Question

State the number of valence electrons for a lithium atom and a chlorine atom.

Short answer

Lithium has 1 valence electron, and chlorine has 7 valence electrons.

Step-by-step solution

Understand Atomic Structure

Atoms consist of a nucleus surrounded by electrons. Electrons are arranged in energy levels or shells around the nucleus. The outermost shell is called the valence shell, and the electrons in this shell are called valence electrons.

Identify Atomic Number and Electron Configuration - Lithium

Lithium has an atomic number of 3, which means it has 3 protons and, in a neutral state, 3 electrons. The electron configuration for lithium is 1s² 2s¹, where 1s² represents the first shell and 2s¹ represents the valence shell.

Determine Valence Electrons - Lithium

Since the outermost shell for lithium (2s¹) has 1 electron, lithium has 1 valence electron.

Identify Atomic Number and Electron Configuration - Chlorine

Chlorine has an atomic number of 17, meaning it has 17 protons and, in a neutral state, 17 electrons. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁵. The electrons in the outermost shell (3s² 3p⁵) make up the valence electrons.

Determine Valence Electrons - Chlorine

For chlorine, the third shell (3s² 3p⁵) has a total of 7 electrons. Thus, chlorine has 7 valence electrons.

Key concepts

Atomic Structure

Atoms are the basic building blocks of matter. They consist of a small dense nucleus, which contains protons and neutrons, surrounded by a cloud of electrons. These electrons move rapidly around the nucleus in specific regions called shells or energy levels.
Understanding atomic structure is crucial because it tells us about how atoms interact and bond with one another to form elements and compounds.

• The nucleus contains protons, which are positively charged, and neutrons, which have no charge. Together, they define the mass of the atom.
• Electrons, which are negatively charged, occupy the space around the nucleus. They are organized in energy levels or shells based on energy states.
• The number of protons in the nucleus is equal to the atomic number, which uniquely identifies an element.

By studying atomic structure, we can understand why certain elements behave the way they do, which is especially important when exploring how atoms form chemical bonds.

Electron Configuration

Electron configuration is a method of describing how electrons are distributed within an atom. Each atom's structure is organized into energy levels or shells that can hold a maximum number of electrons.
This configuration helps us recognize how elements will interact, form bonds, and take part in chemical reactions.

• Electrons fill energy levels starting from the lowest energy, moving to higher levels only when the lower ones are filled.
• The notation for electron configuration uses numbers and letters to denote shells and subshells, such as \([1s^2 2s^2 2p^6]\)."
• It provides a roadmap to understand the arrangement of electrons which influences the chemical properties of an element.

For example, lithium has the electron configuration of \(1s^2 2s^1\), indicating its valence electron is in the second shell. Chlorine's configuration, \(1s^2 2s^2 2p^6 3s^2 3p^5\), reveals seven valence electrons, influencing its ability to form compounds like sodium chloride.

Energy Levels

Energy levels, or shells, are regions surrounding the nucleus where electrons are located. These levels are sometimes compared to the orbits of planets around the sun.
Each shell corresponds to a specific energy state, and electrons must occupy these levels based on the Pauli exclusion principle and Hund's rule.

• The first energy level closest to the nucleus can hold up to 2 electrons. Each subsequent level holds more.
• Electrons fill these levels, starting from the one with the lowest energy, which is closer to the nucleus.
• The behavior and interaction of electrons in these levels help us understand atomic reactivity and bonds formed between elements.

In the case of lithium, its energy levels include a filled first shell with 2 electrons and one electron in the second shell, making it highly reactive. Chlorine, with its additional shells and 7 valence electrons, tends to gain an electron during reactions to reach a stable configuration, similar to a noble gas like argon.