Block-5 lecture-1

• Matter


  Anything that takes up space and has mass
• All matter is made of atoms
• Atoms


  The building blocks of all matter
• Atoms


  • They are incredibly small, with a radius of only 1 × 10-10 m
  • About one hundred million atoms could fit side by side across your thumbnail
• Atom structure


  • Tiny, dense nucleus at the centre
  • Electrons orbiting around the nucleus
  • The radius of the nucleus is over 10,000 times smaller than the whole atom, but it contains almost all of the mass of the atom

  
• Particles in the nucleus

  • Protons - positively charged particles with a relative atomic mass of one unit
  • Neutrons - no charge, and also with a relative atomic mass of one unit
• Electrons


  • Negative charge with almost no mass (1/2000 the mass of a proton or neutron)
  • Move around the nucleus
  • Cover a lot of space
  • Occupy shells around the nucleus
  • These shells explain the whole of chemistry
• Although atoms contain particles of different charge, the total charge within an atom is zero
• The number of electrons is equal to the number of protons
• Ionized atom

  An atom that has lost electrons
• Nuclear notation


  Symbols used to describe particular nuclei by their element symbol, atomic number and mass number

  
• Determining the number of protons and electrons in a carbon-12 atom

  1. Count the number of protons in the carbon nucleus (6)

  2. The number of electrons is equal to the number of protons (6)

  
• Atomic number


  The number of protons in an atom
• Elements in the periodic table are ordered by their atomic number

  
• The atomic number of a particular element is always the same
• The atomic number is also equal to the number of electrons in an atom
• Mass number


  The total number of particles in the nucleus of an atom
• Determining the number of neutrons in a sodium atom

  1. Mass number of sodium is 23

  2. Atomic number of sodium is 11

  3. Number of neutrons = Mass number - Atomic number = 23 - 11 = 12
• Nuclear notation


  Writing the mass number and atomic number with the atomic symbol