Periodic Table Trends: Differences in Element Properties

Alkali Metals

Lithium

• Lithium is harder than other alkali metals.
• It has higher melting and boiling points than other alkali metals.
• It is the least reactive alkali metal.
• It is a strong reducing agent compared to other alkali metals.
• It is the only alkali metal that forms its monoxide.
• It is not capable of forming solid hydrogen carbonates, unlike other alkali metals.
• It does not react with ethyne to form ethynide, while other alkali metals do.
• It reacts slowly with bromine compared to other alkali metals.
• It is the only alkali metal that reacts with nitrogen to give lithium nitride (Li₃N).

Alkaline Earth Metals

Beryllium

• Beryllium is harder than other members of its group.
• It has higher melting and boiling points than other members of its group.
• Its electronegativity (1.5) is higher than that of any other element in the family.
• It does not react with water at high temperatures, while other alkaline earth metals do (Mg + H₂O = MgO + O₂).
• It forms covalent compounds, whereas other members form ionic compounds.
• Carbides of beryllium are covalent, whereas carbides of other members are ionic.

Carbon Group

Carbon vs. Silicon

Carbon and silicon, the first two elements of this group, share a number of properties due to their similar electron configurations. They form similar hydrides, halides, oxides, and oxyacids. However, some important differences exist:

• Atomic Size: Carbon atoms are much smaller than silicon atoms.
• d Orbitals: Carbon lacks d orbitals.
• Catenation: Carbon has a high capacity for catenation.

Other key differences:

• Carbon is harder and has higher melting and boiling points than silicon.
• Graphite (a form of carbon) is a good conductor of electricity, while silicon is a poor conductor.
• Carbon can form pi bonds with oxygen involving p orbitals due to its small size, while silicon cannot.
• Carbon forms thousands of compounds due to its high capacity for catenation, while silicon has a limited number of compounds.
• Carbon is an essential constituent of living organisms, while silicon is found in non-living materials like rocks and soil.

Halogens

Fluorine

• Fluorine is the most electronegative element and exhibits only a negative oxidation state of -1.
• It is the most reactive halogen.
• Due to its high electronegativity, fluorine extensively forms hydrogen bonds in its hydrides.
• The maximum covalency of fluorine is one.
• Most fluorides are ionic.
• It has a strong tendency to form complex ions like [AlF₆]^3- and [FeF₆]^3-.

Oxygen Group

Oxygen

• Oxygen is a gas, while other members (sulfur, selenium, tellurium, polonium) are solids.
• Oxygen is diatomic (O₂), while others have complex molecular structures.
• Oxygen is non-metallic due to its high electronegativity. Selenium and tellurium are weak non-metals, and polonium is a metal.
• Oxygen is more ionic in its compounds than the other members due to its high electronegativity.
• Oxygen exhibits an oxidation state of -2, except in OF₂ where it is +2.
• Oxygen extensively forms hydrogen bonds due to its high electronegativity.
• The oxygen molecule is highly stable.
• The maximum covalency of oxygen is two.

Boron Group

Boron

• Boron is closer to non-metals, whereas other members are metallic.
• It consistently shows a +3 oxidation state in its compounds, while other elements show +1 and +3.
• Boron generally forms covalent compounds, while others also form electrovalent compounds.
• Trihalides of boron exist as monomers, while those of aluminum exist as dimers.
• Boron is not attacked by hydrochloric acid, while aluminum dissolves in it, evolving hydrogen.
• Oxides and hydroxides of boron are acidic, while higher members have basic oxides and hydroxides.
• Boron has no d-orbital and exhibits a maximum covalency of four, while other elements can exhibit covalency of six or more.

Nitrogen Group

Nitrogen

• Nitrogen is a gas, while other members (phosphorus, arsenic, antimony, bismuth) are solids.
• Nitrogen is diatomic (N₂) with a strong triple bond.
• Nitrogen is non-metallic due to its high electronegativity, while arsenic and antimony are metalloids, and bismuth is a metal.
• Nitrogen exhibits a large number of oxidation states (+1, +2, +3, +4, -1, -2, -3), while other elements do not.
• The hydride of nitrogen (NH₃) is stable, while hydrides of other elements are not.
• Nitrogen forms various oxides (N₂O, NO, N₂O₃, N₂O₄, N₂O₅), while others do not exhibit such a variety.