Periodicity Flashcards
How are elements in the periodic table ordered?
In order of increasing atomic number and arranged in groups (columns) where elements have the same number of electrons in the outer shell. Elements in the same period have the same number of electron shells.
Why is tungsten classed as a d block element?
Its outer electrons are d sub-shell electrons.
Why is sodium classed as an s block element?
Its outer electrons are s sub-shell electrons.
Why is aluminium classed as a p block element?
Its outer electrons are p sub-shell electrons.
Why is uranium classed as an f block element?
Its outer electrons are f sub-shell electrons.
What is the trend in atomic radius across period 3?
Atomic radius decreases across the period.
Why does this trend occur?
- Increase in nuclear charge across the period.
- No change in shielding from first two energy levels.
- Increased force of attraction between nucleus and outer electron.
What is the general trend in first ionisation energy across period 3?
Increases across the period.
* Increase in nuclear charge across the period.
* No change in shielding across period.
* More energy required in order to remove highest energy electron, as these are held by a large nuclear charge
Which two elements deviate from this trend?
Aluminium and sulfur
* Aluminium has its outer electron in a 3p orbital of higher energy level.
* The 3p sub-shell is shielded by the 3s subshell.
* Less energy is needed to remove the 3p electron from its orbital.
* Sulfur has four electrons in the p subshell.
* Two electrons share the same orbital and repel each other.
* Less energy is needed to remove the shared electron from its orbital.
How do the melting points change across the three elements?
Increases from sodium to aluminium. The charge on the metal ion increases: Na +, Mg 2+, Al 3+.
The size of the ion decreases: Na>Mg>Al due to increasing charge density.
More energy is needed to overcome the increasing attraction between positive ions and delocalised electrons.
What type of bonding and structure is present in silicon?
Bonding: Covalent
Structure: Giant covalent or macromolecular
Why are the melting and boiling points
so high?
Lots of strong, covalent bonds (four per atom), requires a lot of energy to break these covalent bonds.
The order of melting points (lowest to highest) is Cl, P, S.
Why is this?
Melting points are linked to strength of Van der Waals forces between molecules, which is linked to the size of the molecule.
Chlorine is Cl2, (mass 70.0)
Phosphorus is P4 (mass 124.0)
Sulfur is S8 (mass 256.8)
The larger the molecule or the more electrons the molecule contains, the greater the Van der Waals forces and the more energy is needed to overcome the force of attraction.
Argon exists as single atoms, how does this affect its melting point?
Only very weak Van Der Waals forces exist between atoms of argon.
Argon’s low mass and low number of electrons means that it has a very low melting point
