2.2 Evolution of Atomic Theory
4 min read•june 24, 2024
has evolved from ancient Greek ideas to modern quantum mechanics. Scientists like Dalton, , and made key discoveries about atoms' structure and components. Their work laid the foundation for our current understanding of subatomic particles.
Protons, , and electrons are the building blocks of atoms. Isotopes, atoms with the same number of protons but different neutrons, have important applications in chemistry and nuclear science. Understanding these concepts is crucial for grasping atomic structure and behavior.
History and Development of Atomic Theory
Atomic theory through history
Top images from around the web for Atomic theory through history
Niels Bohr – Wikipedia tiếng Việt View original
Is this image relevant?
The quantum atom View original
Is this image relevant?
Evolution of Atomic Theory | Chemistry for Majors View original
Is this image relevant?
Niels Bohr – Wikipedia tiếng Việt View original
Is this image relevant?
The quantum atom View original
Is this image relevant?
1 of 3
Top images from around the web for Atomic theory through history
Niels Bohr – Wikipedia tiếng Việt View original
Is this image relevant?
The quantum atom View original
Is this image relevant?
Evolution of Atomic Theory | Chemistry for Majors View original
Is this image relevant?
Niels Bohr – Wikipedia tiếng Việt View original
Is this image relevant?
The quantum atom View original
Is this image relevant?
1 of 3
- Ancient Greek philosophers
- Democritus proposed the idea of indivisible particles called atoms smallest units of matter that cannot be further divided
- 's atomic theory (early 19th century)
- All matter is composed of atoms fundamental building blocks of matter
- Atoms of the same element are identical have the same properties (mass, size, chemical behavior)
- Atoms of different elements have different properties unique characteristics that distinguish them
- Atoms cannot be created, divided, or destroyed are indestructible and unchangeable
- Compounds are formed by the union of atoms in simple whole-number ratios (water: H2O, dioxide: CO2)
- 's discovery of the (1897)
- demonstrated the existence of negatively charged particles (electrons)
- Proposed the "plum pudding" model of the electrons embedded in a positively charged "pudding"
- 's (1909)
- Discovered the atomic small, dense, positively charged core of the
- Proposed the nuclear model of the atom surrounded by electrons
- 's model of the atom (1913)
- Electrons orbit the nucleus in fixed specific distances from the nucleus
- Explained the emission and absorption spectra of discrete lines in the hydrogen spectrum
- Modern atomic theory
- describes the behavior of electrons using quantum mechanics
- orbitals with probabilistic nature regions where electrons are likely to be found
- Incorporates the concept of , describing electrons as both particles and waves
Contributions to atomic understanding
- J.J. Thomson
- Discovered the electron through the experiment first subatomic particle discovered
- Proposed the "plum pudding" model of the atom, with electrons embedded in a positively charged "pudding" early attempt to describe atomic structure
-
- (1909) determined the charge and mass of an electron
- Measured the charge of an electron by balancing the electric force and gravitational force on oil droplets
- Ernest Rutherford
- Gold foil experiment (1909)
- Alpha particles were fired at a thin gold foil
- Most particles passed through, but some were deflected at large angles
- Concluded that the atom is mostly empty space with a small, dense, positively charged nucleus
- Discovered the atomic nucleus central core of the atom containing protons
- Proposed the nuclear model of the atom, with a small, dense, positively charged nucleus surrounded by electrons
- Gold foil experiment (1909)
Quantum Mechanical Model and Atomic Structure
- Energy levels: Discrete energy states in which electrons can exist within an atom
- : Electrons in the outermost energy level, responsible for chemical bonding and reactivity
- : Unique patterns of light emitted or absorbed by atoms, used in to identify elements
- Spectroscopy: Technique for analyzing atomic spectra to determine the composition and properties of matter
- : Fundamental limit to the precision with which certain pairs of physical properties can be determined simultaneously
Subatomic Particles and Isotopes
Properties of subatomic particles
- Protons
- Positively charged subatomic particles elementary charge
- Located in the nucleus central core of the atom
- Mass: kg ( )
- Neutrons
- Electrically neutral subatomic particles no charge
- Located in the nucleus along with protons
- Mass: kg ( unit)
- Stabilize the nucleus by providing additional strong nuclear force
- Electrons
- Negatively charged subatomic particles elementary charge
- Located in electron orbitals surrounding the nucleus
- Mass: kg ( atomic mass unit)
- Determine chemical properties and bonding behavior of an atom
Isotopes and chemical significance
- Isotopes are atoms of the same element with different numbers of neutrons
- Same (number of protons) defines the element
- Different (total number of protons and neutrons) distinguishes isotopes
- notation:
- : chemical symbol (C for carbon, H for hydrogen)
- : mass number (protons + neutrons) (12, 13, 14 for carbon isotopes)
- : atomic number (number of protons) (6 for carbon)
- Examples of isotopes
- Carbon: (stable), (stable), (radioactive)
- Hydrogen: (protium), (deuterium), (tritium, radioactive)
- : (fissile), (most abundant)
- Significance in chemistry
- Isotopes have similar chemical properties (reactivity, bonding) but different physical properties (mass, radioactivity)
- Used in radiometric dating (carbon-14), medical diagnostics (positron emission tomography), and nuclear power generation (uranium-235)
- Atomic mass: Weighted average of the masses of all naturally occurring isotopes of an element
Key Terms to Review (55)
Alpha particles (α particles): Alpha particles (α particles) are helium nuclei consisting of two protons and two neutrons. They are emitted during certain types of radioactive decay, such as alpha decay.
Atom: An atom is the smallest unit of an element that retains the properties of that element. It consists of a nucleus containing protons and neutrons, surrounded by electrons.
Atom: An atom is the fundamental unit of matter, consisting of a central nucleus surrounded by a cloud of negatively charged electrons. Atoms are the building blocks of all elements and the smallest units that retain the chemical properties of a substance.
Atomic Mass: Atomic mass is a measure of the average mass of an atom of a particular element. It is a fundamental property that reflects the combined mass of the protons and neutrons that make up the nucleus of an atom, and it is an important factor in understanding the behavior and properties of elements in the periodic table.
Atomic Mass Unit: The atomic mass unit (amu) is a unit of mass used to express the masses of atoms and molecules. It is defined as one-twelfth the mass of a carbon-12 atom in its ground state, which is a widely accepted standard for atomic and molecular masses.
Atomic Number: The atomic number is a fundamental property of an element that represents the number of protons in the nucleus of an atom. It is a unique identifier for each element and is a crucial concept in understanding the structure and behavior of atoms, as well as their placement in the periodic table.
Atomic number (Z): The atomic number (Z) is the number of protons found in the nucleus of an atom. It determines the element's identity and its position on the periodic table.
Atomic Spectra: Atomic spectra refer to the characteristic patterns of light emitted or absorbed by atoms when their electrons transition between different energy levels. This phenomenon provides valuable insights into the structure and behavior of atoms, which is crucial for understanding the evolution of atomic theory and the Bohr model.
Atomic Theory: Atomic theory is the scientific model that describes the fundamental structure and behavior of matter. It is the foundation for understanding the composition and properties of all substances in the universe, from the smallest atoms to the largest celestial bodies.
Bohr Model: The Bohr model is a representation of the atom that was developed by Danish physicist Niels Bohr in 1913. It describes the structure of an atom, depicting electrons orbiting the nucleus in discrete energy levels or shells, and provides a framework for understanding the behavior of atoms and their interaction with electromagnetic radiation.
Carbon: Carbon is a fundamental element that is essential for the formation of organic compounds and the sustenance of life. It is a versatile element that can form a wide range of structures and participate in numerous chemical reactions, making it a crucial component in various fields, including chemistry, biology, and materials science.
Cathode ray: A cathode ray is a stream of electrons observed in vacuum tubes. These rays are emitted from the negative electrode (cathode) when voltage is applied across the electrodes.
Cathode Ray Experiment: The cathode ray experiment was a pivotal experiment in the early development of atomic theory, which involved the study of the nature and properties of cathode rays emitted from a vacuum tube. This experiment helped to establish the existence of electrons and provided important insights into the structure of atoms.
Chadwick: James Chadwick was an English physicist who discovered the neutron in 1932. His discovery was crucial for the development of nuclear physics and the atomic model.
Dalton’s atomic theory: Dalton's atomic theory is a fundamental theory in chemistry stating that all matter is composed of indivisible atoms, each element has identical atoms, and chemical reactions involve rearrangement of these atoms. Proposed by John Dalton in the early 19th century, this theory laid the groundwork for modern atomic science.
Electron: An electron is a subatomic particle with a negative electric charge, found in all atoms. It plays a key role in chemical bonding and electricity.
Electron: An electron is a subatomic particle that carries a negative electric charge and is found in all atoms. Electrons play a crucial role in the evolution of atomic theory and in the process of radioactive decay.
Electron Orbital: An electron orbital is a region in an atom where an electron is likely to be found. It is a mathematical function that describes the wave-like behavior of an electron in an atom, and it defines the probability distribution of the electron's position and momentum.
Energy Levels: Energy levels refer to the discrete, quantized states that electrons can occupy within an atom. These energy levels represent the specific amounts of energy an electron can have as it orbits the nucleus of an atom. The concept of energy levels is fundamental to understanding the structure and behavior of atoms, as well as the evolution of atomic theory, the Bohr model, and the electronic structure of atoms.
Ernest Rutherford: Ernest Rutherford was a pioneering New Zealand-born physicist who made significant contributions to the understanding of atomic structure and radioactivity. His groundbreaking experiments and theories laid the foundation for modern nuclear physics and our current model of the atom.
Geiger: A Geiger counter is a device used for detecting and measuring ionizing radiation. It consists of a Geiger-Müller tube that produces an electrical signal when radiation is detected.
Gold Foil Experiment: The gold foil experiment, also known as the Rutherford scattering experiment, was a groundbreaking scientific investigation that provided crucial evidence for the existence of the atomic nucleus and helped shape our understanding of atomic structure.
Hydrogen: Hydrogen is the simplest and lightest element in the periodic table, with a single proton and electron in its neutral state. It is a highly reactive nonmetal that plays a crucial role in various chemical processes and is a fundamental component of many compounds, making it a key topic across several areas of chemistry.
Hydrogen bonding: Hydrogen bonding is a strong type of dipole-dipole interaction that occurs between molecules when hydrogen is covalently bonded to electronegative atoms like oxygen, nitrogen, or fluorine. This bond results in higher boiling and melting points for substances.
Isotope: Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons, resulting in different atomic masses. This concept is fundamental to understanding the evolution of atomic theory, nuclear structure and stability, nuclear equations, and transmutation and nuclear energy.
J.J. Thomson: J.J. Thomson was a British physicist who made significant contributions to the understanding of the atom and the discovery of the electron. His work laid the foundation for the modern atomic theory and the development of our current understanding of the structure of matter.
John Dalton: John Dalton was an English scientist who is best known for his pioneering work in the development of atomic theory, which laid the foundation for our modern understanding of the structure and behavior of matter. Dalton's contributions were crucial in the early ideas of atomic theory and the subsequent evolution of this theory over time.
Marsden: Marsden is best known for his work on the gold foil experiment, which provided critical evidence for the nuclear model of the atom. He worked alongside Ernest Rutherford and Hans Geiger to demonstrate that atoms have a small, dense nucleus.
Mass Number: The mass number, also known as the nucleon number, is the total number of protons and neutrons in the nucleus of an atom. It is a fundamental property that helps identify the specific isotope of an element and is denoted by the symbol 'A'.
Mass number (A): Mass number (A) is the total number of protons and neutrons in an atomic nucleus. It determines the mass of an atom.
Millikan: Millikan refers to Robert A. Millikan, an American experimental physicist who is best known for his oil-drop experiment that measured the charge of the electron. This experiment provided crucial evidence for the quantization of electric charge.
Nagaoka: Hantaro Nagaoka was a Japanese physicist who proposed an early model of the atom resembling a miniature solar system, where electrons orbit a central nucleus. This model, known as the Saturnian model, was one of the first to suggest that atoms had internal structure.
Neutron: A neutron is an electrically neutral subatomic particle found in the nucleus of an atom. It plays a crucial role in the stability and structure of atomic nuclei, as well as in various nuclear processes and transformations.
Neutrons: Neutrons are subatomic particles found in the nucleus of an atom, with no electric charge and a mass slightly greater than that of protons. They play a crucial role in the stability of atomic nuclei.
Niels Bohr: Niels Bohr was a Danish physicist who made significant contributions to the understanding of atomic structure and the development of quantum theory. He is best known for his model of the atom, which provided a new way of visualizing the behavior of electrons within an atom.
Nucleus: The nucleus is the small, dense region at the center of an atom that contains protons and neutrons. It is responsible for most of the atom's mass.
Nucleus: The nucleus is the central and most important part of an atom, containing protons and neutrons, which determines the atom's chemical properties and behavior. It is a critical component in understanding the evolution of atomic theory, atomic structure, the Bohr model, covalent bonding, and nuclear stability and structure.
Oil Drop Experiment: The oil drop experiment, conducted by physicist Robert Andrews Millikan and his student Harvey Fletcher in 1910-1913, was a groundbreaking experiment that provided evidence for the quantized nature of electric charge and helped determine the charge of an electron.
Plum Pudding Model: The plum pudding model, also known as the Thomson model, was an early 20th-century model of the atom proposed by British physicist J.J. Thomson. It describes the atom as a positively charged sphere with negatively charged electrons embedded within it, similar to the structure of a plum pudding dessert.
Proton: A proton is a subatomic particle found in the nucleus of an atom, carrying a positive electric charge. Protons contribute to the atomic number and define the element.
Proton: A proton is a subatomic particle that carries a positive electric charge and is found in the nucleus of an atom. Protons are fundamental to the structure and behavior of atoms, and they play crucial roles in various areas of chemistry, including the evolution of atomic theory, acid-base chemistry, the properties of hydrogen, and nuclear physics.
Quantum Mechanical Model: The quantum mechanical model is a fundamental theory in physics that describes the behavior of matter and energy at the atomic and subatomic scale. It provides a comprehensive understanding of the wave-particle duality of particles and the probabilistic nature of their properties, revolutionizing our knowledge of the microscopic world.
Robert Millikan: Robert Andrews Millikan was an American physicist who is best known for his oil drop experiment, which provided the first accurate measurement of the charge of an electron. His work on the photoelectric effect also helped confirm the quantum nature of light and contributed to the development of atomic theory.
Rutherford: Ernest Rutherford was a physicist known for his pioneering work in nuclear physics and the development of the Rutherford model of the atom. He discovered the nucleus through his gold foil experiment, fundamentally changing our understanding of atomic structure.
Soddy: A Soddy is a historic unit of measurement that represents the number of atoms in a molecule, specifically used to refer to Avogadro's hypothesis regarding equal volumes of gases containing an equal number of molecules.
Spectroscopy: Spectroscopy is the study of the interaction between matter and electromagnetic radiation. It is a powerful analytical tool used to investigate the structure and properties of atoms, molecules, and materials by analyzing the absorption, emission, or scattering of light or other forms of radiation.
Thomson: J.J. Thomson was a British physicist who discovered the electron and proposed the 'plum pudding' model of the atom. His work laid the foundation for modern atomic theory.
Transuranium elements: Transuranium elements are chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. They are typically synthetic and produced through nuclear reactions.
Uncertainty Principle: The uncertainty principle is a fundamental concept in quantum mechanics that states that the precise measurement of certain pairs of physical properties, such as position and momentum or energy and time, is impossible. This principle was formulated by the physicist Werner Heisenberg and has profound implications for our understanding of the behavior of matter and energy at the smallest scales.
Unified atomic mass unit (u): The unified atomic mass unit (u) is a standard unit of mass that quantifies the mass of atoms and molecules. It is defined as one twelfth the mass of a carbon-12 atom.
Uranium: Uranium is a radioactive chemical element that is found naturally in the Earth's crust. It is a dense, silvery-white metal that is used as the primary fuel in nuclear reactors and as the main component in nuclear weapons. Uranium is a key player in the evolution of atomic theory and the development of nuclear energy.
Valence electrons: Valence electrons are the outermost electrons of an atom and are involved in forming chemical bonds. They determine an element's chemical properties and reactivity.
Valence Electrons: Valence electrons are the outermost electrons in an atom that participate in chemical reactions and bonding. They are the electrons in the highest occupied energy level of an atom and are responsible for an element's chemical properties and behavior.
Wave-particle duality: Wave-particle duality is the concept in quantum mechanics that every particle or quantic entity exhibits both wave and particle properties. This dual nature is fundamental to the behavior of particles at atomic and subatomic levels.
Wave-Particle Duality: Wave-particle duality is a fundamental concept in quantum mechanics that describes the dual nature of matter and energy, exhibiting characteristics of both waves and particles. This principle is central to understanding the behavior of subatomic particles and the evolution of atomic theory, electromagnetic energy, and the development of quantum theory.