CLASS 11 chemistry ch 3

CLASSIFICATION OF ELEMENTS AND PERIODICITY 

 IN PROPERTIES OF ELEMENTS CHAPTER 3 CLASS 11 

Mandeleev’s Periodic Law:- The properties of the elements are the periodic function of their atomic masses.Moseley, the English physicist showed that atomic number is more fundamental property of an element than its atomic mass. Therefore, the position of an element in the periodic table depends on its atomic number than its atomic mass.

Modern Periodic Law: The physical and chemical properties of elements are the periodic functions of their atomic numbers.

Types of Elements: s-, p-, d- and f- blocks.

MAIN GROUP ELEMENTS/ REPRESENTATIVE ELEMENTS:

The s- and p- block elements are called main group elements or representative elements.

s- block elements: Group-1 (Alkali metals) and Group-2 lements (Alkaline earth metals) which respectively have ns1 and ns2 outermost electronic configurations

p- Block elements: They belongs to group- 13 to 18. The outer most electronic configuration is ns2 np1-6. He (1s2) is a s- block element but is positioned with the group 18 elements (ns2 np6) because it has completely filled valence shell and as a result, exhibits properties characteristic of other noble gases.

d- block elements (Transition elements) are the elements of group 3 to 12 having outer electronic configuration (n-1) d1-10 ns1-2. Four transition series are 3d, 4d, 5d and 6d. The 6d- series is incomplete. Atomic adius generally decreases across a period and increases as we descend the group.

f-Block elements (Inner- transition Series)

Lanthanoids charecterised by the filling of4 f-orbitals, are the elements following lanthanum from 58Ce to 71Lu. Actinoids characterised by filling of 5f-orbitals, are the elements following actinium from 70Th to 103Lr. haracteristic outer electronic configuration is (n-2) f1-14 (n-1) d0-1 ns2.

Noble Gases : The gaseous elements of group 18 are called noble gases. The general outermost electronic configuration of noble gases (except He) is ns2 np6. He exceptionally has 1s2 configuration. Thus the outermost shell of noble gases is completely filled.

PERIODICITY

The repetition of similar properties after regular intervals is called periodicity.

Cause of Periodicity: The properties of elements are the periodic repetition of similar electronic configuration of elements as the atomic number increases.

ATOMIC PROPERTIES

The physical characteristics of the atom of an element are called atomic properties. The properties such as atomic radius, ionic radius, ionisation energy, electro-negativity, electron affinity and valence etc., called atomic properties.

ATOMIC RADIUS-

The distance from the centre of the nucleus to the outermost shell of the electrons in the atom of any element is called its atomic radius.

Periodicity-

(a) In periodP - Atomic radius of elements decreases from left to right in a period.

(b) In Group- Atomic radius of elements increases on moving top to bottom in a group.

COVALENT RADIUS-

Half the inter-nuclear distance between two similar atoms of any element which are covalently bonded to each other by a single covalent bond is called covalent radius.

VAN DER WAALS’ RADIUS:

Half the inter-nuclear separation between two similar adjacent atoms belonging to the two neighbouring molecules of the same substance in the solid state is called the van der waals’radius of that atom.

METALLIC RADIUS:

Half the distance between the nuclei of the two adjacent metal atoms in a close packed lattice of the metal is called its metallic radius.

Van der Waals’radius  >   Metallic radius  >  Covalent radius

IONIC RADIUS:

The effective distance from the centre of the nucleus of an ion upto which it has an influence on its electron cloud is called its ionic radius. A cation is smaller but the anion is larger than the parent atom. In case of iso- electronic species, the cation with greater positive charge has smaller radius but anion with greater negative charge has the larger radii.

IONISATION ENTHALPY:

Ethalpia ionization is a change in molecular italia that is accompanied by the removal of an electron from an atom or a gas phase ion in its ground state.  Thus, the change in ethalpia to the reaction;  M (g) → M + (g) + e- Is ethalpy from ionization I element M.?  For such a sequence ionization of ionization energies, the sequence of ionization may also be called ionization.

 etalpi second ionization (HrH2), etalpia third ionization (HrH3) և etc.  The term ionization ethalia is taken from the first ionization italia (HrH1) expressed in kilogram mol or eV.

 patrol.

 I) In general, ionization ethalpies are well regulated (with few exceptions).  (HrH1) <(HrH2) <(HrH3)

 2) Etalpia has a lower ionization rate when moving from top to bottom in the group.

 (3) The ionization rate increases from left to right over a period of time.

 Electron to conduct ENTALP Y.

 The electalp etalpia gain (∆egH) is a change in the ethalpia molecule when an atom or ion gas gas in its ground state adds an electron to form the corresponding anion, thus changing the ethalpia of the reaction.  X (g) + e- → X - e) The electrical wire gain of the element X is called (Heg H).  The gain H can be positive or negative.  Second, third, etc. to add sequential values.  An electron, called the second and third.  Others receive electrons.  For example,

 X (g) + e- → X- (g) =H = ∆eg H1 is called the first electron gain

 Italy

 X (g) + e- → X2- (g) ∆H = ∆eg H2 is called the second electron gain

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 X2- (g) + e- → X3- (g) ∆H = Heg H3 is called the third electron gain.

 (I) the period.  Simultaneously, italia is growing electronically from left to right.

 (Ii) in the group.  The resulting ethereal ellipse slopes from the top of the set.

 Electricity.

 "The relative direction of an atom in a molecule to capture one pair of electrons is called its own electricity."

 patrol.

 (I) the period.  Electrical negativity increases with time from left to right.

 (Ii) in the group.  The electrical negativity decreases from the top of the group.

 Valencia families.

 Electrons in the outer circumference are called valence electrons.  Because the electrons at the outer edge determine the valence of the element.

 OLUTI VALENCIA.

 The amount of a hydrogen or halogen atom or the number of oxygen atoms multiplied with one element is equal.  According to the electronic concept of loyalty, "the number of professors who lose or acquire an atom or share it with another atom to achieve the formation of an honest gas is called its health."

 patrol.

 (I) the period.  First, parity increases, and at some point it falls from left to right.

 (Ii) in the group.  Parity remains stable above and below the group

 Electrical position or metal case.

 The tendency of an element to lose electrons and form positive ions (cations) is called an electrical or mineral nature.  Elements with low ionization energy tend to have a greater tendency to lose electrons, so they are electrified or metallic in their behavior.  Alkali metals are the most electrifying elements.

 patrol.

 During the period.  Electrical or metallic letters drop from left to right during a time period.  In the group - the electric or metal characters in the group increase from top to bottom.

 Electron - not least of the metal products

 The tendency of an element to accept an electron to receive the anion is called its non-metallic or negative electron nature.  Elements with a high electronegativity tend to have a greater propensity for electrons and anion formation.  Consequently, the elements at the top right of the periodic table are of an electrical or non-metallic nature.

 patrol.

 (I) the period.  Electrical or non-metallic characters grow from left to right over a period of time.

 (ii) In group- The electro-negative or non-metallic characters decreases from top to bottom in a group.

REACTIVITY OF METALS: Periodicity: 

(i)  In period- The tendency of an element to lose electrons decreases in a period. So the reactivity of metals decreases from left to right in a period.

(ii) In group- The tendency of an element to lose electrons increases in a period. So the reactivity of metals increases from top to bottom in a group.

REACTIVITY OF NON- METALS:

(i)  In period- The tendency of an element to gain electrons increases in a period. So the reactivity of non-metals increases from left to right in a period.

(ii) In group- The tendency of an element to gain electrons decreases in a group. So the reactivity of non-metals increases from top to bottom in a group.

SOLUBILITY OF ALKALI METALS CARBONATES AND BICARBONATES:

PERIODICITY IN GROUP:

The solubility of alkali metal carbonates and bicarbonates in water increases down the group (From Lithium to Caesium).

SOLUBILITY OF ALKALINE EARTH METAL HYDROXIDES AND SULPHATES:

PERIODICITY IN GROUP: The solubility of alkaline earth metal hydroxide and sulphates in water increases down the group (From Beryllium to Barium).

BASIC STRENGTH OF ALKALINE EARTH METAL HYDROXIDES: PERIODICITY IN GROUP:

The basic strength of alkaline earth metal hydroxide in water increases down the group (From Beryllium to Barium), i.e.,

Be(OH)2    <  Mg(OH)2    <   Ca(OH)2    <   Sr(OH)2     <   Ba(OH)2

       Basic strength increases

THERMAL STABILITY OF CARBONATES OF ALKALI AND ALKALINE EARTH METALS:

Except lithium carbonate, (LiCO3), the carbonates of all other alkali metals are stable towards heat, i.e., carbonates of alkali metals (except LiCO3) do not decompose on heating. LiCO3 decomposes on heating to give lithium oxide (LiCO3).

The carbonates of alkaline earth metals are relatively less stable. On heating, they decompose to give corresponding oxide and CO2 gas. The decomposition temperature for alkaline earth metal carbonates increases as we go down the group.

Anomalous Properties of Second Period Elements 

Their anomalous behaviour is attributed to their small size, large charge/radius ratio, high electro negativity, non- availability of d- orbitals in their valence shell. the first member of each group of p-Block elements displays greater ability to form pp-pp multiple bonds to itself (e.g. C=C, C≡C O=O, N≡N) and to other second period elements (e.g. C=O, C≡N, N=O) compared to subsequent member of the group.