Look at the relative positions of each pair of atoms listed here in the periodic table. How many core electrons does each have? How many valence electrons does each have?
c. nitrogen and phosphorus
d. magnesium and calcium

Verified step by step guidance

1. Step 1: Recall the periodic table structure. Elements are arranged in periods (rows) and groups (columns). Core electrons are the inner electrons that are not involved in bonding, while valence electrons are the outermost electrons in the highest energy level.
2. Step 2: For nitrogen (N), locate it in Group 15 (or Group 5A) and Period 2. Nitrogen has an atomic number of 7, meaning it has 7 electrons. Its electron configuration is 1s² 2s² 2p³. The core electrons are those in the 1s orbital (2 electrons), and the valence electrons are in the 2s and 2p orbitals (5 electrons).
3. Step 3: For phosphorus (P), locate it in Group 15 (or Group 5A) and Period 3. Phosphorus has an atomic number of 15, meaning it has 15 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p³. The core electrons are those in the 1s, 2s, and 2p orbitals (10 electrons), and the valence electrons are in the 3s and 3p orbitals (5 electrons).
4. Step 4: For magnesium (Mg), locate it in Group 2 (or Group 2A) and Period 3. Magnesium has an atomic number of 12, meaning it has 12 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s². The core electrons are those in the 1s, 2s, and 2p orbitals (10 electrons), and the valence electrons are in the 3s orbital (2 electrons).
5. Step 5: For calcium (Ca), locate it in Group 2 (or Group 2A) and Period 4. Calcium has an atomic number of 20, meaning it has 20 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². The core electrons are those in the 1s, 2s, 2p, 3s, and 3p orbitals (18 electrons), and the valence electrons are in the 4s orbital (2 electrons).

Key Concepts

Core Electrons

Core electrons are the electrons that are located in the inner shells of an atom, which are not involved in chemical bonding. These electrons are typically closer to the nucleus and are shielded from the effects of external electric fields. The number of core electrons can be determined by subtracting the number of valence electrons from the total number of electrons in an atom.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom and are crucial for determining how an atom interacts with others during chemical reactions. The number of valence electrons influences an element's reactivity, bonding behavior, and overall chemical properties. For main group elements, the number of valence electrons corresponds to the group number in the periodic table.

Periodic Table Trends

The periodic table organizes elements based on their atomic number and electron configuration, revealing trends in properties such as electronegativity, ionization energy, and atomic size. As you move down a group, core electrons increase, while valence electrons remain in the same shell, affecting the chemical behavior of elements. Understanding these trends is essential for predicting how different elements, like nitrogen and phosphorus or magnesium and calcium, will interact.