Question

Using only a periodic table as a guide, write the condensed electron configurations for the following atoms: (a) Se, (b) \(\mathrm{Rh}\), (c) \(\mathrm{Si}\), (d) \(\mathrm{Hg}\), (e) Hf.

Short answer

(a) Se: \([\mathrm{Ar}]~3d^{10} ~4s^2~4p^4\) (b) Rh: \([\mathrm{Kr}]~4d^8 ~5s^1\) (c) Si: \([\mathrm{Ne}]~3s^2~3p^2\) (d) Hg: \([\mathrm{Xe}]~4f^{14}~5d^{10}~6s^2\) (e) Hf: \([\mathrm{Xe}]~4f^{14}~5d^{2} ~6s^2\)

Step-by-step solution

(a) Selenium (Se) electron configuration

First, look for the atomic number of Se on the periodic table, which is 34. To write the condensed electron configuration, find the noble gas that comes before Se, which is Ar (with an atomic number of 18). Now describe the electron distribution from that point: \[ [\mathrm{Ar}]~3d^{10} ~4s^2~4p^4 \]

(b) Rhodium (Rh) electron configuration

For Rhodium, the atomic number is 45. The noble gas that comes before Rh is Kr (with an atomic number of 36). Now, distribute the electrons from that point: \[ [\mathrm{Kr}]~4d^8 ~5s^1 \]

(c) Silicon (Si) electron configuration

Find the atomic number for Silicon (Si) on the periodic table, which is 14. The noble gas that comes before Si is Ne (with an atomic number of 10). Distribute the electrons from that point: \[ [\mathrm{Ne}]~3s^2~3p^2 \]

(d) Mercury (Hg) electron configuration

Mercury (Hg) has an atomic number of 80. The noble gas that comes before Hg is Xe (with an atomic number of 54). Now, distribute the electrons from that point: \[ [\mathrm{Xe}]~4f^{14}~5d^{10}~6s^2 \]

(e) Hafnium (Hf) electron configuration

Finally, Hafnium (Hf) has an atomic number of 72. The noble gas before Hf is Xe (with an atomic number of 54) as well. Distribute the electrons from that point: \[ [\mathrm{Xe}]~4f^{14}~5d^{2} ~6s^2 \]

Key concepts

The Periodic Table: A Map of Elements

Imagine a map that guides you through the landscape of elements, each with its own unique characteristics and address. This 'map' is known as the periodic table and is a central tool in chemistry for understanding how elements relate to each other. Each element on the table is represented by its atomic symbol and atomic number, indicating its position in the sequence of known elements.

Elements are arranged in order of increasing atomic number, and are laid out in such a way that those with similar chemical properties form columns, also known as groups. The rows, called periods, signify the filling of different electron shells. The periodic table allows chemists to quickly glean a vast amount of information about an element, including its electron configuration, which is crucial for predicting how an element will react chemically.

Noble Gas Notation: A Shortcut to Electron Configurations

Writing out the full electron configuration for an element can be cumbersome, especially for those with a high atomic number. This is where noble gas notation comes in handy—it's a shortcut that uses the electron configuration of the nearest noble gas (elements found in the last group of the periodic table known for their stability) as a reference point.

To use this notation, you find the noble gas that comes before your element of interest in the periodic table. You then denote this noble gas in brackets followed by the remaining electron distribution. This method is effective because the noble gases have complete electron shells, which provides a 'zero point' from which to count additional valence electrons for elements that come after them in the table.

Atomic Number: Identifying Elements

Every element is defined by its atomic number, which is the number of protons present in the nucleus of an atom. This number also determines an element's position on the periodic table and is key to understanding its electron configuration. The atomic number is unique for each element and serves as an identifier much like a personal ID number.

When writing down the electron configuration of an element, the atomic number guides you to know how many electrons you're distributing among the orbitals since, in a neutral atom, the number of electrons equals the number of protons. For instance, if an element has an atomic number of 34, like Selenium (Se), it will have 34 electrons, which need to be arranged according to the rules that govern electron distribution.

Electron Distribution: Laying Out the Electrons

Electron distribution, often referred to as 'electron configuration', is the arrangement of electrons in an atom's orbitals. This arrangement follows a set of principles such as the Pauli Exclusion Principle, Hund's Rule, and the Aufbau Principle, which instruct the order at which electrons fill subatomic orbitals.

Orbitals are filled in a way that minimizes the energy of the atom. They are commonly divided into blocks on the periodic table—s, p, d, and f—which correspond to the shape of the space where you're most likely to find the electrons. The notation reflects this organization, with numbers denoting the energy level, and letters representing the orbital type followed by a superscript indicating how many electrons are in that orbital. Understanding electron distribution is vital for predicting how an element will behave in chemical reactions.