“atom”的概念、定义、翻译、参考文献-科学参考

atom

Physics

The smallest part of an element that can exist. Atoms consist of a small dense nucleus of protons and neutrons surrounded by moving electrons. The number of electrons equals the number of protons so the overall charge is zero. The electrons may be thought of as moving in circular or elliptical orbits (see Bohr theory) or, more accurately, in regions of space around the nucleus (see orbital).

The electronic structure of an atom refers to the way in which the electrons are arranged about the nucleus, and in particular the energy levels that they occupy. Each electron can be characterized by a set of four quantum numbers, as follows: (1) The principal quantum number n gives the main energy level and has values 1, 2, 3, etc. (the higher the number, the further the electron from the nucleus). Traditionally, these levels, or the orbits corresponding to them, are referred to as shells and given letters K, L, M, etc. The K-shell is the one nearest the nucleus. (2) The orbital quantum number l, which governs the angular momentum of the electron. The possible values of l are (n − 1), (n − 2),…, 1, 0. Thus, in the first shell (n=1) the electrons can only have angular momentum zero (l=0). In the second shell (n=2), the values of l can be 1 or 0, giving rise to two subshells of slightly different energy. In the third shell (n=3) there are three subshells, with l=2, 1, or 0. The subshells are denoted by letters s (l=0), p (l=1), d (l=2), f (l=3). The orbital quantum number is sometimes called the azimuthal quantum number. (3) The magnetic quantum number m, which governs the energies of electrons in an external magnetic field. This can take values of +l,+(l − 1), …, 1, 0, −1, …, −(l − 1), −l. In an s-subshell (i.e. l=0) the value of m=0. In a p-subshell (l=1), m can have values +1, 0, and −1; i.e. there are three p-orbitals in the p-subshell, usually designated p_x, p_y, and p_z. Under normal circumstances, these all have the same energy level. (4) The spin quantum number m_s, which gives the spin of the individual electrons and can have the values +½ or −½.

According to the Pauli exclusion principle, no two electrons in the atom can have the same set of quantum numbers. The numbers define the quantum state of the electron, and explain how the electronic structures of atoms occur. See Atomic Theory (Chronology).

Mathematics

In measure theory, a set which has strictly positive measure, with the property that any subset either has equal measure or has zero measure.

Astronomy

The smallest part of a chemical element that can take part in a chemical reaction. An atom is composed of a nucleus made up of protons and neutrons, surrounded by electrons orbiting at different energy levels. The number of protons in the nucleus of an element's atom is referred to as the atomic number of the element or atom; the total number of protons and neutrons is the mass number. In a neutral atom the number of protons is equal to the number of electrons.

Chemistry

The smallest part of an element that can exist chemically. Atoms consist of a small dense nucleus of protons and neutrons surrounded by moving electrons. The number of electrons equals the number of protons so the overall charge is zero. The electrons are considered to move in circular or elliptical orbits (see Bohr theory) or, more accurately, in regions of space around the nucleus (see orbital).
The electronic structure of an atom refers to the way in which the electrons are arranged about the nucleus, and in particular the energy levels that they occupy. Each electron can be characterized by a set of four quantum numbers, as follows:
1. (1) The principal quantum number n gives the main energy level and has values 1, 2, 3, etc. (the higher the number, the further on average the electron from the nucleus). Traditionally, these levels, or the orbits corresponding to them, are referred to as shells and given letters K, L, M, etc. The K-shell is the one nearest the nucleus. The maximum number of electrons in a given shell is 2n².
2. (2) The orbital quantum number l, which governs the angular momentum of the electron. The possible values of l are (n – 1), (n – 2),…1, 0. Thus, in the first shell (n = 1) the electrons can only have angular momentum zero (l = 0). In the second shell (n = 2), the values of l can be 1 or 0, giving rise to two subshells of slightly different energy. In the third shell (n = 3) there are three subshells, with l = 2, 1, or 0. The subshells are denoted by letters s(l = 0), p(l = 1), d(l = 2), f(l = 3). The number of electrons in each subshell is written as a superscript numeral to the subshell symbol, and the maximum number of electrons in each subshell is s², p⁶, d¹⁰, and f¹⁴. The orbital quantum number is sometimes called the azimuthal quantum number.
3. (3) The magnetic quantum number m, which governs the energies of electrons in an external magnetic field. This can take values of +l, +(l – 1),…1, 0, –1,…–(l – 1), –l. In an s-subshell (i.e. l = 0) the value of m = 0. In a p-subshell (l = 1), m can have values +1, 0, and –1; i.e. there are three p-orbitals in the p-subshell, usually designated p_x, p_y, and p_z. Under normal circumstances, these all have the same energy level.
4. (4) The spin quantum number m_s, which gives the spin of the individual electrons and can have the values +½‎ or –½‎.
According to the Pauli exclusion principle, no two electrons in the atom can have the same set of quantum numbers. The numbers define the quantum state of the electron, and explain how the electronic structures of atoms occur. See Atomic Theory Chronology.

Chemical Engineering

The smallest particle of an element that can exist and which can take part in a chemical reaction and cannot be chemically divided any further into smaller parts. It is identifiable as that element by its nucleus. The nucleus contains neutrons and protons and is surrounded by a cloud of orbiting electrons. The number of electrons equals the number of protons such that the overall charge is zero.

Computer

A value that cannot be decomposed further. In Lisp an atom is a representation of an arbitrary string of characters or the special atom NIL, i.e. nothing. The word is also used as a predicate in Lisp-like languages to determine whether an arbitrary value is or is not an atom:
$(atom (cons (h, t)))$
always yields FALSE but
$(atom, NIL)$
and
$(atom, ‘word’)$
evaluate to TRUE.

单词	atom
释义	atom Physics The smallest part of an element that can exist. Atoms consist of a small dense nucleus of protons and neutrons surrounded by moving electrons. The number of electrons equals the number of protons so the overall charge is zero. The electrons may be thought of as moving in circular or elliptical orbits (see Bohr theory) or, more accurately, in regions of space around the nucleus (see orbital). The electronic structure of an atom refers to the way in which the electrons are arranged about the nucleus, and in particular the energy levels that they occupy. Each electron can be characterized by a set of four quantum numbers, as follows: (1) The principal quantum number n gives the main energy level and has values 1, 2, 3, etc. (the higher the number, the further the electron from the nucleus). Traditionally, these levels, or the orbits corresponding to them, are referred to as shells and given letters K, L, M, etc. The K-shell is the one nearest the nucleus. (2) The orbital quantum number l, which governs the angular momentum of the electron. The possible values of l are (n − 1), (n − 2),…, 1, 0. Thus, in the first shell (n=1) the electrons can only have angular momentum zero (l=0). In the second shell (n=2), the values of l can be 1 or 0, giving rise to two subshells of slightly different energy. In the third shell (n=3) there are three subshells, with l=2, 1, or 0. The subshells are denoted by letters s (l=0), p (l=1), d (l=2), f (l=3). The orbital quantum number is sometimes called the azimuthal quantum number. (3) The magnetic quantum number m, which governs the energies of electrons in an external magnetic field. This can take values of +l,+(l − 1), …, 1, 0, −1, …, −(l − 1), −l. In an s-subshell (i.e. l=0) the value of m=0. In a p-subshell (l=1), m can have values +1, 0, and −1; i.e. there are three p-orbitals in the p-subshell, usually designated p_x, p_y, and p_z. Under normal circumstances, these all have the same energy level. (4) The spin quantum number m_s, which gives the spin of the individual electrons and can have the values +½ or −½. According to the Pauli exclusion principle, no two electrons in the atom can have the same set of quantum numbers. The numbers define the quantum state of the electron, and explain how the electronic structures of atoms occur. See Atomic Theory (Chronology). Mathematics In measure theory, a set which has strictly positive measure, with the property that any subset either has equal measure or has zero measure. Astronomy The smallest part of a chemical element that can take part in a chemical reaction. An atom is composed of a nucleus made up of protons and neutrons, surrounded by electrons orbiting at different energy levels. The number of protons in the nucleus of an element's atom is referred to as the atomic number of the element or atom; the total number of protons and neutrons is the mass number. In a neutral atom the number of protons is equal to the number of electrons. Chemistry The smallest part of an element that can exist chemically. Atoms consist of a small dense nucleus of protons and neutrons surrounded by moving electrons. The number of electrons equals the number of protons so the overall charge is zero. The electrons are considered to move in circular or elliptical orbits (see Bohr theory) or, more accurately, in regions of space around the nucleus (see orbital). The electronic structure of an atom refers to the way in which the electrons are arranged about the nucleus, and in particular the energy levels that they occupy. Each electron can be characterized by a set of four quantum numbers, as follows: (1) The principal quantum number n gives the main energy level and has values 1, 2, 3, etc. (the higher the number, the further on average the electron from the nucleus). Traditionally, these levels, or the orbits corresponding to them, are referred to as shells and given letters K, L, M, etc. The K-shell is the one nearest the nucleus. The maximum number of electrons in a given shell is 2n². (2) The orbital quantum number l, which governs the angular momentum of the electron. The possible values of l are (n – 1), (n – 2),…1, 0. Thus, in the first shell (n = 1) the electrons can only have angular momentum zero (l = 0). In the second shell (n = 2), the values of l can be 1 or 0, giving rise to two subshells of slightly different energy. In the third shell (n = 3) there are three subshells, with l = 2, 1, or 0. The subshells are denoted by letters s(l = 0), p(l = 1), d(l = 2), f(l = 3). The number of electrons in each subshell is written as a superscript numeral to the subshell symbol, and the maximum number of electrons in each subshell is s², p⁶, d¹⁰, and f¹⁴. The orbital quantum number is sometimes called the azimuthal quantum number. (3) The magnetic quantum number m, which governs the energies of electrons in an external magnetic field. This can take values of +l, +(l – 1),…1, 0, –1,…–(l – 1), –l. In an s-subshell (i.e. l = 0) the value of m = 0. In a p-subshell (l = 1), m can have values +1, 0, and –1; i.e. there are three p-orbitals in the p-subshell, usually designated p_x, p_y, and p_z. Under normal circumstances, these all have the same energy level. (4) The spin quantum number m_s, which gives the spin of the individual electrons and can have the values +½‎ or –½‎. According to the Pauli exclusion principle, no two electrons in the atom can have the same set of quantum numbers. The numbers define the quantum state of the electron, and explain how the electronic structures of atoms occur. See Atomic Theory Chronology. Chemical Engineering The smallest particle of an element that can exist and which can take part in a chemical reaction and cannot be chemically divided any further into smaller parts. It is identifiable as that element by its nucleus. The nucleus contains neutrons and protons and is surrounded by a cloud of orbiting electrons. The number of electrons equals the number of protons such that the overall charge is zero. Computer A value that cannot be decomposed further. In Lisp an atom is a representation of an arbitrary string of characters or the special atom NIL, i.e. nothing. The word is also used as a predicate in Lisp-like languages to determine whether an arbitrary value is or is not an atom: $(atom (cons (h, t)))$ always yields FALSE but $(atom, NIL)$ and $(atom, ‘word’)$ evaluate to TRUE.
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