Periodicity Flashcards
(24 cards)
What is periodicity?
The repeating pattern of physical or chemical properties going across the periods.
What is period 1?
Hydrogen and helium.
Describe the trend atomic radius across a period.
Decreases due to increased nuclear charge. Shielding is the similar for electrons in the same shell.
Describe first ionisation energy across a period.
Increases across a period.
Nuclear charge increases (stronger attraction between nucleus and outer electrons)
Shielding has no change (they’re in the same electron shell)
Greater attraction (due to nuclear charge meaning more energy is required to remove electrons)
Which groups are s block?
1 and 2
Which groups are p block?
3 4 5 6 7 0
Which groups are d block?
Transition metals.
What do all elements in a group have in common?
The number of outer electrons.
Describe atomic radius down a group?
Increases down a group.
There are increased electron shells down a group.
Shielding increases (reduces attraction between nucleus and outer electrons)
Nuclear charge increases but the increased electron shells and shielding effect is stronger.
Describe ionisation energy down a group.
Decreases down a group
Atomic radius increases - less electrostatic attraction between nucleus and outermost electrons.
Shielding increases
Weaker attraction between nucleus and outermost electrons - less energy to remove electrons.
Describe the melting points of Na, Mg and Al.
They have metallic bonding. Their melting points increase due to greater positive charged ions (Na +1, Mg +2, Al +3). This also means more electrons are released as free electrons.
Describe the melting point of silicon.
It is macromolecular so it has a very strong covalent structure. The covalent bonds require a lot of energy to break so it has a high melting point.
Describe the melting point of phosphorus, sulphur and chlorine.
Simple covalent molecules. Held with weak van der waal forces. Doesn’t require much energy to overcome these forces. So they have a low melting point.
Describe the melting point of argon.
It is a noble gas. It is an individual atom with a full outer shell of electrons. This makes the atom very stable and the VDW forces are weak. Thus, low melting point.
Explain, in terms of crystal structure and bonding, why silicon(IV) oxide has a higher melting point than phosphorus(V) oxide.
- SiO2 is macromolecular
- Strong covalent bonds between atoms which need a lot of energy to overcome
- P4O10 is simple covalent molecule
- Weak van der Waals forces between molecules.
How does aluminium deviate from the trend of an increase in ionisation energy in group 3.
Outer electron in 3p orbital is higher in energy than 3s.
Explain why the atomic radius decreases across Period 3, from sodium to chlorine.
Nuclear charge increases
Shielding is similar
What does the melting point of period 3 elements depend on?
Structure of element
Bond strength
Describe the melting and boiling points across period 3.
Increases from Na -> Si then decreases Si -> Argon.
Describe the melting points of Na and Mg.
Metallic bonding. As delocalised electrons and the charge of metal ion increase, the strength of the metallic bond increases. Thus it takes a lot of energy to break the bonds.
Describe the melting point of Al.
Metallic bonding. More delocalised electrons and smaller ions meaning stronger bonds.
Describe the melting point of Si.
Giant covalent structure. Strong covalent bonds. Needs a lot of energy to break the bonds.
Describe the melting points of P and S.
Simple molecular structure. Strong covalent bonds. Weak van der waal forces. S8 forms larger molecules with stronger VDW compared to P4.
Describe the melting points of Cl.
Simple molecular. Weak VDW forces. Lower melting point.
