Atomic Structure, Isotopes & Electron Shells

• In the center of every atom is a nucleus which contains individual protons and neutrons.
• The subatomic particles which make up the nucleus of an atom are protons and neutrons
• Neutrons have no charge

  Protons have positive charge +1

  Electrons have a negative charge -1
• Protons and Neutrons both have a relative mass of 1
• Orbiting around the nucleus in shells are electrons

  Which are 2000 times smaller than protons or neutrons
• In the periodic table each box is known as a nucleus symbol and represents a particular element
• The atomic number is how many protons the atoms of that element have

  The number of protons and electrons in an atom is the same
• The number of protons in an atom determines which element it is.
• The mass number is the total number of protons and neutrons together. (protons + neutrons)
• The isotopes of an element are atoms with the same number of protons (the atomic number) but different number of neutrons.
• Generally only one or two of an element's isotope's are actually stable, the other isotopes are unstable and can decay into other elements by emitting radiation like alpha, beta, gamma or sometimes neutrons.

  This process is called radioactive decay
• 1. Electrons orbit the nucleus at specific energy levels which are also called shells.
  2. The shells get progressively further from the nucleus and increase in energy level.
  3. Electrons can absorb electromagnetic radiation and jump to a higher energy level / shell. In these cases we say that the electron has become 'excited'.
  4. Excited electrons can later fall back to a lower energy level, and emit electromagnetic radiation in the process.
  5. Electrons can also absorb enough energy to leave the atom altogether, this is known as ionisation.
• Once an electron leaves the atom, the amount of protons is greater than the electrons, so it is left with a positive charge.

  Meaning we call it a positive ion rather than an atom