1.1 A simple model of the atom & symbols Flashcards
What is an atom?
An atom is the smallest part of an element that can exist
What is an element?
An element is a substance of only one type of atom
How are the elements listed and approximately how many are there?
They are listed in the periodic table and there are approximately 100
Elements may combine through chemical reactions to form new products; what are
these new substances called?
Compounds
What is a compound?
Two or more elements combined chemically in fixed proportions which can be represented by formulae
Do compounds have the same properties as their constituent elements?
No, they have different properties.
Describe the plum-pudding model
The atom is a ball of positive charge with negative electrons randomly placed in it.
Describe the Bohr / nuclear model and how it came about
The nuclear model suggests that electrons orbit the nucleus at specific
distances (shells) – it came about after Rutherford’s alpha scattering experiment
Later experiments led to the discovery of smaller, positive
particles in the nucleus; what are
these particles called?
Protons
Who discovered the neutron? What year?
James Chadwick, 1932
Describe the structure of an
atom
The atom has a small central nucleus (made up of protons and neutrons) around which there are electrons
What is the radius of an atom?
0.1 nm
What is the radius of a nucleus and
what is it compared to that of the atom?
1 x 10^-14 m and 1/10000
What name is given to the
number of protons in the nucleus?
Atomic number
Atoms of the same element have the same number of which particle in the nucleus?
Protons
Where is the majority of the mass of an atom?
The nucleus
How do you calculate the
number of neutrons using mass number and atomic number?
Subtract the atomic number from the mass number
What is the mass number?
The total number of protons and neutrons
Atoms of the same element have the same number of which particle in the nucleus?
Protons
What is an isotope? Do isotopes of a certain element have the same chemical properties?
Atoms of the same element (same proton number) that have a different number of neutrons.
They have the same chemical properties as they have the same electronic structure
Who discovered the electron? What year?
J.J. Thomson, 1897
Who proposed the plum pudding model?
J.J. Thomson
Who discovered the proton? What year?
Ernest Rutherford, 1917
Who proposed the nuclear model?
Ernest Rutherford
Who proposed the planetary model?
Niels Bohr
Who discovered electron shells? What year?
Niels Bohr, 1913
Who theorised atoms? What year?
Democritus, 500 BC
What was Rutherford’s alpha scattering experiment?
In 1905, Ernest Rutherford conducted an experiment to test the plum pudding model. He directed a beam of alpha particles at a very thin gold leaf suspended in a
vacuum.
-Most of the alpha
particles did pass
straight through
the foil
-A small number of
alpha particles
were deflected by
large angles (> 4°)
as they passed
through the foil
-A very small
number of alpha
particles came
straight back off
the foil
.
What was concluded after Rutherford’s alpha scattering experiment?
The fact that most alpha particles went straight through the foil is evidence for the atom being mostly empty space
A small number of alpha particles being deflected at large angles suggested that there is a concentration of positive charge in the atom - like charges repel, so the positive alpha particles were being repelled by positive charges
The very small number of alpha particles coming straight back suggested that the positive charge and mass are concentrated in a tiny volume in the atom (the nucleus)
Why was a vacuum used in Rutherford’s alpha scattering experiment?
The vacuum is important because any deflection of the alpha particles would only be because of collisions with the gold foil and not due to deflections off anything else.
Why was gold foil used in Rutherford’s alpha scattering experiment?
Gold was used because it was the only metal that could be rolled out to be very, very thin without cracking.
