1.How did Mendeleev come up with the first periodic table of the elements?
2.Which part of John Dalton’s theory was disproved by J.J. Thomson’s cathode-ray tube experiments?
3.Which information did Millikan contribute to the understanding of electrons?
4.How does the Coulomb force affect charge interactions?
5.Which observation by Ernest Rutherford and his students refuted the plum pudding model?
1. Mendeleev came up with the first periodic table of elements by organizing the known elements based on their chemical properties and arranging them in order of increasing atomic mass. He noticed that when the elements were arranged in this way, certain patterns and similarities emerged.
2. J.J. Thomson's cathode-ray tube experiments disproved John Dalton's theory that atoms were indivisible and had no internal structure. Thomson's experiments showed that atoms contained subatomic particles called electrons.
3. Millikan's contribution to the understanding of electrons was the determination of the exact charge and mass of an electron through his famous oil-drop experiment. This experiment helped to establish the concept of quantized electric charge and provided precise measurements of the electron's charge.
4. The Coulomb force, also known as electrostatic force, describes the attraction or repulsion between charged particles. Like charges (positive-positive or negative-negative) repel each other, while opposite charges (positive-negative) attract each other. The strength of the force depends on the magnitude of the charges and the distance between them.
5. The observation by Ernest Rutherford and his students that refuted the plum pudding model was the highly-scattered alpha particles during their famous gold foil experiment. Instead of passing straight through the gold foil as predicted by the plum pudding model, some alpha particles were deflected at large angles, indicating the presence of a small, dense, and positively charged nucleus within the atom. This discovery led to the development of the modern atomic model.
1. Dmitri Mendeleev developed the first periodic table of elements by arranging elements in order of increasing atomic mass and grouping them based on their chemical and physical properties. He noticed that when elements were arranged in this manner, there was a periodic repetition of properties. Mendeleev also left gaps in his table for elements that were yet to be discovered, accurately predicting their properties based on their location in the table.
2. J.J. Thomson's cathode-ray tube experiments disproved the part of John Dalton's theory that stated atoms were indivisible and indestructible. Thomson discovered that cathode rays (streams of negatively charged particles) could be manipulated by electric and magnetic fields. This led him to propose the existence of subatomic particles, later named electrons, which are much smaller than atoms.
3. Physicist Robert Andrews Millikan contributed to the understanding of electrons by conducting the famous oil drop experiment. He measured the rate at which charged oil droplets fell in an electric field to determine the charge of individual electrons. His experiments determined the charge of an electron to be -1.6 x 10^-19 coulombs and provided a more accurate value for the mass of an electron.
4. The Coulomb force, also known as electrostatic force, affects charge interactions by determining the strength and direction of the force between charged objects. Like charges (positive-positive or negative-negative) repel each other, resulting in a force that pushes them apart. On the other hand, opposite charges (positive-negative) attract each other, leading to a force that pulls them together. The magnitude of the Coulomb force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
5. Ernest Rutherford and his students conducted the famous gold foil experiment, during which they bombarded a thin gold foil with alpha particles. According to the plum pudding model of the atom, proposed by J.J. Thomson, atoms consisted of positive charges evenly spread out within a sea of negatively charged electrons. However, Rutherford's experiment revealed that most of the alpha particles passed through the gold foil without deflection, but a few were deflected at large angles. This observation led Rutherford to propose the nuclear model of the atom, where he suggested that an atom's positive charge and most of its mass were concentrated in a tiny, dense nucleus, with electrons surrounding it in fixed orbits.
1. Mendeleev came up with the first periodic table of the elements through a combination of empirical observation and careful organization of the elements. Here's how you can understand his process:
a. Gather data on the elements: Mendeleev collected information about the properties of various elements known at that time, such as atomic mass, chemical reactivity, and other characteristics.
b. Arrange elements by atomic mass: He arranged the elements in order of increasing atomic mass, recognizing that there was a periodic repeat in the properties based on this ordering.
c. Notice patterns and create groups: By organizing the elements according to their properties, Mendeleev noticed that elements with similar properties appeared at regular intervals. This led him to form groups or columns in his periodic table based on similarities in chemical behavior.
d. Leave gaps for undiscovered elements: Mendeleev cleverly left gaps in his periodic table for elements that were yet to be discovered. He predicted their properties based on his understanding of the periodic patterns and their placement in the table.
2. John Dalton's atomic theory proposed that atoms were indivisible particles and that all elements were made up of identical atoms. However, J.J. Thomson's cathode-ray tube experiments disproved the notion of indivisible atoms. Here's how Thomson's experiments challenged Dalton's theory:
a. Cathode-ray tube experiments: Thomson studied the properties of cathode rays, which are streams of charged particles emitted from a negatively charged electrode (cathode) in a vacuum tube.
b. Discovery of electrons: Through his experiments, Thomson discovered that cathode rays were made up of negatively charged particles that he called "electrons." This discovery implied that atoms were not indivisible as Dalton had proposed.
c. Plum pudding model: Dalton's theory suggested that atoms were solid, indivisible spheres. However, Thomson's discovery of electrons led him to propose the "plum pudding model," which suggested that atoms were a positively charged substance with negatively charged electrons distributed within it, much like raisins in a plum pudding.
3. Robert Millikan contributed to our understanding of electrons through his famous oil drop experiment. Here's how he made his important contribution:
a. The oil drop experiment: Millikan designed an experiment that involved suspending tiny oil droplets in an electric field.
b. Determining the charge of an electron: By measuring how the electric field affected the motion of the oil droplets, Millikan was able to measure the charge on an individual droplet. He observed that the charges were quantized, meaning they occurred in discrete amounts.
c. Calculating the charge of an electron: Millikan's experiments allowed him to calculate the charge of an electron accurately. This information contributed significantly to our understanding of the fundamental properties of electrons.
4. The Coulomb force affects charge interactions by describing the interaction between charged particles. Here's how it works:
a. Coulomb's law: The Coulomb force is described by Coulomb's law, which states that the force between two charged objects is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
b. Attraction and repulsion: If two objects have opposite charges (positive and negative), they attract each other due to the Coulomb force. Similarly, if two objects have the same charge (either positive or negative), they repel each other due to the Coulomb force.
c. Strength of interactions: The Coulomb force becomes stronger as the charges on the objects increase and weaker as the distance between them increases. This force is responsible for various electrical phenomena, such as the attraction of electrons to positively charged nuclei in atoms or the repulsion between like charges.
5. Ernest Rutherford's observation, along with his students, refuted the plum pudding model through their gold foil experiment. Here's an explanation of how this experiment challenged the existing model:
a. Gold foil experiment: Rutherford and his team directed a beam of alpha particles (positively charged particles) at a thin sheet of gold foil.
b. Unexpected results: According to the plum pudding model, the alpha particles were expected to pass straight through the gold foil or deviate slightly. However, Rutherford observed that a small fraction of the particles were deflected at large angles and even bounced back.
c. Nuclear model of the atom: This unexpected deflection of the alpha particles led Rutherford to propose a new model known as the nuclear model of the atom. He concluded that atoms consisted mostly of empty space, with a tiny, dense, positively charged nucleus at the center. The electrons were then thought to orbit the nucleus at a distance.
This experiment refuted the plum pudding model's idea of electrons being evenly distributed throughout an atom, as the deflections showed the presence of a solid nucleus and the majority of an atom's mass being located in the center.