4.1🫧 Flashcards
What is an atom?
The smallest part of an element that can exist
What is a compound?
Formed from elements by chemical reactions.
(2 or more elements chemically combined)
What is a chemical reaction?
Involve the formation of one or more new substances and often involve and energy change
How can compounds be separated into elements?
Chemical reactions
What is a mixture?
2 or more elements not chemically combined together.
What happens to the chemical properties in a mixture?
They remain unchanged
How can mixtures be separated? (Give examples)
They are separated by physical processes such as: filtration, crystallisation, simple distillation, fractional distillation and chromatography.
What was the first model of the atom?
John Dalton - an atom is a sphere that cannot be divided.
What model came next?
The plum pudding model - JJ Thompson
Describe the plum pudding model:
This model suggested that atoms exist as a ball of positive charge with negative electrons scattered in it.
What was the name of the experiment that led to the displacement of the plum pudding model
The alpha scattering experiment
Describe the alpha scattering experiment and its findings:
A Beam of alpha particles was fired at a thin piece of gold foil, suspended in a vacuum.
Most particles went straight through which showed that the atom was mostly empty space. Some alpha particles were
Deflected so the nucleus must be positively charged. Few alpha particles were deflected at a 90° angle which showed that the mass of an atom is concentrated in the nucleus.
This showed that the plum pudding must be an incorrect explanation of the atom.
What model was constructed after this experiment?
The nuclear model - Rutherford
Describe the nuclear model:
Positive nucleus, electrons orbiting the nucleus.
What did Neil’s Bohr contribute to the development of the atom?
He said that electrons exits in shells / energy levels, and each energy level is a fixed distance from the nucleus. (2,8,8 rule).
