Problem 142 - Introductory Chemistry Atoms First

Question

Name each element and tell how many valence electrons it has: (a) \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{2}\) (b) \([\mathrm{Ne}] 3 \mathrm{~s}^{1}\) (c) \([\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{3}\)

Step-by-Step Solution

Answer

(a) Silicon (Si) with 4 valence electrons. (b) Sodium (Na) with 1 valence electron. (c) Arsenic (As) with 5 valence electrons.

Step 1: (a) Identify the element and valence electrons for \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{2}\)

We can determine the total number of electrons by adding the superscript of all the terms: \(1s^{2}\) has 2 electrons \(2s^{2}\) has 2 electrons \(2p^{6}\) has 6 electrons \(3s^{2}\) has 2 electrons \(3p^{2}\) has 2 electrons Adding all electrons, we get: 2+2+6+2+2=14 electrons An element with 14 electrons is Silicon (Si). The valence electrons are the outermost electrons, present in the 3rd shell: \(3s^{2} 3p^{2}\). Thus, Silicon has a total of 4 valence electrons.

Step 2: (b) Identify the element and valence electrons for \([\mathrm{Ne}] 3 \mathrm{~s}^{1}\)

This electron configuration begins with the noble gas Neon (Ne) and has an additional electron in the \(3s^{1}\) orbital. Neon has 10 electrons; therefore, this element has 11 electrons in total. An element with 11 electrons is Sodium (Na). Since the additional electron is in the 3rd shell, Sodium has 1 valence electron.

Step 3: (c) Identify the element and valence electrons for \([\mathrm{Ar}] 4 s^{2} 3 d^{10} 4 p^{3}\)

This electron configuration stars with the noble gas Argon (Ar) and has additional electrons in the \(4s^{2}\), \(3d^{10}\), and \(4p^{3}\) orbitals. Argon has 18 electrons; therefore, with the additional electrons, this element has 18+2+10+3 = 33 electrons in total. An element with 33 electrons is Arsenic (As). The valence electrons are in the 4th shell: \(4s^{2} 4p^{3}\). Thus, Arsenic has a total of 5 valence electrons.

Key Concepts

Electron Configuration

Electron configuration is like a map that tells us where the electrons are in an atom. Each element has its unique configuration based on its number of electrons. Imagine electrons filling in shells around the nucleus of an atom – starting from the closest. This is called the Aufbau principle, which means 'building up'. The electrons start filling the lowest energy levels first and then move up to higher levels.

• The configuration is written using numbers and letters, like '1s²2s²2p⁶' which shows how many electrons are in each shell and subshell.
• The numbers (1, 2, 3...) represent energy levels or shells around the atom, while the letters (s, p, d, and f) stand for the subshells within those levels.
• Superscripts next to the letters tell us how many electrons are in that subshell.

Understanding electron configurations helps in identifying elements and their properties, and predicting how they will react chemically.

Periodic Table

The periodic table is like a giant map for chemists, bringing order to all the known chemical elements. It arranges elements in rows and columns based on their atomic number, electron configurations, and recurring chemical properties.

• Elements are grouped in columns called "groups". Elements in the same group often share similar properties and the number of valence electrons.
• Rows are called "periods" and represent the outermost energy level occupied by electrons.
• Noble gases, found in the far right column, are known for having a complete outer shell of electrons, making them very stable and mostly non-reactive.

Using the periodic table, students can efficiently determine an element's electron configuration and understand its reactivity.

Chemical Elements

Chemical elements are pure substances made entirely of one type of atom. Every element has a specific number of protons, which defines the element and is reflected by its atomic number. The elements make up all matter in the universe, from the air we breathe to the stars in the sky.

• Each element is unique and has its own symbol, like O for oxygen, Na for sodium, and Si for silicon.
• There are over 100 elements, organized in the periodic table, from hydrogen with one proton to heavier elements like uranium.
• Elements combine in countless ways to form compounds, which are the building blocks of everything we observe.

By understanding chemical elements, students gain insight into the fundamental makeup and behavior of matter. This knowledge is essential for studying chemistry and understanding the world around us.