Exploring 74 Important Trends in S and P Block Elements

In this post, you will find the list of important trends in s and p block elements presented in a convenient tabular format. These trends are most important from the examination point of view for Class 11 and 12 and also for competitive exams IIT JEE and NEET.

S and P block elements

Understanding the increasing and decreasing order of s and p block compounds, i.e., important trends in s and p block compounds, is crucial in the field of chemistry. By examining these trends, we can gain valuable insights into the properties and reactivity of elements within these blocks.

In the s block, elements are known for their low ionization energies, which means they readily lose electrons to form positive ions. As we move down the periodic table, ionization energies generally decrease due to increased shielding from inner electron shells. This leads to a trend of increasing metallic character and reactivity within the s block compounds.

On the other hand, the p block contains elements that exhibit a wide range of properties. As we move across a period from left to right, electronegativity generally increases, resulting in stronger attraction for electrons. This makes it more difficult for elements on the right side of the p block to lose electrons and form positive ions. Thus, there is a decreasing trend in metallic character across a period.

However, as we move down a group within the p block, atomic size increases due to additional energy levels being added. This results in weaker attraction for electrons and an increasing trend in metallic character.

Check out: List of 100+ Important Organic Reagents in Organic Chemistry

By understanding these trends in s and p block compounds, chemists can predict and explain various chemical reactions and behaviours. This knowledge is invaluable when it comes to designing new materials or developing innovative chemical processes.

Important trends in S and P block elements

S. No.	Question	Answer/Explanation
1.	Decreasing order of ionic size: Mg2+, O2-, Na+, F–	O2- > F– > Na+ >Mg2+ All the four species are isoelectronic (1s2 2s2 2p6). The number of positive charge in the nucleus decreases in the Mg > Na >F > O. Hence O2- involved minimum nucleus-electrons attraction and maximum electron-electron repulsion while Mg2+ involves maximum nucleus electrons attraction and minimum electron-electron repulsion. These factors make the size of anion greater than the corresponding neutral atom and that of cation lesser than the corresponding atom.
2.	Increasing order of acidic strength: ZnO, Na2O2, P2O5, MgO	Na2O2 < MgO < ZnO < P2O5 Oxides of electropositive elements are alkaline while those of electronegative element are acidic. Alkaline property will increase with increase in electropositive character of metal and acidic characteristics increase with increase in electronegative characteristics of non-metals. Since the electro-negativity increases in the order Na < Mg < Zn < P, the acidic character of oxide will also increase in the same order.
3.	Increasing order of bond length: F2, N2, Cl2, O2	N2 < O2 < F2 < Cl2 Nitrogen contains triple bond, oxygen contains double bond and fluorine and chlorine contain a single bond each. Chlorine involves bonding of 3p orbitals while fluorine involves 2p orbitals.
4.	Increasing order of size: Cl–, S2-, Ca2+	Ca2+ < Cl– < S2– The given species are isoelectronic. So more the number of proton more attraction on electrons so use radius.
5.	Increasing order of acidic strength: HClO3, HClO4, HClO2, HClO	HClO < HClO2 < HClO3 < HClO4 More the oxidation number of central metal atom more the acidic strength.
6.	Increasing order of oxidation number of iodine: I2, HI, HIO4, ICl	HI < I2 < ICl < HIO4 The oxidation states of iodine in HI, I2, ICl and HIO4 are –1, 0 + 1 and +7, respectively.
7.	Increasing order of thermal stability: HOCl, HOClO2, HOClO3, HOClO	HOCl < HOClO < HOClO2 < HOClO3 The stability is explained by the increasing number of electrons involved in the formation of sigma and pi bonds in going from HOCl to HOClO3. In ClO4– ion all the valence orbitals and electrons of chlorine are involved in the formation bonds.
8.	Increasing order of bond enthalpy: N2, O2, F2, Cl2	F2 < Cl2 < O2 < N2 N2 involves a triple bond, O2 involves a double bond, F2 and Cl2 involve a single bond each F2, has a lower bond enthalpy than Cl2. This is due to more repulsion of nonbonding electrons in F2. Besides this, there is a possibility of multiple bonding in Cl2 involving d orbitals.
9.	Increasing order of acidic strength: CO2, N2O5, SiO2, SO3	SiO2 < CO2 < N2O5 < SO3 Increasing electronegativity of an element makes its oxide more acidic.
10.	Increasing order of ionic size: N3-, Na+, F–, O2-, Mg2+	Mg2+ < Na+ < F_ < O2-
11.	Increasing strength of hydrogen bonding: O, S, F, Cl, N	S < Cl < N < O < F The negative charge on X in HX increases with increasing electronegative of X. This makes the hydrogen bonding more strong.
12.	Increasing order of ionic radii in water: Li+, Na+, K+, Rb+, Cs+	Cs+ < Rb+ < K+ < Na+ < Li+ The ions in a solution are present as hydrated ions. The smaller the size of the on, the greater the extent of hydration. So the size of hydrated ions becomes larger for smaller sized ion and vice versa.
13.	Increasing order of molar conductivity in water: Li+, Na+, K+, Rb+, Cs+	Li+ < Na+ < K+ < Rb+ < Cs+ Li+ ion being heavily hydrated has the lowest mobility and Cs+ ion being less hydrated has the highest mobility.
14.	Increasing order of reactivity with water: Li, Na, K, Rb, Cs	Li < Na < K < Rb < Cs The reactivity increases on descending the group 1.
15.	Increasing order of basic nature of hydroxides: LiOH, NaOH, KOH, RbOH, CsOH	LiOH < NaOH < KOH < RbOH < CsOH The basic nature of hydroxides of elements of Group I increases on descending the group.
16.	Increasing order of covalent character: LiCl, LiBr, LiI	LiCl < LiBr < LiI The smaller sized Li+ ions polarizes the larger anion more predominantly giving larger covalent character.
17.	Increasing order of ionic character: CaCl2, BeCl2, MgCl2, BaCl2, SrCl2	BeCl2 < MgCl2 < CaCl2 < BaCl2 < SrCl2
18.	Increasing order of solubility: BeCO3, MgCO3, CaCO3, BaCO3	BaCO3 < CaCO3 < MgCO3 < BeCO3 On moving down the group, the lattice energies of carbonates do not decrease much while the degree of hydration of the metal ions increases significantly leading to decreased solubility.
19.	Increasing order of solubility: Be(OH)2, Mg(OH)2, Ca(OH)2, Ba(OH)2	Be(OH)2 < Mg(OH)2 < Ca(OH)2 < Ba(OH)2
20.	Increasing order of basicity: Be(OH)2, Mg(OH)2, Ca(OH)2, Ba(OH)2	Be(OH)2 < Mg(OH)2 < Ca(OH)2 < Ba(OH)2
21.	Increasing order of hydration of ions: Be2+, Mg2+, Ca2+, Sr2+, Ba2+	Ba2+ < Sr2+ < Ca2+ < Mg2+ < Be2+ The extent of hydration of ion decreases with increase in ionic size.
22.	Increasing order of reactivity with water: Be, Mg, Ca, Sr, Ba	Be < Mg < Ca < Sr < Ba The reaction of alkaline-earth metals become increasingly vigorous with increasing atomic number.
23.	Increasing order of reactivity towards air: Be, Mg, Ca, Sr, Ba	Be < Mg < Ca < Sr < Ba
24.	Increasing order of solubility: BeSO4, MgSO4, CaSO4, SrSO4, BaSO4	BaSO4 < SrSO4 < CaSO4 < MgSO4 < BeSO4 Hydration of ion plays a dominating role as compared to lattice energy.
25.	Increasing order of ionic character: BCl3, AlCl3, GaCl3	BCl3 < AlCl3 < GaCl3 Increase in the electropositive of element increases its ionic character.
26.	Increasing strength of Lewis acid: BF3, BCl3, BBr3	BF3 < BCl3 < BBr3 Besides sigma bond between boron and halogen atoms, there exist additional pπ-pπ bond between the two atoms resulting from back-donation of electrons from fluorine to boron (back bonding). The tendency to form pπ-pπ bond is maximum in BF3 (2pπ-2pπ back bonding) and falls rapidly on passing to BCl3 (2pπ-3pπ back bonding) and BBr3 (3pπ-4pπ back bonding). The tendency to accept electron pair, therefore, increases from BF3 to BBr3.
27.	Increasing strength of Lewis acid: AlCl3, GaCl3, InCl3	InCl3 < GaCl3 < AlCl3 With increase in size of element of Group 13, the tendency to accept electron pair is decreased.
28.	Increasing order of reducing power: GeCl2, SnCl2, PbCl2	PbCl2 < SnCl2 < GeCl2 The stability of element in +H oxidation state increases on ascending the group 14. This is due to inert-pair effect.
29.	Increasing order of oxidizing power: GeCl4, SnCl4, PbCl4	GeCl4 < SnCl4 < PbCl4 The stability of element in +IV oxidation state decreases on ascending the Group 14. This is due to inert pair effect.
30.	Increasing order of basic character: NH3, AsH3, SbH3, PH3	SbH3 < AsH3 < PH3 The decrease in electronegativity and increase in size of element cause the decrease in tendency to accept proton.
31.	Increasing order of thermal stability: NH3, AsH3, SbH3, PH3	SbH3 < AsH3 < PH3 < NH3
32.	Increasing order of acidic strength: HNO3, H3PO4, H3AsO4, H3SbO4	H3SbO4 < H3AsO4 < H3PO4 < HNO3
33.	Increasing order of solubility in water: HNO3, H3PO4, H3AsO4, H3SbO4	H3SbO4 < H3AsO4 < H3PO4 < HNO3
34.	Increasing order of order of +5 oxidation state: N, P, As, Sb and Bi	Bi < Sb < As < P < N
35.	Increasing order of stability of hydrides: H2O, H2S, H2Se, H2Te	H2Te < H2Se < H2S < H2O
36.	Increasing order of poisonous nature: H2S, H2Se, H2Te, H2Po	H2S < H2Se < H2Te < H2Po
37.	Increasing order of acidic strength: H2O, H2S, H2Se, H2Te	H2O < H2S < H2Se < H2Te Larger the size of X (=O, S, Se, Te) weaker its bonds with hydrogen and more easily H+ gets lost in aqueous solution.
38.	Increasing order of strength of oxoacids: H2SO3, H2SeO3, H2TeO3	H2TeO3 < H2SeO3 < H2SO3 Decreasing size and increasing electronegativity from Te to S withdraws electrons from O—H bond towards itself, thus, facilitating the release of proton.
39.	Increasing order of stability of oxoacids: H2SO3, H2SeO3, H2TeO3	H2TeO3 < H2SeO3 < H2SO3
40.	Increasing order of stability of oxoacids: H2SO4, H2SeO4, H2TeO4	H2TeO4 < H2SeO4 < H2SO4
41.	Increasing order of stability of oxoacids: H2SO4, H2SeO4, H2TeO4	H2TeO4 < H2SeO4 < H2SO4
42.	Decreasing order of electron affinity: F, Cl, Br, I	Cl > F > Br > I
43.	Increasing order of reducing power: HF, HCl, HBr, HI	HF < HCl < HBr < HI
44.	Increasing order of affinity for hydrogen: F2, Cl2, Br2, I2	I2 < Br2< Cl2 < F2
45.	Increasing order of acidic strength: HF, HCl, HBr, HI	HF < HCl < HBr < HI
46.	Increasing order of boiling point: HF, HCl, HBr, HI	HCl < HBr < HI < HF Anomalous behaviour of HF is due to hydrogen bonding.
47.	Increasing order of stability: HFO3, HClO3, HBrO3, HIO3	HFO3 < HClO3 < HBrO3 < HIO3 Ions of these acids are stabilized due to strong pπ-pπ bonding between full 2p orbital on oxygen and empty orbitals on the halogen atom. Fluorine has no d orbitals and cannot form pπ-dπ bonds. Thus oxoacids of fluorine are not known
48.	Increasing order of covalent character: TiCl2, TiCl3, TiCl4	TiCl2 < TiCl3 < TiCl4 Increasing oxidation state of Ti increases charge density on the metal leading to increase in the polarization of the anionic charge cloud and thus covalency increases.
49.	Increasing order of magnetic moment: Ti3+, Ni2+, Cr2+, Co2+, Zn2+	Zn2+ < Ti3+ < Ni2+ < Co2+ < Cr2+ Increasing number of unpaired electrons increases magnetic moment. The number of unpaired electrons in the given species are as follows. Ti3+ one, Ni2+ two, Co2+ three, Cr2+ four and Zn2+ zero.
50.	Increasing order of ionic character: VCl2, VCl3, VCl4	VCl4 < VCl3 < VCl2 Decreasing oxidation state of element increases the ionic character.
51.	Increasing order of basic characteristics: Li2O, BeO, B2O3, CO2	CO2 < B2O3 < BeO < Li2O
52.	Increasing order of electronegativity: As, P, S, Cl	As < P < S < Cl
53.	Increasing order of acidic strength: HOCl, HOBr, HOI	HOI < HOBr < HOCl
54.	Increasing order of thermal stability: HF, HCl, HBr, HI	HI < HBr < HCl < HF
55.	Increasing order of bond enthalpy: N2, O2, F2, Cl2	F2 < Cl2 < O2 < N2
56.	Increasing order of melting point: CaF2, CaCl2, CaBr2, CaI2	CaI2 < CaBr2 < CaCl2 < CaF2
57.	Increasing order of oxidizing power: O, S, Se, Te	Te < Se < S < O
58.	Increasing order of oxidizing power: F, Cl, Br, I	I < Br < Cl < F
59.	Increasing order of single bond strength: N—N, O—O, F—F	N—N < O—O < F—F
60.	Increasing order of stability of hydrides: LiH, NaH, KH, CsH	CsH < KH < NaH < LiH
61.	Increasing order of pH of aqueous solution: LiCl, BeCl2, MgCl2, AlCl3	LiCl > MgCl2 > BeCl2 > AlCl3 Hydrolysis of cations depends on two factors; larger charge and smaller size favour more hydrolysis, hence more free H+ (i.e. lesser pH).
62.	Increasing order of acidic strength: Al2O3, MgO, SiO2, P4O10	MgO < Al2O3 < SiO2 < P4O10
63.	Increasing order of basicity: F–, Cl–, Br–, I–	I– < Br– < Cl– < F– Stronger the acid, weaker its conjugate base.
64.	Increasing order of basic strength: F–, OH–, NH2–, CH3–	F– < OH– < NH2– < CH3– More electronegative the atom, lesser its tendency to give a lone pair of electrons.
65.	Increasing order of thermal stability: BeCO3, MgCO3, CaCO3, BaCO3	BeCO3 < MgCO3 < CaCO3 < BaCO3 Increasing size of cation decreases its polarizing ability towards carbonate making the compound more stable.
66.	Increasing order of paramagnetism: Ca, Al, N, O	Ca < Al < O < N Paramagnetism increases with increase of number of unpaired electrons.
67.	Increasing order of ionic character: LiBr, NaBr, KBr, RbBr, CsBr	LiBr < NaBr < KBr < RbBr < CsBr The larger the difference between the electro-negativities, greater the ionic character.
68.	Increasing order of hydration energy: Be2+, Mg2+, Ca2+, Ba2+, Sr2+	Ba2+ < Sr2+ < Ca2+ < Mg2+ < Be2+ The smaller the size, more the hydration energy.
69.	Increasing order of bond angle: NH3, PH3, AsH3	AsH3 < PH3 < NH3 The increasing size and lower electronegativity of the central atom permit the bonding electrons to be drawn out further, thus decreasing repulsion between bonding pairs.
70.	Increasing order of bond angle: NF3, PF3, AsF3	AsF3 < PF3 < NF3
71.	Increasing order of bond angle: H2O, H2S, H2Se	H2Se < H2S < H2O
72.	Increasing order of bond angle: NF3, NCl3	NF3 < NCl3 The bonding pair repulsion in NF3 is less than that in NCl3.
73.	Increasing order of bond angle: NO2+, NO2, NO2–	NO2+ < NO2 < NO2– There is maximum repulsion between free electron(s) on nitrogen and bonding pairs.
74.	Increasing order of bond angle: NH3, NF3	NF3 < NH3 There is lesser repulsion in bonding pairs in NF3.

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