Question

Bohr solved the potassium problem by putting its last electron where? How did he justify this?

Short answer

Bohr placed the last electron of potassium in the fourth energy level, represented by the electron configuration K(2, 8, 8, 1). He justified this by stating that the first three energy levels are filled to their "stable" capacities (2 in the first, 8 in the second, and 8 in the third) and the electron occupies the next available energy level. This is consistent with the observed chemical properties and reactivities of potassium, which behave similarly to elements with one electron in their outermost shells, like sodium and lithium.

Step-by-step solution

Identify the potassium atom configuration

Potassium has an atomic number of 19, which means it has 19 electrons. According to Bohr's theory, electrons are arranged in discrete energy levels around the nucleus. The electron configuration for potassium can be written as K(2, 8, 8, 1) to represent the distribution of electrons in energy levels (shells).

Bohr's placement of potassium's last electron

Bohr placed the last (19th) electron of potassium in the fourth energy level (shell). This arrangement is represented by the electron configuration K(2, 8, 8, 1).

Justification using Bohr's theory

Bohr justified the placement of potassium's last electron in the fourth energy level based on his theory of electrons occupying discrete energy levels with increasing energy. The first energy level (closest to the nucleus) can hold a maximum of 2 electrons, the second can hold up to 8 electrons, and the third can hold up to 18 electrons. However, the third energy level is considered "stable" when it holds 8 electrons, which is the case for elements in the first three periods of the periodic table. In the case of potassium, the first three energy levels are filled to their "stable" capacities: 2 electrons in the first level, 8 electrons in the second, and 8 electrons in the third. This leaves the 19th electron with no room in these lower energy levels. Therefore, according to Bohr's theory, the electron occupies the next available energy level, which is the fourth energy level. Bohr's justification is in line with the observed chemical properties and reactivities of potassium, as it behaves similarly to other elements with one electron in their outermost shells, like sodium and lithium.

Key concepts

Electron Configuration

The electron configuration of an atom is a critical concept in understanding the chemical behavior of elements. It represents the arrangement of electrons in orbital shells around an atom's nucleus. These configurations follow a set of rules, beginning with the Pauli Exclusion Principle, which states that no two electrons can have the same set of quantum numbers, implying unique positions for every electron. Additionally, Hund's Rule guides us that electrons will fill empty orbitals in a subshell before pairing up.

For potassium, with an atomic number of 19, the electron configuration is 2-8-8-1. This notation demonstrates that the first shell contains 2 electrons, the second shell 8, the third shell another 8, and the one remaining electron goes into the fourth shell. This arrangement, especially the single electron in the last shell, plays a crucial role in the chemical reactivity of the element.

Energy Levels

Energy levels, or shells, are like the layers of an onion, encompassing the nucleus of an atom. Electrons reside in these levels, and each shell can only accommodate a fixed number of electrons. The shells are arranged concentrically around the nucleus, and the capacity of each shell increases with its distance from the nucleus.

For instance, the first energy level can hold up to 2 electrons, while the second can hold up to 8. These shells are filled sequentially, respecting the Aufbau Principle which states that electrons fill lower energy levels before the higher ones. As electrons move to higher energy levels, they gain energy. Thus, the last electron of potassium is in the fourth shell, a higher energy state compared to the filled first three shells.

Atomic Number

The atomic number, a fundamental identifier for elements, is equal to the number of protons in the nucleus of an atom. Since atoms are electrically neutral, this number also reflects the number of electrons in a neutral atom. The atomic number is integral to the organization of the periodic table, with elements ordered increasing atomic numbers.

In Bohr's explanation of potassium's electron configuration, the atomic number 19 means there are 19 electrons to be placed in energy levels. Knowledge of atomic number is crucial for determining the electron configuration and understanding the reactions between elements based on their placements in the periodic table.

Periodic Table

The periodic table is a systematic arrangement of the chemical elements, positioned by increasing atomic number. The layout reveals patterns that correlate with a range of element properties, predicting how they will behave chemically and physically. Elements in the same column (group) typically have similar properties and share the same number of electrons in their outermost shell, affecting their reactivity.

Knowing where potassium stands on the periodic table (Group 1, Period 4) explains its chemical behavior stemming from its electron configuration. Thus, the periodic table is not merely a collection of element information, it is a map of atomic behavior, guiding us through the relationships and characteristics of every element.