Question

Write the complete electron configurations for atoms of the following elements. (a) \(\mathrm{Sc}\) (b) \(\mathrm{As}\) (c) \(\mathrm{Ba}\)

Short answer

The electron configurations are: Sc - \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1\), As - \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3\), Ba - \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2\).

Step-by-step solution

Identify atomic numbers

Find the atomic numbers of Sc, As, and Ba on the periodic table. The atomic numbers are: Sc - 21, As - 33, Ba - 56.

Write electron configuration for Sc

Sc has 21 electrons. Based on the energy levels and sublevels in order, the electron configuration is: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1\]

Write electron configuration for As

As has 33 electrons. The electron configuration is \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3\]

Write electron configuration for Ba

Ba has 56 electrons. So, the electron configuration is \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2\]

Verify electron count

Count the superscript totals for each electron configuration. They should equal the atomic numbers: Sc - 21, As - 33, Ba - 56.

Key concepts

Atomic Numbers

The concept of atomic numbers is fundamental in the world of chemistry and physics. An atomic number represents the number of protons found in the nucleus of an atom. Since atoms are electrically neutral, the atomic number also equals the number of electrons around the nucleus. This unique number identifies an element and determines its position on the periodic table.

To locate an atom's atomic number, simply check the periodic table, which lists elements in order of increasing atomic numbers. For example, scandium (Sc) has an atomic number of 21, arsenic (As) has an atomic number of 33, and barium (Ba) is 56. These numbers are crucial as they guide us in determining the electron configuration of an element. Understanding atomic numbers lets chemists and students predict an element's chemical behavior and energetics.

Periodic Table

The periodic table is an organized chart of all known chemical elements. It is designed in a structured manner based on increasing atomic number and recurring chemical properties. Periods are horizontal rows, while groups are vertical columns, which make it easy to decipher the elemental properties.

• Elements in the same group have similar properties due to their valence electrons.
• Periods represent the number of energy levels in an atom's electron configuration.

Understanding the periodic table helps us locate elements and deduce their properties and electronic structure. For instance, scandium (Sc) lies in Group 3 and Period 4, indicating that it has electrons in four energy levels. Arsenic (As), being in Period 4 as well, suggests a comparable number of electron shells, although its chemical behavior differs due to its placement in Group 15. Barium (Ba) is in Group 2 and Period 6, highlighting its characteristic as an alkaline earth metal with a fuller range of energy levels.

Energy Levels

In atomic physics and chemistry, energy levels define the regions where electrons exist around the nucleus. Each atom has several discrete energy levels (or shells), which can be filled with electrons following specific rules and principles.

• Each level holds a specified number of electrons: 2 in the first shell, 8 in the second, 18 in the third, and so on.
• Within these levels, electrons further distribute into sublevels (s, p, d, f), forming the basis of electron configurations.

The sequential order of filling these energy levels determines the electron configuration of an atom and thus its chemical properties. Scandium (Sc), for instance, fills up to the 3d sublevel, whereas arsenic (As) has its highest electrons in the 4p sublevel. For barium (Ba), its electrons extend to the 6s sublevel. By grasping the concept of energy levels, students can decode each element's electron arrangement, predict its reactivity, and understand its embedding within the periodic table.