Atoms & Isotopes Flashcards
All 51 cards in this deck
What is the approximate radius of an atom?
About m
How does the radius of a nucleus compare with the radius of an atom?
The nucleus has a radius less than of the radius of the atom.
Describe the basic structure of an atom.
A positively charged nucleus made of protons and neutrons, surrounded by negatively charged electrons.
What are the charges of the proton, neutron and electron?
Proton: positive. Neutron: neutral (no charge). Electron: negative.
Where is most of the mass of an atom concentrated, and why?
In the nucleus — protons and neutrons are far more massive than electrons.
True or false? Electrons make up most of the mass of an atom.
False. Almost all the mass is in the nucleus; electrons have very little mass.
True or false? A nuclear radius of about m is smaller than an atomic radius of m.
True. A more negative power of ten means a smaller number.
How are electrons arranged in an atom?
At different distances from the nucleus, in different energy levels (shells).
What happens to an electron when it absorbs electromagnetic radiation?
It moves to a higher energy level, further from the nucleus.
What happens when an electron moves to a lower energy level, closer to the nucleus?
It emits energy in the form of electromagnetic radiation.
True or false? An electron must emit electromagnetic radiation to move further from the nucleus.
False. It must absorb electromagnetic radiation to move to a higher energy level.
True or false? Absorbing electromagnetic radiation changes the number of protons in an atom.
False. It only changes the energy level of an electron; the nucleus is unaffected.
What is the atomic number of an atom?
The number of protons in its nucleus.
What is the mass number of an atom?
The total number of protons and neutrons in the atom.
In the nuclear symbol , what do and stand for?
is the mass number; is the atomic number (number of protons).
What are the steps to find the number of neutrons in an atom from its nuclear symbol?
e.g.
- Read the mass number (top):
- Read the atomic number (bottom):
- Neutrons = mass number − atomic number =
What decides which element an atom is?
Its number of protons (atomic number) — all atoms of an element have the same number of protons.
True or false? Two atoms with the same mass number must be the same element.
False. Only the same atomic number (number of protons) means the same element.
What are isotopes?
Atoms of the same element with the same number of protons but different numbers of neutrons.
How can you tell from two nuclear symbols that the atoms are isotopes of the same element?
e.g. and
Same atomic number (bottom number) but different mass number (top number) — both have protons, so they are isotopes of carbon.
True or false? Isotopes of the same element have different numbers of electrons.
False. They have the same number of electrons; only the neutron number differs.
True or false? Isotopes of an element have different mass numbers.
True. Extra neutrons increase the mass number.
What does a number written after an element's name, as in carbon-14, tell you?
The mass number (total protons + neutrons).
Why do atoms have no overall electrical charge?
The number of electrons equals the number of protons, so the negative and positive charges cancel.
How does an atom turn into a positive ion?
By losing one or more outer electrons.
True or false? An atom becomes a positive ion by gaining protons.
False. It becomes a positive ion by losing outer electrons; the proton number never changes in ionisation.
True or false? A positive ion has more protons than electrons.
True. It has lost electrons, so protons outnumber electrons.
What is the plum pudding model of the atom?
A ball of positive charge with negative electrons embedded in it.
What discovery led to the plum pudding model?
The discovery of the electron (1897).
What were atoms thought to be before the electron was discovered?
Tiny spheres that could not be divided.
Give one key difference between the plum pudding model and the nuclear model.
In the plum pudding model positive charge is spread through the whole atom; in the nuclear model it is concentrated in a tiny central nucleus.
True or false? The plum pudding model contained a nucleus.
False. It had no nucleus — electrons were embedded in a ball of positive charge.
What was fired at what in the alpha particle scattering experiment?
Alpha particles were directed at a thin sheet of gold foil.
In alpha particle scattering, what does it show that most alpha particles passed straight through the foil undeflected?
The atom is mostly empty space.
In alpha particle scattering, what does it show that a few alpha particles were deflected back towards the source?
The mass of the atom is concentrated at the centre in a nucleus, and the nucleus is charged.
Why is an alpha particle repelled as it passes close to a nucleus?
The alpha particle and the nucleus both have positive charge, and like charges repel.
Why is the path of one alpha particle more tightly curved than another's in the scattering experiment?
It passes closer to the nucleus, so experiences a stronger repulsive force (stronger electric field).
Which model of the atom did the results of the alpha particle scattering experiment replace, and with what?
It replaced the plum pudding model with the nuclear model.
True or false? The plum pudding model predicted that some alpha particles would bounce straight back off the foil.
False. It predicted all alpha particles would pass through with little or no deflection.
How did Niels Bohr adapt the nuclear model of the atom?
He suggested that electrons orbit the nucleus at specific distances (energy levels / shells).
Why was Bohr's model of the atom accepted?
His theoretical calculations agreed with experimental observations.
True or false? Bohr rejected the idea of a nucleus.
False. He kept the nuclear model and adapted it, adding electrons in fixed orbits.
What is the name given to the small particles of positive charge in the nucleus, each with the same amount of charge?
Protons.
Whose experimental work provided evidence for the existence of neutrons?
James Chadwick.
How long after the nucleus became an accepted idea was the neutron shown to exist?
About 20 years later.
True or false? The neutron was discovered before the proton.
False. The proton (1920) came first; Chadwick's evidence for the neutron came in 1932.
Put in order: discovery of the electron, the nucleus, the proton, the neutron.
Electron (1897), nucleus (1911), proton (1920), neutron (1932).
What can cause a scientific model to be changed or replaced?
New experimental evidence that the existing model cannot explain.
Name, in order, the atomic models from the indivisible sphere to Bohr's model.
Indivisible sphere → plum pudding model → nuclear model → Bohr model.
True or false? Scientific models of the atom stay the same once experiments have supported them.
False. New experimental evidence may lead to a model being changed or replaced.
Which experiment provided the evidence that led to the nuclear model of the atom?
The alpha particle scattering experiment.