M3 ,, Periodicity Flashcards
What is periodicity?
A repeating pattern across different periods
Atomic radius?
Atomic radius will decrease as you move from left to right across a period because the increased number of protons create a more positive charge attraction for electrons which are in the same shell similar shielding
First ionisation energy?
The energy needed to remove an electron form each atom of one mole of gaseous atoms
H(g) —> H+(g) + e-
Factors that affect ionisation energy?
The attraction of the nucleus - the more protons the greater the attraction
Distance of electrons from the nucleus - bigger atom the further outer e- are from nucleus so weaker attraction to nucleus
Electron shielding - electron in outer shell is repelled by electrons in complete inner shells weakening attraction of the nucleus
Successive ionisation energies?
The patterns in successive ionisation energies or an Element give us important info ant the electronic structure for that element
Why are successive ionisation energies always larger?
The second ionisation energy of an element is always bigger than the first ionisation energy. This is because the ion formed, is smaller than the atom and the proton to electron ratio in the 2+ ion is greater than in the 1+ ion. The attraction between nucleus and electron is therefore stronger
Why has Helium the largest first ionisation energy?
Its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. He has a bigger first ionisation energy than H as it has one more proto
Why do first ionisation energies decrease down a group?
As one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller
Why is there a general increase in first ionisation energy across a period?
As one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective attraction of the nucleus greater.
Why has Na a much lower first ionisation energy than Neon?
This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. So Na’s outer electron is easier to remove and has a lower ionisation energy.
Define metallic bonding?
Metallic bonding is the electrostatic force of attraction between the positive metal ions and the delocalised electrons
The three main factors that affect the strength of metallic bonding?
- Number of protons/ Strength of nuclear attraction.
The more protons the stronger the bond - Number of delocalised electrons per atom (the outer shell electrons are delocalised)
The more delocalised electrons the stronger the bond - Size of ion.
The smaller the ion, the stronger the bond.
Diamond?
Macro molecular
Tetrahedral arrangement of carbon atoms. 4 covalent bonds per atom
Graphite?
Macro molecular
Planar arrangement of carbon atoms in layers. 3 covalent bonds per atom in each layer. 4th outer electron per atom is delocalised. Delocalised electrons between layers.
Why do macromolecular structure have very high bp’s?
macromolecular structures have very high melting points because of strong covalent forces in the giant structure. It takes a lot of energy to break the many strong covalent bonds
Bonding, structure, examples of macromolecular structure?
Bonding - covalent (shared pair of electrons)
Structure - giant molecular structures
Examples - diamond, graphite, silicon dioxide, silicon
Bonding, structure, examples of giant metallic structures?
Bonding - metallic bonding (force of attraction between metal + ions and delocalised electrons)
Structure - giant metallic lattice
Examples - all metals
Properties of macromolecular structures?
High mp and by because of many strong covalent bonds in macromolecular structure take a lot of energy to break the many strong bonds
Insoluble in water
When diamond and sand are solid conductivity is poor because electrons cannot move
When graphite is solid conductivity is good as there’s delocalised electrons between layers
Conductivity when molten is poor
Properties of giant metallic structures?
High mp and by because strong electrostatic forces between positive ions and sea of delocalised electrons
Insoluble in water
When solid conductivity is good cuz delocalised electrons can move through structure
Conductivity when molten is good
Shiny, malleable
Attractive forces in the lattice are the same whichever ions are adjacent
