PHY121 Ch 6 Notes

PHY121 Ch 6 Notes - Astronomy Chapter 6: Atoms and...

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Astronomy Chapter 6: Atoms and Starlight - An atom consists of a nucleus surrounded by a cloud of electrons. The nucleus is made up of positively charged protons and uncharged neutrons. - An atom is mostly empty space; most of the mass is in the nucleus, and most of the space is filled with the electron cloud. Nucleus: the central core of an atom containing protons and neutrons that carries a positive net charge Electrons: low-mass atomic particle carrying a negative charge Protons: a positively charged atomic particle contained in the nucleus of an atom. The nucleus of a hydrogen atom. Neutrons: an atomic particle with no charge and about the same mass as a proton - The number of protons in an atom determines which element it is (i.e. carbon has six protons, nitrogen has seven protons, etc.) . The number of protons in an element is fixed - Atoms of the same element (with same number of protons) with different numbers of neutrons are called isotopes. Carbon has two stable isotopes – one has 6 protons and 6 neutrons “carbon- 12” and one has 6 protons and 7 protons “carbon-17” - Electrons in an atom can vary; they are held loosely in the electron cloud A neutral atom is surrounded by a number of negatively charged electrons equal to the number of protons in the nucleus. An atom that has lost or gained an electron is said to be ionized and is called an ion . - Two or more atoms joined together form a molecule . Only in the coolest stars are the collisions gently enough to permit bonding; the presence of certain molecules (i.e. TiO) in a star is a clue that it’s very cool. - The electrons in an atom are attracted to the nucleus by the Coulomb force . - As described by quantum mechanics , nature permits only certain amounts (quanta) of binding energy - The binding energy that holds electrons in an atom is limited to certain energies, and that means the electrons may occupy only certain permitted orbits ; this means that the orbits can only be certain sizes. The electron can occupy any permitted orbit but not orbits in between. -
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PHY121 Ch 6 Notes - Astronomy Chapter 6: Atoms and...

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