Atoms, Isotopes, amu, average aomic mass原子，同位素，阿姆河，平均原子质量.pptVIP

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2018-06-19 发布于福建
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Atoms, Isotopes, amu, average aomic mass原子，同位素，阿姆河，平均原子质量.ppt

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Atoms, Isotopes, amu, average aomic mass原子，同位素，阿姆河，平均原子质量

Atoms, Isotopes, Amu, Average atomic mass Brief History of the Atom Around 400 B.C. Democritus, a Greek philosopher, proposed that matter was made up of small hard, indivisible particles, which he called atoms Atomic Number (copy this slide) Atoms are composed of electrons, protons, and neutrons. The protons and neutrons make up the small, dense nucleus. The electrons surround the nucleus and occupy most of the volume of the atom. The Atomic Number is the number of protons an atom has. It never changes. In neutral atoms the number of protons equals the number of electrons. Atom size (copy this slide) Electrons take up most of the space More protons and neutrons = bigger nucleus Put the following in order of size: Hydride ion (H-) Alpha particle (He nucleus) Helium atom Hydrogen ion (H+) Mass Number (copy this slide) The total number of protons and neutrons in the nucleus is called the mass number. Number of neutrons = atomic mass – atomic number Isotopes (copy this slide) Isotopes are atoms of an element that differ by the number of neutrons in the nucleus. Isotopes of an element are chemically the same, since the electrons and protons, not the neutrons, determine the atom’s chemical properties. Stability of nucleus depends on ratio of protons to neutrons Some isotope unstable and will lose neutrons over time- turning into another isotope Eg. carbon 14 - carbon 12 Bigger atoms with more protons need more neutrons. Eg. C 6P-6N = 1:1 SN 50P:118.5N ~ 1:2 Lr 103P:260N = 1:2.6 Atomic Mass Units (AMU) (copy this slide) Since the mass of an atom is so small (anywhere between 10-24 to 10-22 g), it is not a convenient quantity to work with. Thus the amu was defined. The definition of this unit is based on the carbon-12 isotope. The mass of one atom of the carbon -12 isotope is defined to be exactly 12.0000 amu. Since a carbon-12 atom has 6 protons and 6 neutrons, and the protons and neutrons have nearly the same mass, the mass of one proton or neutron is 1 amu. Calc