Periodicity

• How are elements ordered in the periodic table?

  By proton number
• What does atomic radius mean?

  The distance from the nucleus to the electrons
• Describe the trend in atomic radius for period 3

  The outer electrons are in the same energy level so atoms have the same electron shielding

  Atoms gain protons along the period so the nuclear charge increases

  Therefore, there is a stronger attraction between the nucleus and the outer electron

  So the atomic radius decreases
• What is the trend in atomic radius down a group?

  Increases

  More electron shells are filled
• Define electronegativity

  The ability of an atom to attract electrons in a covalent bond
• Describe the trend in electronegativity across a period

  The nuclear charge increases and so the atomic radius decreases

  Therefore, the bonding pair of electrons is closer to the nucleus

  So the pair in a covalent bond is more attracted to the nucleus

  So, electronegativity increases across a period
• Describe the trend in electronegativity up a group

  Smaller atomic radius so the nucleus is closer to the bonding pair of electrons

  So, there is stronger attraction between the bonding pair and the nucleus

  So electronegativity increases
• Define ionisation energy

  The minimum amount of energy required to remove a mole of electrons from a mole of gaseous atoms
• Describe the general trend for ionisation energy across a period

  The outer electrons are closer to the nucleus

  Atoms gain more protons so the nuclear charge increases

  Therefore, there is greater attraction between the nucleus and outer electron so the ionisation energy increases
• What are the deviations from the trend across a period for ionisation energy?

  Aluminium

  Sulfur
• Describe how Aluminium deviates from the trend for ionisation energy

  The outer electron is being removed from the p sub shell rather than the s subshell

  The p sub shell is further from the nucleus

  The outer electron is easier to remove

  Ionisation energy decreases
• Describe how sulfur deviates from the trend for ionisation energy

  There are two electrons in the same orbital

  The electrons repel each other

  So, less energy is needed to remove an electron and ionisation energy decreases
• Describe the trend in successive ionisation energy

  The general trend is that it increases

  Jumps occur when removing an electron from a closer sub shell
• Describe the trend in ionisation energy down a group

  The atomic radius increases so the outer electron is further from the nucleus

  The electron shielding increases

  The weaker attraction between the outer electron and the nucleus makes it easier to remove

  Ionisation decreases
• Describe the trend in melting and boiling points for Na, Mg and Al

  All metallic bonding has positive metal ions surrounded by a sea of delocalised electrons so the electrostatic attraction is between the positive ions and electrons

  Across from Na to Al, the size of charge increases, the ionic radius decreases and there are more delocalised electrons so there is stronger metallic bonding

  Therefore, higher melting and boiling points
• Describe the melting and boiling point in Si

  Silicon is giant covalent with lots of strong covalent bonds which require a lot of energy to break

  So, has a very high melting and boiling point
• Describe the melting and boiling point in P, S, Cl and Ar

  P, S and Cl are simple molecular and so are small molecules connected by covalent bonds with weak Van der Waals between molecules

  Van der Waals increases with size and number of electrons:

  P4, S8, Cl2 so S8 has the largest melting point

  Ar exists alone and has only weak Van der Waals between atoms which require very little energy to break so has the lowest melting point