Periodicity-inorganic chemistry Flashcards
(17 cards)
How are elements classified into s, p, d, or f blocks?
Elements are classified into blocks based on the sub-shell (orbital) their highest-energy electron occupies:
s-block: Highest-energy electron in an s-orbital (Groups 1 & 2, plus hydrogen and helium).
p-block: Highest-energy electron in a p-orbital (Groups 13-18).
d-block: Highest-energy electron in a d-orbital (Transition metals, Groups 3-12).
f-block: Highest-energy electron in an f-orbital (Lanthanides & Actinides).
How does the proton number determine an element’s position in the periodic table?
Proton number (atomic number) determines the number of electrons in an atom.
Electrons fill orbitals in a specific order (Aufbau principle), placing elements into different blocks.
Example: Carbon (Z = 6) has an electron configuration 1s² 2s² 2p², so it is in the p-block.
How does atomic radius change across Period 3 (Na → Ar)?
Atomic radius decreases across the period because:
✔️ Increased nuclear charge (more protons).
✔️ Same shielding effect (electrons added to the same energy level).
✔️ Stronger attraction between nucleus and outer electrons, pulling them closer.
How does first ionisation energy change across Period 3?
First ionisation energy generally increases because:
Increased nuclear charge (stronger attraction between nucleus & outer electron).
Same shielding (no additional inner energy levels).
Smaller atomic radius, so electrons are held more tightly.
How does melting point change across Period 3?
Melting points vary due to different bonding types:
Metals (Na → Al): Melting point increases due to stronger metallic bonding (more delocalised electrons).
Si (Giant Covalent): Highest melting point because of strong covalent bonds in a giant lattice.
Non-metals (P → Ar): Melting point decreases as they exist as simple molecules with weak van der Waals forces.
How does atomic radius change down Group 2 (Mg → Ba)?
Increases down the group.
More electron shells, so the outer electrons are further from the nucleus.
Increased shielding weakens nuclear attraction.
Despite increased nuclear charge, the outermost electrons experience weaker attraction.
Mg < Ca < Sr < Ba (increasing atomic radius).
How does first ionisation energy change down Group 2?
Decreases down the group.
Increased atomic radius (outer electron further from nucleus).
More shielding, so weaker nuclear attraction.
Less energy needed to remove the outer electron.
How does melting point change down Group 2?
Generally decreases due to weaker metallic bonding.
Larger atomic radius = delocalised electrons further from nuclei, so weaker attraction.
Exception: Mg has an unusually low melting point due to a different crystal structure.
✅ Ca > Sr > Ba > Mg (irregular trend).
How do Group 2 metals react with water?
General equation:
M+2𝐻2O→M(OH)2+𝐻2
Mg reacts very slowly with cold water but faster with steam.
Ca, Sr, Ba react increasingly vigorously down the group, forming hydroxides and hydrogen gas.
✅ Reactivity increases down the group.
How is magnesium used to extract titanium?
Titanium (IV) chloride (TiCl₄) is reduced by Mg in an inert atmosphere:
TiCl4+2M𝑔→Ti+2𝑀𝑔𝐶l2
Magnesium acts as a reducing agent.
✅ This prevents oxygen contamination, which would make titanium brittle.
How does solubility of Group 2 hydroxides change down the group?
Increases down the group.
More dissociation into OH⁻ ions → more alkaline solution.
Mg(OH)₂ is sparingly soluble, but Ba(OH)₂ is highly soluble.
What are the uses of Mg(OH)₂ and Ca(OH)₂?
Mg(OH)₂ (Milk of Magnesia): Used as an antacid to neutralise stomach acid.
Mg(OH)2+2𝐻𝐶𝑙→MgCl2+2𝐻2𝑂
Ca(OH)₂ (Slaked Lime): Used in agriculture to neutralise acidic soil.
✅ Both act as bases and neutralise acids.
How is SO₂ removed from flue gases?
CaO or CaCO₃ reacts with SO₂ to form calcium sulfite (CaSO₃), which prevents acid rain.
Equations:
CaO+𝑆O2→CaSO3
CaSO3 +𝑆𝑂2→CaSO3+𝐶𝑂2
This process is called flue gas desulfurisation.
How does solubility of Group 2 sulfates change down the group?
Decreases down the group.
BaSO₄ is completely insoluble in water.
MgSO₄ is soluble, but BaSO₄ is insoluble.
Why is BaSO₄ used in medicine?
Barium sulfate (BaSO₄) is used as a contrast agent in X-rays.
It is insoluble and non-toxic (even though barium ions are toxic).
Barium meals help doctors see digestive organs in X-ray scans.
How does BaCl₂ test for sulfate ions?
Ba²⁺ reacts with SO₄²⁻ to form BaSO₄, a white precipitate:
Ba2++SO42-→BaSO4(𝑠)
BaSO₄ is insoluble → confirms presence of sulfate ions.
HCl or HNO₃ is added to remove CO₃²⁻ ions, which could give a false positive result.
