Atomic structure

• Atom


  The smallest part of matter
• Element


  Different orientations of atoms, with different orders in protons, neutrons, and electrons, having different chemical properties to each other
• Compound


  2 or more atoms/elements chemically bonded to each other
• Mixture


  2 or more substances not chemically bonded
• Chemical reaction


  1. Reactants on the left hand side

  2. Products on the right
• Chemical reaction


  • New compounds are formed, or older ones are broken up
  • Measurable energy change can be detected
  • At least 1 new substance is created
  • No atoms are created or destroyed
• Word equation


  Gives the name of each compound or elements involved in the reaction
• Symbol equation


  Has to be balanced to show that no atoms are created or destroyed, and show the state (solid, liquid, gas, or aqueous)
• Mixture


  Combinations of elements, substances, or compounds which have not been chemically bonded
• Real life examples of mixtures

  • Air, combinations or nitrogen, oxygen, carbon dioxide
  • Pasta and vegetables
• Separation techniques


  1. Chromatography

  2. Filtration

  3. Evaporation

  4. Crystallisation

  5. Simple Distillation

  6. Fractional distillation
• The modern periodic table - All known elements are organised by groups and periods, and also the discovery of isotopes and protons shows that mendeleev ordered elements by atomic number. Mendeleev's gaps are filled
• Metals


  • Found on the left side of the periodic table
  • Have fewer electrons in their outer shells, meaning they always lose electrons in their reactions, forming positive ions
  • High melting and boiling points
  • Good conductors of heat and electricity
  • All except mercury are solid at room temperature
• Non-metals


  • Found on the right side of the periodic table
  • Have more electrons on their outer shell, gaining electrons to form negative ions (ionic bonding), or share electrons to form neutral molecules (covalent bonding)
  • Lower melting and boiling points
  • Generally don't conduct heat and electricity (apart from some like hydrogen)
  • Often found as gases at room temperature
• Molecular formula


  The actual amount of atoms in each molecule of the substance
• Empirical formula


  Shows the simplest ratio that the substance can be written in
• Isotopes


  Different numbers of neutrons for an element with the same proton number, as the number of protons determine what element it is
• Hydrogen isotopes


  • Protium - 1 proton, 0 neutrons
  • Deuterium - 1 proton, 1 neutron
  • Tritium - 1 proton, 2 neutrons
• Every element's isotopes always have the same number of protons
• Corrosion of metals


  The metals react with oxygen in the air to gain more mass
• Burning of wood


  The mass of wood would decrease, as carbon dioxide and water would be released into the atmosphere
• Zinc + Hydrochloric acid reaction

  The mass of product would decrease, as hydrogen gas is released into surroundings
• Uncertainty


  Every measuring tool has an uncertain resolution, e.g a digital thermometer has 0.1 C resolution, with the lower bound of results being 0.05 C and upper bound 0.15
• The uncertainty is why we repeat experiments, to reduce uncertainty by calculating an average from concordant results
• Finding relative atomic mass of 2 isotopes


  (33 X 75) X (38 X 25) /100 = 2475 + 950 /100
• Relative atomic mass


  The average mass of all of the isotopes of an element, taking into account the abundance of certain isotopes
• Electron structure


  • The closer a shell is to the nucleus, the less energy it has
  • Electrons have 4 shells - With the structure by shell being, 2,8,8, and any extra electrons in the last shell
• Metals


  • Elements that lose electrons in a reaction with another element
• Atoms can be represented by symbols that include their chemical symbol (e.g., Na) and mass number (e.g., 23).
• Isotopes are atoms with different numbers of neutrons but the same number of protons, resulting in different masses.
• The number of protons is equal to the atomic number.
• The atomic number represents the number of protons in an atom.
• Isotopes are different versions of the same element with varying numbers of neutrons but the same number of protons.
• What did scientists attempt to do before the discovery of protons, neutrons, and electrons?

  They attempted to classify the elements by arranging them in order of their atomic weights.
• Why were the early periodic tables considered incomplete?

  Some elements were placed in inappropriate groups if the strict order of atomic weights was followed.
• How did Mendeleev address the issues with the early periodic tables?

  He left gaps for undiscovered elements and changed the order based on atomic weights.
• What was significant about the elements that were discovered after Mendeleev's predictions?

  They filled the gaps that Mendeleev had left in the periodic table.
• How did knowledge of isotopes contribute to the understanding of atomic weights?


  It made it possible to explain why the order based on atomic weights was not always correct.
• What are the key steps in the development of the periodic table?

  • Classification of elements by atomic weights
  • Incomplete early periodic tables with inappropriate group placements
  • Mendeleev's introduction of gaps for undiscovered elements
  • Adjustments in order based on atomic weights
  • Discovery of elements that filled the gaps
  • Understanding of isotopes explaining atomic weight discrepancies
• What may lead to a scientific model being changed or replaced?

  New experimental evidence