Chapter 8 : Model of matter - Atoms and molecules

• Structure of an atom

  Each atom is made up of even smaller particles known as sub-atomic particles
• Structure of an atom

  • An atom consists of mostly empty space
  • The protons and neutrons are densely packed in the nucleus
  • The electrons move around the nucleus in fixed positions
• Sub-atomic particles

  Proton

  location : packed in the nucleus

  relative charge : 1 (+)

  relative mass : 1
• Sub-atomic particles

  Neutron

  Location : packed in the nucleus

  relative charge : 0

  relative mass : 1
• Sub-atomic particles

  Electron

  Location : moves around the nucleus in fixed orbits (electron shells)

  relative charge : -1

  relative mass : 1/1840
• The mass of an atom is contributed mainly by the mass of the protons and neutrons.

  Electrons are so much lighter compared to protons and neutrons the mass of electrons are negligible and not considered in the mass of an atom
• Isotopes

  The number of protons in the atom of each element is unique
• Molecule

  A molecule is made up of 2 or more atoms that are chemically combined

  • A molecule of an element consists of only 1 type of element that is chemically combined
  • A molecule of a compound consist of a fixed ratio of 2 or more types of atoms that are chemically combined. The ratio of these atoms of different elements is fixed regardless of the state
• Application

  Metal coating

  • Scientists have managed to coat living plant material with gold atoms to make gold-plated orchids from Singapore
• Application

  Radiation therapy

  • The properties of atoms are applied in radiation therapy to cure diseases
• Application

  Medical imaging

  • Medical imaging tools such as Magnetic Resonance Imaging (MRI) and X-ray
• Application

  Nanotechnology

  • Field of science that involves nanoscale objects and their applications
  • A nanometer is only 10 atoms thick
• Application

  Nuclear energy

  • Energy from atoms is used in nuclear power plant and atomic bombs
  • Nuclear plants have provided an alternative source of energy to fossil fuels
  • However, accidents at nuclear plants can lead to loss of lives and environmental pollution
  • The use of atomic bombs can bring about destructive effects
• An atom is always electrically neutral. This means that the number of positive charges and negative charges in an atom is balanced
• Number of protons = number of electrons