Problem 100 - Chemistry Matter and Change

Question

Zinc A zinc atom contains a total of 18 electrons in its \(3 \mathrm{s}, 3 \mathrm{p},\) and 3 \(\mathrm{d}\) orbitals. Why does its electron-dot structure show only two dots?

Step-by-Step Solution

Answer

Zinc has 2 valence electrons in the 4s orbital, shown as 2 dots in its electron-dot structure.

Step 1: Understand Electron Configuration Notation

Zinc (Zn) has an atomic number of 30, meaning it has 30 electrons. The electron configuration for Zn is given by: \[ \text{Zn: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^{10} \, 4s^2 \] This configuration shows the distribution of electrons in different orbitals up to the atomic number.

Step 2: Identify Valence Electrons

The valence electrons for an atom are the electrons in the outermost shell. For zinc, that's the electrons in the 4s orbital. According to its electron configuration, Zn has 2 electrons in the 4s orbital, making it the valence shell electrons.

Step 3: Count the Electrons in 3s, 3p, and 3d Orbitals

The 3rd energy level includes the 3s, 3p, and 3d orbitals. For zinc, the electrons in these orbitals are: - 3s: 2 electrons - 3p: 6 electrons - 3d: 10 electrons Together, these account for 18 electrons as given in the problem statement.

Step 4: Explain the Electron-Dot Structure

Electron-dot structures (or Lewis dot structures) typically represent only the valence electrons of an atom. As established, zinc has 2 valence electrons in its 4s orbital. These 2 electrons are what's shown as dots in its electron-dot structure.

Key Concepts

Valence Electrons

Valence electrons are like the outermost guardians of an atom. They are the electrons that reside in the atom's outermost electron shell. For zinc (Zn), the valence electrons reside in the 4s orbital. This is evident from zinc's electron configuration:

• \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 3d^{10} \, 4s^2 \)

Even though zinc has many electrons, only the two electrons in the 4s shell are the valence electrons. These electrons play a major role in how zinc interacts with other elements. They determine chemical bonding and the formation of compounds.
Valence electrons are important for understanding an element's reactivity and ability to form chemical bonds. In simple terms, these electrons are like social connectors that allow atoms to "hold hands" with other atoms, forming molecules.

Electron-Dot Structure

Electron-dot structures, also called Lewis dot structures, provide a simple way to represent an atom's valence electrons. In these structures, only the valence electrons are shown around an element's symbol. Since we've established that zinc has two valence electrons in the 4s orbital, the electron-dot structure for zinc is represented as:

• Zn with two dots surrounding it: one dot on each side.

These dots symbolize the electrons available for bonding. Even though zinc has many electrons in various orbitals, the electron-dot structure emphasizes just the valence electrons because these are the ones involved in chemical reactions and bonding.
Electron-dot structures are useful by providing insights into how an atom might bond with others. They help predict the types of bonds an atom can form. This visualization simplifies many concepts in chemistry, making learning about chemical bonds more approachable.

Atomic Orbitals

Atomic orbitals are regions around the nucleus of an atom where electrons are likely to be found. Imagine these as rooms of a house where electrons "live". Each type of orbital has a different shape and capacity for electrons:

• The s orbital is spherical and can hold up to 2 electrons.
• The p orbital has a dumbbell shape and can hold up to 6 electrons.
• The d orbital is more complex, with a "cloverleaf" shape, capable of holding up to 10 electrons.

Zinc's electron configuration reveals electrons in different orbitals such as 3s, 3p, and 3d, as well as 4s. The 3s, 3p, and 3d orbitals collectively contain 18 electrons.
Atomic orbitals are central to our understanding of electron configurations and the distribution of electrons in an atom. Knowing how electrons are arranged helps us understand chemical reactivity and atomic interactions. It's the arrangement of these electrons in the orbitals that gives each element its unique properties and reactivity profile.