Question

Identify the specific element that corresponds to each of the following electron configurations and indicate the number of unpaired electrons for each: (a) \(1 s^{2} 2 s^{2},\) (b) \(1 s^{2} 2 s^{2} 2 p^{4}\), (c) \([\mathrm{Ar}] 4 s^{1} 3 d^{5}\) (d) \([\mathrm{Kr}] 5 s^{2} 4 d^{10} 5 p^{4}\).

Short answer

(a) Beryllium (Be) has 0 unpaired electrons. (b) Oxygen (O) has 2 unpaired electrons. (c) Chromium (Cr) has 6 unpaired electrons. (d) Tellurium (Te) has 2 unpaired electrons.

Step-by-step solution

Determine the total number of electrons

Count the total number of electrons in the given configuration (a) \(1s^2 2s^2\). There are 2 electrons in the first shell (1s) and 2 electrons in the second shell (2s). So, the total number of electrons is 4.

Identify the element

With 4 electrons, the element has an atomic number of 4. Using the periodic table, we can see that this corresponds to the element Beryllium (Be). #Step 2: Determine the number of unpaired electrons in configuration (a)#

Check for unpaired electrons in each subshell

Both 1s and 2s subshells are full, with no capacity for additional electrons, so there are 0 unpaired electrons in this configuration. #Step 3: Repeat the process for the electron configuration (b)#

Electron configuration (b)

Count the total electrons in the configuration (b) \(1s^2 2s^2 2p^4\). There are 2 electrons in the 1s shell/1s-subshell, 2 electrons in the 2s-subshell, and 4 electrons in the 2p-subshell. There are a total of 8 electrons, so the element corresponding to this configuration is Oxygen (O). For unpaired electrons, as 2p has 4 electrons, 2 are paired and the other 2 are unpaired. #Step 4: Repeat the process for electron configuration (c)#

Electron configuration (c)

The given configuration (c) is [\(\mathrm{Ar}\)] \(4s^1 3d^5\). As Ar (Argon) has 18 electrons, the element now has a total of 18 (Ar) + 1 (4s) + 5 (3d) = 24 electrons. The element with 24 electrons is Chromium (Cr). In this configuration, the 4s subshell has 1 unpaired electron, and the 3d subshell has 5 unpaired electrons, making a total of 6 unpaired electrons. #Step 5: Repeat the process for electron configuration (d)#

Electron configuration (d)

The given configuration (d) is [\(\mathrm{Kr}\)] \(5s^2 4d^{10} 5p^4\). As Kr (Krypton) has 36 electrons, the element now has a total of 36 (Kr) + 2 (5s) + 10 (4d) + 4 (5p) = 52 electrons. The element with 52 electrons is Tellurium (Te). In this configuration, the 5p subshell has 4 electrons, with 2 being paired and the other 2 unpaired. The rest of the subshells are full, leaving a total of 2 unpaired electrons. #Solution# Here are the results for each electron configuration: (a) Element: Beryllium (Be) - Unpaired electrons: 0 (b) Element: Oxygen (O) - Unpaired electrons: 2 (c) Element: Chromium (Cr) - Unpaired electrons: 6 (d) Element: Tellurium (Te) - Unpaired electrons: 2

Key concepts

Atomic Number

In chemistry, the atomic number is a fundamental property of an element. It represents the number of protons in the nucleus of an atom. Each element on the periodic table has a unique atomic number, making it its DNA. For instance, hydrogen has an atomic number of 1 because it has one proton in its nucleus, while helium has two protons, giving it the atomic number 2.
Knowing the atomic number is vital because it helps in identifying elements through their electron configurations. The number of electrons in a neutral atom is equal to the atomic number. For example, helium, with an atomic number of 2, also has two electrons.

• This property allows chemists to quickly relate electron configurations, like the ones seen in the earlier exercise, to specific elements.
• For example, with an atomic number of 4, Beryllium has an electron configuration of \(1s^2 2s^2\).
• By understanding atomic numbers, we can also interpret the position of elements on the periodic table, providing insights into their chemical behavior and properties.

Unpaired Electrons

Unpaired electrons are an essential concept in understanding chemical reactivity and bonding. Electrons occupy orbitals, and each orbital can hold a maximum of two electrons which must have opposite spins. When an electron is single in an orbital and has no pair, it is termed as an "unpaired electron." These unpaired electrons are significant because:

• They contribute to the magnetic properties of an element. Elements with unpaired electrons tend to be paramagnetic, meaning they are attracted to magnetic fields.
• They often participate in chemical reactions, making elements more reactive. For example, in the electron configuration of Oxygen, \(1s^2 2s^2 2p^4\), the two unpaired electrons make oxygen highly reactive, forming bonds easily.
• Understanding the number of unpaired electrons helps predict the kind of bonds an atom can form, whether covalent or ionic, and the resulting molecular geometry.

Identifying unpaired electrons in an electron configuration allows us to deduce the chemical properties and interaction potential of an element.

Periodic Table Elements

The periodic table is a systematic layout of all known chemical elements. It organizes elements based on their atomic number, electron configurations, and recurring chemical properties. Understanding the periodic table is crucial for studying chemistry as it helps clarify the behavior of elements and their relation to one another.
Each row on the periodic table is called a period, and each column is known as a group. Elements within the same group often have similar chemical properties due to having the same number of valence electrons. For example:

• Group 1 elements, like Lithium (Li) and Sodium (Na), are highly reactive metals known as alkali metals and are keen to lose their single valence electron.
• In contrast, Group 18 elements, known as noble gases, have complete valence shells, making them inert.

Moreover, elements are classified into several blocks based on their electron configurations—the s-block, p-block, d-block, and f-block—each signifying a different type of orbital being filled. Chromium (Cr), with an electron configuration of \[\mathrm{Ar}] 4s^1 3d^5\], lies in the d-block, known for its transition metals which typically have incompletely filled d orbitals, contributing to their unique properties like varied oxidation states.
Thus, recognizing how elements are arranged in the periodic table allows us to hypothesize their chemical behaviors accurately.