Period 3 elements and their oxides

Why does atomic radius decrease?

• outer electrons in the same shell

• more protons in nucleus

• same amount of shielding

• so stronger attraction between nucleus and outer shell electrons 

• so outer electrons pulled closer to the nucleus 

Why does ionisation energy generally increase?

• more protons 

• atoms get smaller 

• therefore stronger attraction from nucleus to outer electron in outer shell

Why is there a drop in ionisation energy between Mg and Al?

• electron is lost from the s orbital in Mg and the p orbital in Al 

• p orbital is of higher energy so easier to lose the electron 

Why is there a drop in ionisation energy between P and S?

• in the outer orbital in S there are two electrons 

• in the outer orbital of P there is only one electron 

• the pair of electrons create repulsion so it is easier to lose the electron

Why does electronegativity increase?

• more protons in the nucleus

• smaller atomic radius 

• so stronger attraction between the nucleus and 2 electrons in the covalent bond 

Describe the difference in melting and boiling points of the period 3 elements?

• sodium, magnesium, and aluminium are all metals, there is a strong attraction between the metal ions and delocalised electrons, mp/bp increase due to higher charge, more delocalised electrons, and smaller ions

• silicon is a giant covalent molecule, so has a higher mp/bp due to many strong covalent bonds 

• phosphorous, sulfur, and chlorine are simple molecules, mp/bp decreases as they are weak VDW forces between molecules, S>P>Cl as bigger molecules have more electrons so more VDW 

• argon is monatomic so very weak VDW forces between atoms, so very low mp/bp

Why is the second ionisation energy of any atom larger than the first ionisation energy?

Electrons are being removed from a positively charged ion, so more energy required.

An element X has the following values (in kJmol-1) for successive ionisation energies: 1093, 2359, 4627, 6229, 37 838, 47 285. What group of the periodic table is it in? How do you know?

Group 4, there is a large jump after the fourth IE, showing that the fifth electron must be nearer the nucleus in the next shell down.

Why are covalent molecules gases, liquids or low melting point solids?

Weak IM forces easy to overcome

What happens when Na and Mg react with water in terms of electrons?

They lose their 3s electrons

Na(s) → Na+(aq) + e-

Mg(s) → Mg2+(aq) + 2e-

What happens when sodium reacts with cold water?

• reacts exothermically 

• forms sodium hydroxide and hydrogen 

2Na(s) + 2H20(l) → 2NaOH(aq) + H2 

Na+ +OH- → NaOH(aq) 

• floats on the surface of the water then melts 

• burns with a yellow flame then dissolves 

• forms a colourless solution of NaOH pH 13 

What happens when Mg reacts with cold water?

• very slow reaction

• magnesium hydroxide and hydrogen formed 

• magnesium hydroxide layer forms on the surface of magnesium causing the reaction to stop as it is insoluble 

Mg(s) + 2H20(l) → Mg(OH)2(s) + H2(g) 

• magnesium reacts readily with steam forming magnesium oxide and hydrogen 

Mg(s) +H2O(g) → MgO(s) + H2(g)

What prevents Al from reacting with water?

It has an invisible oxide layer. If it is heated in steam it reacts

2Al(s) + 3H20(l) → Al2O3(s) + 3H2 (g)

What happens when silicon is put in water?

Nothing as it is insoluble

Why is phosphorous stored under water?

To prevent spontaneous combustion

What happens when sulphur reacts with water?

It is insoluble and does not react under normal conditions

What happens when chlorine reacts with water?

It dissolves to form chlorine water

Cl2 + H2O (reversible reaction) → HOCl + HCl

In sunlight

2Cl2 + 2H2O → 4HCl + O2

Equation of Na and oxygen.

4Na + O2 → 2Na2O

Equation of Mg and oxygen.

2Mg + O2 → 2MgO

Equation of Al and oxygen.

2Al + 3O2 → Al2O3

Equation of Si and oxygen. 

Si + O2 → SiO2 

Equation of P and oxygen.

4P + 5O2 → P4O10

Equation of S and oxygen.

S + O2 → SO2

SO2 + ½ O2 → SO3

What is the reaction of Na2O with water?

• solid ionic structure

• dissolves then reacts with water to form NaOH solution pH 14

Na2O + H20 → 2NaOH

• the nature of the oxide is basic

What is the reaction of MgO and water? 

• solid ionic structure 

• slightly soluble, some dissolves then reacts with water to form a solution pH 10

MgO + H20 → Mg(OH)2 

• the nature of the oxide is basic 

What is the reaction of Al2O3 and water?

• solid ionic structure 

• insoluble due to very high lattice enthalpy 

What is the reaction of SiO2 and water? 

• solid giant covalent structure 

• insoluble due to lattice of atoms linked by strong covalent bonds

What is the reaction of P4O10 and water? 

• solid simple molecule 

• reacts violently 

P4O10 + H20 → 4H3PO4 

• water molecule attach to electron poor P atoms leading to the release of H+ 

• pH 0, nature of the oxide is acidic 

What is the reaction of SO2 and water? 

• simple molecule gas 

• dissolves and then reacts with water to form a solution 

• SO2 + H20 → H2SO3

• water molecules attach to electron poor S atoms leading to the release of H+ atoms 

• pH 3, nature of the oxide is acidic 

What is the reaction between SO3 and water?

• simple molecule gas 

• reacts violently 

• SO3 + H2O → H2SO4

• water molecules attach to electron poor S atoms leading to the release of H+ atoms 

• pH 0, nature of oxide is acidic