"cold neutral atom, the ion 'steals' electrons from the neutral atom, producing a cold ion and an energetic neutral atom(ENA). I + A → A + I where Species 1 and 2 may be the same or different and an exchange of two electrons is possible, e.g. H + H → H + H Proton–hydrogen charge-exchange or He + He → He + He alpha-helium charge-exchange. Due to its charge neutrality, the resulting ENA is subject to gravitational forces only. Because gravitation influences can normally be ignored, it is safe to assume that the ENA preserves the vector momentum of"
"electrons contained in a normal helium atom in a chemical reaction, and then begins to orbit the helium nucleus in the electron's place. This will happen in the case of approximately 3% of the antiprotons introduced to the helium gas. The antiproton's orbit, which has a large principal quantum number and angular momentum quantum number of around 38, lies far away from the surface of the helium nucleus. The antiproton can thus orbit the nucleus for tens of microseconds, before finally falling to its surface and annihilating. Antiprotonic helium atoms are under study by the ASACUSA experiment at CERN. In"
"is that since formula_19 and formula_21 can be varied separately (a fact arising due to the complex nature of the wave function), the quantities can be varied in principle just one at a time. The helium atom consists of two electrons with mass ""m"" and electric charge −""e"", around an essentially fixed nucleus of mass ""M"" ≫ ""m"" and charge +2""e"". The Hamiltonian for it, neglecting the fine structure, is: where ""ħ"" is the reduced Planck constant, ""ε"" is the vacuum permittivity, ""r"" (for ""i"" = 1, 2) is the distance of the ""i""-th electron from the nucleus, and |r"
"emitting a beta particle and has a half-life of 0.8 seconds. Helium-7 also emits a beta particle as well as a gamma ray. The most widely studied heavy helium isotope is helium-8. This isotope, as well as helium-6, are thought to consist of a normal helium-4 nucleus surrounded by a neutron ""halo"" (containing two neutrons in and four neutrons in ). Halo nuclei have become an area of intense research. Isotopes up to helium-10, with two protons and eight neutrons, have been confirmed. Helium-7 and helium-8 are hyperfragments that are created in certain nuclear reactions. , despite being a doubly"
"unstable, and gradually undergo radioactive decay to become another element. The hydrogen nucleus contain just one proton, Its isotope deuterium, or heavy hydrogen, contains a proton and a neutron. Helium contains two protons and two neutrons, and carbon, nitrogen and oxygen - six, seven and eight of each particle, respectively. However, a helium nucleus weighs less than the sum of the weights of the two hydrogen nuclei which combine to make it. The same is true for carbon, nitrogen and oxygen. For example, the carbon nucleus is slightly lighter than three helium nuclei, which can combine to make a carbon"
"Helium compounds Helium is the most unreactive element, so it was commonly believed that helium compounds do not exist at all. Helium's first ionization energy of 24.57 eV is the highest of any element. Helium has a complete shell of electrons, and in this form the atom does not readily accept any extra electrons or join with anything to make covalent compounds. The electron affinity is 0.080 eV, which is very close to zero. The helium atom is small with the radius of the outer electron shell at 0.29 Å. The atom is very hard with a Pearson's hardness of"
"not the 2 charges of a classic ""bare"" helium nucleus. The nucleus of the helium-4 atom is identical with an alpha particle. High-energy electron-scattering experiments show its charge to decrease exponentially from a maximum at a central point, exactly as does the charge density of helium's own electron cloud. This symmetry reflects similar underlying physics: the pair of neutrons and the pair of protons in helium's nucleus obey the same quantum mechanical rules as do helium's pair of electrons (although the nuclear particles are subject to a different nuclear binding potential), so that all these fermions fully occupy 1s orbitals"
"Helion (chemistry) A helion is a short name for the naked nucleus of helium, a doubly positively charged ""helium ion"". In practice, ""helion"" refers specifically to the nucleus of the helium-3 isotope, consisting of two protons and one neutron. The nucleus of the other stable isotope of helium, helium-4 isotope, which consists of two protons and two neutrons, is specifically called an alpha particle. This particle is emitted in the decay of tritium, an isotope of hydrogen: According to CODATA, the mass of a helion particle is 5.006 412 700(62) × 10 kg. Helions are intermediate products in the proton-proton"
"of 206 electrons. They have also prepared the heaviest hydrogen atom analogue by replacing one electron in helium with a negative muon (μ) to form Heμ with an atomic mass of 4.116 amu. Since the negative muon is much heavier than an electron, it orbits much closer to the nucleus, effectively shielding one proton, making Heμ to behave as H. With these exotic species, the reaction of H with H was investigated. Rate constants from reacting the lightest and the heaviest hydrogen analogues with H were then used to calculate the ""k""/""k"" kinetic isotope effect, in which there is a"
"nucleus consists of two neutrons, two protons and a muon, with a single electron outside. Colloquially, it could be called ""helium 4.1"", since the mass of the muon is slightly greater than 0.1 amu. Chemically, muonic helium, possessing an unpaired valence electron, can bond with other atoms, and behaves more like a hydrogen atom than an inert helium atom. Muonic heavy hydrogen atoms with a negative muon may undergo nuclear fusion in the process of muon-catalyzed fusion, after the muon may leave the new atom to induce fusion in another hydrogen molecule. This process continues until the negative muon is"
"Isotopes of helium Although there are nine known isotopes of helium (He) (standard atomic weight: ), only helium-3 () and helium-4 () are stable. All radioisotopes are short-lived, the longest-lived being with a half-life of . The least stable is , with a half-life of , although it is possible that has an even shorter half-life. In the Earth's atmosphere, there is one atom for every million atoms. However, helium is unusual in that its isotopic abundance varies greatly depending on its origin. In the interstellar medium, the proportion of is around a hundred times higher. Rocks from the Earth's"
"chain reaction in stellar fusion. Helion (chemistry) A helion is a short name for the naked nucleus of helium, a doubly positively charged ""helium ion"". In practice, ""helion"" refers specifically to the nucleus of the helium-3 isotope, consisting of two protons and one neutron. The nucleus of the other stable isotope of helium, helium-4 isotope, which consists of two protons and two neutrons, is specifically called an alpha particle. This particle is emitted in the decay of tritium, an isotope of hydrogen: According to CODATA, the mass of a helion particle is 5.006 412 700(62) × 10 kg. Helions are"
"Helium-4 Helium-4 (' or ') is a non-radioactive isotope of the element helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists of two protons and two neutrons. Alpha decay of heavy elements in the Earth's crust is the source of most naturally occurring helium-4 on Earth. While it is also produced by nuclear fusion in stars, most helium-4 in the Sun and in the universe is thought to have been produced by the Big"
"occupy 1s1s orbitals in pairs, none of them possessing orbital angular momentum, and each canceling the other's intrinsic spin. Adding another of any of these particles would require angular momentum, and would release substantially less energy (in fact, no nucleus with five nucleons is stable). This arrangement is thus energetically extremely stable for all these particles, and this stability accounts for many crucial facts regarding helium in nature. For example, the stability and low energy of the electron cloud of helium causes helium's chemical inertness (the most extreme of all the elements), and also the lack of interaction of helium"
"and these orbit at Z=2. Each one sees the nuclear charge of Z=3 minus the screening effect of the other, which crudely reduces the nuclear charge by 1 unit. This means that the innermost electrons orbit at approximately 1/4 the Bohr radius. The outermost electron in lithium orbits at roughly Z=1, since the two inner electrons reduce the nuclear charge by 2. This outer electron should be at nearly one Bohr radius from the nucleus. Because the electrons strongly repel each other, the effective charge description is very approximate; the effective charge Z doesn't usually come out to be an"
"formula_2 is 1.2 fm. One example of a halo nucleus is Li, which has a half-life of 8.6 ms. It contains a core of 3 protons and 6 neutrons, and a halo of two independent and loosely bound neutrons. It decays into Be by the emission of an antineutrino and an electron. Its mass radius of 3.16 fm is close to that of S or, even more impressively, of Pb, both much heavier nuclei. Experimental confirmation of nuclear halos is recent and ongoing. Additional candidates are suspected. Several nuclides including B, N, and N are calculated to have a halo"
"valence electron, and the electron that remains in the 1s orbital is a core electron. Two excited helium atoms can react with a covalent bond to form a molecule called dihelium that lasts for short times of the order of a microsecond up to second or so. Excited helium atoms in the 2S state can last for up to an hour, and react like alkali metal atoms. The first clues that dihelium exists were noticed in 1900 when W. Heuse observed a band spectrum in a helium discharge. However, no information about the nature of the spectrum was published. Independently"
"in a nucleus can accommodate both a spin up particle and a spin down particle. Helium-4 has an anomalously large binding energy because its nucleus consists of two protons and two neutrons, so all four of its nucleons can be in the ground state. Any additional nucleons would have to go into higher energy states. Indeed, the helium-4 nucleus is so tightly bound that it is commonly treated as a single quantum mechanical particle in nuclear physics, namely, the alpha particle. The situation is similar if two nuclei are brought together. As they approach each other, all the protons in"
"argon and then form a cluster ion when the rest of the droplet evaporates. NeHe can be made by ultraviolet photoionisation. Clusters only contain one neon atom. The number of helium atoms n can vary from 1 to 23, but NeHe and NeHe are more likely to be observed. Doubly charged ions of helium with noble gas atoms also exist including ArHe, KrHe, and XeHe. Various metal-helium ions are known. Alkali metal helide ions are known for all the alkalis. The molecule ground state for the diatomic ions is in the XΣ state. The bond length gets bigger as the"
"helium. Much can be learned by studying the distribution and energy of this debris. The Large Hadron Collider smashed its first lead ions in 2010, on 7 November at around 12:30 a.m. CET. The first collisions in the center of the ALICE, ATLAS and CMS detectors took place less than 72 hours after the LHC ended its first run of protons and switched to accelerating lead-ion beams. Each lead nucleus contains 82 protons, and the LHC accelerates each proton to an energy of 3.5 TeV, thus resulting in an energy of 287 TeV per beam, or a total collision energy"
"few millikelvins. It is possible to produce exotic helium isotopes, which rapidly decay into other substances. The shortest-lived heavy helium isotope is helium-5 with a half-life of . Helium-6 decays by emitting a beta particle and has a half-life of 0.8 second. Helium-7 also emits a beta particle as well as a gamma ray. Helium-7 and helium-8 are created in certain nuclear reactions. Helium-6 and helium-8 are known to exhibit a nuclear halo. Helium has a valence of zero and is chemically unreactive under all normal conditions. It is an electrical insulator unless ionized. As with the other noble gases,"
"from the electron cloud. Protons and neutrons are bound together to form a nucleus by the nuclear force. The diameter of the nucleus is in the range of () for hydrogen (the diameter of a single proton) to about for the heaviest atom uranium. These dimensions are much smaller than the diameter of the atom itself (nucleus + electron cloud), by a factor of about 26,634 (uranium atomic radius is about ()) to about 60,250 (hydrogen atomic radius is about ). The branch of physics concerned with the study and understanding of the atomic nucleus, including its composition and the"
"the Bohr model of the structure of an atom, put forward by Niels Bohr in 1913, electrons orbit a central nucleus. The model says that the electrons orbit only at certain distances from the nucleus, depending on their energy. In the simplest atom, hydrogen, a single electron orbits the nucleus and its smallest possible orbit, with lowest energy, has an orbital radius almost equal to the Bohr radius. (It is not ""exactly"" the Bohr radius due to the reduced mass effect. They differ by about 0.1%.) Although the Bohr model is no longer in use, the Bohr radius remains very"
"The odd-""A"" stable nuclides are divided (roughly evenly) into odd-proton-even-neutron, and even-proton-odd-neutron nuclides. Odd-proton-odd-neutron nuclei are the least common. The 148 even-proton, even-neutron (EE) nuclides comprise ~ 58% of all stable nuclides and all have spin 0 because of pairing. There are also 22 primordial long-lived even-even nuclides. As a result, each of the 41 even-numbered elements from 2 to 82 has at least one stable isotope, and most of these elements have ""several"" primordial isotopes. Half of these even-numbered elements have six or more stable isotopes. The extreme stability of helium-4 due to a double pairing of 2 protons"
"forbidden from entering the liquid for the same reason hydrogen atoms are stable: quantum mechanics. The electron and image charge form a bound state, just as an electron and proton do in a hydrogen atom, with a minimum average separation. In this case, the minimum energy is about 1 eV (a moderate amount of energy on an atomic scale)[3]. When an electron is forced into liquid helium rather than floating on its surface, it forms a bubble rather than entering the liquid. The size of this bubble is determined by three main factors (ignoring small corrections): the confinement term, the"
"in pairs, none of them possessing orbital angular momentum, and each cancelling the other's intrinsic spin. Adding another of any of these particles would require angular momentum and would release substantially less energy (in fact, no nucleus with five nucleons is stable). This arrangement is thus energetically extremely stable for all these particles, and this stability accounts for many crucial facts regarding helium in nature. For example, the stability and low energy of the electron cloud state in helium accounts for the element's chemical inertness, and also the lack of interaction of helium atoms with each other, producing the lowest"
"terms of electron shells and subshells which can each hold a number of electrons determined by the Pauli exclusion principle. Thus the ""n"" = 1 state can hold one or two electrons, while the ""n"" = 2 state can hold up to eight electrons in 2s and 2p subshells. In helium, all ""n"" = 1 states are fully occupied; the same for ""n"" = 1 and ""n"" = 2 in neon. In argon the 3s and 3p subshells are similarly fully occupied by eight electrons; quantum mechanics also allows a 3d subshell but this is at higher energy than the"
"principle. However, there are a number of exceptions to the rule; for example palladium (atomic number 46) has no electrons in the fifth shell, unlike other atoms with ""lower"" atomic number. Some entries in the table are uncertain, when experimental data is unavailable. (For example, the elements past 108 have such short half-lives that their electron configurations have not yet been measured.) Electron shell In chemistry and atomic physics, an electron shell, or a principal energy level, may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the"
"""1P-mS"". Helium is in the same category as alkaline earths with respect to spectroscopy, as it has two electrons in the S subshell as do the other alkaline earths. Helium has a diffuse series of doublet lines with wavelengths 5876, 4472 and 4026 Å. Helium when ionised is termed He and has a spectrum very similar to hydrogen but shifted to shorter wavelengths. This has a diffuse series as well with wavelengths at 6678, 4922 and 4388 Å. Magnesium has a diffuse series of triplets and a sharp series of singlets. Calcium has a diffuse series of triplets and a"
"the Earth's heterosphere, a part of the upper atmosphere, helium and other lighter gases are the most abundant elements. Most helium on Earth is a result of radioactive decay. Helium is found in large amounts in minerals of uranium and thorium, including cleveite, pitchblende, carnotite and monazite, because they emit alpha particles (helium nuclei, He) to which electrons immediately combine as soon as the particle is stopped by the rock. In this way an estimated 3000 metric tons of helium are generated per year throughout the lithosphere. In the Earth's crust, the concentration of helium is 8 parts per billion."
"in the middle, the two nuclei (holding the same charge) repulse each other. Therefore, it would require more energy to hold the two atoms together through the antibonding orbital. Each electron in the valence 1""s"" shell of hydrogen come together to fill in the stabilizing bonding orbital. So, hydrogen prefers to exist as a diatomic, and not monatomic, molecule. When looking at helium, the atom holds two electrons in each valence 1""s"" shell. When the two atomic orbitals come together, they first fill in the bonding orbital with two electrons, but unlike hydrogen, it has two electrons left, which must"
"Lithium atom A lithium atom is an atom of the chemical element lithium. Lithium is composed of three electrons bound by the electromagnetic force to a nucleus containing three protons along with either three or four neutrons, depending on the isotope, held together by the strong force. Similarly to the case of the helium atom, a closed-form solution to the Schrödinger equation for the lithium atom has not been found. However, various approximations, such as the Hartree–Fock method, can be used to estimate the ground state energy and wavefunction of the atom. The quantum defect is a value that describes"
"nuclei, they are also sometimes written as or indicating a Helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom . Alpha particles are a hugely ionizing form of particle radiation. When they result from radioactive alpha decay they have low penetration depth. In this case they can be absorbed by a few centimeters of air, or by the skin. More powerful, long range alpha particles from ternary fission are three times as energetic, and penetrate proportionately farther in"