Atomic Structure and Periodicity of Elements - Chemistry (Undergraduate Foundation)

This course provides a complete guide to the modern theory of the atom. It traces the historical development of atomic models, from Dalton's foundational theory to the modern understanding of electronic structure. The material covers the discovery of subatomic particles, the contributions of Thomson and Rutherford, the Bohr model, and culminates in a full treatment of electronic configuration and its direct relationship to the periodic trends of the elements. A command of atomic theory is the absolute foundation of modern chemistry. The electronic structure of the atom dictates all chemical properties and bonding behaviour. This knowledge is essential for understanding the periodic table, predicting chemical reactions, and is the prerequisite for the study of spectroscopy, materials science, and quantum mechanics. By the end of this course, you will be able to describe the historical evolution of atomic theory. You will also be able to explain the structure of the atom, including the roles of protons, neutrons, and electrons, determine the electronic configuration of any element, and use periodic trends to predict and justify atomic properties like size, ionization potential, and electronegativity. This course is for students who have completed an introductory chemistry course. It is a mandatory prerequisite for any student pursuing a degree in chemistry, chemical engineering, materials science, or physics.

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Enrolment valid for 12 months
This course is also part of the following learning track. You may join the track to gain comprehensive knowledge across related courses.
[NUC Core] CHM 101: General Chemistry I
[NUC Core] CHM 101: General Chemistry I
This learning track delivers the complete NUC CCMAS curriculum for General Chemistry I. It is a comprehensive programme designed to build a robust, university-level foundation in modern chemistry. The track systematically covers all essential topics, from atomic theory, chemical bonding, and the states of matter, to the quantitative principles of stoichiometry, equilibrium, thermodynamics, and kinetics. This programme is for first-year undergraduates in science, technology, engineering, and mathematics (STEM) faculties who are required to take CHM 101. It is also essential for any student or professional globally who needs a rigorous and complete foundation in first-year university chemistry for further study or career development. This track delivers a full skill set in chemical theory and quantitative problem-solving. Graduates will be able to determine molecular structures, calculate reaction quantities, analyse the energetics and rates of reactions, and solve complex equilibrium problems. This programme provides the non-negotiable prerequisite knowledge for all subsequent chemistry courses and for any degree in the physical sciences, engineering, or medicine.

This learning track delivers the complete NUC CCMAS curriculum for General Chemistry I. It is a comprehensive programme designed to build a robust, university-level foundation in modern chemistry. The track systematically covers all essential topics, from atomic theory, chemical bonding, and the states of matter, to the quantitative principles of stoichiometry, equilibrium, thermodynamics, and kinetics. This programme is for first-year undergraduates in science, technology, engineering, and mathematics (STEM) faculties who are required to take CHM 101. It is also essential for any student or professional globally who needs a rigorous and complete foundation in first-year university chemistry for further study or career development. This track delivers a full skill set in chemical theory and quantitative problem-solving. Graduates will be able to determine molecular structures, calculate reaction quantities, analyse the energetics and rates of reactions, and solve complex equilibrium problems. This programme provides the non-negotiable prerequisite knowledge for all subsequent chemistry courses and for any degree in the physical sciences, engineering, or medicine.

Course Chapters

1. Introduction
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This chapter provides the roadmap for the course. It outlines the progression from early atomic theories to the modern understanding of atomic structure and its direct relationship to the periodic table. Key learning objectives include: understanding the overall course structure and appreciating the historical and experimental development of atomic theory.

Chapter lessons

1-1. Welcome
6:35

This lesson provides a brief overview of the course, outlining the key topics from Dalton's postulates to electronic configuration and periodic trends.

2. Early Atomic Models
6

This chapter traces the origin of atomic theory, starting with the empirical laws that led to Dalton's foundational model. It then covers the pivotal discovery of the electron, the first experimental proof that the atom is divisible, which forced the initial theory to evolve. Key topics include the laws of chemical combination, Dalton's atomic postulates and their critical shortcomings, and the experiments by Thomson and Millikan that discovered and characterised the electron, leading to the 'plum pudding' model.

Chapter lessons

2-1. Laws of chemical combination
11:05

This lesson examines the laws governing mass relationships in chemical reactions. We cover conservation of mass, definite proportions, and multiple proportions. Understand these principles as the quantitative evidence for Dalton's atomic theory.

2-2. Dalton's atomic theory
9:58

This lesson covers the four fundamental postulates of John Dalton's atomic theory, which established the first scientific model of the atom.

2-3. Shortcomings of Dalton's theory
7:23

Dalton's theory was foundational but flawed. This lesson identifies its critical shortcomings, namely the divisibility of atoms and the existence of isotopes. Understanding these failures is necessary to trace the progression to modern atomic models.

2-4. Thomson's cathode ray experiment
10:00

This lesson details J.J. Thomson's cathode ray experiment. The experiment provides the definitive evidence for the electron and allows for the calculation of its charge-to-mass ratio. This discovery proved the atom is divisible, refuting a key part of Dalton's theory.

2-5. Milikan's Oil drop experiment
11:18

This lesson details Millikan's Oil drop experiment, which established the elementary electric charge. By using Thomson's charge-to-mass ratio, this experiment allowed for the first accurate calculation of the electron's mass.

2-6. Shortcomings of Thomson's model
7:09

This lesson examines the failure of Thomson's 'plum pudding' model. The model was invalidated by Rutherford's gold foil experiment, as it could not explain the large-angle scattering of alpha particles and some other concept.

3. The Nuclear Model
5
2

This chapter covers the development of the nuclear atom, from Rutherford's definitive gold foil experiment to Chadwick's discovery of the neutron. It establishes the modern planetary model of the atom and immediately addresses its critical failure, demonstrating why classical physics is insufficient. Key topics include the experimental evidence for the nucleus, the discovery of the neutron, the shortcomings of Rutherford's classical model, and the fundamental properties of protons, neutrons, and electrons.

Chapter lessons

3-1. Rutherford's gold foil experiment
11:48

This lesson examines Rutherford's pivotal gold foil experiment. The surprising deflection of a few alpha particles at large angles invalidated the Thomson model. This observation was only explainable by concentrating the atom's mass and positive charge into a tiny nucleus.

3-2. Shortcomings of Rutherford's nuclear model
6:40

Rutherford's model is fundamentally unstable according to classical physics. An orbiting electron must radiate energy, causing it to rapidly spiral into the nucleus. This lesson explains why this contradiction forced the development of a quantum model of the atom.

3-3. Chadwick's nuclear bombardment
4:57

This lesson details Chadwick's bombardment experiment, which provided the evidence for the neutron. By observing the neutral radiation from alpha particle bombardment of beryllium, he identified a new nuclear particle. This completed the proton-neutron atomic model.

3-4. Sub-atomic particles
9:42

This lesson defines the fundamental properties of the three subatomic particles. We will detail the relative mass and charge of the proton, neutron, and electron. A firm command of these values is required for all subsequent atomic calculations.

3-5. Isotopy
6:06

This lesson defines isotopy, where atoms of the same element possess different numbers of neutrons. We will examine how this affects mass number whilst the atomic number remains constant, using key examples like the isotopes of hydrogen and carbon.

4. Bohr's Model
3
1

This chapter details Niels Bohr's model, the first attempt to solve the failures of the classical nuclear atom using quantum theory. Understanding this transitional model is critical to grasping the full conceptual leap to modern quantum mechanics. Topics include: Bohr's postulates, explaining hydrogen's emission spectrum, energy level calculations, and the model's ultimate shortcomings.

Chapter lessons

4-1. Introduction
8:16

This lesson reviews the critical failures of Rutherford's classical atomic model, specifically its inability to account for atomic stability and line spectra. We establish the context for Bohr's revolutionary quantum hypothesis, which directly addresses these shortcomings.

4-2. Energy levels
8:07

This lesson explains how Bohr's model of quantized energy levels accounts for the hydrogen emission spectrum. We will demonstrate how electron transitions between these discrete energy levels produce the specific lines observed, and define the principal quantum number, n.

4-3. Shortcomings
12:31

This lesson details the critical failures of the Bohr model, focusing on its inability to describe multi-electron atoms and its violation of the Heisenberg Uncertainty Principle. Understanding these shortcomings is essential to appreciate the necessity of the modern quantum mechanical model.

5. Wave-Particle Duality
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2

This chapter details wave-particle duality, the principle that all matter has wave properties. This concept explains the failure of Bohr's fixed orbits and establishes the necessary theoretical foundation for the modern quantum mechanical model of the atom. Key topics include: De Broglie’s wave hypothesis, applying the de Broglie relation (λ = h/mv), and calculating the wavelength of moving particles based on their mass and velocity.

Chapter lessons

5-1. De Broglie’s Theory
4:04

This lesson explains de Broglie’s proposal that all matter exhibits wave properties. It introduces the relation λ = h/mv and shows how this idea connects particle motion to quantised electron states.

6. The Quantum Model
6
1

This chapter introduces the modern quantum mechanical model, replacing Bohr's flawed orbits with probabilistic orbitals. Mastery of this model is non-negotiable, as it provides the definitive framework for describing electron behaviour and predicting all chemical properties. Key topics include: the four quantum numbers, defining orbital shapes (s, p, d, f) and their spatial orientation, and applying the Aufbau principle, Pauli exclusion, and Hund's rule to write correct electronic configurations.

Chapter lessons

6-1. Fundamental quantum numbers
13:00

This lesson introduces Schrödinger’s equation as the foundation of atomic structure. It explains how its solutions give the principal and azimuthal quantum numbers.

6-2. Shapes of orbitals
4:59

This lesson describes the spatial shapes of s, p, d, and f orbitals. It explains how quantum numbers determine these forms and their significance in atomic structure.

6-3. Magnetic quantum number
8:16

This lesson defines the magnetic quantum number and its role in atomic structure. It explains how it determines the spatial orientation and distinction of orbitals within a subshell.

6-4. Orientation of orbitals
8:50

This lesson explains how orbitals orient themselves in three-dimensional space. It relates each orientation to the magnetic quantum number and the distinct shapes of atomic orbitals.

6-5. Spin quantum number
4:23

This lesson defines the spin quantum number and explains how electron spin distinguishes paired and unpaired electrons within an orbital.

6-6. Electronic configuration
30:31

This lesson explains how electrons occupy orbitals using the Aufbau principle, Pauli exclusion, and Hund’s rule to determine the electronic configuration of any element.

7. Periodicity
4
3

This chapter explains how the electronic structure of atoms leads to predictable, periodic trends in their properties across the periodic table. The focus is on justifying these trends based on concepts like shielding and effective nuclear charge. Key learning objectives include: defining and explaining the trends in atomic radii, ionization energies, and electronegativity across a period and down a group.

Chapter lessons

7-1. The periodic table
24:45

This lesson reviews the structure of the modern periodic table, defining periods and groups. We establish the direct link between an element's position and its electronic configuration, which is the foundation for understanding periodicity.

7-2. Atomic and ionic radii
14:11

This lesson defines atomic and ionic radii, explaining the trends across periods and down groups. We will justify these size changes using the concepts of effective nuclear charge and electron shielding.

7-3. First ionisation energy

This lesson explains the periodic trend of first ionisation energy across periods and down groups. We will justify these variations using effective nuclear charge, electron shielding, and orbital stability.

7-4. Electronegativity

This lesson defines electronegativity as the ability of an atom to attract electrons in a chemical bond and explains its periodic trends.

8. Conclusion
2

This concluding chapter summarises the key concepts of atomic theory. It reinforces the understanding of atomic structure and its connection to the periodic properties of the elements. This summary prepares the student for the next course, 'Chemical Bonding and Molecular Geometry', where electronic structure is used to predict how atoms form molecules.

Chapter lessons

8-1. Course summary

This lesson consolidates knowledge by reviewing the progression from early atomic models to the modern understanding of electronic structure and periodic trends.

8-2. Next steps

This final lesson looks ahead, explaining how the principles of electronic configuration and periodicity are the direct prerequisites for understanding chemical bonding.