Introduction

 

A. . The  first 20 elements of the periodic table

Physical properties

1

H

2

He

3

Li

4

Be

5

B

6

Ca

7

N

8

O

 

F

 

Ne

 

Na

 

Mg

 

Al

 

Si

 

P

 

S

 

Cl

 

Ar

 

K

 

Ca

Electronegativity

Increasing the trend of electronegativity across the elements in a periodic manner.

Atomic radii

There is a periodicity in the atomic radii. It decreases H to He, Lithium ot Neon, Sodium to Argon. Metallic elements show greater atomic radii than non-metals. Reduction of atomic radii is due to increase in nuclear charge.

Boiling point

Periodicity in boiling points increases. It increases across every few elements and this pattern is repeated.

Density

Density also increases in a periodic fashion. Increases across succeeding elements and then decreases.  The pattern is repeated at the beginning of the next period.

First I.E.

The first ionization energy also shows a periodicity across these elements. Maximum IE is displayed by Helium and then there is a zig zig pattern of increasing IE, a peak and decrease and then repetition.

Melting points

There is a periodic increase in meting points as we go from element 1 to element twenty. And at points the periodicity repeats ( H to C, Nitrogen to Silicon). There is an erratic pattern between Phosphorus to Calcium.  Nonmetals show the least melting points while metallic elements will show the higher melting points on account of their ionic nature of their interactions. The trends in melting points in  a period would show a gradual increase in melting point till it reaches a peak and then falling off

 

 

There is a periodicity in their properties which tends to increase or decrease across the period as the atomic number increases. (Visual elements: patterns in the periodic table,n.d.) (Atomic radius and ionization energies, n.d.)

Description: http://www.chem1.com/acad/webtext/atoms/atpt-images/IEtable.jpg

Description: ionization energys - first 20 elements

(Periodic Table of the elements, 2014)

 

 

 

B. Trends in the physical and chemical properties of the elements in period 3.

The elements of period three are: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon, ranging from atomic numbers 11 to 18.  The number of electrons in the outermost orbital range from 1 to 8. The last element, Argon has eight electrons in its outermost shell and has thus attained noble gas configuration. (Elements, 2014)

 The physical properties:

1. Density

Increases and then decreases across the period

Description: image showing Density of solid: period 3 periodic periodicity for 3s and 3p chemical elements 

(Periodic Table of the elements, 2014)

 

2. Electrical conductivity- Sodium, Magnesium and Aluminium are good conductors of electricity as they lose electrons easily.  The melting and boiling points decrease from sharply from Si to Argon.  Silicon is a non metal and has a high melting point on account of its covalent structure and is a semi conductor.

 

3. The remaining elements show low melting and boiling points as well as poor electrical conductivity on account of being held together by weak van der Waals forces of attraction, which can be easily broken. Electrons are not free to move as they are held in covalent bonds.

 Chemical properties

1. Ionization energies (Elements, 2014)

Description: http://www.chemguide.co.uk/inorganic/period3/iechart.gif

 The ionization energies show an increasing trend across the period from Na to Argon.  Argon requires the largest amount of ionisation energy to lose one electron. Aluminium and Sulphur goes against this trend. Sodium has the least ionisation energy and can get ionised very easily to form Sodium ions. Factors which affect the ionisation energy are the charge on the nucleus, how far the outermost electron is from the nucleus, what is the extent of screening by the inner electrons and whether the electron is paired or not.   Exception observed in case of Aluminium is that the increased nuclear charge is offset by the fact the electorn is a 3p orbital which is farther to the nucleus and hence the ionization energies are lower.  In case of Sulphur, both its electrons belong to the same orbital, show repulsion and hence an electron can be easily removed. (Elements, 2014)

 

2. Atomic radii

This shows a decreasing trend across the period from left to right with Sodium having the largest atomic radii and Cl having the smallest radii. Sodium, Magnesium and Aluminium are metallic and exhibit ionic bond formation while the next four exhibit covalent bonding i.e. they enter into bonding by sharing electrons.   The radii decreases as due to the number of protons increasing in the nucleus, the nuclear charge also increases which is more than enough to negate the effect of increasing electrons as these electrons get added to the same energy shell  and owing to the strong nuclear pull, the radii decreases. (Saunders, n.d.)

 

Description: Graph of atomic radii of Period 3 elements

(Saunders, n.d.)

 

3. Electronegativity

The tendency of an atom to gain an electron or to attract the electrons of a pair towards itself  is referred to as electronegativity. And in period three, this tendency increases from Sodium to Chlorine. This is because as we go across the period, the number of screening electrons increases, number of protons increases, as charge increases, electrons are pulled more towards the nucleus with the result that sharing of electrons becomes the trend rather than losing electrons

C. Trends in the chemical and physical properties of the oxides and chlorides of period 3.

 

1. Oxides
The metallic oxides and the oxide of silicon will have high melting and boiling points because of their structure (ionic and covalent bonds) whereas the molecular oxides are held together by less stronger  forces of attraction ( van der Waals forces) and hence have lower melting and boiling points.

1. electrical  conductivity- In the solid state, none of them can conduct electricity as they have no free electrons. But the metallic oxides can do so in the liquid state

2. electronegativity of these oxides increase as you move from left to right of the period.

3. Acid-Base behaviour- The oxides range from strongly basic on the left side of the period to strongly acidic on the right side. Aluminium oxide is amphoteric i.e. can act as both acid and base. Sodium oxide for e.g. is strongly basic and can form NaOH with water and NaCl with acids.

 

2. Chlorides

The chlorides of period 3 elements include Sodium Chloride, Magnesium Chloride, Aluminium Chloride, Silicon tetrachloride, Phosphorus pentachloride and Sulphurous chloride. 

1. Sodium and Mgnesium chlorides can dissolve in water readily owing to the ionic nature, while other chlorides react vigorously with water owing to the greater number of chlorine atoms attached to the atoms.

2. Sodium and Magnesium chlorides show electrical conductivity in molten state owing to their ionic nature while others do not show.

3. Boiling and Melting points of Sodium and Magnesium chlorides are high owing to their ionic nature. Rest are low melting solids or liquids. ( Physical properties and reactions of period 3 chlorides, n.d.) (period 3 chlorides, n.d.)(chlorides od period 3, n.d.)

 

                                                     

EXPERIMENT 1

Aim:  To study the reactions of period 3 elements with water

Procedure:

1. A measured amount of each sample is added to an amount of water in separate test tubes.

2. The observations are taken down on the kind and intensity of reaction

3. Observations were recorded in a table.

 

 

 

 

Observations:

 

 

Element

Na

Mg

Al

Si

P

S

Cl

Ar

Reaction with water

Intense and heat producing  reaction resulting in sodium hydroxide

Mild reaction with cold water and thin layer of Magnesium hydroxide forms on the surface

Only when heated in steam then produces Aluminium oxide

No reaction

No reaction

No reaction

Reacts to produce a green solution of hydrochloric acid

No reaction

pH solution

Alkaline

alkaline

              No change in pH

Acidic

No reaction

 

 

Discussion:

A. The equations of the reactions

 1. Sodium: Description: \mathsf{2Na_{(s)} + 2H_2O_{(g)} \longrightarrow 2NaOH_{(aq)}} + H_{2(g)}}

 

2. Magnesium: Description: \mathsf{Mg_{(s)} + H_2O_{(g)} \longrightarrow MgO_{(s)} + H_{2(g)}}

 

3. Chlorine: Description: \mathsf{Cl_{2(g)} + H_2O \longrightarrow HOCl_{(aq)} + HCl_{(aq)}}


4. Sulphur, phosphorus and silicon don't react.

 

5. Aluminium: Description: \mathsf{2Al_{(s)}+ Cl_{2(g)} \longrightarrow AlCl_{3(s)}}

(equations of reactions of period 3 elements, n.d.)

 

B. Order of reactivity with water

Sodium shows the maximum reactivity, followed by Magnesium and Chlorine. Aluminium reacts with water vapour. Others do not show any reaction in their normal state,

C. What trend do you notice in the pH value?

 The ph values resulting due to interaction of the elements  with water,  moves from alkaline to acidic  as we go from left to right in the period 3 elements.

 

 

EXPERIMENT 2

 

Aim: To study the reactions of the period 3 elements with oxygen.

 

Procedure:

1. Set up a number of dry gas jars filled with oxygen and covered them up.

2. Took a small sample of each of the elements in a combustion spoon with the exception of Aluminium foil and Magnesium ribbon which were held in tongs

3. Each sample was ignited carefully over a Bunsen flame and then lowered into the specific jar. Observations were noted in a table.

4. Repeated for all the elements.

 

Observations:

 

Element

Na

Mg

Al

Si

P

S

Cl

Ar

Reaction with oxygen

Burns in oxygen with orange flame.

Produces oxide and peroxide

Heating of metal is needed

Burns intensely in oxygen with white intense flame ,

White solid oxide

Heating needed

Only powdered aluminium reacts with the oxygen to form aluminium oxide

 

 

High temperatures needed

Silicon will react with oxygen, with white flame ,  when heated strongly to produce silicon dioxide

Burns spontaneously,

With white smoke,

Produces two kinds of oxides

Burns with blue flame

 

Heating needed

No reaction

Does not react

pH

Basic pH

Basic ph

Amphoteric

Weakly acidic

acidic

acidic

Strongly acidic

No reaction

 

 

Discussion:

A. Write equations in your table for the reactions which occur. Look up the formulae of the products if necessary.

·         Sodium: Description: \mathsf{4Na_{(s)} + O_{2(g)} \longrightarrow 2Na_2O_{(s)}}

 

·         Sodium: Description: \mathsf{2Na_{(s)} + O_{2(g)} \longrightarrow Na_2O_{2(s)}}

 

·         Magnesium: Description: \mathsf{2Mg_{(s)} + O_{2(g)} \longrightarrow  2MgO_{(s)}}

 

·         Aluminium: Description: \mathsf{4Al_{(s)} + 3O_{2(g)} \longrightarrow 2Al_2O_{3(s)}}

 

·         Silicon: Description: \mathsf{Si_{(s)} + O_{2(g)} \longrightarrow SiO_{2(s)}}

 

·         Phosphorus: Description: \mathsf{P4_{(s)}   + 5O_{2(g)} \longrightarrow P_4O_{10(s)}}

 

·         Sulphur: Description: \mathsf{S_{(s)}  + O_{2(g)} \longrightarrow SO_{2(g)}}

 

·         Sulphur: Description: \mathsf{2S_{(s)}  + 3O_{2(g)} \longrightarrow 2SO_{3(g)}}

 

(equations of reactions of period 3

B. As far as possible place the elements in decreasing order of reactivity with oxygen.

Reactivity with oxygen decreases as you go down the period. Heating and high temperature required. Chlorine and Argon do not react. Aluminium however will react only in powdered form. The

C. Does the order you have noted follow the ability to lose electrons.

It does not. The ability to lose electrons decreases across the period and the tendency to gain and share electrons via covalent bonding increases. This explains why there is only one form of the oxide of the metallic elements while there are a number of oxides formed for the non-metals with oxygen.  Therefore, the reactivity with oxygen is independent of the ability to lose electrons.

 

EXPERIMENT 3

 Aim: To investigate the solubility in water of the following oxides Na2O, MgO, Al2O3, P2O5, SO2.

Procedure:

1. Created an observation table describing the appearance and physical state of the oxide.

2. Measured a small amount of each oxide and added to about 2ml of distilled water.

3. Added a small piece of indicator paper and noted the pH. Observed their solubility.

4.  For the oxides, which did not dissolve in water, determined their solubility in hydrochloric Acid and dilute Sodium hydroxide. Used  2ml of the acid or alkali. Warming of the mixture was carried out if it still did not dissolve in water.

Observations:

The physical appearance and state of the oxides and their solubilities in water were noted as below.

 

 

Formula of oxide

Na2O

MgO

Al2O3

P2O5

SO2

Appearance and state

Strong basic oxide. White solid

Basic oxide but not as strong as Sodium oxide. White solid, which absorbs moisture

White solid

White poweder

Colorless gas at room temperature

Solubility oxide in water

Soluble. Reacts violently

Na2O(s) + H2O(l) → 2NaOH(aq) - pH 14
 (reactions of period 3 elements)

Slightly soluble

MgO(s) + H2O(l) → Mg(OH)2(aq) - pH 12

](reactions of period 3 elements)

Insoluble in water and ethanol

P2O5(S) + 3H2O(l) → 2H3PO4(awweak acids

 

(reactions of period 3 elements/)

 

O3(g) + H20(l) → H2SO4(aq)

Sulphurous acid

 (reactions of period 3 elements/)

 

pH of solution

High pH 14

High pH 12

Neutral pH

Low pH 2.15

Low pK1

1.8

Reaction of oxide with dilute HCl

Strong base. Hence reacts with acids and produces sodium chloride with hydrochloric acid.

 

Not as strong a base as sodium oxide. Soluble. Produces Magnesium chloride with hydrobhloric acid

Reacts with  acid to form aluminium chloride solution

Na

na

Reaction with dilute NaOH

 na

na

Reacts to produce tetrahydroxoaluminate 

salts

Salts

 

Classification (acidic, basic or amphoteric)

 

Strongly Basic

Strongly basic

amphoteric

Acidic

Acidic

(trends in period 3 elements, n.d.) ](reactions of period 3 elements) (acid base behaviour of period 3 element oxides)

 

 1. Trends about acid/base properties and bonding in the oxides

 Acid/base properties of the oxides of period tends to go from acidic to basic with  the oxide of aluminium being amphoteric i.e. behaving as both an acid and a base. Sodium oxide is a very strong basic oxide while phosphorous and sulphur oxides are acidic oxides. Bonding in the sodium and magnesium oxides are ionic interactions.

 

                                                            

                                                             EXPERIMENT 4

Aim:  To study the solubilities of the chlorides of period 3 elements and to determine the pH.

 

Procedure:

1. Created an observation table for noting down the reactions of the various chlorides of the period 3 elements.

2.  A sample of each chloride was added to 2 ml of distilled water in a test tube.  The pH of the solution was determined using pH paper.

3. Recorded the observations in the table.

4. Repeated with each of the other chlorides in turn.

Formula of chloride

NaCl

Ionic,

 

MgCl2

ionic

AlCl3

Ionic/covalent depending on state

PCl5

Ionic/covalent depending on state

Reaction with water

Dissolves in water simply to form a neutral solution. Hydrolysis occurs.

Na+(aq) + 6H2O → [Na(H2O)6]2+(aq)

Dissolves in water simply. As the ionic charge on Magnesium is higher than Sodium, hydrolysis is lesser. [Mg(H2O)6]2+(aq) + H2O (l) → [Mg(OH)(H20)5]+(aq) + H3O+(l)

Covalent in nature but soluble in water. Hydrolysis occurs. Vigorous reaction with water.

AlCl3(s) + 6H2O(l) → [Al(H2O)6]3+(aq) + 3Cl-(aq)

Covalent in nature. But reacts violently y with water as the umber of chlorines are more. Hydrolysis occurs. Steamy acidic solution

pH of solution

Neutral

pH 7

Slightly acidic

pH 6.5

Highly acidic. pH3

Ph 0-2

(periodicity, n.d.) ( trends in period 3 elements, n.d.)

Discussion:

Describe the trends in the pH of the chloride solutions in water.

The chloride ion in case of all these chlorides do not have that much charge density to attract the water strongly to hydrolyse it. Hence the reactions of the period 3 chlorides in water is entirely due to the property of the ion attached to the chlorine atom.  The trend is as the atomic number and number of available electrons to bind to chlorine atoms increase, the reaction with water increases, the strength of hydrolysis increases and hence the pH of the resulting solutions display a shift from neutral to strongly acidic. Sodium and Magnesium chlorides form neutral and slightly acidic solutions with water. But the remaining elements possess higher charge density and hence can cause vigorous hydrolysis. ( reaction of period three chlorides, n.d.)

  

 

List of References

 

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