CHEM 205 lecture 2

• Democritus and Leucippos (400 B.C.) proposed concept of tiny particles
• Robert Boyle 1627-1691


  A substance cannot be further broken down, didn't believe metals were elements
• Lavoisier (father of chemistry)


  Introduced systematic terminology and quantitative experiment
• John Dalton atomic theory


  All matter is made of atoms, a compound always has the same amount and types of atoms, all atoms are identical (not true), chemical reactions reorganize their atoms but the atoms aren't changed
• Marie Curie: atoms are made of smaller particles
• J.J. Thomson


  Cathode ray tubes, hypothesis: electrons are negatively charged
• Robert Millikan


  Oil-drop experiment, charge on electron
• Eugene Goldstein


  Canal rays, protons positively charged
• Ernest Rutherford


  Gold foil experiment, protons in nucleus
• Dmitri Mendeleev


  Developed the modern periodic table
• Radioactivity: disintegration of atoms using unusual beams
• Nucleus


  Small dense, positive core, contains protons
• Electrons


  Surround nucleus
• Mass number


  Protons + neutrons
• Number protons


  Number electrons
• Isotopes


  Atoms with same number protons, same number electrons, but different number neutrons
• Hydrogen isotopes


  • 1H = protium, 1 proton, 0 neutrons
  • 2H = deuterium, 1 proton, 1 neutron
  • 3H = tritium, 1 proton, 2 neutrons
• Element types


  • Metal
  • Nonmetal
  • Metalloid
• Metals


  • Conduct heat and electricity, malleable, ductile, shiny, exists as solids
• Nonmetals


  • Insulators, non-malleable, gases, liquids, non-shiny, exists as diatomic molecules
• Metalloids


  • Same properties of metals and nonmetals
• Reactivity pattern


  • Highest reactivity is the bottom left and top right (halogen – Fluorine)
  • Noble gases do not react
  • Metals lose electrons = more reactive as they go down the group
  • Nonmetals steal or share electrons, more reactive as you go up the group
• Cation


  Less electrons than protons: positive ion
• Anion


  More electrons than protons: negative ion
• Hydrogen


  Its own group not part of alkali metals, main component of stars, minor component of air, in most reactions forms H+ ions, loses electron like alkali metals, in some reactions, forms H- ions, gains electron like halogens
• Alkali metals


  • Group 1, highly reactive so we keep them submerged in oils, Fr (Francium) being radioactive
• Alkali earth metals


  • Group 2, highly reactive not as strong as alkali metals
• Group 3A or 13


  • Contains rare earth metals, first group of metalloids
• Group 4A or 14


  • Carbon has 3 allotropes: graphite, diamond, fullerene
• Pnictogens: group 5A or 15


  • Nitrogen is a very unreactive gas, building blocks of ammonia and amines, Phosphorus: elemental forms are highly reactive: white phosphorus and red phosphorus
• Chalcogens: group 6A or 16


  • Oxygen is a colourless gas, quite reactive, Allotrope: ozone (smell rain), S, Se, Te: very smelly and toxic
• Halogens group 7A or 17


  • Very reactive with alkali metals cause alkali metals want to lose 1 electron and halogens want to gain 1 electrons, exist as diatomic molecules
• Noble gases: group 8A or 18


  • Most unreactive elements, used to protect things that are highly reactive like oxygen
• Valence electrons


  Outermost shells, = group number, bond to other atoms to fill their atom electrons to have the same as noble gases (8)
• Covalent bonding


  Sharing electrons A – B
• Ionic bonding


  Stealing electrons or giving them away, forming ions A : B
• Electronegativity


  Ability of an atom to pull shared electrons towards itself, the closer they are the more electronegative, nonmetals: medium-to-high electronegativity, metals: very low in electronegativity