How is the positive charge of a nucleus related to protons?
It is a whole number of equal positive charges, each associated with a proton.
AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher · 5.1.1.3
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How is the positive charge of a nucleus related to protons?
It is a whole number of equal positive charges, each associated with a proton.
What is a neutron?
An uncharged particle within the nucleus.
Whose experimental work provided evidence for neutrons?
James Chadwick’s.
When did evidence for neutrons appear relative to the acceptance of the nucleus?
About 20 years after the nucleus became an accepted scientific idea.
What did the alpha particles that passed straight through the foil reveal about atoms?
Atoms are mostly empty space.
What did the large-angle deflections and occasional bounce-backs of alpha particles reveal about atoms?
Most of an atom’s mass and all its positive charge are concentrated in a tiny central region.
What is the structure of an atom in the nuclear model?
A small, dense, positively charged nucleus sits at the centre, with electrons outside it.
How do the nuclear and plum pudding models differ in their distribution of positive charge?
The nuclear model concentrates it in the nucleus; the plum pudding model spreads it throughout the atom.
How were atoms pictured before the discovery of electrons?
As tiny, solid spheres that could not be divided.
Why did the discovery of the electron require the earlier model of the atom to change?
It showed that atoms contain smaller parts.
How does the plum pudding model describe an atom?
A sphere of positive charge, spread throughout the atom, with negative electrons embedded in it.
What are the size, charge and position of an atom’s nucleus?
It is small and positively charged, at the centre of the atom.
How are electrons arranged around the nucleus in the Bohr model?
They occupy fixed shells, or energy levels, at specific distances from the nucleus.
Why did scientific models of atomic and nuclear structure change over time?
New evidence became available.
How did the plum pudding model represent an atom?
Positive charge was spread through the atom, with electrons embedded in it.
How did Rutherford’s nuclear model represent the distribution of positive charge and mass?
Positive charge and most of the mass were concentrated in a small central nucleus.
Before the neutron was discovered, which particles were sometimes thought to make up nuclei?
Protons and electrons.
Who discovered the neutron, and in what year?
Chadwick, in 1932.
What model of the nucleus did Chadwick’s discovery support?
Nuclei contain protons and neutrons.
Why can nuclei of the same element have different masses?
They have the same number of protons but different numbers of neutrons.