Atomic structure and Periodic table

• Atoms are the smallest part of an element that can exist
• Examples of atoms


  • Lithium atom
  • Helium atom
• Atomic symbols


  Capital O is oxygen, capital Li is lithium, capital H is helium
• There are about 100 different elements, each with their own separate symbols
• Elements


  Substances that cannot be broken down into simpler substances by chemical means
• Compounds


  Two or more elements chemically combined in fixed proportions
• Compounds


  • Carbon dioxide
  • Water
• Chemical reaction


  Sodium reacts with chlorine to form sodium chloride
• Balanced formula equation


  The number of each atom on each side of the arrow is the same
• Rules for balancing equations: cannot add or change small numbers, cannot add large numbers between elements
• Mixtures


  Two or more elements or compounds that are not chemically combined, each substance keeps its chemical properties
• Methods for separating mixtures

  • Filtration
  • Crystallization
  • Simple distillation
  • Fractional distillation
  • Chromatography
• Mixtures


  • Salt solution
  • Air
  • Sandy water
• Filtration


  Separates an insoluble solid from a liquid
• Crystallization


  Separates a soluble solid from a solvent
• Simple distillation


  Separates two different liquids based on their different boiling points
• Fractional distillation


  Separates many liquids at the same time
• Chromatography


  Separates inks or pigments from a mixture
• Plum pudding model of the atom


  • Atoms are tiny spheres that cannot be divided, electrons embedded in a ball of positive charge
• Nuclear model of the atom

  • Positively charged nucleus, electrons orbit the nucleus
• Alpha particle scattering experiment

  Led to the nuclear model of the atom replacing the plum pudding model
• Bohr's model of the atom

  • Electrons orbit the nucleus at specific distances in shells
• Atoms are always neutral, number of electrons equals number of protons
• Subatomic particles


  • Protons: +1 charge, mass 1
  • Neutrons: 0 charge, mass 1
  • Electrons: -1 charge, very small mass
• Drawing an atom from periodic table information

  Find number of protons from atomic number, number of electrons equals number of protons, number of neutrons is mass number minus atomic number
• Electronic structure


  Electrons fill the lowest available shells, maximum 2 in first shell, 8 in second and third shells
• Isotopes


  Atoms of the same element with the same number of protons but different number of neutrons
• Calculating relative atomic mass

  Use formula: (% abundance x relative mass of isotope 1) + (% abundance x relative mass of isotope 2) / 100
• Isotopes


  Same number of protons but different number of neutrons, have same chemical properties but different physical properties
• Calculating relative atomic mass with given abundance of Isotopes

  Percentage abundance times relative atomic mass of one isotope + percentage abundance times relative atomic mass of another isotope, divide by 100
• Relative atomic mass of chlorine is 35.5
• Early periodic table


  • Arranged by atomic weight, every 8th element had similar properties, some elements not in appropriate places
• Mendeleev's periodic table


  Followed atomic weights but left gaps for undiscovered elements, changed positions to match groups more closely
• Knowledge of isotopes explained why order based on atomic weight was not always correct
• Modern periodic table


  • Arranged in order of atomic number, elements with similar properties in groups, rows are called periods
• Metals


  React to form positive ions
• Differences between metals and non-metals

  • Metals are hard, shiny, high density, good conductors of electricity and heat, malleable

  Non-metals are dull, low density, poor conductors of electricity and heat, brittle
• Group 0 (noble gases)


  • Unreactive, have full outermost shell, boiling points increase down group
• Group 1 (alkali metals)


  • Have 1 electron in outermost shell, react with oxygen to form metal oxides, react with chlorine to form metal chlorides, react violently with water to form metal hydroxides and hydrogen gas
• Reactivity of group 1 elements

  Increases down the group due to increasing distance between outermost electron and nucleus