periodicity

• what does periodicity mean?

  trends that occur (in physical and chemical properties) as you move across the periods.
• what is an example of periodicity?

  metal to non-metal is a trend that occurs going left to right in each period.
• how is the periodic table arranged?

  periods (rows) and groups (columns) by atomic (proton) number.
• what do all the elements within a period have?

  the same number of electrons in their outer shell so they have similar properties.
• what does group number tell?

  the number of electrons in the outer shell. eg: group 1 elements have 1 electron in their outer shell.
• what is the exception to the group number rule?

  group 0. Group 0 elements all have full outer shells, so 2 electrons for helium and 8 for all the others.
• what blocks are the periodic table split into?


  s block, d block, p block and f block.
• what is s block?

  
• what is d block?

  
• what his f block?

  
• what is p block?

  
• how does atomic radius change across a period?

  atomic radius decreases across a period.
• why does atomic radius decrease across a period?

  as the number of protons increases, the positive charge of the nucleus increases. This means electrons are pulled closer to the nucleus, making the atomic radius smaller. The extra electrons that the elements gain across a period are added to the outer energy level so they don't really provide any extra shielding effect as shielding is mainly provided by the electrons in the inner shells.
• what happens to melting point across a period?

  it varies as they depend on structure of elements and bonding within them.
• what are sodium, magnesium and aluminium?

  metals.
• how do melting points and boiling points of sodium, magnesium and aluminium change across a period?

  they increase across a period as the metal-metal bonds get stronger, the bonds get stronger because the metal ions have an increasingly positive charge, an increasing number of delocalised electrons and a decreasing radius.
• why does silicon have a high melting point?

  silicon is macromolecular with a tetrahedral structure, strong covalent bonds link all its atoms together. A lot of energy is needed to break these bonds so silicon has a high melting point.
• what are phosphorus, sulphur and chlorine?

  molecular substances.
• what does the melting point of molecular substances depend on?

  the strength of the van Der Waals forces between the molecules. Van Der Waals forces are weak and easily overcome so these elements have low melting points.
• what does more atoms in a molecule mean?

  stronger Van der Waals forces.
• what is the biggest molecule? so?

  sulphur so it has a higher melting point than phosphorus or chlorine.
• why does argon have a very low melting point?

  because it exists as individual atoms (its monatomic) resulting in very weak van Der Waals forces.
• how does ionisation energy change across a period?

  ionisation increases across a period because of the increasing attraction between the outer shell electrons and the nucleus because of the number of protons increasing. (there are a few anomalies).