Question

Use the periodic table to determine each quantity. $$\begin{array}{l}{\text { a. the number of } 2 \text {s electrons in Li }} \\\ {\text { b. the number of 3} d \text { electrons in } \mathrm{Cu}} \\\ {\text { c. the number of } 4 p \text { electrons in } \mathrm{Br}} \\ {\text { d. the number of } 4 d \text { electrons in } Z \mathrm{r}}\end{array}$$

Short answer

a. 1 b. 10 c. 5 d. 2

Step-by-step solution

Determine the Number of 2s Electrons in Li

Look at the periodic table and find the element Lithium (Li). Lithium has an atomic number of 3, which means it has 3 protons and typically 3 electrons in a neutral atom. Its electron configuration is 1s^2 2s^1. The superscript in 2s^1 indicates that there is 1 electron in the 2s subshell.

Determine the Number of 3d Electrons in Cu

Locate Copper (Cu) on the periodic table which is in the d-block of period 4 and group 11. Copper has an atomic number of 29. The electron configuration ends with 3d^10. The superscript in 3d^10 indicates that there are 10 electrons in the 3d subshell.

Determine the Number of 4p Electrons in Br

Find Bromine (Br) on the periodic table in group 17 and period 4. Bromine has an atomic number of 35. The electron configuration ends with 4p^5. The superscript in 4p^5 indicates that there are 5 electrons in the 4p subshell.

Determine the Number of 4d Electrons in Zr

Zirconium (Zr) is located in group 4 and period 5 of the periodic table. Zirconium has an atomic number of 40. The electron configuration ends with 4d^2. The superscript in 4d^2 indicates that there are 2 electrons in the 4d subshell.

Key concepts

Understanding the Periodic Table

The periodic table is the cornerstone of chemistry, where elements are organized according to their atomic number, chemical properties, and electronic configurations. Elements are arranged in rows called periods and columns known as groups.

Let's look at Lithium (Li), as mentioned in our exercise, which resides in the second row (period 2) and first column (group 1). The position of an element provides valuable information about its electron configuration. For instance, Lithium's placement indicates it has electrons in the first and second energy levels. As we explore this organized array, remember that each period correlates to the energy level of electrons, starting with 1 at the top and increasing as you move down.

The groups are indicative of the number of valence electrons, which are crucial for bonding, and they help in predicting an element's reactivity. For example, group 18 contains noble gases, which are known for their stability and lack of reactivity due to having a full valence shell.

Deciphering Subshell Electrons

Electrons within an atom occupy specific energy levels, which are further divided into subshells designated as s, p, d, and f. The first two subshells, 's' and 'p,' are found in the main-block elements, while 'd' and 'f' subshells are characteristic of the transition and inner transition elements.

The case of Copper (Cu) provides an excellent demonstration of this concept, with its electron configuration concluding in 3d^10. Each subshell type (s, p, d, f) has a fixed capacity of electrons it can hold: s can hold 2, p can hold 6, d can hold 10, and f can hold 14.

The superscript notation, like the '10' in Cu's 3d^10, tells us exactly how many electrons are present in that specific subshell. Recognizing subshell capacity is key to understanding an element's chemical characteristics, as the arrangement of electrons affects bonding and chemical reactions.

Atomic Number Significance

The atomic number is a fundamental identifier for an element and is always located above the element symbol in the periodic table. It represents the number of protons found in the nucleus of an atom, and in a neutral atom, it also equals the number of electrons surrounding the nucleus.

The atomic number is paramount when determining an element's electron configuration. As we have seen with Bromine (Br), an atomic number of 35 means there are 35 electrons to be distributed across the various energy levels and subshells in a pattern that follows specific rules. These rules, such as the Aufbau principle, Hund's rule, and the Pauli exclusion principle, guide the orderly filling of subshells.

So, the atomic number does more than just count protons; it steers us through the complex process of figuring out where electrons are within an atom. The understanding of atomic number eases the journey through the periodic landscape, ensuring learners know exactly where each unique atomic voyage begins.