Chemistry Unit 5 Worksheet 1

Chemistry Unit 5 Worksheet 1: Atomic Structure and Periodic Trends

As we delve into the world of chemistry, understanding the atomic structure and periodic trends is crucial. In this worksheet, we will explore the fundamental concepts of atomic structure, periodic trends, and electron configuration.

Atomic Structure

The Atom: The atom is the building block of matter, consisting of three main particles: protons, neutrons, and electrons. Protons and neutrons reside in the nucleus, while electrons orbit around it.

Key Components:

• Protons: positively charged particles that determine the atomic number (number of protons in an atom’s nucleus)
• Neutrons: particles with no charge that contribute to the atomic mass (total number of protons and neutrons in an atom’s nucleus)
• Electrons: negatively charged particles that occupy specific energy levels or orbitals around the nucleus

Atomic Number and Mass Number:

• Atomic Number (Z): the number of protons in an atom’s nucleus, which defines the element’s identity
• Mass Number (A): the total number of protons and neutrons in an atom’s nucleus, which determines the atom’s mass

Electron Configuration

Electron configuration is the arrangement of electrons in an atom’s orbitals. The Aufbau principle and the Pauli Exclusion Principle govern electron configuration.

Aufbau Principle: Electrons occupy the lowest available energy levels or orbitals.

Pauli Exclusion Principle: Each orbital can hold a maximum of two electrons with opposite spins.

Periodic Trends

The periodic table is a powerful tool for predicting an element’s properties based on its position. Periodic trends include:

• Atomic Radius: decreases from left to right across a period and increases down a group
• Electronegativity: increases from left to right across a period and decreases down a group
• Ionization Energy: increases from left to right across a period and decreases down a group

Blocks of the Periodic Table

The periodic table is divided into blocks based on the orbital type that is being filled.

• s-Block: elements in the first two groups (alkali metals and alkaline earth metals)
• p-Block: elements in the last six groups (boron group to noble gases)
• d-Block: elements in the middle section (transition metals)
• f-Block: elements at the bottom of the periodic table (lanthanides and actinides)

📝 Note: Understanding the periodic trends and electron configuration is crucial for predicting an element's properties and behavior.

Electron Configuration Notation

Electron configuration notation is used to describe the arrangement of electrons in an atom’s orbitals.

• 1s2 2s2 2p6: represents the electron configuration of an oxygen atom
• 1s2 2s2 2p5: represents the electron configuration of a fluorine atom

Valence Electrons and Valency

Valence electrons are the electrons in the outermost energy level of an atom.

• Valence Electrons: determine an element’s reactivity and ability to form bonds
• Valency: the number of bonds an atom can form, which is equal to the number of valence electrons

Worksheet Questions

1. What is the atomic number of carbon?
2. What is the mass number of oxygen?
3. Write the electron configuration for the element chlorine.
4. Identify the block of the periodic table where the element neon is located.
5. What is the valency of the element nitrogen?

Answer Key:

1. 6
2. 16
3. 1s2 2s2 2p6 3s2 3p5
4. p-Block
5. 3

In conclusion, understanding atomic structure, electron configuration, and periodic trends is essential for predicting an element’s properties and behavior. By mastering these concepts, you will be better equipped to tackle more advanced topics in chemistry.