, methane, and ammonia2 Formation of the innerand outer planets4 Outer planetse● The© Diagram Visual Information Ltd.outer planets have low densitiesand are composed primarily ofhydrogen and helium.● The outer planets are huge incomparison to the inner planets.● Jupiter and Saturn, the largest of thegas giants, contain the greatestpercentages of hydrogen and helium;the smaller Uranus and Neptunecontain larger fractions of water,ammonia, and methane.dmJupiter andSaturnond denser inner planetse less dense outer planetsm liquid hydrogen and heliumn small rocky centero radii:Jupiter = 11 × radius of EarthSaturn = 9 × radius of Earth11Planet compositionATOMIC STRUCTUREKey words1 Basic composition of the planetsabcatmospherecarbonatecrustmantlenitratedIron/ nickel core shell of silicon and other elementsoxidesulfate1 Basic composition of theplanets● Theeinner planets—Mercury, Venus,Earth, and Mars—consist of aniron–nickel core surrounded by a shellof silicon and other elements.● The outer planets—Jupiter, Saturn,Uranus, and Neptune—consist largelyof solid or liquid methane, ammonia,liquid hydrogen, and helium.● Pluto is not included in thiscomparison because it is atypical ofthe other outer planets, and its originsare uncertain.f2 Composition of EarthLiquid hydrogen and heliumghSolid/ liquid water, methane, and ammoniaa Mercuryb Venusc Earthd Marse Jupiterf Saturng Uranush Neptune2 Composition of Earthimjkli crustj mantle (oxygen, silicon, aluminum, iron)k outer core (liquid – nickel and iron)nCompositionof Earth%oxygensiliconaluminumironcalciumsodiumpotassiummagnesium4628854332l inner core (solid – nickel and iron)m crust, mantle, and oceans = 2/ 3 of mass)n core = 1/ 3 of massconsists of a dense, solid innercore and a liquid outer core of nickeland iron.
The core is surrounded bythe m an tle (a zone of dense, hotrock), and finally by the cru st, which isthe surface of Earth.● Since most of the materials of Earthare inaccessible (the deepest drilledholes only penetrate a small distanceinto the crust), we can only estimatethe composition of Earth by looking atthe composition of the materials fromwhich Earth formed. Meteoritesprovide this information.● Oxygen is the most common elementon Earth, and about one fifth ofEarth’s atm osphere is gaseous oxygen.● Oxygen is also present in manycompounds, including water ( H2O),carbon dioxide ( CO2), and silica( SiO2), and metal salts such as oxides,carbon ates, n itrates, and su lfates.© Diagram Visual Information Ltd.● Earth12Key wordsatmospherecarbon dioxidechlorophyllphotosynthesisPlanetary density, size,and atmosphere1 Densities and radii of the planetse71 Densities and radii of theplanets2 Atmospheric compositionof the inner planets© Diagram Visual Information Ltd.● Earth’satm osphere was probablysimilar to that of Venus and Mars whenthe planets formed.
However, theparticular conditions on Earth allowedlife to start and flourish. With thiscame drastic changes to thecomposition of the atmosphere. Ofparticular importance is the evolutionof green plants.● Green plants contain a pigment calledchlorophyll. Plants use this pigment totrap energy from sunlight and makecarbohydrates. The process is calledphotosyn thesis.● As Earth became greener, theproportion of carbon dioxide in theatmosphere fell until it reached thepresent level of about 0.04 percent.● The green plants provided a means ofturning the Sun’s energy into food,which in turn, provided animals withthe energy they needed to survive.Thus, animals could evolve alongsideplants.● Conditions on the two planetsadjacent to Earth—Venus and Mars—were not suitable for life as we knowit, and the atmospheres on theseplanets have remained unchanged.f6● Thea60 ,0 0 0cb5Density (relative to water)inner planets—Mercury, Venus,Earth, and Mars—are relatively smallbut have a higher density than theouter planets.● The outer planets—Jupiter, Saturn,Uranus, and Neptune—are relativelylarge but have a lower density than theinner planets.70 ,0 0 050 ,0 0 0Radiusd440 ,0 0 0330 ,0 0 0hg220 ,0 0 0heg110 ,0 0 0acbdDensityf01,0 0 02,0 0 0Distance from Sun (in millions of miles)a Mercuryb Venusc Earthg Uranush Neptuned Marse Jupiterf Saturn2 Atmospheric composition of the inner planetsMarsVenusEarthCarbon dioxideNitrogenOxygenOthers3,0 0 0Radius (in km)ATOMIC STRUCTURE13Atomic structureATOMIC STRUCTURE1 Principle subatomic particlesParticleKey wordsRelative atomic massRelative chargeElectron11836–1Neutron10Proton11atomatomic numberelectronisotopemass numberneutronnucleusprotonsubatomicparticle1 Principle subatomicparticles2 The atom● Anproton+nucleusneutronelectron+ +++ +++++ ++atom is the smallest particle of anelement.
It is made up of even smallersu batom ic particles: negativelycharged electron s, positively chargedproton s, and n eu tron s, which have nocharge.2 The atom● Anatom consists of a n u cleu s ofprotons and neutrons surrounded bya number of electrons.● Most of the mass of an atom iscontained in its nucleus.● The number of protons in the nucleusis always equal to the number ofelectrons around the nucleus. Atomshave no overall charge.73 Li3 Representing an element● Elementscan be represented usingtheir m ass n u m ber, atom ic n u m ber,and atomic symbol:3 Representingan elementmass numberatomic number++Symbol● Theatomic number of an atom is thenumber of protons in its nucleus.● The mass number is the total numberof protons and neutrons in its nucleus.Thus, an atom of one form of lithium( Li ), which contains three protons andfour neutrons, can be represented as:+73 Li4 Isotopes4 Isotopes+++Hydrogen 1Hydrogen 2Hydrogen 3atoms of the same element havethe same atomic number; however,they may not have the same massnumber because the number ofneutrons may not always be the same.Atoms of an element that havedifferent mass numbers are calledisotopes.
The diagram at left illustratesisotopes of hydrogen.© Diagram Visual Information Ltd.● All14ATOMIC STRUCTUREKey wordsalpha particleatomatomic massGeiger and Marsden’sapparatusbDeveloping the atomicmodel© Diagram Visual Information Ltd.● Atend of the 19th century, scientiststhought that the atom was a positivelycharged blob with negatively chargedelectrons scattered throughout it. Atthe suggestion of British physicistErnest Rutherford, Johannes Geigerand Earnest Marsden conducted anexperiment that changed this view ofthe atomic model.● Scientists had recently discovered thatsome elements were radioactive—theyemitted particles from their nuclei as aresult of nuclear instability.
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