Chemistry Unit 1

Chemistry Unit 1

1. Atoms and Isotopes

   • Ionisation energy highest in Level 1 because the electrons are closest to the nucleus
   • Energy Level 1 - 1s sublevel, Energy Level 2 - 2s and 2p sublevels, Energy Level 3 - 3s, 3p and 3d sublevels, Energy Level 4 - 4s, 4p, 4d and 4f sublevels
   • First Ionisation Energy = The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of positive ions
   • The further away from the nucleus the electrons in an atom are, the lower the nuclear attraction due to more shielding
   • There is a general increase in First Ionisation Energy across a period before dropping at the start of another period
     • There is a decrease in First Ionisation Energy as you move down a group as there is a greater distance between the nucleus and the electrons and more shielding
   • Isotopes = Atoms with the same number of protons but a different number of neutrons
   • Ionisation = gaseous atoms have an electron knocked off by a high speed electron gun to become positive ions
     • Acceleration = ions pass through an electric field where they are accelerated through slits into a beam
       • Deflection = beam of ions passes through a magnetic field and are deflected according to their m/z ratio
         • Detection = the ions hit a negative plate and generate an electric current when they gain an electron to become an atom

2. Amount of Substance

   • Atom Economy molecular mass of desired product / sum of molecular mass of all products x 100
   • moles = mass / Mr
     • moles = conc x vol
   • Ideal Gas Equation = pV=nRT

3. Bonding

   • Molecular Shapes- Linear, Trigonal Planar, Tetrahedral, Trigonal Bipyramidal, Octahedral
   • Chemical Bonds - ionic, covalent, co-ordinate, metallic
     • Physical Bonds - van der Waals forces, dipole-dipole, hydrogen bonds
   • Ionic Bonding occurs between those that need to gain electrons and those that need to lose them (oppositely charged ions) i.e. sodium chloride
     • Ionic compounds have high melting points, are very brittle, conduct electricity when molten or in aqueous solution and are soluable in water
   • Covalent bonding consists of a shared pair of electrons, one being supplied by each atom in the bond
     • Covalently bonded compounds don't conduct electricity, are soluble in organic compounds and have a low boiling point
   • Macromolecular compounds have an extremely high boiling point, don't conduct electricity (apart from graphite) and and very hard
   • Metallic bonding is a lattice of positive ions surrounded by delocalised electrons
     • Has a high melting point, is malleable and ductile
   • Coordinate bond = a chemical bond between two atoms where the shared pair of electrons are supplied by one atom

4. Periodicity

   • Electrons always enter the lowest energy sublevel available
   • There is a drop in First Ionisation Energy from Mg to Al because there is increased shielding as the electron is in a 3p sublevel
   • There is a drop in First Ionisation Energy from P to S as the outer electron is paired with an electron in the 3p sublevel, which causes repulsion making the electron easier to remove
   • Electronegativity = the ability of an atom to attract the pair of electrons in a covalent bond

5. Organic Chemistry

   • Molecular Formula = The exact number of atoms of each element present in a molecule
   • Empirical Formula = The simplest ratio of atoms in a molecule
   • Structural Formula = The arrangement of atoms in a molecule without showing all the bonds
   • Displayed Formula = The arrangement of atoms in a molecule showing all the bonds
   • Homologous series = compounds that have the same general formula and similar properties but differ by one variable

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