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.)
(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
(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)
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.)
(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
|
