Atom Legal Definition

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Atoms of the same element have the same number of protons called atomic number. Within the same element, the number of neutrons can vary and determine the isotope of that element. The total number of protons and neutrons determines the nuclide. The number of neutrons relative to protons determines the stability of the nucleus, with some isotopes decaying radioactively. [50] The ubiquity and stability of atoms are based on their bonding energy, which means that an atom has a lower energy than an unbound system of nucleus and electrons. When the temperature is much higher than the ionization potential, matter exists as plasma – a gas of positively charged ions (possibly bare nuclei) and electrons. When the temperature drops below the ionization potential, the atoms become statistically favorable. Atoms (with bound electrons) were dominated by charged particles 380,000 years after the Big Bang – a time called recombination when the expanding universe cooled to such an extent that electrons could be bound to nuclei. [126] Other exotic atoms were created by replacing one of the protons, neutrons or electrons with other particles with the same charge. For example, an electron can be replaced by a more massive muon that forms a muon atom. These types of atoms can be used to test the basic predictions of physics.

[153] [154] [155] Chemical bonds between atoms were explained in 1916 by Gilbert Newton Lewis as the interactions between their constituent electrons. [24] Since it was known that the chemical properties of the elements are widely repeated according to periodic law,[25] the American chemist Irving Langmuir suggested in 1919 that this could be explained if the electrons of an atom were connected or grouped together in some way. Groups of electrons are thought to occupy a series of electron layers around the nucleus. [26] Atomic dimensions are a thousand times smaller than wavelengths of light (400-700 nm), so they cannot be viewed with an optical microscope, although individual atoms can be observed with a scanning tunneling microscope. To visualize the smallness of the atom, consider that a typical human hair has a width of about 1 million carbon atoms. [83] A single drop of water contains about 2 sextillions (2×1021) of oxygen atoms and twice as many hydrogen atoms. [84] A single-carat diamond with a mass of 2×10−4 kg contains about 10 sextillion (1022) carbon atoms. [Note 2] If an apple were increased to the size of the earth, then the atoms in the apple would be about the same size as the original apple. [85] All nuclides with an atomic number greater than 82 (lead) are known to be radioactive.

No nuclearid with an atomic number greater than 92 (uranium) exists on Earth as a primordial nuclide, and heavier elements usually have shorter half-lives. Nevertheless, an “island of stability” could exist, comprising relatively long-lived isotopes of superheavy elements[145] with atomic numbers 110 to 114. [146] Predictions of the half-life of the island`s most stable nuclide range from minutes to millions of years. [147] In any event, superheavy elements (with Z > 104) would not exist without a stabilizing effect due to the increasing coulomb rejection (which leads to spontaneous splitting with shorter and shorter half-lives). [148] The magnetic field generated by an atom – its magnetic moment – is determined by these different forms of angular momentum, just as a rotating charged object conventionally generates a magnetic field, but the most dominant contribution comes from the spin of the electron. Due to the nature of electrons, obeying the Pauli exclusion principle, in which two electrons cannot be found in the same quantum state, the bound electrons pair with each other, with one member of each pair in a spin-up state and the other in the opposite, spin-down state. Thus, these spins cancel each other out and reduce the total magnetic dipole moment in some atoms with an even number of electrons at zero. [90] Spectra of excited states can be used to analyze the atomic composition of distant stars. Specific wavelengths of light contained in the observed light of stars can be separated and related to quantified transitions in free gas atoms. These colors can be reproduced with a gas discharge lamp that contains the same element. [116] Helium was discovered in the Sun`s spectrum 23 years before it was discovered on Earth.

[117] Atoms do not have a well-defined outer boundary, so their dimensions are usually described as an atomic radius. This is a measure of how far the electron cloud extends from the nucleus. [75] It is assumed that the atom has a spherical shape that is followed only for atoms in a vacuum or free space. Atomic rays can be derived from the distances between two nuclei when the two atoms are connected in a chemical bond. The radius varies with the position of an atom on the atomic map, the type of chemical bond, the number of neighboring atoms (coordination number), and a quantum mechanical property known as spin. [76] In the periodic table of elements, atomic size tends to increase when columns are moved downwards, but decreases as it moves along the rows (from left to right). [77] Therefore, the smallest atom is helium with a radius of 32 pm, while one of the largest cesium is at 225 pm. [78] Electron emission techniques such as X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), which measure the binding energies of nuclear electrons, are used to non-destructively identify the atomic species present in a sample. With proper focus, both can be designed specifically for the area.

Another method of this type is electron energy loss spectroscopy (EELS), which measures the energy loss of an electron beam in a transmission electron microscope when interacting with part of a sample. Although the word atom originally referred to a particle that cannot be cut into smaller particles, in modern scientific usage, the atom consists of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron. At 9.11×10−31 kg, the electron is by far the least massive of these particles, with a negative electric charge and a size too small to be measured using available techniques. [42] It was the lightest particle with a positive residual mass measured until the discovery of neutrino mass. Under normal conditions, electrons are bound to the positively charged nucleus by the force of attraction generated by opposing electric charges. If an atom has more or fewer electrons than its atomic number, then it is negatively or positively charged as a whole; An charged atom is called an ion. Electrons have been known since the late 19th century, mainly thanks to J.J. Thomson; See History of Subatomic Physics for more details. Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden had doubts about the thomson model after struggling to build an instrument to measure the charge-to-mass ratio of alpha particles (these are positively charged particles emitted by certain radioactive substances such as radium).

The alpha particles were dispersed by air in the detection chamber, making the measurements unreliable. Thomson had encountered a similar problem in his work on cathode rays, which he solved by creating an almost perfect void in his instruments. Rutherford didn`t think he would face the same problem because alpha particles are much heavier than electrons. According to Thomson`s atom model, the positive charge in the atom is not concentrated enough to create an electric field strong enough to deflect an alpha particle, and the electrons are so light that they should be easily discarded by the much heavier alpha particles. But there was distraction, so Rutherford and his colleagues decided to study this dispersion carefully. [18] By definition, any two atoms with the same number of protons in their nuclei belong to the same chemical element. Atoms with the same number of protons but a different number of neutrons are different isotopes of the same element. For example, all hydrogen atoms allow exactly one proton, but isotopes exist without neutrons (hydrogen-1, by far the most common form,[63] also called protium), one neutron (deuterium), two neutrons (tritium), and more than two neutrons.

The known elements form a set of atomic numbers, from the single proton element hydrogen to the element 118 protons Oganesson. [64] All known isotopes of elements with an atomic number greater than 82 are radioactive, although the radioactivity of element 83 (bismuth) is so low that it is practically negligible. [65] [66] Since the Big Bang, which produced neither carbon nor heavier elements, the atomic nuclei of stars have been combined by the process of nuclear fusion to produce more helium from the element, and (via the triple-alpha process) the sequence of elements from carbon to iron; [127] See Stellar Nucleosynthesis for more details.

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