Our study guide is meticulously designed to align with the SEAB learning objectives for GCE O Level Chemistry. In this post, we will be focusing on the chapter of Atomic Structure. Firstly, we will explore how these subatomic particles are organized within the atom. Subsequently, we will examine key concepts such as atomic number, mass number, and isotopes. Finally, we will highlight their significance in understanding the fundamental principles of chemistry.
Understanding atomic structure not only allows you to grasp chemical reactions and bonding, but it also equips you with the essential knowledge to analyze and predict the behavior of elements in various contexts. Furthermore, it enables you to make connections between different concepts in chemistry, thereby deepening your overall comprehension.
Electrons, however, are located outside the nucleus, arranged in atomic shells that surround it. The outermost electron shell is also called the valence electron shell.
The first electron shell can take up to a maximum of 2 electrons, while subsequent electron shells can take up to a maximum of 8 electrons.
In atoms, the number of electrons precisely equals the number of protons, ensuring electrical neutrality.
Checkpoint! Use your periodic table to find the atomic number and mass number of the following elements.
Question 5:
Using ideas about subatomic particles, explain why a hydrogen ion is also known as a “proton”.
Check your answers! Did you get it right?
Relative Mass and Charge
It is essential to understand the relative masses and charges of subatomic particles. To begin with, grasping this information helps in comprehending the overall structure and behavior of atoms. Moreover, the table below provides a concise overview of the masses and charges of electrons, protons, and neutrons.
Atomic Structure – What’s Inside?
Protons and neutrons reside inside the nucleus of an atom, collectively known as nucleons.
Electrons, however, are located outside the nucleus, arranged in atomic shells that surround it. The outermost electron shell is also called the valence electron shell.
The first electron shell can take up to a maximum of 2 electrons, while subsequent electron shells can take up to a maximum of 8 electrons.
Atomic Number & Mass Number
In atomic structure, the nucleon number refers to the total sum of protons and neutrons present within an atom’s nucleus. Specifically, it signifies the total number of these subatomic particles, which define the atom’s mass. The proton number, or atomic number, specifically denotes the total number of protons within an atom. Notably, it uniquely identifies the element’s identity that you see in the periodic table.
In atoms, the number of electrons precisely equals the number of protons, ensuring electrical neutrality.
Checkpoint! Use your periodic table to find the atomic number and mass number of the following elements.
- Nitrogen
- Sodium
- Tungsten
| Atomic Number | Mass Number | |
| Nitrogen |
7 |
14 |
| Sodium |
11 |
23 |
| Tungsten |
74 |
184 |
Atomic Isotopes
Atomic isotopes are variants of an element that share the same number of protons (atomic number) but, conversely, differ in their number of neutrons (nucleon number) within the nucleus. This variance in neutrons results in isotopes having different atomic masses. Despite these differences, isotopes share the same chemical properties due to their identical numbers of protons, but they may differ in their physical properties.Relative Atomic Mass
Relative atomic mass (RAM) is a measure of the average mass of atoms of an element, taking into account the relative abundances of all its naturally occurring isotopes. Specifically, it is expressed as an average of all isotopes. To calculate the relative atomic mass of an element, we can use the formula: (Mass No. of Isotope 1 % of Isotope 1) + (Mass No. of Isotope 2 % of Isotope 2) / 100Test your Understanding of the Atomic Structure!
Checkpoint! Use your periodic table and answer the following questions. Question 1: Which subatomic particle has no charge? Question 2: What is the total number of neutrons in the nucleus of a neutral atom that has 19 electrons and a mass number of 39? Question 3: Fill in the blank. The weighted average of the atomic masses of the naturally occurring isotopes of an element is the ____________________. Question 4: The table below shows the number of subatomic particles in atom A and B. Name the element that atom A and B are isotopes of.| Subatomic Particles in Two Atoms | |||
| Atom | Number of Protons | Number of Neutrons | Number of Electrons |
| A |
6 |
6 |
6 |
| B |
6 |
7 |
6 |
