Problem 9 - Chemistry The Central Science In Si Units

Question

(a) True or false: An element's number of valence electrons is the same as its atomic number. (b) How many valence electrons does a nitrogen atom possess? (c) An atom has the electron configuration \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{2} .\) How many valence electrons does the atom have?

Step-by-Step Solution

Answer

(a) False. (b) 5 valence electrons. (c) 4 valence electrons.

Step 1: Understanding Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They determine an atom's chemical properties and reactivity. For main group elements, the number of valence electrons is usually the same as the group number.

Step 1: Evaluate Statement (a)

For statement (a), the atomic number of an element represents the total number of protons. The number of valence electrons depends on the shell configuration, typically related to the group of the periodic table. Therefore, the statement is false.

Step 2: Determine Nitrogen's Valence Electrons in Part (b)

The atomic number of nitrogen is 7, meaning it has 7 electrons with the electron configuration of \(1s^2 2s^2 2p^3\). The electrons in the outermost shell are 2s and 2p, giving a total of 5 valence electrons.

Step 3: Count Valence Electrons in Provided Configuration for Part (c)

The provided electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^2\). The valence electrons are those in the outermost principle quantum number, which is 3 in this case. Therefore, the total valence electrons are 2 (from 3s) + 2 (from 3p) = 4 valence electrons.

Key Concepts

Atomic Number

The atomic number of an element is a fundamental property that tells us how many protons are in the nucleus of an atom. Each element on the periodic table has a unique atomic number, which acts like the element's fingerprint. This means no two different elements will have the same atomic number. For example, hydrogen has an atomic number of 1, which indicates it has one proton in its nucleus.

In the context of electron configuration and valence electrons, it's important to recognize that the atomic number also tells us the number of electrons in a neutral atom. This helps us predict the way elements interact with each other, as the number of electrons determines how they form bonds. However, it's worth noting that the atomic number does not directly indicate the number of valence electrons. Instead, valence electrons are determined by the electron arrangement in the outermost shell of an atom.

Electron Configuration

Electron configuration refers to the detailed arrangement of electrons in an atom. Electrons fill atomic orbitals in a specific order based on the energy levels defined by quantum mechanics. Understanding electron configurations can help predict the chemical properties and reactivity of elements.

The configuration is often represented using notation, such as the one you might have seen like: \(1s^2 2s^2 2p^6 3s^2 3p^2\). Each part of this notation tells us which electron orbital is filled and how many electrons are present in that orbital:

• The numbers represent the principal quantum levels, starting from 1 and going upwards.
• The letters (s, p, d, f) refer to the type of orbital, each with a specific shape and capacity for electrons.
• The superscripts denote the number of electrons in each orbital type.

For the configuration \(1s^2 2s^2 2p^6 3s^2 3p^2\), the valence electrons are found in the third level (3s and 3p), adding up to 4 valence electrons.

Periodic Table Group

The periodic table groups elements into columns, known as groups or families, which share similar chemical properties. This similarity largely comes from the fact that elements within a group have the same number of valence electrons.

For instance, all elements in Group 1 have one valence electron, which makes them highly reactive, particularly with elements in Group 17 that have seven valence electrons. It is these valence electrons that dictate how elements bond and interact with each other. As you proceed from left to right in the periodic table, each successive element in a period increases by one valence electron, which alters their chemical behavior significantly as they transition from metals to non-metals.

Thus, understanding which group an element belongs to can provide insights into its potential reactions and compounds it might form. Importantly, while the atomic number gives us the total count of electrons, the periodic table grouping helps identify how those electrons are distributed, particularly the ones in the outermost shell that are key to chemical reactivity.