Which of the following three spheres represents a Ca atom, which an Sr atom, and which a Br atom?

Verified step by step guidance

1. Step 1: Identify the given atomic radii for Ca, Sr, and Br atoms.
2. Step 2: Recall the periodic trends for atomic radii. Generally, atomic radii increase down a group and decrease across a period.
3. Step 3: Compare the given radii with the typical atomic radii of Ca, Sr, and Br. Calcium (Ca) and Strontium (Sr) are in the same group (alkaline earth metals) with Sr being below Ca, so Sr should have a larger radius than Ca. Bromine (Br) is a halogen and typically has a smaller radius compared to alkaline earth metals.
4. Step 4: Match the given radii with the elements based on the periodic trends. The largest radius (260 pm) should correspond to Sr, the intermediate radius (125 pm) to Ca, and the smallest radius (70 pm) to Br.
5. Step 5: Assign the spheres based on the radii: Sphere I (260 pm) is Sr, Sphere II (70 pm) is Br, and Sphere III (125 pm) is Ca.

Key Concepts

Atomic Radius

Atomic radius is a measure of the size of an atom, typically defined as the distance from the nucleus to the outermost electron shell. It varies across the periodic table, generally increasing down a group due to the addition of electron shells and decreasing across a period due to increased nuclear charge, which pulls electrons closer to the nucleus.

Periodic Trends

Periodic trends refer to the predictable patterns observed in the properties of elements as you move across or down the periodic table. Key trends include atomic radius, ionization energy, and electronegativity, which help in understanding the behavior of elements, such as why calcium (Ca) has a larger atomic radius than bromine (Br) and strontium (Sr).

Element Identification

Identifying elements based on their atomic properties involves comparing their atomic radii, atomic mass, and other characteristics. In this context, recognizing that calcium (Ca) has a larger atomic radius than strontium (Sr) and bromine (Br) allows us to match the spheres in the image to the correct elements based on their respective sizes.