atomic structure y9

• Atom


  The smallest part of an element that can exist
• John Dalton proposed in 1804 that atoms are tiny, indivisible spheres
• The word 'atom' comes from the Greek 'atomos' meaning 'uncuttable'
• Modern atomic model


  • Atoms are composed of electrons, protons and neutrons arranged in a particular way
• Development of the atomic model

  1. Propose hypothesis

  2. Devise experiment to test hypothesis

  3. If evidence backs up predictions, the theory becomes better
• Our understanding of the atomic structure has developed over centuries as new evidence emerged
• Hypothesis


  A proposed explanation for a phenomenon that can be tested through further investigation and experimentation
• Testing a hypothesis


  1. Devise an experiment

  2. Collect evidence

  3. If evidence backs up predictions, it becomes a better theory

  4. Understanding is improved
• The model of the atom has developed throughout history
• Atom (200 years ago)


  Tiny solid spheres that cannot be divided
• John Dalton


  Proposed the idea of atoms as tiny spheres that cannot be divided (1804)
• Current model of the atom

  Composed of electrons, protons and neutrons arranged in a particular way
• History of ideas about the atom

  1. John Dalton - Atoms as miniature spheres

  2. JJ Thomson - Plum pudding model with electrons inside

  3. Rutherford - Nucleus with orbiting electrons

  4. Bohr - Electrons in specific energy shells

  5. Protons and neutrons discovered
• JJ Thomson's plum pudding model

  Atoms as a positively charged dough with negatively charged electrons embedded
• Rutherford's gold foil experiment


  Showed Thomson's plum pudding model was incorrect
• Rutherford's nuclear model


  Atom has a positively charged nucleus with electrons orbiting around it
• Bohr's model


  Electrons orbit the nucleus in specific energy shells or levels
• Protons


  Positively charged particles in the nucleus
• Neutrons


  Uncharged particles in the nucleus
• The current model of the atom includes a nucleus of protons and neutrons, with orbiting electrons
• Before the discovery of the electron, people thought atoms were tiny spheres that could not be divided
• Protons


  Positively charged particles in the nucleus of an atom
• Electrons


  Negatively charged particles orbiting the nucleus of an atom
• Neutrons


  Particles with no charge in the nucleus of an atom
• Atomic number


  The number of protons in the nucleus of an atom, which defines the element
• Mass number


  The total number of protons and neutrons in the nucleus of an atom
• The number of protons in an atom is equal to the number of electrons, so atoms have no overall charge
• Electron shells


  • Electrons occupy specific energy levels or shells around the nucleus
  • The shells closer to the nucleus have lower energy electrons
  • The shells further from the nucleus have higher energy electrons
  • Each shell can only hold a certain maximum number of electrons
• Electron arrangement of sodium

  • 2,8,1
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons
• Relative atomic mass


  The average mass of all the isotopes of an element, taking into account their relative abundances
• Calculating relative atomic mass

  1. Multiply mass number of each isotope by its abundance

  2. Add these values together to get the relative atomic mass
• Isotopes


  Atoms of the same element with different numbers of neutrons
• This is the fifth episode in an eight-part series on atomic structure and the periodic table
• Pure substance


  One that is only made from one type of element or compound
• Substances are rarely 100% pure - they often have other substances mixed in</b>
• Physical separation processes


  Methods that don't involve chemical reactions and don't create new substances
• Filtration


  1. Separating an insoluble solid from a liquid

  2. Liquid passes through filter paper (filtrate)

  3. Solid is left behind (residue)
• Crystallisation


  1. Separating a soluble solid from a liquid

  2. Liquid evaporates leaving solid crystals
• No new substances are made in physical separation processes