Atoms & Isotopes (AQA GCSE Physics): Flashcards
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- FrontAtomic Structure
Define nucleus.
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Define nucleus.
The nucleus is the tiny, dense centre of an atom, which contains almost all of its mass.
What is the approximate radius of an atom?
About 1 × 10⁻¹⁰ m.
How does the radius of the nucleus compare with the radius of the whole atom?
The radius of the nucleus is over 10,000 times smaller than the radius of the whole atom, even though it contains almost all of the atom's mass.
Define a proton.
A proton is a positively charged particle found in the nucleus, with a relative atomic mass of one unit.
Define a neutron.
A neutron is a particle found in the nucleus with no charge, and a relative atomic mass of one unit.
What are the charge and relative mass of an electron?
An electron has a negative charge and a mass of about 1/2000 the mass of a proton or neutron.
Electrons orbit the nucleus at particular distances, known as ______.
Electrons orbit the nucleus at particular distances, known as energy levels.
How many electrons can occupy the first, second and third energy levels?
The first energy level holds up to two electrons. The second and third energy levels each hold up to eight electrons.
True or False?
Electrons in higher energy levels are closer to the nucleus.
False.
The higher the energy level, the further the electron is from the nucleus, and the greater its potential energy.
Why is the overall charge of an atom zero?
Because the number of electrons is equal to the number of protons, so the positive and negative charges cancel out.
What happens to an electron when it absorbs electromagnetic radiation?
It moves to a higher energy level.
Give two examples of electromagnetic radiation that can be absorbed by electrons in an atom.
Visible light and infrared radiation.
Why are dark coloured objects good absorbers of radiation?
They do not reflect the energy that hits them.
Lower energy levels are ______ to the nucleus, while higher energy levels are further away.
Lower energy levels are closer to the nucleus, while higher energy levels are further away.
Why is an electron unstable after absorbing electromagnetic radiation and moving to a higher energy level?
It will eventually move back down to its original, lower energy level.
What happens when an electron moves back down to its original energy level?
It emits a wave of electromagnetic radiation.
True or False?
All of the colours in the visible spectrum are produced by electrons moving down energy levels and emitting electromagnetic radiation.
True.
The light waves come from electrons moving down energy levels and emitting electromagnetic radiation.
Define atomic number.
The atomic number is the number of protons in an atom. It is also equal to the number of electrons.
Define mass number.
The mass number is the total number of protons and neutrons in the nucleus of an atom.
Number of neutrons = ______ number − atomic number.
Number of neutrons = mass number − atomic number.
A sodium atom has a mass number of 23 and an atomic number of 11. How many neutrons does it have?
23 − 11 = 12 neutrons.
True or False?
The atomic number of a particular element can vary between atoms of that element.
False.
The atomic number of a particular element is always the same, since it determines which element the atom is.
In nuclear notation, what does the top number represent?
The mass number (the total number of protons and neutrons).
In nuclear notation, what does the bottom number represent?
The atomic number (the total number of protons).
A gold atom has an atomic number of 79 and a mass number of 197. How many protons, neutrons and electrons does it have?
79 protons, 118 neutrons (197 − 79) and 79 electrons.
Define isotopes.
Isotopes are atoms of the same element that have an equal number of protons but a different number of neutrons.
How does the number of neutrons in an atom affect its chemical properties, such as charge?
It does not affect chemical properties, since neutrons have no charge. It only affects the atom's mass.
Why is chlorine's mass number given as 35.5 rather than a whole number?
Chlorine has two isotopes, with mass numbers 35 and 37. Chlorine-35 is more abundant than chlorine-37, so the average mass number is closer to 35 than 37, giving 35.5.
The number of electrons and protons in different isotopes of an element remains the ______.
The number of electrons and protons in different isotopes of an element remains the same.
True or False?
Some isotopes are unstable because they have an imbalance of protons and neutrons.
True.
An imbalance of protons and neutrons can make an isotope unstable.
Chlorine-35 and chlorine-37 both have 17 protons. How many neutrons and electrons does each isotope have?
Chlorine-35: 18 neutrons, 17 electrons.
Chlorine-37: 20 neutrons, 17 electrons.
Define an ion.
An ion is an atom or particle with a non-zero (overall) charge.
Name three ways electrons can be removed from an atom.
By friction (rubbing objects together), by absorbing electromagnetic radiation, or from chemical reactions.
Why does an atom become positively charged when it loses one or more electrons?
Electrons are negatively charged, so losing them leaves the atom with more positive charge than negative, making it a positive ion.
True or False?
Protons can move between atoms to cause charging.
False.
Protons are locked away in the nucleus and cannot move between atoms. It is always the movement of electrons that causes charging.
If a neutral atom ______ electrons, it becomes negatively charged.
If a neutral atom gains electrons, it becomes negatively charged.
How does the reactivity of ions generally compare to that of neutral atoms?
Ions are often more chemically reactive than neutral atoms because of their charge, although reactivity also depends on the specific reaction taking place.
Define a scientific model (of the atom).
A model is a way of describing something in order to explain the way it behaves.
What were atoms thought to be, before the discovery of the electron?
Indivisible — tiny spheres that could not be divided.
What discovery led to a new model of the atom being developed?
The discovery of the electron led to the development of a new model of the atom.
Describe the Plum Pudding model of the atom.
The atom consists of negatively charged electrons (the 'plums') embedded within a positively charged 'dough' or 'pudding'.
Why was the rest of the atom thought to be positively charged in the Plum Pudding model?
Because electrons are negatively charged, so the rest of the atom had to be positive to make the atom overall neutral.
Further experiments involving ______ particle scattering produced results that could not be explained by the Plum Pudding model.
Further experiments involving alpha particle scattering produced results that could not be explained by the Plum Pudding model.
True or False?
The Plum Pudding model was replaced after experiments in 1909 produced results it could not explain.
True.
The Plum Pudding model was replaced by the nuclear model.
Define alpha particle.
An alpha particle is a helium nucleus, represented as a He²⁺ ion, fired at the gold foil in Rutherford's scattering experiment.
Who conducted the alpha scattering experiment, under the instruction of Ernest Rutherford?
Hans Geiger and Ernest Marsden conducted the alpha scattering experiment.
What result did scientists expect to see if the Plum Pudding model was correct?
They expected the alpha particles to travel straight through the gold foil, with at most a small change in direction.
Describe the three findings of the alpha scattering experiment.
Most alpha particles passed straight through the foil, some changed direction but continued through the foil, and a few bounced back off the foil.
True or False?
The bouncing back of alpha particles could be explained by the Plum Pudding model.
False.
The bouncing back of alpha particles could not be explained by the Plum Pudding model, so a new model had to be created.
In the nuclear model, nearly all of the mass of the atom is concentrated in the ______, which is positively charged.
In the nuclear model, nearly all of the mass of the atom is concentrated in the nucleus, which is positively charged.
Describe the arrangement of electrons in the nuclear model.
Negatively charged electrons orbit the nucleus at a distance.
Define energy level.
An energy level is one of the different fixed distances at which electrons orbit the nucleus in the Bohr model.
Who proposed the Bohr model of the atom, and what earlier model did he use as its basis?
Niels Bohr proposed the model, using the nuclear model as its basis.
How many electrons can occupy the first energy level, and how many can occupy the second and third energy levels?
Up to two electrons can occupy the first energy level, and up to eight electrons can occupy each of the second and third energy levels.
The Bohr model was accepted because it could explain the processes of ______ and ______ of electromagnetic radiation.
The Bohr model was accepted because it could explain the processes of absorption and emission of electromagnetic radiation.
Give two reasons the Bohr model became the accepted model of the atom.
It could explain the findings of experiments better than the nuclear model, and theoretical calculations made using the model agreed with experimental results.
True or False?
The Bohr model describes electrons as orbiting the nucleus at random, changing distances.
False.
In the Bohr model, electrons orbit the nucleus at fixed, distinct energy levels, not random distances.
Define proton.
A proton is a positively charged particle found in the nucleus, originally identified as the smallest whole-number unit of positive charge.
Who discovered that the nucleus could be broken down into smaller, positively charged particles?
Ernest Rutherford discovered this.
What does the word "proto" mean, and why is this an appropriate origin for the name proton?
"Proto" means original; protons are named this because they are the original unit of positive charge.
How many protons and electrons does an alpha particle contain, and what is its overall charge?
An alpha particle contains two protons and no electrons, giving it an overall charge of +2.
Who proved the existence of the neutron?
James Chadwick proved the existence of the neutron.
A neutron has a mass similar to the ______, but it has ______ charge.
A neutron has a mass similar to the proton, but it has no charge.
Describe the model of the atom produced after the discovery of the neutron.
A positive, dense nucleus made from neutrons and protons, with negative electrons orbiting on different energy levels.
True or False?
It took scientists about twenty years after the nucleus became an accepted scientific idea to confirm the existence of the neutron.
True.
Many scientists suspected another particle existed, but it took about twenty years after the nucleus became an accepted scientific idea before the neutron's existence was confirmed.
What determines whether a scientific model is considered the best model of the atom?
The model that can best explain the evidence from experiments.
What replaced the Plum Pudding model as a result of Rutherford's alpha scattering experiment?
The nuclear model replaced the Plum Pudding model.
The nuclear model could explain why alpha particles ______ from the gold foil, which the Plum Pudding model could not.
The nuclear model could explain why alpha particles bounced back from the gold foil, which the Plum Pudding model could not.
In Rutherford's gold foil experiment, what did scientists observe about the proportion of alpha particles deflected by very large angles?
Only a very small proportion of alpha particles were deflected by very large angles.
Why did the unexpected results of the gold foil experiment lead to a new model of the atom?
The results could not be explained using the Plum Pudding model, so it was disproved, and the nuclear model was devised to match the results.
Why is it important that Rutherford's predicted proportions of deflected alpha particles matched the experimental results?
It supports the nuclear model as an accurate description of the atom.
True or False?
Once a scientific model is accepted, it can never be replaced, even if new evidence is found.
False.
Scientific models of the atom have changed and improved throughout history as new evidence emerged.
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