Cognito

• Just like living organisms are made up of lots of tiny cells, everything, whether living, non-living, or even a cell itself, is made up of lots of tiny particles called atoms
• A single cell probably contains more than 100 trillion atoms
• Basic structure of an atom

  Central nucleus surrounded by electrons which orbit around the nucleus in rings called shells
• Structure of an atom

  Central nucleus made up of protons and neutrons, surrounded by electrons in shells
• Relative mass and charge of particles in an atom

  Protons and neutrons have the same mass (relative mass of one), protons are positive (one plus charge), neutrons are neutral, electrons are negative (minus one charge)
• Protons and neutrons


  Have the same mass (relative mass of one)
• Protons

  Positive charge (one plus charge)
• Neutrons

  Neutral charge
• Electrons


  Negative charge (minus one charge)
• Atoms have a radius of around 0.1 nanometers
• Most of an atom is actually empty space
• Comparison to the solar system

  One big thing in the middle (nucleus) with smaller things orbiting it (electrons), mostly empty space between them
• The nucleus is 10,000 times smaller than the width of the atom itself
• In the drawn atom, there are three protons in the nucleus and three electrons orbiting it
• When the number of protons and electrons is equal, the atom is neutral
• Atoms can lose or gain electrons, causing the overall atom to become charged
• Because the number of protons and electrons is equal, the positive and negative charges balance out, and so overall the atom is neutral
• Atoms can lose or gain electrons, in which case the charges would no longer balance, and the overall atom would become charged
• When an atom loses or gains electrons, we stop calling it an atom and instead call it an ion
• Examples of ions

  • One minus negative ion
  • Two minus negative ion
  • One plus positive ion
• When an atom loses electrons

  It becomes a positive ion
• Details about elements are found in the periodic table


  Each box in the table represents a different type of atom called an element
• Box in the periodic table is called a nucleus symbol and provides information about the element
• Elemental symbol represents the element, e.g., O for oxygen and Li for lithium
• Atomic number indicates the number of protons in the atom
• Mass number indicates the total number of neutrons and protons in the atom
• Finding the number of neutrons in an atom

  Mass number minus atomic number
• The number of protons and electrons in an atom is always the same
• The atomic number also tells us how many electrons the atom has