Examples of atomic number in the following topics:
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- In alpha decay an atomic nucleus emits an alpha particle and transforms into an atom with smaller mass (by four) and atomic number (by two).
- As the result of this process, the parent atom transforms ("decays") into a new atom with a mass number smaller by four and an atomic number smaller by two.
- Because an alpha particle is the same as a helium-4 nucleus, which has mass number 4 and atomic number 2, this can also be written as:
- Alpha decay is by far the most common form of cluster decay, in which the parent atom ejects a defined daughter collection of nucleons, leaving another defined product behind (in nuclear fission, a number of different pairs of daughters of approximately equal size are formed).
- An atomic nucleus emits an alpha particle and thereby transforms ("decays") into an atom with a mass number smaller by four and an atomic number smaller by two.
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- The stability of an atom depends on the ratio and number of protons and neutrons, which may represent closed and filled quantum shells.
- The stability of an atom depends on the ratio of its protons to its neutrons, as well as on whether it contains a "magic number" of neutrons or protons that would represent closed and filled quantum shells.
- Of the 254 known stable nuclides, only four have both an odd number of protons and an odd number of neutrons:
- An atomic nucleus emits an alpha particle and thereby transforms ("decays") into an atom with a mass number smaller by four and an atomic number smaller by two.
- Explain the relationship between the stability of an atom and its atomic structure.
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- In the case of an electron being released, atomic mass (A) remains the same as a neutron is converted into a proton, raising atomic number by 1:
- In the case of a positron being released, atomic mass remains constant as a proton is converted to a neutron, lowering atomic number by 1:
- Alpha decay is the only type of radioactive decay that results in an appreciable change in an atom's atomic mass.
- In each step, the total atomic mass of all species is a constant value of 236.
- Finally, nuclear fusion follows the Law of Conservation of Nucleon Number.
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- In thermal equilibrium the number of atoms in a particular state is proportional to $ge^{-\beta E}$ where $\beta=1/kT$ and $g$ is the statistical weight or degeneracy of the state (for $L-S-$ coupling $g=2(2J+1)$), so we find that
- where $ N$ is the total number of atoms and $U$ is a normalization factor
- Atoms generally have a certain ionization energy (for example, hydrogen has 13.6~eV) but there are an infinite number of states between the ground state and the ionization level so $e^{-\beta E_i}$ approaches a constant for large $i$ and $g_i$ typically increases so $U$ will diverge.
- Second is that atoms don't live in spendid isolation.
- The size of the highly excited states of atoms increases as $n^2$ so we only have to sum over the states until we reach
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- Atoms contain negatively charged electrons and positively charged protons; the number of each determines the atom's net charge.
- The number of protons in an atom defines the identity of the element (an atom with 1 proton is hydrogen, for example, and an atom with two protons is helium).
- As such, protons are relatively stable; their number rarely changes, only in the instance of radioactive decay.
- In the ground state, an atom will have an equal number of protons and electrons, and thus will have a net charge of 0.
- Atoms in such a state are known as ions.
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- Atoms with more than one electron are referred to as multielectron atoms.
- Atoms with more than one electron, such as Helium (He) and Nitrogen (N), are referred to as multielectron atoms.
- As an approximation, the effective nuclear charge on each electron can be estimated by: Zeff=Z−σZ_\text{eff} = Z - \sigma, where $Z$ is the number of protons in the nucleus and σ\sigma is the average number of electrons between the nucleus and the electron in question. σ\sigma can be found by using quantum chemistry and the Schrodinger equation or by using Slater's empirical formula.
- For example, consider a sodium cation, a fluorine anion, and a neutral neon atom.
- Each has 10 electrons, and the number of nonvalence electrons is two (10 total electrons minus eight valence electrons), but the effective nuclear charge varies because each has a different number of protons:
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- The electrons of an atom are bound to the nucleus by the electromagnetic force.
- Democritus called this the atom.
- It was Avogadro who developed the idea of a fixed number of atoms and molecules in a mole.
- This special number is called Avogadro's number in his honor ($6.022 \cdot 10^{23}$).
- Describe postulates of Dalton's atomic theory and the atomic theories of ancient Greek philosophers
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- Philosophical proposals regarding atoms have been suggested since the years of the ancient Greeks, but John Dalton was the first to propose a scientific theory of atoms.
- For this reason, Dalton is considered the originator of modern atomic theory.
- Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
- Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
- Atoms can be broken down into smaller pieces, and atoms of a given element can vary in mass and other properties (see isotopes and ions).
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- Atom is a basic unit of matter that consists of a nucleus surrounded by negatively charged electron cloud, commonly called atomic orbitals.
- The electrons of an atom are bound to the nucleus by the electromagnetic (Coulomb) force.
- Hydrogen-1 (one proton + one electron) is the simplest form of atoms, and not surprisingly, our quantum mechanical understanding of atoms evolved with the understanding of this species.
- Thereafter, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to be observed.
- One of the hydrogen's atomic transitions (n=2 to n=1, n: principal quantum number) has been measured to an extraordinary precision of 1 part in a hundred trillion.
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- The electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
- The electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.
- An infinite number of electronic configurations are needed to exactly describe any multi-electron system, and no energy can be associated with one single configuration.
- However, the electronic wave function is usually dominated by a very small number of configurations and therefore the notion of electronic configuration remains essential for multi-electron systems.
- In the Aufbau Principle, as electrons are added to atoms, they are added to the lowest orbitals first.