periodicity

periodicity definition

trends in the chemical properties of elements across a period

• elements in the same group have similar properties

Shielding definition

when inner electrons block the attraction between the nucleus and outer electrons

atomic radius along a period

decreases

• no. of protons increases, so nuclear charge increases

• attraction between nucleus and electrons increases

• same shielding

atomic radius down a group

increases

• nuclear charge decreases

• greater distance between nucleus and electrons

ionisation energy along a period

increases

• atomic radius decreases

• nuclear charge increases

• attraction between electrons and nucleus increases

• same shielding

ionisation energy definition

the energy required to remove one mole of electrons from one mole of atoms in the gaseous state, to form one mole of gaseous ions

ionisation energy down a group

decreases

• atomic radius increases

• as you go down the group there is more shielding

ionisation energy along a period

increases

• nuclear charge increases

• atomic radius decreases

• same shielding

explain why the second ionisation energy of magnesium is greater than the first ionisation energy of magnesium

because the electron is being removed a positive ion

• therefore it more energy is needed

first ionisation energy graph for period 3 elements

reason for the dip in ionisation energy at aluminium

electronic configuration: 1s²2s²2p⁶3s²3p¹

• outer electron in 3p orbital

• 3p orbital is higher in energy than 3s

reason for the dip at sulfur

electronic configuration: 1s²2s²2p⁶3s²3p⁴

• paired electron in (3)p-orbital
  - (remember the bus stop method for electron pairing in orbitals)

• the electron pair repels

suggest why the first ionisation energy of krypton is lower than the first ionisation energy of argon

krypton has more shielding than argon

explain why the second ionisation energy of sodium is greater than the second ionisation energy of magnesium

electronic configuration of sodium: 1s²2s²2p⁶3s¹

electronic configuration of magnesium: 1s²2s²2p⁶3s²

• for the second I.E, sodium loses an electron from a 2p orbital whereas magnesium loses energy from a 3s orbital

• less shielding in sodium

  • therefore more attraction between electrons and nucleus

metallic bonding

• contains lattice of positive metal ions and delocalised electrons

• strong attraction between them

explain how metals conduct electricity

delocalised electrons flow in a given direction

explain why sodium has a lower boiling point than magnesium

• Mg has more protons than Na

• Mg is a smaller atom than Na

• therefore greater attraction between nucleus and delocalised electrons

  • (delocalised bc were talking abt metals)

• so therefore stronger metallic bonding

explain why metals are malleable

have layers of atoms/ions that can slide over one another

state the structure shown by a crystal of silicon and explain why the melting point of silicon is very high

• giant covalent structure

• has strong covalent bonds, which require lots of energy to break

state the structure shown by crystals of sulfur and phosphorous. explain why the melting point of sulfur is higher than the melting point of phosphorus

• simple molecular structure

• sulfur molecule (S₈) is a larger molecule than phosphorus molecule (P₄)

• therefore stronger vdw’s forces between sulfur molecules

• requires more energy to overcome these forces

explain, in terms of crystal structure and bonding, why silicon(IV) dioxide has a higher melting point than phosphorus(V) oxide

• silicon dioxide is a giant covalent molecule whereas phosphorus dioxide is a simple covalent compound

• silicon dioxide has strong covalent bonds which needs lots of energy to be broken

• whereas phosphorus dioxide only has vdw’s forces between its molecules

in terms of atomic structure, explain why van der Waals’ forces in liquid argon are very weak

• argon are single atoms/monoatomic, with the electrons closer to the nucleus

• therefore they cannot be easily polarised

which ion has the largest radius:

1. F⁻

2. Mg²⁺

3. Na⁺

4. O²⁻

O²⁻

which of these elements has the highest second ionisation energy and why:

1. Na

2. Mg

3. Ne

4. Ar

Na

• bc removing electron will make noble gas configuration, which will make it very difficult to remove 2nd electron