Problem 27 - Chemistry Matter and Change

Question

An atom of an element has a total of 13 electrons. What is the element, and how many electrons are shown in its electron-dot structure?

Step-by-Step Solution

Answer

The element is Aluminum (Al), and its electron-dot structure shows 3 electrons.

Step 1: Determine the Element from Electron Count

The atomic number of an element indicates the number of protons and, because the atom is neutral, also the number of electrons. Here, the element has 13 electrons. Therefore, the atomic number must be 13. By looking at the periodic table, the element with atomic number 13 is Aluminum (Al).

Step 2: Identify the Valence Electrons

Electron-dot structures (also known as Lewis structures) represent only the valence electrons of an atom. For Aluminum, which is in Group 13 of the periodic table, it has 3 valence electrons. Group numbers can guide us about valence electrons for main group elements.

Step 3: Draw the Electron-Dot Structure

The electron-dot structure for Aluminum will only show its 3 valence electrons. These are typically represented as dots around the chemical symbol for Aluminum (Al). For Aluminum, it will have three dots around its symbol, like this: \[ \text{Al} \cdot \cdot \cdot \].

Key Concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding and reactions. They are located in the outermost electron shell, or energy level, and determine how an element will interact with other elements. For main group elements, which are found in the s and p blocks of the periodic table, the number of valence electrons can be identified by their group number.
For example, aluminum (Al) is situated in Group 13. This indicates that it has three valence electrons. These electrons are represented as dots in Lewis structures, also known as electron-dot structures. Valence electrons are key participants in the forming of bonds between atoms and helping atoms achieve a full outer shell, often matching the configuration of noble gases. For covalent bonding, sharing of valence electrons keeps atoms connected and stable.

Periodic Table

The periodic table is an organized system that displays all known elements. Its layout is based on increasing atomic number and recurring chemical properties. The atomic number equals the number of protons in an atom’s nucleus and, for neutral atoms, this also equals the number of electrons. This table consists of rows called periods and columns known as groups or families.
Within each column or group, the elements share similar chemical characteristics. This is primarily due to having the same number of valence electrons. For instance, elements in Group 13, like aluminum (Al), all have three valence electrons.
The periodic table helps in predicting the properties of elements and explaining the trends in their chemical behavior. By identifying an element’s position, you can easily determine how it will react chemically, and what kind of bonds it might form.

Electron Configuration

Electron configuration describes the arrangement of electrons in an atom’s electron shells. Understanding this configuration is key to predicting an atom’s chemical properties, including reactivity and bonding capabilities. Each atom has a set of energy levels, typically noted as shells, which are filled with electrons in a specific manner.
Electrons are added into orbitals of increasing energy, primarily in the order of s, p, d, and f orbitals. For example, aluminum (Al) has an atomic number of 13, which means it has 13 electrons to distribute in its electron configuration. Following the order of filling, its configuration is written as: \[ 1s^2 2s^2 2p^6 3s^2 3p^1 \]
This layout shows that the valence shell (the outermost shell) contains three electrons — two in the 3s orbital and one in the 3p orbital. This structure helps in understanding the atom's potential to donate or share electrons, thus illustrating its reactive behavior in forming compounds or bonds.