Atoms and Electrons

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  • Atoms and Elements
    • Isotopes
      • 'Isotopes are atoms of the same element with different numbers of neutrons'
      • 'An isotope is an atom of an element with a specified number of neutrons'
      • 'The mass number of an isotope is the number of nucleons in an atom of the isotope'
      • 'Isotopes of the same element have almost identical chemical and physical properties'
    • Sub-atomic Particles
      • Electron: Charge= -1 Relative Mass= 1/2000
      • Proton: Charge= +1 Relative Mass= 1
      • Neutron: Charge= 0 Relative Mass= 1
      • Protons and neutrons are packed together very tightly in the nucleus called nucleons
      • The electrons are in different shells at various distances outside the nucleus
    • Atomic Number
      • 'The atomic number of an element is the number of protons in one atom of that element'
      • All atoms of an element have the same atomic number and each element has a different atomic number
      • A neutral atom must have the same number of electrons as protons, so the atomic number of a neutral atom is also the number of electrons
      • In the periodic table, the elements are arranged in orfer of increasing atomic number from left to right
    • Ions
      • 'An ion is an atom or group of atoms that has lost or gained one or more electrons'
      • If an atom loses one or more electrons it becomes a positive ion
      • If an atom gains one or more electrons it becomes a negative ion
    • Electrons
      • Orbitals
        • 'A region of space that can hold up to 2 electrons with opposite spins'
        • 'The region of space in which there is a high probability of finding an electron'
        • Each orbital can hold up to two electrons and has a specific energy level
        • Type of Orbital
          • Orbitals have diffferent shapes and sizes. Their shapes are denoted by the letter s,p,d or f
          • An s orbital has a spherical boundary surface
          • A p orbital has a 'dumbell' shape
      • Shells and Subshells
        • A shell is a group of orbitals whose distance from the nucleus is about the same
        • As the number of the shell increases, the orbitals within the shell become larger, so the average distance from the nucleus of the electrons increases
        • The first shell contains one s-orbital called 1s. It can hold a maximum of 2 electrons
        • The second shell contains an s-orbital and a subshell called 2p which contains three p-orbitals. It can hold 8 electrons
        • The third shell contains an s-orbital (3s), three p-orbitals and 5 d-orbitals. It can hold a maximum of 18 electrons


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