Episode 2

After three months, mrs job was yet to give birth has she lost hope completely.

Mrs job was a teacher in great star high school, she is a teacher of chemistry. One day in the class she entered and wrote the topic on the board '' element " .

Mrs job:who can define an element.

John: an element is a atom which can take part in a chemical reaction.

Mrs job looked at him and asked anyone else?,praise stood up.

Praise: an element is the smallest part of a substance which can not be broken down by ordinary chemical means.

Mrs job:give him a clap.just has praise had said,an element is the smallest particle of a substance which cannot be broken down into simpler form by ordinary chemical means.

CHEMICAL ELEMENT

Cosmic abundances of the elements

The relative numbers of atoms of the various elements are usually described as the abundances of the elements. The chief sources of data from which information is gained about present-day abundances of the elements are observations of the chemical composition of stars and gas clouds in the Galaxy, which contains the solar system and part of which is visible to the naked eye as the Milky Way; of neighbouring galaxies; of the Earth, Moon, and meteorites; and of the cosmic rays.

Stars and gas clouds

Atoms absorb and emit light, and the atoms of each element do so at specific and characteristic wavelengths. A spectroscope spreads out these wavelengths of light from any source into a spectrum of bright-coloured lines, a different pattern identifying each element. When light from an unknown source is analyzed in a spectroscope, the different patterns of bright lines in the spectrum reveal which elements emitted the light. Such a pattern is called an emission, or bright-line, spectrum. When light passes through a gas or cloud at a lower temperature than the light source, the gas absorbs at its identifying wavelengths, and a dark-line, or absorption, spectrum will be formed.

BRITANNICA QUIZ

27 True-or-False Questions from Britannica's Most Difficult Science Quizzes

How much do you know about Mars? How about energy? Think it'll be easier if you have to pick only true or false? Find out what you know about science with this challenging quiz.

Thus, absorption and emission lines in the spectrum of light from stars yield information concerning the chemical composition of the source of light and of the chemical composition of clouds through which the light has traveled. The absorption lines may be formed either by interstellar clouds or by the cool outer layers of the stars. The chemical composition of a star is obtained by a study of absorption lines formed in its atmosphere.

The presence of an element can, therefore, be detected easily, but it is more difficult to determine how much of it there is. The intensity of an absorption line depends not only on the total number of atoms of the element in the atmosphere of the star but also on the number of these atoms that are in a state capable of absorbing radiation of the relevant wavelength and the probability of absorption occurring. The absorption probability can, in principle, be measured in the laboratory, but the whole physical structure of the atmosphere must be calculated to determine the number of absorbing atoms. Naturally, it is easier to study the chemical composition of the Sun than of other stars, but, even for the Sun, after many decades of study, there are still significant uncertainties of chemical composition. The spectra of stars differ considerably, and originally it was believed that this indicated a wide variety of chemical composition. Subsequently, it was realized that it is the surface temperature of a star that largely determines which spectral lines are excited and that most stars have similar chemical compositions.

There are, however, differences in chemical composition among stars, and these differences are important in a study of the origin of the elements. Studies of the processes that operate during stellar evolution enable estimates to be made of the ages of stars. There is, for example, a clear tendency for very old stars to have smaller quantities of elements heavier than helium than do younger stars. This suggests that the Galaxy originally contained little of the so-called heavy elements (elements beyond helium in the periodic table); and the variation of chemical composition with age suggests that heavy elements must have been produced more rapidly in the Galaxy's early history than now. Observations are also beginning to indicate that chemical composition is dependent on position in the Galaxy as well as age, with a higher heavy-element content near the galactic centre.

In addition to stars, the Galaxy contains interstellar gas and dust. Some of the gas is very cold, but some forms hot clouds, the gaseous nebulae, the chemical composition of which can be studied in some detail. The chemical composition of the gas seems to resemble that of young stars. This is in agreement with the theory that young stars are formed from the interstellar gas.

Cosmic rays

High-energy electrons and atomic nuclei known as cosmic rays reach the Earth from all directions in the Galaxy. Their chemical composition can be observed only to a limited extent, but this can give some information about their place of origin and possibly about the origin of the chemical elements.

The cosmic rays are observed to be proportionately richer in heavy elements than are the stars, and they also contain more of the light elements lithium, beryllium, and boron, which are very rare in stars. One particularly interesting suggestion is that transuranium nuclei may have been detected in the cosmic rays. Uranium is element 92, the most massive naturally occurring on Earth; 20 elements beyond uranium (called the transuranium series) have been created artificially. All transuranium nuclei are highly unstable, which would seem to indicate that the cosmic rays must have been produced in the not too distant past.

Roger John Tayler

Solar system

Direct observations of chemical composition can be made for the Earth, the Moon, and meteorites, although there are some problems of interpretation. The chemical composition of Earth's crust, oceans, and atmosphere can be studied, but this is only a minute fraction of the mass of Earth, and there are many composition differences even within this small sample. Some information about the chemical properties of Earth's unobserved interior can be obtained by the study of the motion of earthquake waves and by Earth's magnetic field, which originates in the interior (see below Geochemical distribution of the elements).

Until recently, more was known about element abundances in distant stars than in Earth's nearest neighbour, the Moon. The lunar landings have provided samples that have been intensively analyzed in many laboratories throughout the world. The data for the Apollo 11 material, collected in the Sea of Tranquility (Mare Tranquillitatis), are given in the Table. Analyses of Apollo 12 collections are similar for most of the elements. Comparison of the analytical data with those for carbonaceous chondrites (a type of meteorite that provides a good average sample of nonvolatile solar system material) shows that the lunar material has undergone marked geochemical fractionation (segregation of elements). Meteorites suffer from heating in Earth's atmosphere, so that what is found on Earth is not necessarily the original chemical composition of the meteorites, especially for the volatiles, light gases that are easily lost. When allowance is made for the loss of volatile light gases and for effects of chemical separation, it seems quite possible that the overall chemical composition of Earth, the Moon, the Sun, and the meteorites is essentially the same and that they have a common origin.

READ MORE ON THIS TOPIC

star: Origin of the chemical elements

The relative abundances of the chemical elements provide significant clues regarding their origin. Earth's...

Chemical elements

element

symbol

atomic number

atomic weight

Elements with an atomic weight given in square brackets have an atomic weight that is given as a range. Elements with an atomic weight in parentheses list the weight of the isotope with the longest half-life.

Sources: Commission on Isotopic Abundances and Atomic Weights, "Atomic Weights of the Elements 2015"; and National Nuclear Data Center, Brookhaven National Laboratory, NuDat 2.6.

hydrogen

[1.00784, 1.00811]

helium

4.002602

lithium

[6.938, 6.997]

beryllium

9.0121831

boron

[10.806, 10.821]

carbon

[12.0096, 12.0116]

nitrogen

[14.00643, 14.00728]

oxygen

[15.99903, 15.99977]

fluorine

18.998403163

neon

20.1797

sodium

22.98976928

magnesium

[24.304, 24.307]

aluminum (aluminium)

26.9815385

silicon

[28.084, 28.086]

phosphorus

30.973761998

sulfur (sulphur)

[32.059, 32.076]

chlorine

[35.446, 35.457]

argon

39.948

potassium

39.0983

calcium

40.078

scandium

44.955908

titanium

47.867

vanadium

50.9415

chromium

51.9961

manganese

54.938044

iron

55.845

cobalt

58.933194

nickel

58.6934

copper

63.546

zinc

65.38

gallium

69.723

germanium

72.630

arsenic

74.921595

selenium

78.971

bromine

[79.901, 79.907]

krypton

83.798

rubidium

85.4678

strontium

87.62

yttrium

88.90594

zirconium

91.224

niobium

92.90637

molybdenum

95.95

technetium

(97)

ruthenium

101.07

rhodium

102.90550

palladium

106.42

silver

107.8682

cadmium

112.414

indium

114.818

tin

118.710

antimony

121.760

tellurium

127.60

iodine

126.90447

xenon

131.293

cesium (caesium)

132.90545196

barium

137.327

lanthanum

138.90547

cerium

140.116

praseodymium

140.90766

neodymium

144.242

promethium

(145)

samarium

150.36

europium

151.964

gadolinium

157.25

terbium

158.92535

dysprosium

162.500

holmium

164.93033

erbium

167.259

thulium

168.93422

ytterbium

173.045

lutetium

174.9668

hafnium

178.49

tantalum

180.94788

tungsten (wolfram)

183.84

rhenium

186.207

osmium

190.23

iridium

192.217

platinum

195.084

gold

196.966569

mercury

200.592

thallium

[204.382, 204.385]

lead

207.2

bismuth

208.98040

polonium

(209)

astatine

(210)

radon

(222)

francium

(223)

radium

(226)

actinium

(227)

thorium

232.0377

protactinium

231.03588

uranium

238.02891

neptunium

(237)

plutonium

(244)

americium

(243)

curium

(247)

berkelium

(247)

californium

(251)

einsteinium

(252)

fermium

100

(257)

mendelevium

101

(258)

nobelium

102

(259)

lawrencium

103

(262)

rutherfordium

104

(263)

dubnium

105

(268)

seaborgium

106

(271)

bohrium

107

(270)

hassium

108

(270)

meitnerium

109

(278)

darmstadtium

110

(281)

roentgenium

111

(281)

copernicium

112

(285)

ununtrium

Uut

113

(286)

flerovium

114

(289)

ununpentium

Uup

115

(289)

livermorium

116

(293)

ununseptium

Uus

117

(294)

ununoctium

Uuo

118

Chemical element

For other uses, see Element (disambiguation).

In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nuclei. Unlike chemical compounds, chemical elements cannot be broken down into simpler substances by chemical means. The number of protons in the nucleus is the defining property of an element, and is referred to as its atomic number (represented by the symbol Z) – all atoms with the same atomic number are atoms of the same element.[1] All of the baryonic matter of the universe is composed of chemical elements. When different elements undergo chemical reactions, atoms are rearranged into new compounds held together by chemical bonds. Only a minority of elements, such as silver and gold, are found uncombined as relatively pure native element minerals. Nearly all other naturally-occurring elements occur in the Earth as compounds or mixtures. Air is primarily a mixture of the elements nitrogen, oxygen, and argon, though it does contain compounds including carbon dioxide and water.

The periodic table of the chemical elements

The history of the discovery and use of the elements began with primitive human societies that discovered native minerals like carbon, sulfur, copper and gold (though the concept of a chemical element was not yet understood). Attempts to classify materials such as these resulted in the concepts of classical elements, alchemy, and various similar theories throughout human history. Much of the modern understanding of elements developed from the work of Dmitri Mendeleev, a Russian chemist who published the first recognizable periodic table in 1869. This table organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The periodic table summarizes various properties of the elements, allowing chemists to derive relationships between them and to make predictions about compounds and potential new ones.

By November 2016, the International Union of Pure and Applied Chemistry had recognized a total of 118 elements. The first 94 occur naturally on Earth, and the remaining 24 are synthetic elements produced in nuclear reactions. Save for unstable radioactive elements (radionuclides) which decay quickly, nearly all of the elements are available industrially in varying amounts. The discovery and synthesis of further new elements is an ongoing area of scientific study.

Mrs job:we will stop here for today.

5hours later.

When she got home, she saw mr job at home.

Mrs job:hello dear.

Mr job:fine.

Mrs job:what is the problem.?

Mr job:it is the family again oh.

Mrs job began to cry and cry ,has the husband join her in crying as the both of them started to cry.

After 5 weeks.

Mrs job was going to school when she noticed that she was not feeling OK,so she decided to go to the hospital.

Last Chapter Next Chapter