Atomic Number 2

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The elements of the periodic table sorted by atomic number

  1. Atomic Number 20
  2. Atomic Number 207
  3. Atomic Number 21
  4. Atomic Number 201

click on any elements name for further chemical properties, environmental data or health effects.

Atomic Orbitals, and Electron Configurations. Contents: Quantum Numbers and Atomic Orbitals 1. Principal Quantum Number 2. Angular Momentum (Secondary, Azimunthal) Quantum Number 3. Magnetic Quantum Number (m l) 4. Spin Quantum Number (m s) Table of Allowed Quantum Numbers Writing Electron Configurations Properties of Monatomic Ions References. Helium is a chemical element with atomic number 2 which means there are 2 protons and 2 electrons in the atomic structure. The chemical symbol for Helium is He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements. Atomic Number 2 Atomic Number 2 is belong to element of Helium. Chemical symbol for Helium is He. Number of protons in Helium is 2. The atomic number is the number of protons in the nucleus of an atom. The number of protons define the identity of an element (i.e., an element with 6 protons is a carbon atom, no matter how many neutrons may be present). The number of protons determines how many electrons surround the nucleus, and it is the arrangement of these electrons that.

This list contains the 118 elements of chemistry.

The chemical elements of
the periodic chart sorted by:
Atomic number

Name chemical element

Symbol
- Name alphabetically1HydrogenH
- Atomic number2HeliumHe
- Symbol3LithiumLi
- Atomic Mass4BerylliumBe
- Electronegativity5BoronB
- Density6CarbonC
- Melting point7NitrogenN
- Boiling point8OxygenO
- Vanderwaals radius9FluorineF
- Year of discovery10NeonNe
- Inventor surname11SodiumNa
- Elements in earthcrust12MagnesiumMg
- Elements in human body13AluminumAl
- Covalenz radius14SiliconSi
- Ionization energy15PhosphorusP

For chemistry students and teachers: The tabular chart on the right is arranged by Atomic number.

The first chemical element is Hydrogen and the last is Ununoctium.

Please note that the elements do not show their natural relation towards each other as in the Periodic system. There you can find the metals, semi-conductor(s), non-metal(s), inert noble gas(ses), Halogens, Lanthanoides, Actinoids (rare earth elements) and transition metals.

16SulfurS
17ChlorineCl
18ArgonAr
19PotassiumK
20CalciumCa
21ScandiumSc
22TitaniumTi
23VanadiumV
24ChromiumCr
25ManganeseMn
26IronFe
27CobaltCo
28NickelNi
29CopperCu
30ZincZn
31GalliumGa
32GermaniumGe
33ArsenicAs
34SeleniumSe
35BromineBr
36KryptonKr
37RubidiumRb
38StrontiumSr
39YttriumY
40ZirconiumZr
41NiobiumNb
42MolybdenumMo
43TechnetiumTc
44RutheniumRu
45RhodiumRh
46PalladiumPd
47SilverAg
48CadmiumCd
49IndiumIn
50TinSn
51AntimonySb
52TelluriumTe
53IodineI
54XenonXe
55CesiumCs
56BariumBa
57LanthanumLa
58CeriumCe
59PraseodymiumPr
60NeodymiumNd
61PromethiumPm
62SamariumSm
63EuropiumEu
64GadoliniumGd
65TerbiumTb
66DysprosiumDy
67HolmiumHo
68ErbiumEr
69ThuliumTm
70YtterbiumYb
71LutetiumLu
72HafniumHf
73TantalumTa
74TungstenW
75RheniumRe
76OsmiumOs
77IridiumIr
78PlatinumPt
79GoldAu
80MercuryHg
81ThalliumTl
82LeadPb
83BismuthBi
84PoloniumPo
85AstatineAt
86RadonRn
87FranciumFr
88RadiumRa
89ActiniumAc
90ThoriumTh
91ProtactiniumPa
92UraniumU
93NeptuniumNp
94PlutoniumPu
95AmericiumAm
96CuriumCm
97BerkeliumBk
98CaliforniumCf
99EinsteiniumEs
100FermiumFm
101MendeleviumMd
102NobeliumNo
103LawrenciumLr
104RutherfordiumRf
105DubniumDb
106SeaborgiumSg
107BohriumBh
108HassiumHs
109MeitneriumMt
110DarmstadtiumDs
111RoentgeniumRg
112CoperniciumCn
113NihoniumNh
114FleroviumFl
115MoscoviumMc
116LivermoriumLv
117TennessineTs
118OganessonOg

Click here: for a schematic overview of the periodic table of elements in chart form

Do you need to know the weight of some molecules? Try our Molecular Weight Calculator!

Atomic number 200

Please report any accidental mistake in the above statistics on chemical elements

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Atomic Number 2

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Quantum Numbers,
Atomic Orbitals, and
Electron Configurations

Contents:
Quantum Numbers and Atomic Orbitals
1. Principal Quantum Number (n)
2.Angular Momentum (Secondary, Azimunthal) Quantum Number (l)
3.Magnetic Quantum Number (ml)
4.Spin Quantum Number (ms)
Table of Allowed Quantum Numbers
Writing Electron Configurations
Properties of Monatomic Ions
References

Quantum Numbers and Atomic Orbitals

By solving the Schrödinger equation (Hy = Ey), we obtain a set of mathematical equations, called wave functions (y), which describe the probability of finding electrons at certain energy levels within an atom.

A wave function for an electron in an atom is called an atomic orbital; this atomic orbital describes a region of space in which there is a high probability of finding the electron. Energy changes within an atom are the result of an electron changing from a wave pattern with one energy to a wave pattern with a different energy (usually accompanied by the absorption or emission of a photon of light).

Atomic Number 20

Each electron in an atom is described by four different quantum numbers. The first three (n, l, ml) specify the particular orbital of interest, and the fourth (ms) specifies how many electrons can occupy that orbital.

  1. Principal Quantum Number (n): n = 1, 2, 3, …,
    Specifies the energy of an electron and the size of the orbital (the distance from the nucleus of the peak in a radial probability distribution plot). All orbitals that have the same value of n are said to be in the same shell (level). For a hydrogen atom with n=1, the electron is in its ground state; if the electron is in the n=2 orbital, it is in an excited state. The total number of orbitals for a given n value is n2.
  1. Angular Momentum (Secondary, Azimunthal) Quantum Number (l): l = 0, ..., n-1.
    Specifies the shape of an orbital with a particular principal quantum number. The secondary quantum number divides the shells into smaller groups of orbitals called subshells (sublevels). Usually, a letter code is used to identify l to avoid confusion with n:
l012345...
Letterspdfgh...
Atomic Number 2

The subshell with n=2 and l=1 is the 2p subshell; if n=3 and l=0, it is the 3s subshell, and so on. The value of l also has a slight effect on the energy of the subshell; the energy of the subshell increases with l (s < p < d < f).

Number
  1. Magnetic Quantum Number (ml): ml = -l, ..., 0, ..., +l.
    Specifies the orientation in space of an orbital of a given energy (n) and shape (l). This number divides the subshell into individual orbitals which hold the electrons; there are 2l+1 orbitals in each subshell. Thus the s subshell has only one orbital, the p subshell has three orbitals, and so on.
  1. Spin Quantum Number (ms): ms = +½ or -½.
    Specifies the orientation of the spin axis of an electron. An electron can spin in only one of two directions (sometimes called up and down).
    The Pauli exclusion principle (Wolfgang Pauli, Nobel Prize 1945) states that no two electrons in the same atom can have identical values for all four of their quantum numbers. What this means is that no more than two electrons can occupy the same orbital, and that two electrons in the same orbital must have opposite spins.
    Because an electron spins, it creates a magnetic field, which can be oriented in one of two directions. For two electrons in the same orbital, the spins must be opposite to each other; the spins are said to be paired. These substances are not attracted to magnets and are said to be diamagnetic. Atoms with more electrons that spin in one direction than another contain unpaired electrons. These substances are weakly attracted to magnets and are said to be paramagnetic.

Table of Allowed Quantum Numbers

nlmlNumber of
orbitals
Orbital
Name
Number of
electrons
10011s2
20012s2
1-1, 0, +132p6
30013s2
1-1, 0, +133p6
2-2, -1, 0, +1, +253d10
40014s2
1-1, 0, +134p6
2-2, -1, 0, +1, +254d10
3-3, -2, -1, 0, +1, +2, +374f14

Writing Electron Configurations

The distribution of electrons among the orbitals of an atom is called the electron configuration. The electrons are filled in according to a scheme known as the Aufbau principle ('building-up'), which corresponds (for the most part) to increasing energy of the subshells:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f

It is not necessary to memorize this listing, because the order in which the electrons are filled in can be read from the periodic table in the following fashion:

Or, to summarize:

In electron configurations, write in the orbitals that are occupied by electrons, followed by a superscript to indicate how many electrons are in the set of orbitals (e.g., H 1s1)

Another way to indicate the placement of electrons is an orbital diagram, in which each orbital is represented by a square (or circle), and the electrons as arrows pointing up or down (indicating the electron spin). When electrons are placed in a set of orbitals of equal energy, they are spread out as much as possible to give as few paired electrons as possible (Hund's rule).

examples will be added at a later date

In a ground state configuration, all of the electrons are in as low an energy level as it is possible for them to be. When an electron absorbs energy, it occupies a higher energy orbital, and is said to be in an excited state.

Properties of Monatomic Ions

The electrons in the outermost shell (the ones with the highest value of n) are the most energetic, and are the ones which are exposed to other atoms. This shell is known as the valence shell. The inner, core electrons (inner shell) do not usually play a role in chemical bonding.

Elements with similar properties generally have similar outer shell configurations. For instance, we already know that the alkali metals (Group I) always form ions with a +1 charge; the 'extra' s1 electron is the one that's lost:

IALi1s22s1Li+1s2
Na1s22s22p63s1Na+1s22s22p6
K1s22s22p63s23p64s1K+1s22s22p63s23p6

The next shell down is now the outermost shell, which is now full — meaning there is very little tendency to gain or lose more electrons. The ion's electron configuration is the same as the nearest noble gas — the ion is said to be isoelectronic with the nearest noble gas. Atoms 'prefer' to have a filled outermost shell because this is more electronically stable.

  • The Group IIA and IIIA metals also tend to lose all of their valence electrons to form cations.
IIABe1s22s2Be2+1s2
Mg1s22s22p63s2Mg2+1s22s22p6
IIIAAl1s22s22p63s23p1Al3+1s22s22p6
Atomic
  • The Group IV and V metals can lose either the electrons from the p subshell, or from both the s and p subshells, thus attaining a pseudo-noble gas configuration.
IVASn[Kr]4d105s25p2Sn2+[Kr]4d105s2
Sn4+[Kr]4d10
Pb[Xe]4f145d106s26p2Pb2+[Xe]4f145d106s2
Pb4+[Xe]4f145d10
VABi[Xe]4f145d106s26p3Bi3+[Xe]4f145d106s2
Bi5+[Xe]4f145d10
  • The Group IV - VII non-metals gain electrons until their valence shells are full (8 electrons).

Atomic Number 207

IVAC1s22s22p2C4-1s22s22p6
VAN1s22s22p3N3-1s22s22p6
VIAO1s22s22p4O2-1s22s22p6
VIIAF1s22s22p5F-1s22s22p6
  • The Group VIII noble gases already possess a full outer shell, so they have no tendency to form ions.
  • Transition metals (B-group) usually form +2 charges from losing the valence s electrons, but can also lose electrons from the highest d level to form other charges.
B-groupFe1s22s22p63s23p63d64s2Fe2+1s22s22p63s23p63d6
Fe3+1s22s22p63s23p63d5

Atomic Number 21

References

Martin S. Silberberg, Chemistry: The Molecular Nature of Matter and Change, 2nd ed. Boston: McGraw-Hill, 2000, p. 277-284, 293-307.

Atomic Number 201