Chemistry(topic 1~atoms/periodic table)

• Everything whether it's living, non-living or even a cell itself is made up of lots of tiny particles which we call atoms
• A single cell probably contains more than 100 trillion atoms
• Atom


  Basic structure is a central nucleus surrounded by electrons which orbit around the nucleus in rings that we call shells
• Particles that make up the nucleus

  • Protons
  • Neutrons
• Protons and neutrons

  • Have the same mass, with a relative mass of 1
  • Protons have a positive charge of 1+
  • Neutrons have no charge (are neutral)
• Electrons


  • Have a mass 2000 times smaller than protons and neutrons
  • Have a negative charge of 1-
• The size of an atom depends on which element it is
• Atoms have a radius of around 0.1 nanometers
• Most of an atom is actually empty space
• The nucleus is 10,000 times smaller than the width of the atom
• Electrons are even smaller than the nucleus and would be too small to see in the atom diagram
• Ion


  An atom that has lost or gained electrons, so the positive and negative charges no longer balance
• Ions

  • One minus negative ion (one extra electron)
  • Two minus negative ion (two extra electrons)
  • One plus positive ion (one less electron)
• Periodic table


  Each box represents a different type of atom, which we call an element
• Nuclear symbol


  Provides information about the element, including the elemental symbol, atomic number, and mass number
• The atomic number tells us the number of protons (and electrons) in the atom
• The mass number tells us the total number of protons and neutrons in the atom
• The number of neutrons in an atom is not always the same as the number of protons
• Atom


  Central nucleus comprising protons and neutrons, with electrons orbiting the nucleus
• Protons

  Determine which element the atom is
• Hydrogen

  • Smallest element, with 1 proton and 1 electron
• There are around 100 different elements
• Periodic table

  Organizes elements into boxes, with each box representing a different element
• Nuclear symbol


  The one or two letter symbol that represents the element name
• Atomic number


  The number of protons in the atoms of that element
• Isotopes-Atoms with the same number of protons must be the same element
• Isotopes


  Different forms of the same element that have the same number of protons but a different number of neutrons
• Relative atomic mass

  The average mass of all the isotopes that make up a particular element
• Calculating relative atomic mass


  Multiply each isotope's abundance by its mass, sum these, then divide by the sum of the abundances of all the isotopes
• The relative atomic mass of copper is 63.6
• Separating soluble and insoluble solids from liquids

  1. Filtration

  2. Evaporation

  3. Crystallization
• Mixture

  Liquid and insoluble solid
• Solution

  Liquid and soluble solid, where the solid is the solute and the liquid is the solvent
• Filtration


  Use filter paper with tiny holes to separate insoluble solids from liquids
• Cannot filter out soluble solids from a solution
• Evaporation


  Place solution in evaporating dish/crucible, heat to evaporate solvent and leave behind solid crystals
• Evaporation is quick but some solids may decompose when heated
• Crystallization


  1. Place solution in evaporating dish, heat gently to evaporate some solvent, then cool to allow crystals to form

  2. Filter out crystals

  3. Dry the crystals
• Solids are less soluble at colder temperatures
• Thermal decomposition can occur when heating some solids