Question

Group IIA metals are (1) harder and have high cohesive energies and melting points than group I metals (2) softer and have lower cohesive energies and melting points than group I metals (3) softer and have lower cohesive energies and higher melting points than group I metals (4) harder and have higher cohesive energies and lower melting points than group I metals

Short answer

Option (1)

Step-by-step solution

Identify Characteristics of Group IIA Metals

Group IIA metals, also known as alkaline earth metals, include elements like beryllium, magnesium, calcium, strontium, barium, and radium. They generally have two valence electrons and are harder than Group I metals.

Compare Hardness

Group IIA metals are typically harder than Group I metals (alkali metals), which include lithium, sodium, potassium, rubidium, cesium, and francium.

Compare Cohesive Energies

Cohesive energy refers to the energy required to break bonds between atoms in the solid state. Group IIA metals have higher cohesive energies compared to Group I metals because their atoms are more tightly bonded.

Compare Melting Points

Group IIA metals also generally have higher melting points than Group I metals due to stronger metallic bonds.

Analyze the Options

Given the characteristics observed: (1) Group IIA metals are harder, (2) they have higher cohesive energies, and (3) they have higher melting points than Group I metals.

Select the Correct Option

With these characteristics, the accurate statement is: (1) harder and have high cohesive energies and melting points than group I metals.

Key concepts

alkaline earth metals

Group IIA metals are also known as alkaline earth metals. This group includes six elements: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These elements are found in the second column of the periodic table and typically have two valence electrons.

Alkaline earth metals are characterized by their silver luster and high reactivity, although they are not as reactive as the Group I metals (alkali metals).

These metals also have a higher density and are harder compared to the alkali metals. They play significant roles in various chemical and biological processes. For example, calcium is essential for bone formation, while magnesium is a crucial component in the process of photosynthesis.

cohesive energy

Cohesive energy refers to the amount of energy required to break the bonds that hold a solid together. In simpler terms, it's the energy needed to separate atoms in a solid to the point where they become individual, isolated atoms.

For metals, cohesive energy is a crucial property that affects their hardness and melting point. Group IIA metals have relatively high cohesive energies compared to Group I metals (alkali metals).

This higher cohesive energy is due to their stronger metallic bonds, which are caused by their smaller atomic radius and the presence of two valence electrons. These tightly bonded atoms make the alkaline earth metals more stable and harder compared to alkali metals. This is why Group IIA metals generally require more energy to break these bonds, resulting in higher cohesive energy.

melting points

Melting points of metals are influenced by the strength of the bonds between their atoms. Group IIA metals have higher melting points compared to Group I metals. This is due to their stronger metallic bonds, which need more energy to break.

The stronger bonds in Group IIA metals are a result of their increased number of valence electrons and smaller atomic size. For example:

• Beryllium has a melting point of 1287°C
• Magnesium melts at 650°C
• Calcium melts at 842°C

These melting points are significantly higher than those of Group I metals, such as lithium (180.5°C) and sodium (98°C). Hence, when you compare the melting points, it's evident that Group IIA metals need more heat to transition from a solid to a liquid state.

chemical properties comparison

When comparing the chemical properties of Group IIA metals (alkaline earth metals) with Group I metals (alkali metals), several differences arise:

• Reactivity: Alkaline earth metals are generally less reactive than alkali metals. This is because their higher ionization energies make it harder for them to lose electrons.
• Valence Electrons: Group IIA metals have two valence electrons, whereas Group I metals have just one. This difference influences their bonding and reactivity.
• Compounds Formation: Group IIA metals tend to form divalent cations (e.g., Ca^2+), while Group I metals form monovalent cations (e.g., Na+).
• Oxides and Hydroxides: Alkaline earth metals form less soluble oxides and hydroxides compared to alkali metals, which form very soluble compounds.

These distinctions in chemical properties arise from their differences in electron configuration and bond strength, making each group unique in their behavior and applications.