chapter 5

• in the n=1 shell there are 2 electrons, in the n=2 shell there are 8 electrons, in the n=3 shell there are 18 electrons, and in the n=4 shell there are 32 electrons
• shells are made of atomic orbitals. an orbital is a region around the nucleus that can hold up to two electrons in opposite spins
• the different types of orbitals are: s p d and f
• s orbitals are spherical, p orbitals are in the shape of a dumbbell
• n=1 shell has 1 s orbital

  n=2 shell has 1 s orbital and 3 p orbitals

  n=3 shell has 1 s orbital, 3 p orbitals and 5 d orbitals

  n=4 shell has 1 s orbitals, 3 p orbitals, 5 d orbitals and 7 f orbitals
• orbitals of the same type within a shell are grouped together as sub shells
• order of fillings=

  n=1- 1s

  n=2- 1s 2s 2p

  n=3- 1s 2s 2p 3s 3p 3d

  n=4- 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f
• the 3d sub shell is at a higher energy level than the 4s shell, so the 4s sub shell fills before the 3d shell
• in the electron box model:

  -draw only two electrons represented by arrows in each box

  -they must be in opposite directions

  -in a subshell, each box must fill with at least one electron first
• the electron configuration of carbon is :

  1s2 2s2 2p2
• cations are positive ions, anions are negative ions
• ionic bonding is the strong electrostatic force of attraction between positive and negative ions acting in all directions
• in ionic bonding, the outer shell of electrons for the cation are transferred to the outer shell of the anion to have a full outer shell
• ionic compounds with ionic bonds form a giant ionic lattice where each ion is surrounded by oppositely charged ions
• ionic compounds are solid at room temp as there is insufficient energy to overcome the strong electrostatic attraction between the ions. a high temp gives the energy needed to overcome the attraction so ionic compounds have a high melting and boiling point
• the mp and bp are higher for ionic lattices containing ions with greater ionic charges
• many ionic compounds dissolve in polar substances as the polar molecules break down the lattice by attracting and surrounding each ion. in a ionic compound with large charges, it may not be as soluble as the ionic attraction is too strong even for a polar substance to break
• ionic compounds can only conduct electricity melted or dissolved, as the ions are free to carry charge around the structure
• covalent bonding is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
• a covalent bond is the overlap of atomic orbitals , each containing one electron, to give a shared pair of electrons
• the attraction in a covalent bond is localised, meaning it only acts between the pair of electrons and the nuclei, resulting in a small unit called a molecule
• paired electrons that are not shared with another element are called lone pairs. they also need to be added to the displayed formula
• a double covalent bond is the electrostatic attraction between 2 pairs of shared electrons and the nuclei of the bonding atoms
• a dative or coordinate bond is a covalent bond where the shared pair of electrons has been supplied by only one of the bonding atoms. the shared electron pair would originally be a lone pair of one of the bonded atoms