Topic 2 (Chemistry) Flashcards
What were the key points of Dalton’s atomic model?
All matter consists of tiny particles called atoms.
Atoms are indivisible and identical within an element.
Atoms cannot be created or destroyed.
What was JJ Thomson’s plum pudding model and when was it proposed?
Description: Atom as a sphere of positive charge with embedded electrons.
Proposed in 1897 after the discovery of the electron.
What experiment did Rutherford conduct, and what were its key findings?
Experiment: Directed alpha particles at a thin gold foil.
Findings: Most passed through, some deflected, few reflected.
What conclusions did Rutherford draw from his experiment?
Most of an atom is empty space.
There is a positive nucleus at the center.
Electrons orbit the nucleus.
What were the key findings of Rutherford’s gold foil experiment, and what conclusions did he draw from them?
In Rutherford’s experiment, most alpha particles passed straight through the gold foil, but some were deflected at large angles, and a few were reflected back. From these results, Rutherford concluded that most of an atom is empty space, there is a dense positive nucleus at the center of the atom, and electrons orbit the nucleus.
What did Bohr observe about the light emitted by heated atoms, and how did he interpret it?
Bohr observed that the light emitted by heated atoms always had specific amounts of energy. He concluded that electrons orbit the nucleus in fixed energy levels, and each energy level corresponds to a specific amount of energy. This led to the development of the Bohr model of the atom.
What is sublimation?
Sublimation is the process in which a substance transitions directly from a solid to a gas phase without passing through the intermediate liquid phase.
Define melting.
Melting is the process in which a solid substance changes to its liquid phase as a result of an increase in temperature.
What is evaporation?
Evaporation is the process in which a liquid substance changes to its gas phase at the surface, typically at a temperature below its boiling point.
Describe the characteristics of a solid
Arrangement: Closely packed, fixed position.
Movement: Particles vibrate around their fixed positions.
Kinetic energy: The least.
Describe the characteristics of a liquid.
Arrangement: Close together, no fixed position.
Movement: Particles can move or flow while maintaining contact with each other.
Kinetic energy: Some.
Describe the characteristics of a gas.
Arrangement: Far apart, random position.
Movement: Particles move very fast and randomly.
Kinetic energy: The most.
What is condensation?
Condensation is the process in which a gas changes to its liquid phase due to a decrease in temperature.
Define freezing.
Freezing is the process in which a liquid substance changes to its solid phase as a result of a decrease in temperature.
What is desublimation?
Desublimation, also known as deposition, is the process in which a substance transitions directly from a gas to a solid phase without passing through the intermediate liquid phase.
What is a pure substance?
A pure substance is made up of only one type of element or compound.
What is an impure substance or mixture?
An impure substance or mixture is made of two or more substances that are not chemically joined together.
Define an element.
An element is a substance made of one type of atom only.
Define a compound.
A compound is a substance formed when two or more elements are chemically bonded together.
What is an atom?
An atom is the smallest part of an element that can exist.
How do pure substances differ from mixtures?
Pure substances contain only one type of element or compound, while mixtures contain two or more substances that are not chemically bonded.
Give an example of a pure substance.
An example of a pure substance is pure gold (Au) or pure water (H2O).
Give an example of a mixture.
An example of a mixture is air, which contains a combination of gases such as nitrogen, oxygen, carbon dioxide, and others.
What is the melting point of a substance?
The melting point is the temperature at which a substance changes from a solid to a liquid phase.
Define the boiling point of a substance.
The boiling point is the temperature at which a substance changes from a liquid to a gas phase.
How can the physical state of a substance be predicted using its melting and boiling points?
If the temperature is below the melting point, the substance is in a solid state. If it is between the melting and boiling points, it is in a liquid state. If it is above the boiling point, it is in a gaseous state.
Provide an example illustrating the prediction of a substance’s physical state based on its melting and boiling points.
For example, water has a melting point of 0°C and a boiling point of 100°C. If the temperature is 52°C, water would be in a liquid state because it is between its melting and boiling points.
What physical state is a substance in if the temperature is below its melting point?
If the temperature is below the melting point, the substance is in a solid state.
At what temperature is a substance in a gaseous state?
A substance is in a gaseous state when the temperature is above its boiling point.
What physical state is a substance in if the temperature is between its melting and boiling points?
If the temperature is between the melting and boiling points, the substance is in a liquid state.
What do heating/cooling curves show?
Heating/cooling curves show the changes in temperature of a substance as it is being heated or cooled.
Describe the behavior of particles in a solid as it is heated
Particles in a solid vibrate faster on their fixed position, and their kinetic energy increases.
What happens to the temperature at the melting point of a substance?
At the melting point, the temperature remains constant because the attractive forces between solid particles are being overcome, causing particles to vibrate faster.
How does the heating curve of a pure substance differ from that of an impure substance?
The heating curve of a pure substance will have horizontal lines at the melting and boiling points, indicating a constant temperature during phase change. In contrast, the heating curve of an impure substance will have a shallow gradient at the melting and boiling points due to different particles melting/boiling over a range of temperatures.
