Periodicity Flashcards
Describe and explain whether atomic radius increases or decreases across period 3
Decreases. Proton number increases and electrons are added to the same shell hence there is no increase in shielding. Nuclear attraction for valence electrons increases, causing radius to decrease
Describe and explain whether ionic radius increases or decreases across period 3
From Na to Al there is a loss of electrons to form cations. The cations have two shells of electrons. The cations all have 10 electrons, nuclear charge increases causing their size to decrease.
From P to Cl there is a gain of electrons to form anions. The anions have 3 shells of electrons. The anions are bigger than the cations due to extra shell. Then anions all have 18 electrons. Increasing nuclear charge cause their size to decrease
Describe and explain whether melting points increases or decreases across period 3
Na, Mg, Al have increasing metallic bond strength due to increase in number of valence electrons.
Si has a high melting point due to giant covalent lattice.
P4, S8, Cl2, Ar are simple molecular, they have weak VDW, low melting point. S8 has higher melting point due to more electrons
Describe and explain whether electrical conductivity increases or decreases across period 3
Metals have free delocalised electrons. Number of delocalised electrons per atom increases from Na, Mg to Al.
Si is giant molecular but has some free electrons. It is a semi-conductor.
P, S, Cl, Ar are simple molecular. No delocalised electrons thus they do not conduct electricity
Description of Na with oxygen
Sodium burns with an orange flame to produce a white solid mixture of sodium oxide and sodium peroxide
Description of Mg with oxygen
Magnesium burns with an intense white flame to give white solid magnesium oxide
Description of Al with oxygen
Aluminium will burn in oxygen if it is powdered, otherwise the strong oxide layer on the aluminium tends to inhibit the reaction
Description of Si with oxygen
Silicon will burn in oxygen if heated strongly enough
Description of P with oxygen
White phosphorus catches fire spontaneously in air, burning with a white flame and producing clouds of white smoke.
P4 + 5O2 —–> P4O10
Description of S with oxygen
Sulfur burns in oxygen on gentle heating with a pale blue flame. A colourless gas is produced.
S + O2 —> SO2
Description of Na with chlorine
Sodium burns in chlorine with a bright orange flame. White solid sodium chloride is produced
Description of Mg with chlorine
Magnesium burns with an intense white flame to give white magnesium chloride
Description of Al with chlorine
Aluminium burns in the steam of chlorine to produce very pale yellow aluminium chloride. This sublimes and collects further down the test tube
Description of Si with chlorine
If chlorine is passed over silicon powder heated in a tube, it reacts to produce silicon tetrachloride. This is a colourless liquid
Si + 2Cl2 —–> SiCl4
Description of P with chlorine
White P burns spontaneously in chlorine to produce a mixture of phosphorus (III) chloride and phosphorus (V) chloride which is an off white solid.
P4 + 10Cl2 —> 4PCl5
