C8 periodicity

• the periodic table is a list of all the elements in order of increasing atomic number
• atomic number is the number of protons in the nucleus of an atom
• the periodic table can be used to predict the properties of a given element based on its position, and to explain similarities and trends in properties between elements
• a row in the periodic table is called a period
• all elements in the same period have the same number of electron shells
• a column in the periodic table is called a group
• all elements in the same group have the same number of outer electrons
• the periodic table is split into blocks:

  • s-block
  • p-block
  • d-block
  • f-block
• the block on the left of the periodic table is s

  the block on the right of the periodic table is p

  the block in the middle of the periodic table is d

  the block at the bottom of the periodic table is f
• elements in the s-block have outer electrons in an s-orbital
• elements in the p-block have outer electrons in a p-orbital
• elements in the d-block have outer electrons in a d-orbital
• elements in the f-block have outer electrons in an f-orbital
• Na, Mg and Al are all metals so have metallic bonding, they have high melting points, because there is strong electrostatic attraction which requires a lot of energy to overcome, and Na < Mg < Al because they form increasingly positive charges, and release more electrons, therefore the electrostatic attraction between positive ion and delocalised electrons is stronger, so requires more energy to overcome
• Si has covalent bonding, forming a macromolecular structure

  it has a high melting point because it contains strong covalent bonds which require a lot of energy to overcome
• P, S and Cl are all non-metals so have covalent bonding, they have low melting points as they are held together by weak van der Waals forces which do not require a lot of energy to overcome, and Cl < P < S because they form the molecules Cl2, P4 and S8, and increasing number of electrons increases the strength of van der Waals forces
• Ar is a noble gas so exists monatomically, it has a full outer shell and is unreactive, it has a very low melting point
• atomic radii decrease going across a period, because nuclear charge increases but the atoms have the same number of electron shells, so the shells are pulled more towards the nucleus as there is greater nuclear attraction
• atomic radii increase going down a group, because atoms have more electron shells, so distance between outer electrons and nucleus increases, and there is more shielding, so there is lesser nuclear attraction
• first ionisation energy increases going across a period, because number of protons in the nucleus increases but electrons enter the same level, so increased nuclear charge makes it require more energy to remove an electron
• first ionisation energy decreases going down a group, because number of filled inner levels increases, so there is more shielding, and the electron to be removed is further away, so decreased nuclear charge makes it require less energy to remove an electron
• there is a drop in ionisation energy from one period to the next because electrons are in a new main level so atomic radius is increased, the outer electron is further from the nucleus, so is less strongly attracted and is easier to remove
• each period has the same general pattern for ionisation energy, an increase of 2, then 3, then 3
• first ionisation energy drops between group 2 and group 3 because the group 3 atom is losing an electron from a p-orbital, whereas the group 2 atom is losing an electron from an s-orbital, the electron in the p-orbital is further from the nucleus and in a higher energy level, so requires less energy to remove
• first ionistion energy drops between group 5 and group 6 because electrons fill up each orbital separately at first without pairing up until they must, as they repel each other, the group 5 atom is losing an electron from an unpaired orbital, whereas the group 6 atom is losing an electron from a paired orbital, the electron in a pair is easier to remove as there is repulsion so less energy is required to remove it
• sodium and magnesium oxides form an alkaline solution when they react with water because they contain O(2-) ions which react with the water to produce OH(-) ions

  the equation is O(2-) + H2O -> 2OH(-)