Period 3 Elements Flashcards
Describe the structure of period 3 elements
- Na, Mg and Al are metals and form giant metallic structures.
- Si is metalloid and forms a giant molecular/covalent structure in which each silicon atoms is tetrahedrally bonded to four other silicon atoms by strong covalent bonds.
- P, S, Cl and Ar form simple molecular structures consisting of discreet molecules joined by weak van der waal forces but the atoms within each molecule joined by strong covalent bonds.
What is the trend in atomic radius of period 3 elements?
Atomic radius decreases across the period from Na to Cl
Explanation:
- From one element to the next from Na to Cl, a proton is added to the nucleus and an electron to the same outer shell.
- This increases the nuclear charge but the screening effect remains constant.
- As a result the nuclear charge outweighs the screening effect which increases the effective nuclear charge from sodium to chlorine.
- As the effective nuclear charge increases the atomic radius reduces as the electrons are pulled closer to the nucleus.
Describe the trend in melting point of period 3 elements
Melting point increases from sodium through magnesium, aluminium to silicon and generally decreases from Si to Ar with exception of sulpur that has a higher melting point than phosphorous.
Explanation
- For metals the melting point increases from sodium through magnesium to aluminium.
- From sodium to aluminium the number of delocalized electrons per atom contributed to the charge cloud increases from one to three, the charge on the metal ion increases and the ionic radius decreases.
- This increases the strength of the electrostatic attraction between the metal ions and the delocalized electrons.
- As a result the strength of the metallic bond increases and more heat energy required to break the metallic bond resulting into higher melting point from sodium to aluminium.
- There is a sharp increase in the melting point from aluminium to silicon because silicon forms a giant covalent structure consisting of very many strong covalent bonds which requires a lot of heat energy to break.
- Phosphorous, sulphur, chlorine and argon form simple molecules i.e. P4, S8, Cl2 and Ar respectively.
- The melting points of these elements depends on the strength of the Van der waal forces between their molecules which in turn depends the molecular mass; the higher the molecular mass, the stronger the Van der waal forces and the higher the melting point.
- Phosphorous has a lower melting point than sulphur because the P4 molecules have lower molecular mass and form weaker van der waal forces than the S8 molecules.
- From sulphur to argon the melting points decreases as the molecular mass and the strength of the Van der waal forces decrease.
Why does phosphorus have a lower melting point than sulphur?
The P4 molecules have lower molecular mass and form weaker van der waal forces than the S8 molecules.
What is the trend in electronegativity of period 3 elements?
Electronegativity increases from sodium to chlorine
Explanation:
- From one element to the next the nuclear charge increases by one unit due to an extra proton added to the nucleus while the screening effect stays constant because the extra electron is added to the same outer shell.
- As a result the nuclear charge outweighs the screening effect causing an increase in the effective nuclear charge and the power of the atom to attract bonding electrons towards its self.
What is the trend in electropositivity of period 3 elements?
Electropositivity decreases across the period from sodium from chlorine.
Explanation:
- From one element to the next the nuclear charge increases by one unit due to an extra proton added to the nucleus while the screening effect stays constant because the extra electron added to the same outer shell.
- As a result the nuclear charge outweighs the screening effect causing an increase in the effective nuclear charge meaning that the valency electrons become more strongly attracted to the nucleus.
- This reduces the ability of the atoms to lose electrons.
Define electropositivity
This is the tendency of an atom of an element to lose its valence electrons to become positively charged.
How do period 3 elements react with water?
• Sodium reacts vigorously with cold water forming sodium hydroxide solution and hydrogen gas.
• Magnesium reacts very slowly with cold water forming magnesium hydroxide solution and hydrogen gas.
When strongly heated, magnesium burns vigorously in steam with a very bright white flame forming magnesium oxide, a white powder and hydrogen gas.
• Aluminium does not react with water due to a protective layer of aluminium oxide. Silicon, phosphorus, and sulphur also do not react with water.
• Chlorine reacts with cold water forming hydrochloric acid and hypochlorous acid
How do period 3 elements react with air/ oxygen?
• Sodium readily reacts with air at room temperature forming sodium oxide, a white solid.
- When ignited in limited air, it burns with a bright yellow flame also forming sodium oxide.
- In excess air/oxygen sodium burns vigorously with a bright yellow flame forming sodium peroxide, a pale yellow solid.
• Magnesium burns vigorously in air with a bright white flame on strong heating forming a white ash consisting of magnesium oxide and magnesium nitride.
(If to the products a little water is added and the mixture warmed ammonia gas is evolved)
• Aluminium forms a protective layer of aluminium oxide when exposed to air.
• Silicon: At room temperature and temperatures below 900 degrees centigrade, silicon is protected by a thin layer of silicon(IV) oxide. However if ignited at temperatures beyond 900 degrees centigrade , it burns forming a white solid of silicon(IV) oxide.
• Sulphur: When exposed to a flame sulphur burns in air with a blue flame forming white fumes of sulphur dioxide gas.
• Phosphorous readily reacts with air/oxygen.
When exposed to air phosphorous forms a dense white smoke consisting of a mixture of phosphorous(III) oxide and phosphorous(V) oxide. (If ignited in air, phosphorous burns with a bright yellow flame again forming a mixture of phosphorous (III) oxide and phosphorous(V) oxide ( P4O6 & P4O10))
How do period 3 elements react with dilute sulphuric acid and dilute hydrochloric acid?
• Sodium reacts explosively with acids, so this reaction is never attempted.
• Magnesium reacts with dilute sulphuric acid and dilute hydrochloric acid with vigorous effervescence forming hydrogen gas and a colourless solution consisting of magnesium sulphate and magnesium chloride respectively.
• Aluminium reacts less vigorously with acids than magnesium forming the corresponding aluminium salt and hydrogen gas. The initial rate of reaction is low due to a protective layer of aluminum oxide.
• Silicon, phosphorous, sulphur, chlorine and argon don’t react with dilute acids.
How do period 3 elements react with sodium hydroxide solution?
• Sodium and magnesium do not react with sodium hydroxide solution.
• Aluminium reacts with cold dilute sodium hydroxide with vigorous effervescence
forming hydrogen gas and a soluble complex of sodium tetrahydroxo aluminate. The reaction is highly exothermic.
• Silicon reacts with hot concentrated sodium hydroxide forming sodium silicate solution and hydrogen gas.
• Phosphorus reacts with hot concentrated sodium hydroxide forming sodium phosphinate and phosphine.
• Chlorine reacts with cold dilute sodium hydroxide forming sodium chloride, sodium chlorate(I) and water.
Chlorine reacts with hot concentrated sodium hydroxide forming sodium chloride, sodium chlorate(V) and water.
How do period 3 elements react with chlorine?
• Sodium, magnesium and aluminium metals when heated and plunged into a gas jar of dry chlorine, there is a vigorous reaction, forming white crystals of sodium chloride, magnesium chloride and aluminium chloride respectively. The vigour of the reaction decreases from sodium to aluminium.
• Silicon when heated reacts slowly with dry chlorine forming silicon(IV) chloride a colourless liquid.
• Phosphorous when heated reacts slowly with excess dry chlorine forming phosphorous (V) chloride, a yellow solid.
• Sulphur when heated also reacts slowly with dry chlorine forming disulphur dichloride, a yellow liquid.
What is the structure of period 3 chlorides?
- Sodium chloride and magnesium chloride have giant ionic structures
- Aluminium chloride forms simple molecular structure
- The chlorides of other elements form simple molecular structures with discrete molecules joined by weak Van der waal forces.
How do period 3 chlorides react with water?
• Sodium chloride is not hydrolysed by water; it just dissolves in water forming a neutral solution of pH 7.
• Magnesium chloride is slightly hydrolysed by water forming a slightly acidic solution with pH of about 6.5.
• Aluminium chloride is hydrolysed by water forming an acidic solution with pH of about 3.
Explanation;
The aluminium ion has a small ionic radius and carries a big charge (3+) resulting into high charge density and polarizing power. The aluminium ion therefore exerts a powerful attraction for water molecules forming a soluble complex of hexaaquaaluminium ion, [Al(H2O)6]3+. The high polarizing power of the aluminium ion allows it to form a strong aluminium-oxygen bond in the complex which weakens the oxygen-hydrogen bond and releasing hydrogen ions. This makes the solution acidic.
• Phosphorus(III) chloride and Phosphorus(V) chloride are hydrolysed by water forming phosphorous acid (H3PO3) and phosphoric acid (H3PO4) respectively together with white fumes of hydrogen chloride.
• Disulphur dichloride is hydrolysed by water forming sulphurous acid, a yellow precipitate of sulphur and moist fumes of hydrogen chloride.
• Chlorine reacts water forming hydrochloric acid and hypochlorous acid.
Why does the hydrolysis of AlCl3 by water form an acidic solution.
- The aluminium ion has a small ionic radius and carries a big charge (3+) resulting into high charge density and polarizing power.
- The aluminium ion therefore exerts a powerful attraction for water molecules forming a soluble complex of hexaaquaaluminium ion, [Al(H2O)6]3+.
- The high polarizing power of the aluminium ion allows it to form a strong aluminium-oxygen bond in the complex which weakens the oxygen-hydrogen bond and releasing hydrogen ions.
- This makes the solution acidic.
Covalent or ionic bonding?
NaCl
MgCl2
AlCl3
SiCl4
PCl3, PCl5
SCl2, S2Cl2
Cl2
NaCl - ionic
MgCl2 - ionic
AlCl3 - predominantly covalent
SiCl4 - covalent
PCl3, PCl5 - covalent
SCl2, S2Cl2 -covalent
Cl2 -covalent
Covalent or ionic bonding?
Na2O
MgO
Al2O3
SiO2
P4O6, P4O10
SO2, SO3
Cl2O, ClO2, Cl2O6, Cl2O7
Na2O- ionic
MgO - ionic
Al2O3 - covalent
SiO2 - covalent
P4O6, P4O10 -covalent
SO2, SO3 - covalent
Cl2O, ClO2, Cl2O6, Cl2O7 -covalent
Acidic, Basic or Amphoteric?
Na2O
MgO
Al2O3
SiO2
P4O6, P4O10
SO2, SO3
Cl2O, ClO2, Cl2O6, Cl2O7
Na2O- Basic
MgO- Basic
Al2O3 -Amphoteric
SiO2- Acidic
P4O6, P4O10- Acidic
SO2, SO3- Acidic
Cl2O, ClO2, Cl2O6, Cl2O7- Acidic
