atomic structure & the periodic table

• Atom


  The smallest building blocks of everything in the universe
• Most of the atom is made up of empty space
• Atom


  • Has a nucleus at the centre
  • Made up of 3 subatomic particles: protons, electrons, neutrons
• Nucleus


  The centre of an atom
• Protons


  Subatomic particles found in the nucleus, have a positive charge
• Neutrons


  Subatomic particles found in the nucleus, have no charge
• Electrons


  Subatomic particles that orbit the nucleus in fixed shells (energy levels), have a negative charge
• The nucleus of an atom is 600,000,000 times smaller than the nucleus of a biological cell
• Element


  A substance made up of only one type of atom
• Chemical symbol


  A one or two letter representation of an element, always starts with a capital letter
• There are 118 different elements in the periodic table
• Some non-metal elements exist as molecules made up of two atoms joined together, represented by the symbol followed by a subscripted '2'
• Periodic table


  • Elements are arranged in rows (periods) by increasing atomic number
  • Elements with similar properties are placed in vertical columns (groups)
• Metals


  Elements on the left of the stepped line in the periodic table
• Non-metals


  Elements on the right of the stepped line in the periodic table
• Compound


  A substance made up of different types of atoms chemically bonded together
• Mixture


  A combination of two or more substances that are not chemically bonded
• Mixtures are separated by physical processes, not chemical reactions
• Filtration


  1. Separating an insoluble solid from a liquid

  2. Filter paper has tiny pores that let small molecules/ions through but not larger solid particles
• Crystallisation


  1. Producing solid crystals from a solution by evaporating the solvent

  2. Warm the solution, stop heating when crystals form, then pour off excess liquid and dry the crystals
• Simple distillation


  1. Separating a solvent from a solution by heating, the solvent vapour condenses and is collected

  2. Useful for producing pure water from seawater
• Fractional distillation


  1. Separating different liquids from a mixture by taking advantage of their different boiling points

  2. The mixture is heated and vapours condense at different heights in the column, allowing the liquids to be collected separately
• Chromatography


  1. Separating dissolved substances based on how attracted they are to the stationary and mobile phases

  2. Produces a chromatogram showing the separated substances
• Plum pudding model


  Early model of the atom with positive charge spread throughout and negative electrons embedded
• Nuclear model


  Model of the atom with a dense, positively charged nucleus and electrons orbiting it
• Atomic number


  The number of protons in an atom's nucleus
• Mass number


  The total number of protons and neutrons in an atom's nucleus
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• 1 1 Nitrogen 7 7 14 Carbon C 6 Fe 26 Gold 118 197 Ge 41 Tellurium 128 Copper 20 29 35 64 Co 161
• The periodic table has the elements organised by their atomic number not their atomic mass.
• Isotopes


  Two atoms have the same number of protons, they are the same element. If they have a different number of protons, they are different elements. However, two atoms can have the same number of protons but different numbers of neutrons.
• Chlorine has a mass number of 35.5 and an atomic number of 17. How many neutrons does it have?
• Chlorine naturally exists as two isotopes: Cl-35 and Cl-37. The abundance of Cl-35 is 75% and the abundance of Cl-37 is 25%.
• Relative atomic mass


  The mean mass of all the atoms of an element in the universe
• The table shows the mass numbers and abundances of naturally occurring copper isotopes.
• Electronic structure


  The way in which electrons are arranged in an atom
• The number of electrons an atom has is the same as its atomic number
• Electrons in atoms occupy energy levels, also called electron shells, outside the nucleus. Different shells can hold different maximum numbers of electrons.
• The electronic structure of an atom can be predicted from its atomic number. For example, the atomic number of sodium is 11. Sodium atoms have 11 electrons: 2 in the first shell, 8 in the second shell, and 1 in the third shell.
• Before discovering protons, neutrons and electrons, scientists tried to classify the elements by arranging them in order of their atomic weights.