Question

Identify the elements that have the following electron arrangements: $$ \begin{array}{lllll} & \multicolumn{3}{c} {\text { Energy Level }} \\ \cline { 2 - 5 } & \mathbf{1} & \mathbf{2} & \mathbf{3} & \mathbf{4} \\ \mathbf{a .} & 2 & 5 & & \\ \mathbf{b .} & 2 & 8 & 6 & \\ \text { c. } & 2 & 4 & & \\ \text { d. } & 2 & 8 & 8 & 1 \\ \text { e. } & 2 & 8 & 3 & \end{array} $$

Short answer

a. N; b. S; c. C; d. K; e. Al

Step-by-step solution

Title - Identify electron arrangement pattern

Each electron arrangement given corresponds to energy levels (shells) of atoms. Identify the total number of electrons by summing electrons in each energy level for all cases.

Title - Calculate total electrons

For each element's electron arrangement, calculate the total number of electrons by adding the numbers in each energy level: (a) 2 + 5 = 7 (b) 2 + 8 + 6 = 16 (c) 2 + 4 = 6 (d) 2 + 8 + 8 + 1 = 19 (e) 2 + 8 + 3 = 13

Title - Match total electrons to atomic number

Each total corresponds to an atomic number on the Periodic Table. Match the calculated totals to their respective elements: (a) 7 electrons - Nitrogen (N) (b) 16 electrons - Sulfur (S) (c) 6 electrons - Carbon (C) (d) 19 electrons - Potassium (K) (e) 13 electrons - Aluminum (Al)

Key concepts

atomic number

The atomic number of an element is a crucial concept in chemistry. It represents the number of protons found in the nucleus of an atom. Each element on the periodic table has a unique atomic number, which also determines the element's identity.
For example:

• Hydrogen has an atomic number of 1.
• Oxygen has an atomic number of 8.

The atomic number also equals the number of electrons in a neutral atom. This helps in defining the electron configuration of the element, further linking it to its chemical properties.

energy levels

Energy levels, also known as electron shells, are specific areas around the nucleus of an atom where electrons are likely to be found. These levels are designated by numbers (n=1, n=2, etc.) and can hold a maximum number of electrons.
Key points to remember:

• The first energy level (n=1) can hold up to 2 electrons.
• The second energy level (n=2) can hold up to 8 electrons.
• The third energy level (n=3) can hold up to 18 electrons.

Energy levels are filled from the innermost level (closest to the nucleus) outwards. The arrangement of these electrons across different energy levels dictates the atom’s electron configuration.

periodic table

The periodic table is a comprehensive chart that organizes all known elements based on their atomic number, electron configurations, and recurring chemical properties. Each element in the table is positioned in a specific place that provides information about its characteristics:

• Elements in the same column (group) have similar properties.
• Elements in the same row (period) have the same number of energy levels.

For example, elements in Group 1, like sodium and potassium, have similar reactive properties because they have one electron in their outermost energy level. The periodic table not only helps in identifying an element but also in predicting its behavior and reactivity.

electron configuration

Electron configuration describes the arrangement of electrons in an atom's energy levels, sublevels, and orbitals. It follows specific rules:

• Aufbau Principle: Electrons fill lower energy orbitals first.
• Pauli Exclusion Principle: Each orbital holds a maximum of 2 electrons with opposite spins.
• Hund’s Rule: Electron will fill degenerate (equal energy) orbitals singly before pairing up.

For instance:
Nitrogen (Atomic number 7) has an electron configuration of 1s² 2s² 2p³, indicating 2 electrons in the first energy level and 5 in the second level. Understanding electron configurations helps in predicting chemical bonding and molecule formation.