nats1311 from the cosmos to earth atom definition: the smallest unit of a chemical element that has...

NATS1311 From the Cosmos to Earth

ATOM

DEFINITION:

The smallest unit of a chemical element that has the properties of the element.

The atom consists of a nucleus with orbiting electrons surrounding the nucleus.

NATS 1311 From the Cosmos to Earth .

Nuclear stability diagram.

Number of neutrons vs. number of protons in a nucleus.

NATS 1311 From the Cosmos to Earth

Radioactive Decay Processes

alpha decay

beta minus decay

electron capture

beta plus decay

Changes number of protons and neutrons in decaying nucleus

Type of decay protons neutrons nucleons -2 -2 -4- +1 -1 0ec -1 +1 0+ -1 +1 0 0 0 0

= gamma ray emission from nucleus

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92238U → 90

234Th+24α

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614C→ 7

14N+−10β

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47Be+−1

0e→ 37Li

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814O→ 7

14N++10β


Half life

The time required for one half of a group of nuclei to

decay into their daughter products.

Sometimes called lifetime.


RADIOACTIVE ISOTOPES USED IN GEOCHRONOLOGY

URANIUM → LEAD238U → 206PB

HA LF LIFE: 4.5 BILLION YEARS

STRONTIUM → RUBIDIUM87SR → 87RB

HA LF LIFE: 47 BILLION YEARS

POTASSIUM → ARGON40K → 40AR

HA LF LIFE: 1.3 BILLION YEARS

CARBON → NITROGEN14C → 14N

HA LF LIFE: 5500 YEARS


Besides radioactive decay of an unstable nucleus, nuclei undergo two other process to change for one element to another.

These are fission and fusion.

Fission:Breaking apart a heavy nucleus into two lighter nuclei.

Requres a neutron to activate the process.

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92235U+n→ 92

236U→ 3894Sr+54

140Xe+2n+E


Besides radioactive decay of an unstable nucleus, nuclei undergo two other process to change for one element to another.

These are fission and fusion.

Fusion:Combination of light nuclei into a heavier nucleus producing a large quantity of energy.

4 hydrogen atoms combine into 1 helium atom.

This process requires extremely high temperatures and pressures and occurs in the core of stars.


Nuclear fission and fusion

Binding energyEnergy equivalent to missing mass of a nucleus.

Mass of hydrogen atom 1.0078 amuAdd mass of a neutron 1.0087 amu

2.0165 amuMass of deuterium atom 2.0141 amuMissing mass 0.0024 amu

1 amu (atomic mass unit) = 931 MeVfrom E= m c2

Therefore 0.0024 amu = 2.2 Mev = 3.5x10-13 Joules

This is called the binding energy of deuterium


1 gram of hydrogen produces 1 x 1011 Joules of energy.

Enough to boil 50 tons of water.

Binding energy per nucleon :(the number of protons and neutrons in the Nucleus)

Total binding energy of atomNumber of nucleons in atom


Triple alpha process. Three helium atoms combine to form 1 carbon atom.


C-N-O Process.

4 Hydrogen atoms are added, one at a time to 12C, 13C, 14N, and 15N.

The end products are 12C and a Helium atom.

The net result is 4 hydrogen atoms form 1 helium atom.


Element building

The process of element bulding continues by adding the nucleus of one helium atom at a time to 12C until 56Fe (Iron-56) is obtained.

12C6 +4He2 -›16O8

16O8+ 4He2 -› 20Nel0

20Nel0+4He2 -› 24Mgl2

•• •

52Cr24 +4He2 -› 56Fe26

The process stops here. • maximum stability is reached • the next element has a lower binding energy

and greater relative nuclear mass.

NATS 1311 From the Cosmos to Earth FIG. 14.16

Figure 14.16 Overall, the average mass per nuclear particle declines from hydrogen to iron and then increases. Selected nuclei are labeled to provide reference points. (This graph shows the most general trends only; a more detailed graph would show numerous up-and-down bumps superimposed on the general trend.)


Figure 14.18 This graph shows the observed relative abundances of elements in the galaxy in comparison to the abundance of hydrogen.

For example, the abundance of nitrogen is about 10-4, which means that there are about 10-4 (=0.0001) times as many nitrogen atoms in the galaxy as hydrogen atoms.


LAWS OF RADIATION

Black body:An ideal object that absorbs all radiant energy that reaches its surface. It also emits radiation, the characteristics of which depend on its temperature.

Planck's law:Planck developed a mathematical formula that explainedradiation from black bodies. He assumed light existed in small quanta called photons

E = hfwhere

h = Planck's constantf = frequency of vibration


Spectrum:The amount of radiation given off at each wavelength.

Stefan's law: (Rule 1)The energy emitted by a black body is proportional tothe fourth power of its absolute temperature

E ~T4

Wien's law: (Rule 2)The wavelength at which most energy is emitted from a black body is inversely proportional to its absolute temperature.

NATS1311 From the Cosmos to Earth FIG. 6.10

Figure 6.10 Graphs of idealized thermal radiation spectra. Note that, per unit surface area, hotter objects emit more radiation at every wavelength, demonstrating Rule 1 for thermal radiation. The peaks of the spectra occur at shorter wavelengths (higher energies) for hotter objects, demonstrating Rule 2 for thermal radiation.


Temperature (K) of Black

Body

Wavelength (max) at Which Most Radiation is

Emitted

Type of Radiation

3 0.1 cm Radio waves

300 0.001 cm "Far" Infrared

3,000 1000 nm "Near" Infrared

4,000 750 nm Red Light

6,000 500 nm Yellow Light

8,000 375 nm Violet Light

10,000 300 nm "Near" Ultraviolet

30,000 100 nm "Far" Ultraviolet

300,000 10 nm "Soft" X-Rays

1.5 million 20 nm "hard" x-rays

3 billion 0.001 nm Gamma rays


Spectral classes of stars

Spectral Intrinsic Effective Class color temperature* O electric blue 38,000 B blue 30,000 A blue white 10,800 F yellow white 7,240 G yellow 5,920 K orange 5,240 M red 3,920

*For the hottest spectral type in class, such as A0 in class A.Each class is divided into 10 subgroups labeled 0 - 9. For example, B0 (hottest), or B9 (coolest) in class B.


LUMINOSITIES

Luminosity: ~ r2T4

Apparent magnitude: Apparent brightness of acelestial body based

on a logarithmic scale of

luminosity.

Magnitude scale: 1 is 2.5:12 is 6.3:15 is 100:1

Absolute magnitude: Equivalent to the apparentmagnitude if star were

placed 10 parsecs (32.6 light years) from sun.

NATS 1311 From the Cosmos to Earth 13.1.

Figure 13.1 The inverse square law for light. At greater distances from a star, the same amount of light passes through an area that gets larger with the square of the distance. The amount of light per unit area therefore declines with the square of the distance.


Figure 13.8 A Hertzsprung-Russell (H-R) diagram, one of astronomy's most important tools, shows how the surface temperatures of stars, plotted along the horizontal axis, relate to their luminosities, plotted along the vertical axis.Note - vertical scale is a logarithmic scale. It has 11 decades of range.


Blue supergiants:Bluest, most luminous, hottest; moderately large stars; low densities and large masses, very rare.

Example: Rigel


Red supergiants:Orange to red in color; the largest stars and among the brightest; large masses and extremely low densities; few in number.

Example: Betelguese


Giants:Yellow, orange, and red; considerably larger and brighter than the sun; average to larger than average masses and low densities; fairly scarce.

Example: Arcturus


Middle main sequence stars:White, yellow, and orange; stars higher than the sun on the main sequence are somewhat larger, hotter, more massive, and less dense than the sun; plentiful in number.

Example: Sirius


Middle main sequence stars:

Stars below the sun on the main sequence are somewhat smaller, cooler, fainter, less massive, and denser than the sun; plentiful in number.

Example: Eridani


Figure 13.8 Red dwarfs: Coolest and reddest stars on the low rung of the main sequence; considerably fainter and smaller than the sun; small masses and high densities; the most abundant stars.

Example: Barnard's star


White dwarfs: Mostly white and yellow; extremely faint and tiny by solar standards; enormously high densities; terminal evolutionary development; quite plentiful.

Example: The binary

companion of Sirius


Life Cycle of a Star

1 Protostar Forms in a solar nebula - A swirling mass of gases

and dust particles

Gravitational collapse causes pressure andtemperature increase.

When temperature reaches 10 million degrees, hydrogen fusion in the core begins.

Star's position on Hertzsprung-Russell (H-R) diagram: moves onto the main sequence,


Figure 14.5 The life track of a 1 solar mass star from protostar to main-sequence star. Time for the Sun to reach the main sequence is about 50 million years.


2. Main Sequence

Location on the main sequence depends on the mass of the star.

Massive stars lie at the upper left; low mass stars at the lower right.

O-type stars, more that 8 solar masses, have very high core temperatures and fuse hydrogen into helium very rapidly.Lifetime on main sequence is relatively short - millions of years.


Figure 13.10 Along the main sequence, more massive stars are brighter and hotter but have shorter lifetimes. (Stellar masses are given in units of solar masses: 1 solar mass equals 2 X 1030 kg.)Stars on the main sequence undergo hydrogen fusion in their cores.


Figure 14.6 Life tracks from protostar to the main sequence for stars of different masses.


Figure 14.8 The life track of a 1 solar mass star on an H-R diagram from the end of its main-sequence life until it becomes a red giant.When fusion ceases, core shrinks and star expands; becomes a sub giant. Luminosity increases and star becomes a red giant 100 times diameter of present sun.For Sun, this takes 1 billion years.


Figure 14.9 After a star ends its main-sequence life, its inert helium core contracts while hydrogen shell burning begins. The high rate of fusion in the hydrogen shell forces the star's upper layers to expand outward.


Figure 14.10 (a)Core structure of a helium-burning star. (Triple alpha process)(b) Approximate relative sizes of a low-mass star as a main-sequence star, a red giant, and a helium-burning star. The scale is not precise; in particular, the size of the main-sequence star is even smaller compared to the others.


Figure 14.11 (a)After the helium flash, the rapid initiation of the triple alpha process, a low-mass star's surface shrinks and heats, so the star's life track moves downward and to the left on the H-R diagram.


Figure 14.11 (b) This H-R diagram plots the luminosity and surface temperature of individual stars in a cluster, that is, those stars that have about the same luminosity (i.e., it does not show life tracks, just the location of these stars).


3. Red Giant

A star ends its main-sequence life when all the hydrogen in its core is fused into helium; core collapses raising its temperature to 100 million degrees.

Its inert helium core contracts while hydrogen fusion in a shell outside the core begins. The high rate of fusion in the hydrogen shell forces the star's upper layers to expand outward causing the star to expand greatly in size, moving location on H-R diagram up and to the right to the giant region. Star becomes a red giant.


3. Red Giant

Outer region of star cools.

The core collapses further until the triple alpha process which converts 3 alpha particles into a

carbon nucleus begins, releasing more energy. This is a rapid process, called the helium flash, that causes core collapse to stop.

More massive stars move to the supergiant region. Triple alpha process continues.


Figure 14.12 The life track of a 1 solar mass star from main-sequence star to white dwarf. The dashed line represents the rapid transition from planetary nebulae to white dwarf as the ejected outer layers dissipate, revealing the hot core.


4. Planetary nebula When Helium fusion is complete and the core is carbon, helium fusion moves to the shell outside the

core. A second expansion occurs. The star becomes unstable and eventually blows

away all its outer layers, which are called the planetary nebula, leaving just the core.


Figure 14.13 Planetary nebulae occur when low-mass stars in their final death throes cast off their outer layers of gas, as seen in these photos. The hot core that remains ionizes and energizes the richly complex envelope of gas surrounding it. (a)Ring Nebula (b) Helix Nebula (c) Twin Jet Nebula


5. White dwarfRemaining core of star that is less than 1.4 solar masses.

Core cools slowly and becomes a black dwarf.


Figure 14.12 The life track of a 1 solar mass star from main-sequence star to white dwarf. The dashed line represents the rapid transition from planetary nebulae to white dwarf as the ejected outer layers dissipate, revealing the hot core.


Stars initially having more than 3 time the solar mass.

Life cycle is similar to that of sun.

Elements beyond carbon formed in core due to extremely high

temperature. Alpha particles fuse with carbon nucleus

to build heavier elements up to iron.

Star eventually becomes unstable and explodes in a supernova

event. During supernova event, elements heavier than

iron are formed.


Figure 14.14 The multiple layers of nuclear burning in the core of a high-mass star during the final days of its life.


Figure 14.20 Before and after photos of the location of Supernova 1987A. In the before picture, the arrow indicates the star that exploded. Note that the supernova actually appeared as a bright point of light; it appears larger than a point in the photograph only because of overexposure.



Life cycle is similar to that of sun.

Elements beyond carbon formed in core due to extremely high temperature. Alpha particles fuse with carbon nucleus

to build heavier elements up to iron.

Star eventually becomes unstable and explodes in a supernova event. During supernova event,

elements heavier than iron are formed.

Core collapses into neutron star. Electrons are forced intonucleus to combine with protons to form only

neutrons in nucleus. Extremely dense matter. Mass of the

core lies between 1.4 and 3 solar masses.


Figure 14.17 During the final, catastrophic collapse of a high-mass stellar core, electrons and protons combine to form neutrons, accompanied by the release of neutrinos.


Figure 15.5 (a) A pulsar is a rapidly rotating neutron star that beams radiation along its magnetic axis. (b) This artwork likens a pulsar (top) to a lighthouse (bottom). If a pulsar's radiation beams are not aligned with its rotation axis, they will sweep through space. Each time one of these beams sweeps across Earth, we see a pulse of radiation.



Stars whose core is more than 8 solar masses collapse into black holes. No forces are strong enough to stop the collapse.

Black holes are so massive that nothing, not even light, can escape from them. Their escape velocity is greater than the speed of light.


Figure 14.21 Summary of stellar lives. The life stages of a high-mass star (on the left) and a low-mass star (on the right) are depicted in clockwise sequences beginning with the protostellar stage in the upper left corner.


FORCES IN NATURE:TYPE

gravityweakest of all forces,but dominant in the universe

strong nuclearstrongest force,but very short ranged

electromagneticrelatively weak force,produces electromagnetic radiation and involved in chemical reactions

weak nuclearonly important in deacy of

elementary particles


FUNDAMENTAL PARTICLES

Electrons and neutrinos Lepton type particles - very light mass elementary

particlesNeutrons and protons

Composed of quarks - heavy elementary particles

6 types of quarksUp electric charge +2/3 eDown electric charge -1/3eStrangeCharmedTopBottom


FUNDAMENTAL PARTICLES

Proton - 3 quarks; up, up, down

Electric charge: +2/3, +2/3, -1/3 = 1

Neutron - 3 quarks; up, down, down

Electric charge: +2/3, -1/3, -1/3 = 0

nats1311 from the cosmos to earth atom definition: the smallest unit of a chemical element that has...

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