For helium, it is 4: two protons and two neutrons. For most of the 16 lightest elements up to oxygen the number of neutrons is equal to the number of protons. For most of the remaining elements, there are more neutrons than protons, because extra neutrons are needed to keep the nucleus together by overcoming the mutual repulsion of the increasing numbers of protons concentrated in a very small space.
For example, silicon has 14 protons and 14 neutrons. Its atomic number is 14 and its atomic mass is The most common isotope of uranium has 92 protons and neutrons. The dot in the middle is the nucleus, and the surrounding cloud represents where the two electrons might be at any time. The darker the shade, the more likely that an electron will be there.
A femtometre fm is 10 m. Subsequent shells can hold more electrons, but the outermost shell of any atom holds no more than eight electrons. In the universe, neutrons are abundant, making up more than half of all visible matter.
It has no electric charge and a rest mass equal to 1. The neutron has a mean square radius of about 0. Atomic nuclei consist of protons and neutrons, which attract each other through the nuclear force , while protons repel each other via the electric force due to their positive charge. These two forces compete, leading to various stability of nuclei. There are only certain combinations of neutrons and protons, which forms stable nuclei.
Neutrons stabilize the nucleus , because they attract each other and protons , which helps offset the electrical repulsion between protons. As a result, as the number of protons increases, an increasing ratio of neutrons to protons is needed to form a stable nucleus.
If there are too many or too few neutrons for a given number of protons, the resulting nucleus is not stable and it undergoes radioactive decay. Unstable isotopes decay through various radioactive decay pathways, most commonly alpha decay, beta decay, or electron capture. Many other rare types of decay, such as spontaneous fission or neutron emission are known. It should be noted that all of these decay pathways may be accompanied by the subsequent emission of gamma radiation. Pure alpha or beta decays are very rare.
The periodic table is a tabular display of the chemical elements organized on the basis of their atomic numbers, electron configurations, and chemical properties.
The electron configuration is the distribution of electrons of an atom or molecule or other physical structure in atomic or molecular orbitals. Knowledge of the electron configuration of different atoms is useful in understanding the structure of the periodic table of elements. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms.
The chemical properties of the atom are determined by the number of protons, in fact, by number and arrangement of electrons. It is the Pauli exclusion principle that requires the electrons in an atom to occupy different energy levels instead of them all condensing in the ground state. This fact has key implications for the building up of the periodic table of elements. The first two columns on the left side of the periodic table are where the s subshells are being occupied.
Because of this, the first two rows of the periodic table are labeled the s block. Similarly, the p block are the right-most six columns of the periodic table, the d block is the middle 10 columns of the periodic table, while the f block is the column section that is normally depicted as detached from the main body of the periodic table.
It could be part of the main body, but then the periodic table would be rather long and cumbersome. For atoms with many electrons, this notation can become lengthy and so an abbreviated notation is used.
Silicon is used in glass as silicon dioxide SiO2. Silicon carbide SiC is one of the hardest substances known and used in polishing. Also the crystalline form of silicon is used in semiconductors. Silicon Isotope. Request Silicon isotope quote. Silicon Isotope Applications: Silicon isotope Si isotope , 29Si isotope Silicon isotope is used for studies of impurities and intrinsic defects in semiconductors; Silicon isotope is used for studies of irregularities in materials such as glass, crystals and ceramics via methods of electron paramagnetic resonance EPR ; Silicon isotope is used for instrument calibration when extending the bandwidth of nuclear magnetic resonance NMR ; Silicon isotope is available to order from BuyIsotope.
Answer: 4.
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