Chemical Properties Of Elements in Period 3

According to modern periodic law- The physical and chemical properties of the elements are the periodic function of their atomic numbers and electronic configuration. Chemical properties are observed during chemical reactions and are concerned with the electrons of the outer – shell. Since chemical reaction does not affect the atomic nucleus hence, there are no changes in atomic number, and the periodicity of the periodic table remains unaffected.

Chemical Properties Of Elements in Period 3
Chemical Properties Of Elements in Period 3

Chemical Reactivity of Elements in Period 3

When elements come in contact with one or more substances, the reactants change into certain products through a specific chemical reaction. The reaction in metal is the result of sharing or gaining of electrons. The reactivity of any metal depends upon how readily it can electron be shared. In period 3, Argon doesn’t react due to its complete octet state.

In this section, we will see the reactions of elements of period 3 with oxygen, chlorine, and water.

Reaction with Oxygen

ElementsChemical EquationsObservation
Na4Na (s) + O2 (g) → 2Na2O (s) (Sodium oxide)Sodium burns with an orange flame and forming white powder.
Mg 2Mg (s) + O2 (g)→ 2MgO (s) (Magnesium oxide)Magnesium burns with a bright white flame and produces white powder.
Al 4Al (s) + 3O2 (g) → 2Al2O3 (s) (Aluminium oxide)Aluminium burns in oxygen when the aluminium oxide layer is detached from the metal by powdering the aluminium. White sparkles are produced and white powder is formed.
SiSi (s)+ O2 (g) → SiO2 (s) (Silicon dioxide)Silicon burns in oxygen only after strong heating and produce white sparkles forming white powder.
PP4 (s) + 5O2 (g) → P4O10 (g) ( Phosphorus V oxide)White phosphorus will spontaneously react in the air to produce a yellow or white flame.
SS + O2 → SO2 (Sulphur dioxide)
2SO2 + O2 → 2SO3 (Sulphur trioxide)
Sulphur when heated gently with oxygen burns with blue flame and produces a colorless gas of sulphur dioxide. The product thus formed reacts again with oxygen to form sulphur trioxide.
ClNo reaction directly————————————-
ArNo reaction ————————————-

Reaction with Chlorine

ElementsChemical EquationsObservation
Na2Na (s) + Cl2 (g)→ 2NaCl (s) (Sodium chloride)Sodium burns with a bright orange flame to form white powder of sodium chloride.
Mg Mg (s) + Cl2 (g) → MgCl2 (s) (Magnesium chloride)Magnesium burns with a bright white flame to form a white solid of magnesium chloride.
Al2Al (s) + 3Cl2 (g) → 2AlCl3 (s) (Aluminium chloride)Aluminium burns with chlorine to produce pale yellow aluminium chloride. When heated to high temperature, aluminium chloride (AlCl3) converts into its molecular form Al2Cl6.
Si Si (s) + 2Cl2 (g) → SiCl4 (l) (Silicon tetrachloride)When chlorine gas is passed over the silicon powder, a colorless liquid is formed.
PP4 (s) + 10Cl2 (g) → 4PCl5 (s) (Phosphorus V chloride)White phosphorus burns spontaneously to produce off-white solid phosphorus(V) chloride.
S2S (s) +Cl2(g) → S2Cl2(l) (Disulphur dichloride)Sulphur forms orange liquid when chlorine is passed.
ClNo reaction———————————–
ArNo reaction———————————–

Reaction with Water

ElementsChemical EquationsObservation
Na2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) ( Sodium hydroxide and hydrogen) Sodium forms a colorless solution of sodium hydroxide with cold water and produces bubbles confirming the production of hydrogen. It is a exothermic reaction.
MgMg (s) + H2O (l) → Mg(OH)2 (aq)+ H2 (g) ( Magnesium hydroxide and hydrogen)

Mg (s) + H2O (l) → MgO (s)+ H2 (g) ( Magnesium oxide and hydrogen)
Magnesium reacts slowly with cold water and forms magnesium hydroxide and produces bubbles of hydrogen.

Magnesium burns in water steam with a bright white flame and produces a white product forming magnesium oxide.

Oxides of Elements in Period 3 and their Properties

Oxides of all elements except chlorine and argon are formed with the reaction of respective elements with oxygen. Argon with a complete outer shell cannot react with oxygen, whereas in the case of chlorine, they don’t form stable products, so they are not taken into consideration.

Electronegativity and Bond Type of Oxides

The difference in the electronegativity of oxygen and metal determines the bond type of the oxides

Electronegativity Difference >1.7 → Ionic Bond

Electronegativity Difference < 1.7 → Covalent Bond

OxidesNa2OMgOAl2O3SiO2 P4O10SO2 Cl2O
Bond TypeIonicIonicIonicCovalentCovalentCovalentCovalent

Trend: As we move across left to right in period 3 of the periodic table, the oxides of elements changes from ionic to covalent compound.

Melting Point of Oxides

Melting Point (°C)92028002045170042017-92

The ionic oxides Na2O, MgO, and Al2O3 have a high melting point because they are held by strong electrostatic attraction between positive metal ions and negative oxygen ions. MgO and Al2O3 have high melting points than Na2O because they contain ions with higher charges.

SiO2 has a giant covalent macromolecular structure, so they have a high melting point.

The remaining oxides have a low melting point as they are held by weak intermolecular forces and are simple covalent compounds.

Nature of Oxides


The aqueous solution of oxides of sodium and magnesium forms a basic solution of sodium hydroxide and magnesium hydroxide, respectively. The aluminium oxide doesn’t dissolve with water but reacts with both acids and bases, hence amphoteric.

Variation in Oxidation Number

Oxides of Period 3 ElementsOxidation StateChlorides of Period 3 ElementsOxidation State
P4O10+3, +5PCl3, PCl5+3, +5

Reaction of Oxides with Water of Period 3 Elements

Chemical ReactionChemical Equations
Sodium oxide with water forms a solution of basic solution of sodium hydroxide.Na2O + H2O → 2NaOH
Magnesium oxide undergoes a reaction with water to form basic oxides of Magnesium hydroxide.MgO + H2O → Mg(OH)2
Aluminium oxide does not dissolve in water.No reaction
Silicon dioxide is a giant structure, so it is hard to break the bond of the macromolecule, and it does not react with water.No reaction
Phosphorus(V) oxide reacts with water to form phosphoric acidP4O10 + 6H2O → 4H3PO4
Sulfur dioxide reacts with water to form an acidic solution of sulphurous acidSO2 + H2O → H2SO3
Sulfur trioxide reacts violently with water to produce sulphuric acidSO3 + H2O → H2SO4

Acidic Behaviour of Oxides

Chemical ReactionChemical Equations
Sodium oxide is a strong base that reacts with an acid to form a salt and waterNa2O + 2HCl → 2NaCl + H2O
Magnesium oxide reacts with warm dilute hydrochloric acid to form salt and water.MgO + HCl → MgCl2 + H2O
Aluminium oxide reacts with both the acids and bases. It reacts with warm dilute hydrochloric in the same way as magnesium and sodium:

Aluminium oxide also reacts with bases
Al2O3 + 6HCl → 2AlCl3 + 3H2O

Al2O3 + 2NaOH + 3H2O→ 2NaAl(OH)4
Silicon dioxide reacts with hot concentrated sodium hydroxide solution to form a colorless solution.SiO2 + NaOH → Na2SiO3 + H2O
Phosphorus(V) oxide can form a range of salts when reacted with a base.P4O10 + 12NaOH → 4Na3PO4 + 6 H2O
Sulfur dioxide reacts with a base when bubbled through itSO2 + NaOH → Na2SO3 + H2O
Sulfur trioxide reacts with a base to form sulphuric acid and water.SO3 + 2NaOH → Na2SO4 + H2O

Acidic and Basic Behaviour of Hydroxides

Chemical ReactionChemical Equations
Sodium forms simple basic hydroxideNaOH + HCl → NaCl + H2O
Magnesium hydroxide forms simple basic hydroxidesMg(OH)2 + 2HCl → MgCl2 + 2H2O
Aluminium hydroxide is amphoteric because it reacts with both acids and basesAl(OH)3 + 3HCl → AlCl3 + 3H2O

Al(OH)3 + NaOH → NaAl(OH)4

Reaction with Water and Chlorides of Period 3

Chemical ReactionChemical Equations
Aluminium chloride reacts violently with water and forms misty fumes of hydrogen chloride.

An equilibrium is set up with the product, so H+ ions, and hence HCl, are formed
AlCl3 + 6H2O → [Al(H2O)6 ] 3+ + 3Cl

[Al(H2O)6 ] 3+ ⇌ [Al(H2O)5 (OH)]2+ + H+
Silicon tetrachloride produces hydrogen chloride with water.SiCl4 + 2H2O → SiO2 + 4HCl
Phosphorus(V) chloride also reacts with water and forms the product hydrogen chloridePCl5
H2O → POCl3

The ionic compounds Sodium chloride and magnesium chloride get dissolved in water, forming their respective ions. Disulphur dichloride reacts slowly with water to produce a range of products, including HCl, S, and H2S.


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