دوره (جدول تناوبی)

از ویکی‌پدیا، دانشنامهٔ آزاد
پرش به ناوبری پرش به جستجو
فارسیEnglish

در جدول تناوبی عناصر شیمیایی، عنصرها در ردیف‌هایی به نام دوره یا تناوب مرتب می‌شوند تا عناصر با خواص شیمیایی مشابه در ستون‌های عمودی زیر یکدیگر قرار بگیرند. عنصرهای موجود در هر دسته تعداد لایه‌های الکترونی یکسانی دارند. در عنصرهای یک دوره، هر عنصر از عنصر قبلی‌اش (از نظر شمارهٔ گروه) یک پروتون و یک الکترون بیشتر دارد و خاصیت فلزی کمتر و الکترونگاتیوی و بار مؤثر هستهٔ بیشتری دارد.

Madelung rule.svg

با افزایش عدد اتمی، لایه‌های اتم تقریباً به ترتیبی که در تصویر سمت راست نشان داده شده‌است از الکترون پر می‌شوند. پرشدن هر لایه به معنی رفتن به دورهٔ بعدی در جدول تناوبی است.

در بلوک اس و بلوک پی عناصر هر دوره خواص نسبتاً مشابهی ندارند و شباهت در خواص، بیشتر در عناصر یک گروه دیده می‌شود. اما در بلوک دی در خواص عناصر هر دوره نیز شباهت وجود دارد و در بلوک اف نیز، به‌خصوص در عناصر دستهٔ لانتانیدها شباهیت بسیاری در خواص عناصر هر دوره دیده می‌شود.

با دسته‌بندی عناصری که به‌طور طبیعی در زمین وجود دارند در جدول تناوبی ۷ دوره تشکیل می‌شود.

دورهٔ نخست[ویرایش]

گروه ۱/۱۷ ۲/۱۸
#
نام
۱
H
۲
He

دورهٔ نخست با ۲ عنصر هیدروژن و هلیوم کمترین تعداد عناصر را دارد. این دو عنصر از قاعده هشت‌تایی (اکتت) پیروی نمی‌کنند. هلیوم مانند یک گاز نجیب رفتار می‌کند و بنابراین جزو گروه هجدهم (گازهای نجیب) به‌شمار می‌رود و از طرفی هم به علت ساختار هسته‌ای‌اش به بلوک اس تعلق دارد و بنابراین گاه به عنوان عنصر عضو گروه دوم (قلیایی خاکی) به‌شمار می‌رود، و گاه هر دو. هیدروژن به‌آسانی یک الکترون می‌دهد و می‌گیرد و بنابراین می‌توان آن را جزو هر دو گروه نخست و هفدهم (هالوژن‌ها) به‌شمار آورد.

  • هیدروژن (H) فراوان‌ترین عنصر از میان عناصر است و حدود ۷۵٪ جرم جهان را تشکیل می‌دهد.[۱] هیدروژن یونیده‌شده (بار منفی) در واقع یک پروتون است. ستارگان رشتهٔ اصلی در حالت پلاسما عمدتاً از هیدروژن تشکیل شده‌اند. هیدروژن در حالت عنصر در زمین بسیار کمیاب است و به صورت صنعتی از متان و دیگر هیدروکربن‌ها ساخته می‌شود. هیدروژن با بیشتر عناصر ترکیب می‌شود و در آب و بیشتر ترکیب‌های زیستی وجود دارد.[۲]
  • هلیوم (He) معمولاً در حالت گاز است مگر شرایط خیلی خاص.[۳] دومین عنصر سبک و دومین عنصر فراوان در گیتی است.[۴] بیشتر هلیوم جهان در طی انفجار بزرگ پدید آمد، لیک همواره از راه همجوشی هسته‌ای در ستارگان نیز در حال پدیدآمدن است.[۵] هلیوم در زمین بسیار کمیاب است و فقط به‌طور طبیعی بر اثر واپاشی برخی عناصر رادیواکتیو زمین ساخته می‌شود.[۶]

دورهٔ دوم[ویرایش]

گروه ۱ ۲ ۱۳ ۱۴ ۱۵ ۱۶ ۱۷ ۱۸
#
نام
۳
Li
۴
Be
۵
B
۶
C
۷
N
۸
O
۹
F
۱۰
Ne

در عنصرهای دورهٔ دوم اربیتال‌های درون زیرلایه‌های ۲s و ۲p در حال پرشدن هستند. این دوره شامل عنصرهای مهم زیستی کربن، نیتروژن و اکسیژن است.

  • لیتیم (Li) سبک‌ترین و کم‌چگالی‌ترین عنصر فلز و جامد است.[۷] به علت واکنش‌پذیری زیاد این عنصر فقط به صورت ترکیب در طبیعت یافت می‌شود.
  • بریلیم (Be) از میان فلزهای سبک یکی از بیشترین نقطه‌های ذوب را دارد. بخش کمی از بریلیم جهان در طی انفجار بزرگ ترکیب شد، و سپس‌تر در ستارگان بیشتر آن واپاشید یا وارد واکنش شد و کربن، نیتروژن و اکسیژن را ایجاد کرد. سازمان IARC آن را در گروه نخست سرطان زاها رده‌بندی کرده‌است.[۸] Between 1% and 15% of people are sensitive to beryllium and may develop an inflammatory reaction in their دستگاه تنفسی and پوست، called chronic beryllium disease.[۹]
  • بور (B) does not occur naturally as a free element, but in compounds such as borates. It is an essential plant micronutrient, required for cell wall strength and development, cell division, seed and fruit development, sugar transport and hormone development,[۱۰][۱۱] though high levels are toxic.
  • کربن (C) چهارمین عنصر فراوان گیتی بر پایهٔ جرم پس از هیدروژن، هلیوم و اکسیژن[۱۲] و دومین عنصر فراوان در بدن انسان پس از اکسیژن،[۱۳] و سومین عنصر فراوان بر پایهٔ تعداد اتم‌ها در جهان است.[۱۴] به خاطر توانایی کربن در تشکیل زنجیره‌های طویل پایدار C-C تقریباً به تعداد بی‌نهایت نوع ترکیب از کربن قابل ایجاد است.[۱۵][۱۶] All ترکیب آلیs, those essential for life, contain at least one atom of carbon;[۱۵][۱۶] combined with hydrogen, oxygen, nitrogen, sulfur, and phosphorus, carbon is the basis of every important biological compound.[۱۶]
  • نیتروژن (N) is found mainly as mostly inert مولکول دواتمی gas, N۲, which makes up 78% of the Earth's atmosphere. It is an essential component of proteins and therefore of life.
  • اکسیژن (O) comprising 21% of the atmosphere and is required for respiration by all (or nearly all) animals, as well as being the principal component of آب. Oxygen is the third most abundant element in the universe, and oxygen compounds dominate the Earth's crust.
  • فلوئور (F) is the most reactive element in its non-ionized state, and so is never found that way in nature.
  • نئون (Ne) گازی نجیب است که در لامپ‌های نئون به کار می‌رود.

دورهٔ سوم[ویرایش]

گروه ۱ ۲ ۱۳ ۱۴ ۱۵ ۱۶ ۱۷ ۱۸
#
نام
۱۱
Na
۱۲
Mg
۱۳
Al
۱۴
Si
۱۵
P
۱۶
S
۱۷
Cl
۱۸
Ar

All period three elements occur in nature and have at least one ایزوتوپ پایدار. All but the noble gas آرگون are all essential to basic geology and biology.

دورهٔ چهارم[ویرایش]

گروه ۱ ۲ ۳ ۴ ۵ ۶ ۷ ۸ ۹ ۱۰ ۱۱ ۱۲ ۱۳ ۱۴ ۱۵ ۱۶ ۱۷ ۱۸
عدد اتمی
نام
۱۹
K
۲۰
Ca
۲۱
Sc
۲۲
Ti
۲۳
V
۲۴
Cr
۲۵
Mn
۲۶
Fe
۲۷
Co
۲۸
Ni
۲۹
Cu
۳۰
Zn
۳۱
Ga
۳۲
Ge
۳۳
As
۳۴
Se
۳۵
Br
۳۶
Kr
From left to right, aqueous solutions of: Co(NO3)2 (red); K۲Cr۲O۷ (orange); K۲CrO۴ (yellow); NiCl۲ (green); CuSO۴ (blue); KMnO۴ (purple).

Period 4 includes the biologically essential elements پتاسیم and کلسیم، and is the first period in the بلوک دی with the lighter فلز واسطه. These include آهن، the heaviest element forged in main-sequence stars and a principal component of the earth, as well as other important metals such as کبالت، نیکل، مس، and روی. Almost all have biological roles.

دورهٔ پنجم[ویرایش]

گروه ۱ ۲ ۳ ۴ ۵ ۶ ۷ ۸ ۹ ۱۰ ۱۱ ۱۲ ۱۳ ۱۴ ۱۵ ۱۶ ۱۷ ۱۸
عدد اتمی
نام
۳۷
Rb
۳۸
Sr
۳۹
Y
۴۰
Zr
۴۱
Nb
۴۲
Mo
۴۳
Tc
۴۴
Ru
۴۵
Rh
۴۶
Pd
۴۷
Ag
۴۸
Cd
۴۹
In
۵۰
Sn
۵۱
Sb
۵۲
Te
۵۳
I
۵۴
Xe

Period 5 contains the heaviest few elements that have biological roles, مولیبدن and ید. (تنگستن، a دوره ۶ جدول تناوبی، is the only heavier element that has a biological role.) It includes تکنسیم، the lightest exclusively radioactive element.

دورهٔ ششم[ویرایش]

گروه ۱ ۲ ۳ (Lanthanides) ۴ ۵ ۶ ۷ ۸ ۹ ۱۰ ۱۱ ۱۲ ۱۳ ۱۴ ۱۵ ۱۶ ۱۷ ۱۸
#
نام
۵۵
Cs
۵۶
Ba
۵۷
La
۵۸
Ce
۵۹
Pr
۶۰
Nd
۶۱
Pm
۶۲
Sm
۶۳
Eu
۶۴
Gd
۶۵
Tb
۶۶
Dy
۶۷
Ho
۶۸
Er
۶۹
Tm
۷۰
Yb
۷۱
Lu
۷۲
Hf
۷۳
Ta
۷۴
W
۷۵
Re
۷۶
Os
۷۷
Ir
۷۸
Pt
۷۹
Au
۸۰
Hg
۸۱
Tl
۸۲
Pb
۸۳
Bi
۸۴
Po
۸۵
At
۸۶
Rn

Period 6 is the first period to include the فلزات واسطه داخلی، with the lanthanides (also known as the rare earth elements), and includes the heaviest stable elements. Many of these heavy metals are toxic and some are radioactive, but پلاتین and طلا are largely inert.

دورهٔ هفتم[ویرایش]

گروه ۱ ۲ ۳ (اکتینیدها) ۴ ۵ ۶ ۷ ۸ ۹ ۱۰ ۱۱ ۱۲ ۱۳ ۱۴ ۱۵ ۱۶ ۱۷ ۱۸
#
نام
۸۷
Fr
۸۸
Ra
۸۹
Ac
۹۰
Th
۹۱
Pa
۹۲
U
۹۳
Np
۹۴
Pu
۹۵
Am
۹۶
Cm
۹۷
Bk
۹۸
Cf
۹۹
Es
۱۰۰
Fm
۱۰۱
Md
۱۰۲
No
۱۰۳
Lr
۱۰۴
Rf
۱۰۵
Db
۱۰۶
Sg
۱۰۷
Bh
۱۰۸
Hs
۱۰۹
Mt
۱۱۰
Ds
۱۱۱
Rg
۱۱۲
Cn
۱۱۳
Nh
۱۱۴
Fl
۱۱۵
Mc
۱۱۶
Lv
۱۱۷
Ts
۱۱۸
Og

All elements of period 7 are واپاشی هسته‌ای. This period contains the heaviest element which occurs naturally on earth, اورانیم. All of the subsequent elements in the period have been synthesized artificially. Whilst some of these (e.g. پلوتونیم) are now available in tonne quantities, most are extremely rare, having only been prepared in microgram amounts or less. Some of the later elements have only ever been identified in laboratories in quantities of a few atoms at a time.

Although the rarity of many of these elements means that experimental results are not very extensive, periodic and group trends in behaviour appear to be less well defined for period 7 than for other periods. Whilst فرانسیم and رادیم do show typical properties of Groups 1 and 2 respectively, the آکتینیدها display a much greater variety of behaviour and oxidation states than the لانتانیدها. Initial studies suggest Group 14 element فلروویوم appears to be a noble gas instead of a poor metal, and group 18 element اوگانسون probably is not a noble gas.[۱۷] These peculiarities of period 7 may be due to a variety of factors, including a large degree of spin-orbit coupling and relativistic effects, ultimately caused by the very high positive electrical charge from their massive هسته اتم.

دورهٔ هشتم[ویرایش]

No element of the eighth period has yet been synthesized. A g-block is predicted. It is not clear if all elements predicted for the eighth period are in fact physically possible. There may therefore be no ninth period.

منابع[ویرایش]

  1. Palmer, David (November 13, 1997). "Hydrogen in the Universe". NASA. Retrieved 2008-02-05.
  2. "hydrogen". Encyclopædia Britannica. 2008.
  3. "Helium: physical properties". WebElements. Retrieved 2008-07-15.
  4. "Helium: geological information". WebElements. Retrieved 2008-07-15.
  5. Cox, Tony (1990-02-03). "Origin of the chemical elements". New Scientist. Retrieved 2008-07-15.
  6. "Helium supply deflated: production shortages mean some industries and partygoers must squeak by". Houston Chronicle. 2006-11-05.
  7. Lithium at WebElements.
  8. "IARC Monograph, Volume 58". International Agency for Research on Cancer. 1993. Retrieved 2008-09-18.
  9. Information بایگانی‌شده در ۳۱ مارس ۲۰۰۱ توسط Wayback Machine about chronic beryllium disease.
  10. "Functions of Boron in Plant Nutrition" (PDF). U.S. Borax Inc. Archived from the original (PDF) on 18 August 2003. Retrieved 2 September 2011.
  11. Blevins, Dale G. (1998). "Functions of Boron in Plant Nutrition". Annual Review of Plant Physiology and Plant Molecular Biology. 49: 481–۵۰۰. doi:10.1146/annurev.arplant.49.1.481. PMID 15012243. Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. «Ten most abundant elements in the universe, taken from The Top 10 of Everything, 2006, Russell Ash, page 10. Retrieved October 15, 2008». بایگانی‌شده از اصلی در ۱۰ فوریه ۲۰۱۰. دریافت‌شده در ۲ سپتامبر ۲۰۱۱.
  13. Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. p. 52. ISBN 0-07-110595-6.
  14. Freitas Jr., Robert A. (1999). Nanomedicine,. Landes Bioscience. Tables ۳–۱ & ۳–۲. ISBN 1-57059-680-8. External link in |title= (help)
  15. ۱۵٫۰ ۱۵٫۱ "Structure and Nomenclature of Hydrocarbons". Purdue University. Retrieved 2008-03-23.
  16. ۱۶٫۰ ۱۶٫۱ ۱۶٫۲ Alberts, Bruce. Molecular Biology of the Cell. Garland Science. Unknown parameter |coauthors= ignored (|author= suggested) (help)
  17. See references in the articles فلروویوم، اوگانسون
توجه: ارجاعات دست‌دوم‌اند. منبع اصلی:
In the periodic table of the elements, each numbered row is a period.

A period in the periodic table is a row of chemical elements. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic law. For example, the halogens lie in the second-last column (group 17) and share similar properties, such as high reactivity and the tendency to gain one electron to arrive at a noble-gas electronic configuration As of 2016, a total of 118 elements have been discovered and confirmed.

The Madelung energy ordering rule describes the order in which orbitals are arranged by increasing energy according to the Madelung rule. Each diagonal corresponds to a different value of n + l.

Modern quantum mechanics explains these periodic trends in properties in terms of electron shells. As atomic number increases, shells fill with electrons in approximately the order shown at right. The filling of each shell corresponds to a row in the table.

In the s-block and p-block of the periodic table, elements within the same period generally do not exhibit trends and similarities in properties (vertical trends down groups are more significant). However, in the d-block, trends across periods become significant, and in the f-block elements show a high degree of similarity across periods.

Periods

There are currently seven complete periods in the periodic table, comprising the 118 known elements. Any new elements will be placed into an eighth period; see extended periodic table.

Period 1

Group 1 18
Atomic #
Name
1
H
2
He

The first period contains the least elements than any other, with only two, hydrogen and helium. They therefore do not follow the octet rule. Chemically, helium behaves like a noble gas, and thus is taken to be part of the group 18 elements. However, in terms of its nuclear structure it belongs to the s block, and is therefore sometimes classified as a group 2 element, or simultaneously both 2 and 18. Hydrogen readily loses and gains an electron, and so behaves chemically as both a group 1 and a group 17 element.

  • Hydrogen (H) is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass.[1] Ionized hydrogen is just a proton. Stars in the main sequence are mainly composed of hydrogen in its plasma state. Elemental hydrogen is relatively rare on Earth, and is industrially produced from hydrocarbons such as methane. Hydrogen can form compounds with most elements and is present in water and most organic compounds.[2]
  • Helium (He) exists only as a gas except in extreme conditions.[3] It is the second-lightest element and is the second-most abundant in the universe.[4] Most helium was formed during the Big Bang, but new helium is created through nuclear fusion of hydrogen in stars.[5] On Earth, helium is relatively rare, only occurring as a byproduct of the natural decay of some radioactive elements.[6] Such 'radiogenic' helium is trapped within natural gas in concentrations of up to seven percent by volume.[7]

Period 2

Group 1 2 13 14 15 16 17 18
Atomic #
Name
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne

Period 2 elements involve the 2s and 2p orbitals. They include the biologically most essential elements besides hydrogen: carbon, nitrogen, and oxygen.

  • Lithium (Li) is the lightest metal and the least dense solid element.[8] In its non-ionized state it is one of the most reactive elements, and so is only ever found naturally in compounds. It is the heaviest primordial element forged in large quantities during the Big Bang.
  • Beryllium (Be) has one of the highest melting points of all the light metals. Small amounts of beryllium were synthesised during the Big Bang, although most of it decayed or reacted further within stars to create larger nuclei, like carbon, nitrogen or oxygen. Beryllium is classified by the International Agency for Research on Cancer as a group 1 carcinogen.[9] Between 1% and 15% of people are sensitive to beryllium and may develop an inflammatory reaction in their respiratory system and skin, called chronic beryllium disease.[10]
  • Boron (B) does not occur naturally as a free element, but in compounds such as borates. It is an essential plant micronutrient, required for cell wall strength and development, cell division, seed and fruit development, sugar transport and hormone development,[11][12] though high levels are toxic.
  • Carbon (C) is the fourth-most abundant element in the universe by mass after hydrogen, helium and oxygen[13] and is the second-most abundant element in the human body by mass after oxygen,[14] the third-most abundant by number of atoms.[15] There are an almost infinite number of compounds that contain carbon due to carbon's ability to form long stable chains of C—C bonds.[16][17] All organic compounds, those essential for life, contain at least one atom of carbon;[16][17] combined with hydrogen, oxygen, nitrogen, sulfur, and phosphorus, carbon is the basis of every important biological compound.[17]
  • Nitrogen (N) is found mainly as mostly inert diatomic gas, N2, which makes up 78% of the Earth's atmosphere by volume. It is an essential component of proteins and therefore of life.
  • Oxygen (O) comprising 21% of the atmosphere by volume and is required for respiration by all (or nearly all) animals, as well as being the principal component of water. Oxygen is the third-most abundant element in the universe, and oxygen compounds dominate the Earth's crust.
  • Fluorine (F) is the most reactive element in its non-ionized state, and so is never found that way in nature.
  • Neon (Ne) is a noble gas used in neon lighting.

Period 3

Group 1 2 13 14 15 16 17 18
Atomic #
Name
11
Na
12
Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar

All period three elements occur in nature and have at least one stable isotope. All but the noble gas argon are essential to basic geology and biology.

Period 4

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic #
Name
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
From left to right, aqueous solutions of: Co(NO3)2 (red); K2Cr2O7 (orange); K2CrO4 (yellow); NiCl2 (green); CuSO4 (blue); KMnO4 (purple).

Period 4 includes the biologically essential elements potassium and calcium, and is the first period in the d-block with the lighter transition metals. These include iron, the heaviest element forged in main-sequence stars and a principal component of the Earth, as well as other important metals such as cobalt, nickel, and copper. Almost all have biological roles.

Completing the fourth period are the post-transition metals zinc and gallium, the metalloids germanium and arsenic, and the nonmetals selenium, bromine, and krypton.

Period 5

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic #
Name
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe

Period 5 has the same number of elements as period 4 and follows the same general structure but with one more post transition metal and one fewer nonmetal. Of the three heaviest elements with biological roles, two (molybdenum and iodine) are in this period; tungsten, in period 6, is heavier, along with several of the early lanthanides. Period 5 also includes technetium, the lightest exclusively radioactive element.

Period 6

Group 1 2 3 (Lanthanides) 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic #
Name
55
Cs
56
Ba
57
La
58
Ce
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn

Period 6 is the first period to include the f-block, with the lanthanides (also known as the rare earth elements), and includes the heaviest stable elements. Many of these heavy metals are toxic and some are radioactive, but platinum and gold are largely inert.

Period 7

Group 1 2 3 (Actinides) 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Atomic #
Name
87
 Fr 
88
Ra
89
Ac
90
Th
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cf
99
Es
100
Fm
101
Md
102
No
103
Lr
104
Rf
105
Db
106
Sg
107
Bh
108
Hs
109
Mt
110
Ds
111
Rg
112
Cn
113
Nh
114
Fl
115
Mc
116
Lv
117
Ts
118
Og

All elements of period 7 are radioactive. This period contains the heaviest element which occurs naturally on Earth, plutonium. All of the subsequent elements in the period have been synthesized artificially. Whilst five of these (from americium to einsteinium) are now available in macroscopic quantities, most are extremely rare, having only been prepared in microgram amounts or less. Some of the later elements have only ever been identified in laboratories in quantities of a few atoms at a time.

Although the rarity of many of these elements means that experimental results are not very extensive, periodic and group trends in behaviour appear to be less well defined for period 7 than for other periods. Whilst francium and radium do show typical properties of groups 1 and 2, respectively, the actinides display a much greater variety of behaviour and oxidation states than the lanthanides. These peculiarities of period 7 may be due to a variety of factors, including a large degree of spin-orbit coupling and relativistic effects, ultimately caused by the very high positive electrical charge from their massive atomic nuclei.

Period 8

No element of the eighth period has yet been synthesized. A g-block is predicted. It is not clear if all elements predicted for the eighth period are in fact physically possible. There may therefore be no eighth period.

See also

References

  1. ^ Palmer, David (November 13, 1997). "Hydrogen in the Universe". NASA. Retrieved 2008-02-05.
  2. ^ Jolly, William Lee (9 August 2019). "hydrogen". Encyclopædia Britannica.
  3. ^ "Helium: physical properties". WebElements. Retrieved 2008-07-15.
  4. ^ "Helium: geological information". WebElements. Retrieved 2008-07-15.
  5. ^ Cox, Tony (1990-02-03). "Origin of the chemical elements". New Scientist. Retrieved 2008-07-15.
  6. ^ "Helium supply deflated: production shortages mean some industries and partygoers must squeak by". Houston Chronicle. 2006-11-05.
  7. ^ Brown, David (2008-02-02). "Helium a New Target in New Mexico". American Association of Petroleum Geologists. Retrieved 2008-07-15.
  8. ^ Lithium at WebElements.
  9. ^ "IARC Monograph, Volume 58". International Agency for Research on Cancer. 1993. Retrieved 2008-09-18.
  10. ^ Information about chronic beryllium disease.
  11. ^ "Functions of Boron in Plant Nutrition" (PDF). www.borax.com/agriculture. U.S. Borax Inc. Archived from the original (PDF) on 2009-03-20.
  12. ^ Blevins, Dale G.; Lukaszewski, Krystyna M. (1998). "Functions of Boron in Plant Nutrition". Annual Review of Plant Physiology and Plant Molecular Biology. 49: 481–500. doi:10.1146/annurev.arplant.49.1.481. PMID 15012243.
  13. ^ Ten most abundant elements in the universe, taken from The Top 10 of Everything, 2006, Russell Ash, page 10. Retrieved October 15, 2008. Archived February 10, 2010, at the Wayback Machine
  14. ^ Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. p. 52. ISBN 0-07-110595-6.
  15. ^ Freitas Jr., Robert A. (1999). Nanomedicine. Landes Bioscience. Tables 3-1 & 3-2. ISBN 1-57059-680-8.
  16. ^ a b "Structure and Nomenclature of Hydrocarbons". Purdue University. Retrieved 2008-03-23.
  17. ^ a b c Alberts, Bruce; Alexander Johnson; Julian Lewis; Martin Raff; Keith Roberts; Peter Walter. Molecular Biology of the Cell. Garland Science.