Question

For each of the following, give an atom and its complete electron configuration that would be expected to have the indicated number of valence electrons. a. two b. four c. six d. eight

Short answer

a. Beryllium (Be): \(1s^2 2s^2\) b. Carbon (C): \(1s^2 2s^2 2p^2\) c. Oxygen (O): \(1s^2 2s^2 2p^4\) d. Neon (Ne): \(1s^2 2s^2 2p^6\)

Step-by-step solution

a. Two valence electrons.

An element with 2 valence electrons belongs to Group 2 (or IIA) of the periodic table. Let's consider Beryllium (Be) for this case. Beryllium has an atomic number of 4, which means it has 4 electrons. The electron configuration of Beryllium is: \(1s^2 2s^2\) Since the outermost energy level is the second energy level (n=2), the valence electron number is the total number of electrons in the second energy level, which is 2.

b. Four valence electrons.

An element with 4 valence electrons belongs to Group 14 (or IVA) of the periodic table. Let's consider Carbon (C) for this case. Carbon has an atomic number of 6, which means it has 6 electrons. The electron configuration of Carbon is: \(1s^2 2s^2 2p^2\) Since the outermost energy level is the second energy level (n=2), the valence electron number is the total number of electrons in the second energy level, which is 2 (from 2s) + 2 (from 2p) = 4.

c. Six valence electrons.

An element with 6 valence electrons belongs to Group 16 (or VIA) of the periodic table. Let's consider Oxygen (O) for this case. Oxygen has an atomic number of 8, which means it has 8 electrons. The electron configuration of Oxygen is: \(1s^2 2s^2 2p^4\) Since the outermost energy level is the second energy level (n=2), the valence electron number is the total number of electrons in the second energy level, which is 2 (from 2s) + 4 (from 2p) = 6.

d. Eight valence electrons.

An element with 8 valence electrons belongs to Group 18 (or VIIIA) of the periodic table. Let's consider Neon (Ne) for this case. Neon has an atomic number of 10, which means it has 10 electrons. The electron configuration of Neon is: \(1s^2 2s^2 2p^6\) Since the outermost energy level is the second energy level (n=2), the valence electron number is the total number of electrons in the second energy level, which is 2 (from 2s) + 6 (from 2p) = 8.

Key concepts

Electron Configuration

Understanding electron configuration is essential in determining how atoms interact and bond with each other. The electron configuration is a description of the distribution of an atom's electrons in atomic orbitals. Electrons occupy orbitals starting from the lowest energy level, moving towards the higher levels, following specific rules such as the Aufbau principle, Hund's rule, and the Pauli exclusion principle.

For example, carbon (C), with an atomic number of 6, has an electron configuration of 1s^2 2s^2 2p^2. This notation indicates that carbon has two electrons in its lowest energy level, the 1s orbital, and four electrons in the second energy level, shared between the 2s and 2p orbitals. The concept of orbital filling orders, such as 1s before 2s, and within the p orbitals, is also pivotal. Knowing these configurations is crucial as the outermost electrons, known as valence electrons, determine the chemical properties of the element.

Periodic Table Groups

The periodic table is organized in a way that enables us to predict the properties of elements, including their valence electrons. Elements are arranged into 18 vertical columns known as groups or families. Each group contains elements with similar chemical behaviors. The group number for main-group elements (except helium) is usually the same as the number of valence electrons.

For instance, Group 2 elements, such as beryllium (Be), have two valence electrons, as reflected in its electron configuration 1s^2 2s^2. Conversely, Group 14 elements like carbon have four valence electrons, as seen in carbon's configuration. This uniformity in valence electrons within a group is the reason for the similarities in chemical properties among elements that are part of the same group.

Atomic Number

The atomic number is a fundamental characteristic of an element, denoting the number of protons found in the nucleus of an atom. This number also indicates the number of electrons in a neutral atom, which are equal to the number of protons. The atomic number determines an element's position on the periodic table and its chemical properties.

When we consider an element such as oxygen (O), with an atomic number of 8, we know immediately that it has eight protons and, in a neutral state, eight electrons. The distribution of these electrons can be represented by their electron configuration, 1s^2 2s^2 2p^4, which also informs us that oxygen has six valence electrons. Hence, the atomic number is not only an identifier but also a bridge to understanding an element's reactivity based on its valence electrons.