Why does hydrogen not have a neutron 3
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76 4 Workbook page 44 76.1 Different atomic models: spherical model (Dalton), planetary model (Rutherford), shell model (Bohr), electron cloud model 1. How are atoms structured? As a result of many observations, the idea of the structure of atoms has changed again and again: At first, atoms were thought to be simple compact spheres. When Ernest Rutherford bombarded gold foil with alpha rays in 1911, he realized that an atom must mainly consist of empty space (Fig. 76.2). Inside there is a massive, positively charged nucleus, which is surrounded by a shell of electrons. In 1913, Niels Bohr improved the atomic model by adding a shell-shaped structure to the electron shell. According to today's electron cloud model, the electrons stay like a nebula in spaces of a certain shape, the so-called orbitals. The atomic nucleus consists of positive protons, the number of which (atomic number Z) determines the type of chemical element. The element oxygen (Z = 8), for example, has 8 protons in its nucleus. The uncharged neutrons hold the protons together. Protons and neutrons have roughly the same mass. The mass number A indicates how many protons and neutrons the atom contains. M An atom consists of an atomic nucleus with positive protons and uncharged neutrons. The atomic nucleus is surrounded by a nebula-like shell of negative electrons. The atomic number Z indicates the number of protons. The mass number A indicates the number of all nuclear particles (protons and neutrons). 2. What are isotopes of an element? The atomic nuclei of a certain element always have the same number of protons. For example, hydrogen always has 1 proton. However, the number of neutrons can be different. 99.99% of all hydrogen atoms have no neutron (H-1, Protium). 0.015% have a neutron in their nucleus (H-2, deuterium). A hydrogen atom with two neutrons (H-3, tritium) occurs in small traces. Atoms with the same chemical properties but different numbers of neutrons and masses are called isotopes (isos = equal, topos = place). M isotopes are types of atoms of the same elements with different mass. They differ in the number of neutrons. The number of their protons is the same. Atomic nucleus Atoms of the gold foil α -particle Lead shielding Source of the α -particle Beam of the α -particle Gold foil fluorescent screen 76.2 When a thin gold foil was bombarded, Rutherford was able to recognize the existence of the small atomic nucleus. Atoms - Isotopes - Radioactivity H 1 1 H 2 1 H 3 1 Protium = ordinary hydrogen Deuterium = heavy hydrogen (0.015% of natural hydrogen) Tritium = (occurs mainly during nuclear transformation) 76.3 Isotopes of hydrogen 76.4 The natural isotopes of carbon - material (C-12, C-13, C-14) as a pearl model 76.5 Autunit contains radioactive uranium isotope and fluoresces green in UV light. Worksheets 3xa8vf For testing purposes only - property of the publisher öbv
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