development of the atomic model Flashcards
(20 cards)
When Democritus first conceived of atomic theory, around 500 BC, how did he describe atoms?
- The smallest possible unit of matter
-separated from each other by empty space
In the 1800’s, John Dalton described atoms as solid _______, and suggested that different types of spheres make up the different ________.
Spheres, elements
In 1897 J. J. Thomson theorised that an atom consisted of a ball of positive charge, with negative electrons mixed throughout it. What do we call this model?
Plum pudding model
In Rutherford’s experiments, _______ particles were fired at a thin sheet of gold foil. Most particles passed through, but some were __________ off course.
alpha, deflected
(RUTHERFORD EXPERIMENT) This caused him to hypothesise that there was a dense region of _______ charge at the centre of the atom that repelled the alpha particles. As a result he developed the nuclear model of the atom, in which there was a central positive nucleus, surround by _______ electrons.
Positive, negative
One issue with Rutherford’s nuclear model was that the atom should collapse as the negative electrons would be attracted to the positive nucleus, causing them to rush inwards.
In response to this, in 1913 Bohr suggested that electrons ___________________, which prevents the atom from collapsing.
Orbit the nucleus in shells
Describe the results of the alpha particles scattering experiment
Rather than all of the alpha particles passing straight through the sheet of gold as you would expect from the plum pudding model, some were deflected to the side, and a small number were even deflected backwards.
Who discovered the plum pudding model? In what year?
JJ Thompson 1897
How did Rutherford develop the nuclear model
Alpha particle scattering experiment
Who discovered that electrons orbit the nucleus in shells? When?
Niels Bohr, 1913
In the 20th century, Chadwick discovered neutral particles in the atomic nucleus. What are these particles called?
Neutrons
Summarise John Daltons theory
John Dalton described atoms as solid spheres, and said that different-sized spheres made up the different elements.
Summarise J J Thompson’s findings and resulting theory.
J J Thomson found that atoms contain even smaller, negatively charged particles - electrons.
He proposed a new theory in which the atom was a ball of positive charge, with discrete electrons throughout it. It was known as the ‘plum pudding model’.
What is the nuclear model of the atom, and who proposed it?
-Ernest Rutherford.
-The nuclear model of the atom is the idea that each atom is composed of a small positively charged nucleus at the centre, surrounding by a ‘cloud’ of negative electrons.
What was the main issue with the nuclear model of the atom?
The electrons should be attracted to the positive nucleus, so the atom should just collapse.
What did Niels Bohr propose?
electrons orbit the nucleus in shells, which are a fixed distance from the nucleus.
What did James Chadwick discover?
James Chadwick discovered neutral particles called neutrons
What is the order of development of the atomic model (people)
Democritus, John Dalton, JJ Thompson, Ernest Rutherford, Niels Bohr, Schrödinger and Paul, James Chadwick
What did Schrödinger and Paul discover
Electrons ‘clouds’ and ‘orbitals’
what did john dalton discover
- atoms are indivisible and indestructive
- atoms of the same element are identical
- atoms of different elements differ in some fundamental way
- atoms combine in simpler whole number ratios to form compounds
- atoms are solid spheres
-diff types of spheres represent diff elements
