science

• Elements

  • 118 elements
  • 98 naturally occurring
  • 20 synthetically made
• Hydrogen

  Most abundant element in the universe (75%)
• Atom

  • Basic unit of element
  • Contains 3 subatomic particles: protons (positively charged), neutrons (no charge), electrons (negatively charged)
• Atomic nucleus

  • Small, dense region consisting of protons and neutrons as the center of an atom
  • Discovered in 1911 by Ernest Rutherford based on the 1909 Geiger-Marsden gold foil experiment
• Atomic number

  Number of protons or number of electrons in a neutral atom
• Atomic mass


  Sum of protons and neutrons
• Chemical symbol

  Shorthand way of representing the elements (e.g. Hydrogen (H), Carbon (C), Oxygen (O), Nitrogen (N))
• Dmitri Mendeleev


  • Arranged the periodic table of elements
  • Chief architect of the periodic table
• Periodic table of elements

  • Provides a systematic and logical arrangement of the chemical elements
  • Elements are organized into horizontal rows (periods) and vertical columns (groups)
• Hays-McDaniel Line

  • Heavy zigzag stair step line in the periodic table
  • Left of the line is the region where metals are located
  • Right of the line are non-metals
  • Elements along the line are metalloids
• Properties of metals

  • Solid (except mercury)
  • Hard (except lithium, potassium and sodium)
  • Shiny luster
  • Best conductors of heat
  • Good conductors of electricity
  • Malleable
  • Ductile
  • High melting point
  • Very dense
• Examples of non-metals

  • Solids: carbon, sulfur, phosphorus
  • Liquids: Bromine
  • Gases: Oxygen, Hydrogen, Nitrogen
• Bromine

  • Used in many areas such as agricultural chemicals, dyestuffs, insecticides, pharmaceuticals and chemical intermediates
  • Some uses are being phased out for environmental reasons, but new uses continue to be found
  • Bromine compounds can be used as flame retardants
• Properties of non-metals

  • Dull luster
  • Insulators (do not conduct electricity or heat well)
  • Soft and brittle (except for diamonds)
• Metalloids

  • Elements that have physical properties of both metals and non-metals
  • Some are shiny, some are dull, they are somehow malleable and ductile, and can conduct heat and electricity at a lesser level than metals
  • Some are useful semiconductors, which are used in electronics
• Metalloids

  • Boron, silicon, germanium, arsenic, antimony, tellurium, polonium, astatine
• Compound


  • Forms when two or more different elements join together chemically in definite proportion by mass
  • Has its own unique and definite physical and chemical properties
• Molecule

  • Smallest unit of a compound
  • Compounds can only be separated using chemical methods
• Electrolysis of water


  Decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water
• Chemical bonds

  Forces that hold atoms together to make compounds or molecules
• Classifications of compounds


  • Organic compounds (from living organisms, composition: carbon)
  • Inorganic compounds (from non-living things, composition: metal and other elements)
• Acid

  Substance that releases H+ ions in an aqueous (water) solution
• Strong acid

  Breaks down completely in water and gives off many H+ ions
• Weak acid

  Only partially breaks down, gives off much less H+ than a strong acid
• Characteristics of an acid

  • Sour taste
  • React to metals and carbonates to produce gas
  • Contain hydrogen
• Properties of an acid

  • Conducts electricity
  • Corrosive, can break down certain substances
  • React strongly with metals
  • Turns blue litmus paper to red
• Base


  Solution that has an excess of OH- ions, also known as alkali
• Properties of a base

  • Feels slippery
  • Tastes bitter
  • Corrosive
  • Does not react to metals
  • Turns red litmus paper into blue
• pH

  • Measure of how acidic or basic a solution is
  • Scale ranges from 0-14, with 7 being neutral
  • Pure water has a pH of 7
  • Basic solutions have a pH above 7
  • Acids have a pH from 0-7, lower pH indicates a stronger acid
• Measuring pH

  Using special strips of paper called pH paper
• Factors affecting solubility

  • Effect of stirring
  • Effect of particle size
  • Nature of solute and solvent
  • Temperature
  • Pressure
• Polar molecules

  Electrons are not equally shared, one part of molecule is more negative than the other part
• Non-polar molecules

  Electrons are equally shared, no one part of molecule is distinctly negative or positive
• Effervescence

  Rapid escape of gas
• Henry's law

  At a given temperature, the solubility of gas in liquid is directly proportional to the partial pressure of the gas above the surface of the solution
• Supersaturated solution

  Contains more dissolved solute than a saturated solution given the same temperature, becomes unstable and forms crystals
• Trichophyton rubrum is an infection caused by a fungus
• Fungi play an important role in decomposition of organisms and the cycle of nutrients
• Protists

  Unicellular organisms that do not fit into any kingdom classification
• Types of bacteria


  • Archaebacteria (ancient bacteria that can live in harsh environments)
  • Eubacteria (most abundant bacteria in the environment, have cell walls made of peptidoglycan)