In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers \(12,19,21\) and 38 . Which of these have physical and chemical properties resembling calcium?

Group 2 elements in the Modern Periodic Table are known as the alkaline earth metals. These elements are characterized by having two electrons in their outermost shell. The most common elements in this group are Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra). Alkaline earth metals are all shiny, silvery-white metals. They are somewhat reactive at standard temperature and pressure, but less so than the alkali metals in Group 1. The reactivity increases as you move down the group because the outer electrons are more easily lost as the atomic size increases.

Some key points about Group 2 elements:

• They tend to form +2 oxidation states.
• They are all metals with a high density and melting points compared to Group 1.
• They are all good conductors of electricity and heat.
• Their reactivity with water increases from the top of the group to the bottom.

Calcium (atomic number 20), being part of Group 2, has properties that align with other members of this group. Understanding the positioning of calcium is essential to predict its behavior and identify other elements with similar properties.

The atomic number is a fundamental property of elements in the Periodic Table. It refers to the number of protons in the nucleus of an atom. The atomic number determines an element’s identity and its position in the Periodic Table. For example, calcium has an atomic number of 20, meaning every calcium atom has 20 protons.

The atomic number is crucial because:

• It defines chemical properties and behavior in reactions.
• It dictates the element's placement in the Periodic Table.
• It helps in determining the element’s structure and electron configuration.

In the given exercise, understanding the atomic numbers of the surrounding elements (12, 19, 21, and 38) helps us determine their groups and, thus, compare their properties with calcium. Elements with atomic numbers that place them in the same group as calcium, such as magnesium (12) and strontium (38), will resemble calcium's properties the most closely.

Chemical properties describe how an element reacts with other substances. For the Group 2 elements, they have specific trends based on their position in the Periodic Table. These trends in chemical properties are influenced by their electronic configuration, which impacts their reactivity.

Key chemical properties of Group 2 elements include:

• Reactivity with water: For example, calcium reacts with water to form calcium hydroxide and hydrogen gas.
• Reactivity with oxygen: They form oxides, for instance, calcium oxide (CaO).
• Formation of ionic compounds: They typically form compounds with a +2 charge, due to the loss of their two outermost electrons.

Group 2 elements generally form colorless compounds, and their solubility in water varies. For example, calcium sulfate (CaSO4) is not very soluble in water, whereas magnesium sulfate (MgSO4) is more soluble. By examining calcium's chemical properties, it's clear that it would exhibit similar behavior to other Group 2 elements like magnesium and strontium.