Question

Use the periodic table to determine each quantity. a. the number of \(2 s\) electrons in Li b. the number of \(3 d\) electrons in Cu c. the number of \(4 p\) electrons in Br d. the number of \(4 d\) electrons in \(\mathrm{Zr}\)

Short answer

The number of 2s electrons in Li is 1, the number of 3d electrons in Cu is 10, the number of 4p electrons in Br is 5, and the number of 4d electrons in Zr is 2.

Step-by-step solution

Identify the Electron Configuration of Lithium

First, locate Lithium (Li) on the periodic table. It has an atomic number of 3, which means it has 3 electrons. The electron configuration for Li is '1s^2 2s^1'. This configuration shows that lithium has one electron in its 2s orbital.

Determine the Number of 2s Electrons in Lithium

In the given electron configuration of Li '1s^2 2s^1', we can observe that there is 1 electron in the 2s orbital. Therefore, the number of 2s electrons in lithium is 1.

Identify the Electron Configuration of Copper

Copper (Cu) is located in the 4th period and in the 'd' block of the periodic table. Its atomic number is 29. The electron configuration of Cu is notably written as ' [Ar] 3d^{10} 4s^{1}' after accounting for electron correlation effects in more advanced treatments, this is because one electron from the 4s orbital is promoted to the 3d orbital to provide extra stability.

Determine the Number of 3d Electrons in Copper

Based on the electron configuration of Cu, '[Ar] 3d^{10} 4s^{1}', we can see that there are 10 electrons in the 3d orbital. Thus, the number of 3d electrons in copper is 10.

Identify the Electron Configuration of Bromine

Bromine (Br) has an atomic number of 35, which means it has 35 electrons. The electron configuration is '[Ar] 3d^{10} 4s^{2} 4p^{5}'. This shows that bromine has electrons in the 4p orbital.

Determine the Number of 4p Electrons in Bromine

From the electron configuration of Br, '[Ar] 3d^{10} 4s^{2} 4p^{5}', it's evident that there are 5 electrons in the 4p orbital. Thereby, the number of 4p electrons in bromine is 5.

Identify the Electron Configuration of Zirconium

For zirconium (Zr) with an atomic number of 40, the electron configuration is '[Kr] 4d^{2} 5s^{2}'. Zirconium has electrons in the 4d orbital.

Determine the Number of 4d Electrons in Zirconium

According to Zr's electron configuration, '[Kr] 4d^{2} 5s^{2}', there are 2 electrons in the 4d orbital. Consequently, the number of 4d electrons in zirconium is 2.

Key concepts

Periodic Table

The periodic table is an essential tool for understanding the properties of elements and how they interact with one another. Organized by atomic number, elements are arranged into rows called periods and columns known as groups or families.

Each element on the periodic table is represented by its chemical symbol, atomic number, and, often, its atomic mass. The atomic number, which defines the identity of the element, corresponds to the number of protons in the nucleus and also the number of electrons in a neutral atom. Understanding the layout of the periodic table helps us predict the chemical behavior of an element, including its electron configuration.

The periodic table is also divided into blocks according to the outer electron orbital type being filled—s, p, d, or f. Elements with their highest energy electrons in an s orbital are found in the s-block, for example. The periods indicate the highest energy level of the electron orbitals that are being filled for an element's ground state. For instance, elements in the second period have electrons filling the 2s and 2p orbitals.

Atomic Number

The atomic number of an element is a fundamental characteristic that defines the type of atom. It is equal to the number of protons found in the nucleus of an atom, which also equals the number of electrons in an uncharged (neutral) atom. Hence, it provides a key to the element's position on the periodic table and its electron configuration.

For example, lithium (Li) has an atomic number of 3, thus it will have 3 protons in its nucleus and, in its neutral form, 3 electrons orbiting the nucleus. The atomic number tells us that the first two electrons will fill the 1s orbital, and the remaining one will be in the 2s orbital, as in the electron configuration '1s^2 2s^1'. Understanding atomic numbers is vital when predicting how an element will react and which types of bonds it may form.

Electron Orbitals

Electron orbitals are specific regions around an atom’s nucleus where electrons are most likely to be found. Each orbital can hold a maximum number of two electrons. Orbitals come in various shapes (s, p, d, and f) and are organized by energy levels.

An 's' orbital is spherical and found in all energy levels, starting from 1s. A 'p' orbital is dumbbell-shaped and available beginning at the second energy level (2p). 'd' orbitals, which have a more complex shape, appear in the third energy level and beyond (3d, 4d, etc), while 'f' orbitals, which are even more complex, start at the fourth energy level (4f).

Electrons fill the lowest available energy levels first, following the Pauli exclusion principle and Hund's rule. These principles help us to determine the electron configuration for elements. For instance, copper (Cu) with an atomic number of 29, has electrons filling up to the 3d orbital, which is noted in the configuration '[Ar] 3d^{10} 4s^{1}'. These orbitals and associated rules explain periodic trends and the reactive properties of different elements.