science

• Protons


  Number of protons = number of electrons
• Atomic number


  Number of protons
• Mass number


  Protons + neutrons in the nucleus
• Mass number - atomic number


  Number of neutrons
• Mass number does not equal atomic mass
• Atomic mass


  Average number of protons and neutrons in all the atoms of the element
• Atomic mass - number of protons


  Number of neutrons
• Electrons


  Held in shells, outermost shell is the valence shell containing valence electrons
• Valence electrons


  Determine how reactive an atom is
• Common elements


  • Hydrogen
  • Oxygen
  • Neon
  • Lithium
• Hydrogen


  • 1 proton
  • 0 neutrons
  • 1 electron
• Oxygen


  • 8 protons
  • 8 neutrons
  • 8 electrons
• Neon


  • 10 protons
  • 10 neutrons
  • 10 electrons
• Lithium


  • 3 protons
  • 4 neutrons
  • 3 electrons
• Russian Scientist Dmitri Mendeleev: The birth of the periodic table, proposed periodic law (elements have properties that repeat or recur according to their atomic weight), predicted the properties of the 21 unknown elements at the time and was accurate


  1869
• How Dmirtri Mendeleev made the periodic table


  1. Arranged the elements in columns like Dobereiner's triads

  2. Arranged elements in periods of 7 like Newlands

  3. Arranged the elements according to atomic weight like Newlands
• Other developments to the periodic table


  • Ramsay: discovered and classified the noble gases
  • Moseley: made a minor change to the periodic law -> elements have properties that recur or repeat according to their atomic number
  • Seaborg: used nuclear technology to create new elements that do not occur naturally
• Technological advances


  1. Ramsay used a fridge to liquify and separate components of air and removed H2O, CO2, O2, N and had one gas left which was later argon

  2. Moseley used X-rays to determine the atomic number of each element

  3. Seaborg used nuclear technology to slam neutrons into uranium and created the very first atoms of neptunium and plutonium
• Organisation of elements in the periodic table


  • Groups: Columns
  • Periods: Rows
  • Families: Elements with similar properties, colour coded
• Families


  Elements with similar properties, colour coded
• Number of groups, periods, families


  • 18 Groups
  • 7 Periods
  • 10 families
• Types of elements


  • Metals
  • Non-metals
  • Metalloids
  • Alkali metal
  • Alkaline earth metals
  • Halogens
  • Noble gases
  • Transition metals
  • Lanthanides
  • Adinides
• Physical properties


  A characteristic of a substance that can be observed or measured without changing the identity of the substance
• Chemical properties


  When a substance's properties become evident during or after a chemical reaction, changing the substance's chemical identity to show a quality
• Trends of properties in the periodic table


  • Electronegativity
  • Ionisation energy
  • Atomic Radius
  • Metallic Character
  • Electron Affinity
• Electronegativity


  How easily an atom can form a chemical bond
• Ionisation energy


  The smallest amount of energy that is needed to pull an electron away from an atom in its gas state
• Atomic Radius


  The distance from the nucleus to the valence shell
• Metallic Character


  Most of the elements display some metallic properties
• Electron Affinity


  How easily an atom accepts an electron
• Hydrogen


  • Electronegativity: 2.2
  • Ionisation energy: 1,312 kJ mol−1
  • Atomic Radius: 60 pm
  • Electron Affinity: 73 kJ mol
• Oxygen


  • Electronegativity: 3.44
  • Ionisation energy: 1313.942 kJ mol−1
  • Atomic Radius: 1.10 angstrom
  • Electron Affinity: -142 kJ mol-1/142 kJ mol-1
• Neon


  • Electronegativity: 0
  • Ionisation energy: 2080.662 kJ mol−1
  • Atomic Radius: 1.52 angstrom
  • Electron Affinity: 0
• Lithium


  • Electronegativity: 0.98
  • Ionisation energy: 520.2 kJ mol−1
  • Atomic Radius: 1.54 angstrom
  • Electron Affinity: 59.6 kJ mol‑1
• Neon does not form bonds and does not accept other electrons due to its full valence shells and stability. Therefore, Neon is a noble gas that goes in group 18
• Compounds


  When two or more atoms combine and are bonded together
• Compounds


  • H20: 2 hydrogen, 1 oxygen: water
  • AgNo3: 1 Silver, 1 Nitrate: Silver nitrate
• Molecular Compounds (molecules)


  A chemical compound composed of two or more nonmetal atoms that share electrons with one another in a covalent bond
• Covalent bond


  Shared valence electron pairs between atoms, which stabilises each other by filling their valence electrons
• Nonmetal atoms


  Covalent bonds are common between nonmetal atoms because they have high electronegativities, meaning they can easily form new bonds, and they have a strong tendency to attract electrons