all of chemistry

• Atoms are made up from three different subatomic particles: protons, neutrons and electrons
• Protons


  In the nucleus, have a mass of 1 and a charge of +1
• Neutrons


  In the nucleus, have a mass of 1 and a charge of 0
• Electrons


  Found in the outer shells, have a very small mass (1/1836 of a proton) and a charge of -1
• The actual charge on protons, neutrons and electrons is very small but it is much easier to say +1, 0 and -1 as the relative charge
• The mass of protons, neutrons and electrons has been worked out based on carbon-12 as a reference standard
• The drawing of an atom is not to scale, the nucleus is much smaller compared to the whole atom
• Atomic number


  The number of protons in an element
• Mass number


  The total number of protons and neutrons in an atom
• Isotopes are different versions of an element with the same atomic number but different mass numbers
• Relative molecular mass


  The average mass of a molecule compared to 1/12 the mass of one atom of carbon
• Relative atomic mass


  The average mass of one atom compared to 1/12 the mass of one atom of carbon
• The relative atomic mass on the periodic table is the average of all the naturally occurring isotopes of an element
• First ionization energy


  The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous positive ions
• Second ionization energy


  The energy required to remove one electron from each ion in one mole of gaseous positive ions to form one mole of gaseous positive ions with a +2 charge
• Factors affecting ionization energy include atomic radius, electron shielding/repulsion, and nuclear charge
• Trends in successive ionization energies show a big jump between the 7th and 8th electrons due to the start of a new shell
• Drops in ionization energy between groups provide evidence for electron configuration
• Electron configuration


  The arrangement of electrons in an atom's shells, subshells and orbitals
• The periodic table can be divided into s-block, d-block, f-block and p-block based on electron configuration
• As we move across a period, atomic radius decreases and first ionization energy generally increases
• Metals and non-metals form ionic bonds through the transfer of electrons
• Ionic bond


  The electrostatic attraction between a positive metal ion and a negative non-metal ion
• Ionic compounds have high melting and boiling points, are soluble in water, and conduct electricity when molten or dissolved
• Covalent bond


  The sharing of electrons between two non-metals
• Single, double and triple covalent bonds involve the sharing of 2, 4 and 6 electrons respectively
• Dative covalent bond


  A covalent bond where one element donates both bonding electrons
• Molecular shapes can be linear, trigonal planar, tetrahedral, trigonal pyramidal, and bent based on the number of bonds and lone pairs
• Bond angles are determined by the number of bonds and lone pairs according to the valence shell electron pair repulsion theory
• NH3 and ClO3


  Trigonal pyramidal shape, bond angles around 107 degrees (2.5 less than tetrahedral)
• H2O


  Bent shape, bond angle of 104.5 degrees (2.5 less than trigonal pyramidal), has two lone pairs
• PCl5


  Trigonal bipyramidal, has two different bond angles of 120 degrees and 90 degrees, no lone pairs
• SF6


  Octahedral, all bond angles are 90 degrees, no lone pairs
• VSEPR Theory


  Valence shell electron pair repulsion theory, electrons arrange to be as far apart as possible
• Examples of molecules with 4 pairs of electrons in the outer shell


  • CH4 (109.5 degree bond angle)
  • NH3 (107 degree bond angle)
  • H2O (104.5 degree bond angle)
• Lone pairs


  More repulsive than bonding pairs, cause bond angles to decrease
• Electronegativity


  Measure of how much an element attracts electrons, increases across a period, decreases down a group
• Covalent and ionic bonding


  Part of a spectrum, with pure covalent at one end and pure ionic at the other, partial dipoles can form
• Permanent dipole


  Occurs when atoms with different electronegativities form a covalent bond, leads to higher melting and boiling points
• Induced dipoles (dispersion forces, London forces)


  Temporary dipoles that form due to the random movement of electrons, stronger for larger molecules