Chemical elements

Chemical elements are the building blocks of matter, "the substances from which everything tangible is made." Each element consists of a single type of atom, distinguishable from other elements by virtue of the unique number of protons in each atom's nucleus. Thus, each element has a unique atomic number, Z. This modern definition replaces the dated introduction by John Dalton of a quantitative atomic theory, which defined an element as a substance that neither ordinary physical nor chemical methods can decompose into simpler substances.

On Earth, 94 elements with different atomic numbers occur in nature, each characterized by a unique set of physical and chemical properties.

People from all walks of everyday life know something about many different elements, even if they do not recognize them as chemical elements. They include: Helium (He), used to make party balloons float, Lithium (Li), used to make batteries for cellphones, Oxygen (O), in the air we breathe, Neon (Ne), in 'neon' lights, Sodium (Na), which is present in table salt that nutritionists advise using sparingly in foods and Aluminum (Al), used as foil for wrapping leftovers.

All matter directly perceptible by the human senses — whether solid, liquid or gas — is composed of one or more elements. Typically, elements are found in nature in the form of populations of atoms, often with the atoms of other elements, as compounds (e.g., iron ore, a population of unit compounds each of iron and oxygen atoms) or as mixtures. Some elements are abundant on Earth. For example, the elements hydrogen and oxygen, as the compound water, H₂O, make up the bulk of Earth's oceans, seas, lakes, rivers, and ponds, and make up the bulk (mass) of living cells and multicellular oganisms. For another example, the element carbon supplies the backbone of numerous species of essential compounds of all animal and plant life on Earth as well of all the fossil fuels (natural gas, petroleum and coal), which are the remains of plant material that once lived. Some compounds may consist of one element only, for instance a nugget of pure gold is made up solely of gold atoms arranged in crystalline form. Very often gold is not pure but an alloy — a mixture — of the elements copper, silver, and gold. Oxygen gas consists of entities [see molecule] each having two oxygen atoms chemically bonded to each other, hence the gas consists of the element oxygen only.

Two substances consisting of the same single element may have very different chemical and physical properties, e.g., graphite, used as lubricant, and diamond, used to harden drill tips, both pure carbon. This phenomenon is known as allotropy. Oxygen atoms (O), oxygen gas (O₂), and ozone (O₃) — all found in the atmosphere — are allotropes of the same element, as they have different chemical and physical properties, yet each consists solely of [oxygen] atoms whose nuclei have identical numbers of protons,

Some of the 94 elements , such as the gas neon, are very rare on Earth. Some elements are stable, and will live as long as the universe, while some, known as the radioactive elements, have finite life times and decay into other elements while emitting radiation. For example, plutonium is a well-known radioactive element.

In addition to the 94 elements that occur naturally on Earth, about 23 other known elements that do not occur naturally on Earth have been man-made and are characterized by their constituent atoms having very short life times and being radioactive.

As noted, the atoms of each of the elements are distinguished by a unique atomic number, an integral (whole) number, symbolized Z, indicating the number of protons in the atom's nucleus. As protons each carry a positive charge, Z gives the positive charge of the nucleus in units of the so-called elementary charge, symbolized e. It is known that Z electrons (of charge −e, or negative e, and of much smaller mass than the proton) "orbit" the nucleus of an atom, so that an atom as a whole is electrically neutral. The following elements have their values of Z (Z-values) in brackets: hydrogen(1), oxygen(8), carbon(6), neon(10), plutonium(94). The naturally occurring elements have Z-values from 1 to 94 (with plutonium being extremely rare in nature and mainly man-made). The exclusively man-made elements on Earth run from Z = 95 to 118. The names of the elements are of historical origin and may differ among languages for an element. The atomic number (Z), on the other hand, is a unique and universal label of an element, as is its international chemical symbol consisting of one or two letters.

Whereas an element consists of a single species of atom characterized by a unique atomic number, many such species occur in varieties, called isotopes. The isotopes of an element differ among themselves by the number of neutrons in the nucleus, not in the number of protons. As neutrons have mass, and mass similar to that of protons, the isotopes of a given element have differing masses. For example, the most abundant form of hydrogen has a nucleus consisting only of a proton, the fairly rare isotope deuterium has a nucleus that contains one proton and one neutron, and the rarer isotope, tritium, has a nucleus that contains one proton and two neutrons. All three isotopes, while having differing masses, have by definition the same atomic number (=1) and hence are variations, or isotopes, of the same element.

There is a maximum to the number of unique elements that can exist due to the fact that a nucleus contains Z positively charged particles (protons). Those repel each other by Coulomb forces but can remain together by a special nuclear force referred to as the strong nuclear force. At a certain large number of protons the strong nuclear force will begin to lose out to the Coulomb force — increasingly so with increasing numbers of protons — and the nucleus will no longer be stable. This is likely to happen between Z = 120 and Z = 130.

For a long time, it was thought that elements were unchangeable, that one element could not be converted into another. Alchemists searched for many centuries in vain for the transmutation of the element lead into gold. However, when in 1919 Ernest Rutherford and coworkers showed the transmutation of the element nitrogen into the element oxygen, it became clear that elements can be transmuted.

The modern concept of element differs greatly from the Aristotelian concept. Aristotle recognized four elements: fire, water, earth and air, and postulated that they can be converted into each other. He wrote:

"….the elements are the primary constituents of bodies.... An element, we take it, is a body into which other bodies may be analysed, present in them potentially or in actuality (which of these, is still disputable), and not itself divisible into bodies different in form. That, or something like it, is what all men in every case mean by element….every body is either an element or composed of elements…."     —Aristotle. On the Heavens Book III. Translated by J.L. Stocks.

Tables

See Atomic electron configuration for the orbital occupancies of atoms in their so-called ground state.

See also Periodic Table of Elements.

Chemical elements sorted on chemical symbol (CS)

CS	Name	Z		CS	Name	Z		CS	Name	Z
Ac	Actinium	89		Gd	Gadolinium	64		Po	Polonium	84
Ag	Silver	47		Ge	Germanium	32		Pr	Praseodymium	59
Al	Aluminum	13		H	Hydrogen	1		Pt	Platinum	78
Am	Americium	95		He	Helium	2		Pu	Plutonium	94
Ar	Argon	18		Hf	Hafnium	72		Ra	Radium	88
As	Arsenic	33		Hg	Mercury	80		Rb	Rubidium	37
At	Astatine	85		Ho	Holmium	67		Re	Rhenium	75
Au	Gold	79		Hs	Hassium	108		Rf	Rutherfordium	104
B	Boron	5		I	Iodine	53		Rg	Roentgenium	111
Ba	Barium	56		In	Indium	49		Rh	Rhodium	45
Be	Beryllium	4		Ir	Iridium	77		Rn	Radon	86
Bh	Bohrium	107		K	Potassium	19		Ru	Ruthenium	44
Bi	Bismuth	83		Kr	Krypton	36		S	Sulfur	16
Bk	Berkelium	97		La	Lanthanum	57		Sb	Antimony	51
Br	Bromine	35		Li	Lithium	3		Sc	Scandium	21
C	Carbon	6		Lr	Lawrencium	103		Se	Selenium	34
Ca	Calcium	20		Lu	Lutetium	71		Sg	Seaborgium	106
Cd	Cadmium	48		Md	Mendelevium	101		Si	Silicon	14
Ce	Cerium	58		Mg	Magnesium	12		Sm	Samarium	62
Cf	Californium	98		Mn	Manganese	25		Sn	Tin	50
Cl	Chlorine	17		Mo	Molybdenum	42		Sr	Strontium	38
Cm	Curium	96		Mt	Meitnerium	109		Ta	Tantalum	73
Co	Cobalt	27		N	Nitrogen	7		Tb	Terbium	65
Cr	Chromium	24		Na	Sodium	11		Tc	Technetium	43
Cs	Cesium	55		Nb	Niobium	41		Te	Tellurium	52
Cu	Copper	29		Nd	Neodymium	60		Th	Thorium	90
Db	Dubnium	105		Ne	Neon	10		Ti	Titanium	22
Ds	Darmstadtium	110		Ni	Nickel	28		Tl	Thallium	81
Dy	Dysprosium	66		No	Nobelium	102		Tm	Thulium	69
Er	Erbium	68		Np	Neptunium	93		U	Uranium	92
Es	Einsteinium	99		O	Oxygen	8		V	Vanadium	23
Eu	Europium	63		Os	Osmium	76		W	Tungsten	74
F	Fluorine	9		P	Phosphorus	15		Xe	Xenon	54
Fe	Iron	26		Pa	Protactinium	91		Y	Yttrium	39
Fm	Fermium	100		Pb	Lead	82		Yb	Ytterbium	70
Fr	Francium	87		Pd	Palladium	46		Zn	Zinc	30
Ga	Gallium	31		Pm	Promethium	61		Zr	Zirconium	40

Chemical elements sorted on atomic number (Z)

Z	Name	CS		Z	Name	CS		Z	Name	CS
1	Hydrogen	H		38	Strontium	Sr		75	Rhenium	Re
2	Helium	He		39	Yttrium	Y		76	Osmium	Os
3	Lithium	Li		40	Zirconium	Zr		77	Iridium	Ir
4	Beryllium	Be		41	Niobium	Nb		78	Platinum	Pt
5	Boron	B		42	Molybdenum	Mo		79	Gold	Au
6	Carbon	C		43	Technetium	Tc		80	Mercury	Hg
7	Nitrogen	N		44	Ruthenium	Ru		81	Thallium	Tl
8	Oxygen	O		45	Rhodium	Rh		82	Lead	Pb
9	Fluorine	F		46	Palladium	Pd		83	Bismuth	Bi
10	Neon	Ne		47	Silver	Ag		84	Polonium	Po
11	Sodium	Na		48	Cadmium	Cd		85	Astatine	At
12	Magnesium	Mg		49	Indium	In		86	Radon	Rn
13	Aluminum	Al		50	Tin	Sn		87	Francium	Fr
14	Silicon	Si		51	Antimony	Sb		88	Radium	Ra
15	Phosphorus	P		52	Tellurium	Te		89	Actinium	Ac
16	Sulfur	S		53	Iodine	I		90	Thorium	Th
17	Chlorine	Cl		54	Xenon	Xe		91	Protactinium	Pa
18	Argon	Ar		55	Cesium	Cs		92	Uranium	U
19	Potassium	K		56	Barium	Ba		93	Neptunium	Np
20	Calcium	Ca		57	Lanthanum	La		94	Plutonium	Pu
21	Scandium	Sc		58	Cerium	Ce		95	Americium	Am
22	Titanium	Ti		59	Praseodymium	Pr		96	Curium	Cm
23	Vanadium	V		60	Neodymium	Nd		97	Berkelium	Bk
24	Chromium	Cr		61	Promethium	Pm		98	Californium	Cf
25	Manganese	Mn		62	Samarium	Sm		99	Einsteinium	Es
26	Iron	Fe		63	Europium	Eu		100	Fermium	Fm
27	Cobalt	Co		64	Gadolinium	Gd		101	Mendelevium	Md
28	Nickel	Ni		65	Terbium	Tb		102	Nobelium	No
29	Copper	Cu		66	Dysprosium	Dy		103	Lawrencium	Lr
30	Zinc	Zn		67	Holmium	Ho		104	Rutherfordium	Rf
31	Gallium	Ga		68	Erbium	Er		105	Dubnium	Db
32	Germanium	Ge		69	Thulium	Tm		106	Seaborgium	Sg
33	Arsenic	As		70	Ytterbium	Yb		107	Bohrium	Bh
34	Selenium	Se		71	Lutetium	Lu		108	Hassium	Hs
35	Bromine	Br		72	Hafnium	Hf		109	Meitnerium	Mt
36	Krypton	Kr		73	Tantalum	Ta		110	Darmstadtium	Ds
37	Rubidium	Rb		74	Tungsten	W		111	Roentgenium	Rg

Explanation of names

1. Ag (silver) is from Argentum
2. Au (gold) is from Aurum
3. Cu (copper) is from Cuprum
4. Fe (iron) is from Ferrum
5. Hg (mercury) is from Hydrargyrum
6. K (potassium) is from Kalium
7. Na (sodium) is from Natrium
8. Pb (lead) is from Plumbum
9. Sb (antimony) is from Stibium
10. Si (silicon) is from Silicium
11. Sn (tin) is from Stannum
12. W (tungsten) is from Wolfram
13. Man-made elements Z = 112, ..., 118 are not listed