chem

• 1 Melting points and boiling points of halogens increase:


  group 17

  down the periodic table
• The atomic number of calcium is 20. The electron configuration will be:


  2,8,8,2
• how many valence electrons does fluorine have

  group 17

  7
• Elements


  Pure substances made up of only one type of atom
• Atoms


  The building blocks of the chemical elements
• Atoms are the building blocks of compounds and mixtures
• For thousands of years, alchemists and scientists have searched for patterns in the substances that make up the universe
• The discovery by Lord Rutherford in 1911 that most of the atom was empty space

  discoveries about the particles inside atoms by Niels Bohr provided missing links in the patterns
• Atoms


  • Have the same general structure
  • Main difference is in the numbers of each particle within the atom (the sub-atomic particles)
• Parts of the atom

  1. Nucleus (protons and neutrons)

  2. Electrons orbiting the nucleus
• Protons


  Have a positive electrical charge
• Neutrons


  Have no electrical charge
• Electrons


  Have a negative electrical charge
• Elements


  Pure substances made up of only one type of atom
• Atoms


  The building blocks of the chemical elements
• Atoms are the building blocks of compounds and mixtures
• For thousands of years, alchemists and scientists have searched for patterns in the substances that make up the universe
• The discovery by Lord Rutherford in 1911 that most of the atom was empty space, and subsequent discoveries about the particles inside that atom by Niels Bohr and other scientists, provided the missing links in the patterns
• Atoms


  • Have the same general structure
  • Main difference is in the numbers of each particle within the atom (the sub-atomic particles)
• Parts of the atom

  1. Nucleus (protons and neutrons)

  2. Electrons orbiting the nucleus
• Protons


  Have a positive electrical charge
• Neutrons


  Have no electrical charge
• Electrons


  Have a negative electrical charge
• Atoms have the same number of electrons as protons, so they have no overall electrical charge and are neutral
• Almost all of the mass of an atom is in the nucleus
• Electrons move rapidly around the nucleus and are arranged in a series of energy levels or shells
• Dmitri Mendeleev confidently predicted the properties of the element germanium 15 years before it was discovered
• Periodic table


  A set of rows and columns that arranges all known elements

  
• Gaps in the pattern of the periodic table indicated undiscovered elements
• The properties of new elements are predicted before their discovery, just as they were in Mendeleev's time
• Many new elements are still being discovered today
• Periodic law


  Elements with similar properties occur at regular intervals when all elements are listed in order of atomic weight
• Periods


  Rows of elements on the periodic table
• Groups


  Columns of the periodic table containing elements with similar properties
• By 1864, approximately 50 elements had been discovered
• John Newlands arranged elements in order of increasing atomic weight and found that every eighth element shared similar properties
• In 1869, Mendeleev discovered a way of organising the elements into rows and columns, forming the basis of the periodic table
• German chemist Lothar Meyer came up with a similar arrangement of the elements at about the same time as Mendeleev
• Rows


  Elements in order of increasing mass or atomic weight
• Columns


  Groups of the periodic table containing elements with similar properties