Atomic size:
The average distance between the nucleus and outermost orbits shells of an atom is called atomic size.
Ionic size:
The average distance between the nucleus and outermost orbit of ion is called ionic size.
Trends in atomic or ionic size
Atomic size are ionic size of an element decreases from left to right in the period.
Reason: As we move from left to right in the period, number of shells and shielding effect of all element in a given period remains the same but the effective nuclear charge increases by 1 unit in each element which attracts the valence electron more effectively and hence atomic size decreases.
Question: Why size of inert gases is greater than preceding halogen?
Answer. The size of inert gases is greater than preceding halogens due to interelectronic repulsion of electrons.
Quick quiz 1 The electronic structure of magnesium is 1s2 2s2 2p6 3s2 write down electronic structure of aluminum in the same notation aluminum equal to 1s2 2s2 2p6 3s23p1 ; which of the two elements magnesium are aluminum has the more stable structure?
Answer. Magnesium has more stable structure.
Ionization energy
Ionization energy maybe define as ''the minimum amount of energy required to remove 1 mole of valence electrons from one mole of gaseous atom to produce one mole of uni-positive gaseous ions is called ionization energy
For example
X ----------------------> X+ + e-
Factors of ionization energy
Ionization energy depends upon following factors:
Atomic size: Greater than atomic size, smaller will be ionization energy and vice versa.
Shielding effect/ screening effect: Greater the shielding effect, smaller will be ionization energy and vice versa.
Nature of Orbital: Ionization energy decreases in following order: s>p>d>f
Trends in periodic table:
In general as remove from left right in a period ionization energy of elements increases reason this is due to the fact that nuclear gradually increases and atomic size decreases from left right in the period
Electronegativity
Electronegative is a measure of tenancy of an atom to attract a share pair of electrons towards itself. Units: Electronegativity has no units.
Trends in period in Periodic Table
In Period: On moving from left right in a period electronegativity increases.
Reason: This is due to fact that nuclear charge gradually increases and atomic size decreases from left right in the period, so smaller atomic size with greater nuclear has greater tendency to a shared pair of electrons towards itself.
e.g., electronegativity of F is higher than Li.
In a group: On moving from top to bottom in a group, electronegativity of elements decreases.
Reason: In a group atomic size of an atom increases due to addition of extra shell, so attraction between nucleus and valance electron decreases. However, nuclear charge also increases but its effect is cancelled with increasing shielding effect down the group. e.g., electronegativity of H is greater than C.
Melting and boiling point:
Melting and boiling points indicates about the strength of force among the atoms, ions or molecule in a substance. In case of element, the value of melting and boiling point are according to the binding forces between particle in that element in the period melting and boiling point are according to the binding forces.
Trends in Periodic Table.
The melting and boiling points are high up to middle because these element have increasing number of bonding electron from group I to group III while Si (silicon) has a giant structure.
Melting and boiling points are low from group V (phosphorous) to group VIII (Ar) because these elements exist in the form of simple molecules which have weak intermolecular forces.
Reaction with water
Sodium: sodium has a high exothermic reaction with cold water it produces hydrogen gas and sodium hydroxide.
Na + H2O -----------------> NaOH + 1/2 H2
Magnesium: Magnesium has a very slight reaction with cold water to form magnesium hydroxide.
Mg +2H2O(Cold) -------> Mg(OH)2 + H2
However magnesium produces magnesium oxide and hydrogen gas when reacted with steam.
Mg +H2O (Steam) -------> MgO + H2
Aluminium:
Aluminium powder heated in steam produces aluminium oxide and hydrogen gas. The reaction is very slow due to formation of hard layer of aluminium oxide on the surface of aluminium
Al + 3H2O ----------> Al2O3 + 3H2
Silicon Phosphorus and sulphur
Silicon Phosphorus and sulphur have no reaction with water
Colorine:
Colorine reacts with water to give a green solution it produces mixer of hydrochloric acid and hypochloros acid.
Cl2 + H2O ----------------> HCl + HOCl
In the presence of Sunlight chlorine reacts with water to produce hydrochloric acid and oxygen.
2Cl2 + 2H2O ----------------> 4HCl + O2
Argon: There is no reaction between organ and water.
Reaction with oxygen:
Sodium: Sodium burn in oxygen with yellow flame and produces sodium oxide and sodium per oxide.
Na + O2 ----------------------> Na2O
Na + O2 ----------------------> Na2O2
Magnesium: Magnesium burns in oxygen with white flame 2 give magnesium oxide.
Mg + O2 --------------> MgO
Aluminum: Aluminum reacts with oxygen on heating to produce a thin protective layer of aluminum oxide which prevents further reaction (corrision).
2Al + 3O2 ---------> 2Al2O3
Silicon: Silicon will burn in oxygen if it heated strongly.
Si + O2 ------------> SiO2
Phosphorus: White Phosphorus catches fire spontaneously in air it burns with white flame and cloud of white smoke Phosphorus (III) oxide and phosphorus (V) oxide.
P4 + 3O2 ----------> P4O6
P4 + 5O2 (excess)----------> P4O10
Sulphur:
Sulphur burns in air oxygen with pale blue flame. It produces colorless Sulphur dioxide.
S + O2 -------------> SO2
Chlorine and organ: Despite having a large number of oxides, chlorine doesn't react directly with oxygen. However, Ar does not react directly or indirectly.
Reaction with chlorine:
Sodium: Sodium burns with chlorine to produce white sodium chloride.
Na + Cl2 --------------> NaCl
Magnesium: Magnesium burns with chlorine to produce white MgCl2.
Mg + Cl2 --------------> MgCl2
Aluminum:
Aluminum reacts with chlorine to produce aluminum chloride.
Al + 3Cl2 --------------> AlCl3
Silicon: Silicon reacts with chlorine to produce silicon tetrachloride.
Si + 2Cl2 -------------> SiCl4
Phosphorus: Phosphorus burns with chlorine to produce mixture of pcl3 and PCL5.
P4 + 6 Cl2 --------> 4PCl6
P4 + 10 Cl2 --------> 4PCl5
Sulphur: Sulphur burns with chlorine to produce S2Cl2.
S + Cl2 --------------> S2Cl2
Argon: Argon doesn't react with chlorine
Atomic and physical properties of group 1 elements (Alkali metal )
The average distance between nucleus and valance orbit of an atom are iron is called atomic or ionic radius.
Trends in atomic radius in Periodic Table
As the move from top to bottom in the first group atomic or ionic radii increases.
Reason: This is because an extra shell of electron is added in each element. The other factor in shielding effect. Due to increasing shilling effect, the size of atom also increases.
Ionization energy
Ionization energy maybe define as ''the minimum amount of energy required to remove one mole of balance electron from one mole of gases atom to produce one mole of uni-positive gaseous is called ionization energy.
Factors of ionization: Ionization energy depends upon following factors:
i. Atomic size
ii. Nuclear charge
iii. Shielding effect/ screening effect
iv. Nature of orbital
Trends in Periodic Table
Along the Group
As we move from top to bottom in a group ionization energy decreases. This is because, as we move from top to bottom in a group the distance of ns electron from nucleus increases so its removal become more and more easy. The other factor is shielding effect. As we go from top to bottom in the group, shielding effect increases which decrease is the force our attraction between valance ns electrons and nucleus of an atom and hence ionization energy decreases
This is why ionization energy of Lithium is very high and case of cesium is very low
Electronegativity
Electronegativity is a measure of tenancy of an atom to attract a share pair of electron towards itself. It has no units.
Tends in Periodic Table
On moving from top to bottom in a group electronegativity of elements decreases.
Reason: In a group, atomic size of an atom increases due to addition of extra shell of electrons. So attraction between nucleus and valence electron decreases. As a result, tendency of an atom to attract valence electrons also decreases. However nuclear charge also increases but its effect is cancelled out with increasing shielding effect along the group. For example, electronegativity of hydrogen is greater than Cs.
Melting and boiling point
Melting and boiling point of group 1 element decreases down the group.
Reason: Melting and boiling point decreases down the group because metallic bond becomes weaker as we go from top to bottom in a group.
Density
The mass per unit volume of element is called density of an element. Density of alkali metals is quite low due to large atomic volume. Density of alkali metals decreases with increase in atomic size from Li to Cs. However K is lighter than Na because of unusual increase in atomic size of K.
Chemical Reactions of Alkali Metals
Reaction with water alkali metal
Alkali metals react vigorously with water and release hydrogen gas and metal hydroxide. These reactions are highly exothermic. Hydrogen gas can be burnt due to heat produced during the chemical reaction that is why alkali metal are stored in paraffin or kerosene oil.
Na + H2O --------------> NaOH + H2 + heat
Reactions reactivity of alkali metal with water increases from top to bottom in a group that's why potassium rubidium season can react with ice at minus 100 degree centigrade.
Reaction with oxygen:
Alkali metals react with oxygen or air rapidly to produce their respective oxides. Lithium give monoxide.
Li + O2 ------------> Li2O (normal oxide)
Sodium reactions,
Na + O2 ------------> Na2O
Na + O2 ------------> Na2O2
M + O2 ------------> MO2
M= K, Rb, Cs,
Normal oxides of alkali metals other than Lithium are formed by indirect method.
For example, reaction of peroxide, nitrate and nitrite of metal with metal itself produces of normal oxide.
Na2O2 + Na ----------> Na2O
NaNO2 + 2Na -----------> Na2O + N2
NaNO3 + 10Na ----------> Na2O + N2
Properties of normal oxides
O2- + H2O ----------> OH- + OH-
O22- + 2H2O ----------> H2O2 + OH-
2O21- + 2H2O ----------> H2O2 + O2
reactions of oxide with water and dilute acid the simple oxides him too reaction with water reaction with dilute acid the simple oxides react with water to give metal Hydroxide the simple side react with an asset to give short and water the peroxides and two O2 reaction with water reaction is dilute acid solution of metal hydroxide and hydrogen peroxide is form hydrogen peroxide from decompose into water and oxygen with water metal hydroxide and hydrogen peroxide reaction with dilute acid hydrogen peroxide oxygen
Reactions of alkali metal with chlorine
2Na + Cl2 ---------------> 2NaCl
Lithium and sodium reacts theory with chlorine at room temperature to give lithium chloride (LiCl) and sodium chloride (NaCl).
Molten sodium burns with a brilliant yellow flame in the atmosphere of chlorine to form NaCl. K, Rb and Cs react vigorously with all halogen to form metal halides.
Effect of heat on nitrates and carbonates
Metal carbonate are highly stable to heat and this stability increases from Li to Cs due to increase in electropositive character.
Lithium nitrate
Sodium nitrate
Flame test
Flame test is an analytical procedure used to detect presence of certain metal ion. It is based on each element characteristics emission spectrum.
Procedure
Clean a platinum are nichrome (Nickel chromium Alloy) wire by dipping it into hydrochloric acid and then heat it on Bunsen flame until doesn't produce any color of the flame. When wire is a clean then dip it again in acid and then it into small amount of solid to be tested. Place the wire again on flame and note the color of flame.
Different colour shown by different elements
Li ..... Crimson red
Sodium ----------------Golden yellow
Potassium --------------violet
Rbidium ----------------reddisht violet
Cesium------------------ blue
Calcium ----------------brick red
Strontium ---------------- crimson red
Barium-------------------grassy green
Copper -------------------blue green
Lead-----------------------gyrish white
Origin of flame colour
When metal atom or ion is heated on the Bunsen flame, electrons are excited to higher energy level by obsorbing some amount of energy. When these electrons are deexcited, they release absorb energy in the form of light in visible region of spectrum. Amount of energy absorbed during excitation process is different in different elements. Different colors are produced by different elements on the flame.
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