The atom is one of the most fundamental particles in ordinary matter. A chemical element is entirely determined by the type of atom contained therein, which in turn is determined by the number of protons, neutrons and electrons that constitute the atom. An atom consists of a dense core, consisting of positively charged protons and neutrons electrically neutral, tied together by the strong nuclear force. Around the nucleus at a distance of about 10 000 times the diameter nuclear, are negatively charged electrons, limited by their electrostatic attraction to the nucleas. When the number of protons in the nucleus is equal to the number of electrons, the atom is electrically neutral, if there is an ion and has a net positive or negative charge. An atom is classified according to how many protons and neutrons: the number of protons determines the chemical element and the number of neutrons determines the isotope of the element.
The concept of an atom as an indivisible part of matter was first proposed in early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that some substances could not be broken by chemical methods. During the late 19th and early 20th centuries, physicists subatomic components and the internal structure of the atom, thus showing that the 'atom is not indivisible. The principles of quantum mechanics have been used successfully to the model of the atom. Compared to everyday experience, the atoms are tiny objects with masses of tiny proportion that can not be seen individually using special instruments such as scanning tunneling microscope. More than 99.9% of an atom 's mass is concentrated in the core, with protons and neutrons with roughly the same mass. In atoms with too many or too few neutrons compared to the number of protons, the nucleus is unstable and subject to radioactive decay. The electrons surrounding the nucleus occupy a series of energy levels stable, or orbital, and they can transition between these states by the absorption or emission of photons that reflect the differences between energy levels. The electrons determine the chemical properties of an element, and a strong influence on an atom 's magnetic properties.
The concept of an atom as an indivisible part of matter was first proposed in early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that some substances could not be broken by chemical methods. During the late 19th and early 20th centuries, physicists subatomic components and the internal structure of the atom, thus showing that the 'atom is not indivisible. The principles of quantum mechanics have been used successfully to the model of the atom. Compared to everyday experience, the atoms are tiny objects with masses of tiny proportion that can not be seen individually using special instruments such as scanning tunneling microscope. More than 99.9% of an atom 's mass is concentrated in the core, with protons and neutrons with roughly the same mass. In atoms with too many or too few neutrons compared to the number of protons, the nucleus is unstable and subject to radioactive decay. The electrons surrounding the nucleus occupy a series of energy levels stable, or orbital, and they can transition between these states by the absorption or emission of photons that reflect the differences between energy levels. The electrons determine the chemical properties of an element, and a strong influence on an atom 's magnetic properties.
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