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"During the 20th century, we came to understand that the essence of all substances - their colour, texture, hardness and so forth - is set by their structure, on scales far smaller even than a microscope can see. Everything on Earth is made of atoms, which are, especially in living things, combined together in intricate molecular assemblages." -Martin Rees
As time goes on scientists make impressive discoveries in the field of biology, physics and chemistry. The hard work of a few motivated men and women benefits people all over the world.
Through scientific advancements, we have come to learn more about the reproductive system, the fact that the earth is round, the laws of gravity and that absolutely everything on earth is made up of atoms.
Understanding more about the atomic structure can be done by studying physics in the last few years of secondary school. The GCSE Physics Syllabus, that is offered by exam boards in the United Kingdom, has a total of eight topics and the fourth is atomic structure.
Superprof is here to guide potential students of physics and offer information on what to expect from the GCSE Physics Syllabus. We will now focus on the fourth topic of atomic structure and what is learnt in this section.
Models of the Atom
The exam board that is known as the AQA, divides the atomic structure topic into six parts. The first of these parts is designed to help students understand the basic models of the atom and how the atom is commonly known as the building block of matter.
The first to develop the early ideas of the atom were the Greeks. They thought that matter was made up of thousands or millions fo tiny uncuttable pieces and they called these pieces "atomos" which means uncuttable in Greek.
Centuries later English physicist JJ Thomson, who discovered the electron, suggested that atoms look like plum pudding and that solids cannot be squashed, therefore, the atoms which make the solid matter must be completely solid.
Students in this section analyze the gold foil experiment done by Ernest Rutherford and his associates to test the plum pudding model. This experience was done by directing a beam of alpha particles (a form of nuclear radiation with a large positive charge) at a very thin gold foil that was suspended in a vacuum.
Rutherford and his associates strongly believed that the alpha particles would pass straight through the foil and puncture it. However, the opposite happened with very little alpha particles passing through the foil. Rutherford concluded that the atom is mostly empty space and that there is a concentration of positive charge in the atom.
Nevertheless, in his experiment, Rutherford discovered the nuclear atom which is a small and positively charged nucleus. The nucleus was calculated to be about 1/10,000th the size of the atom.
Rutherford and Thomson were not the only pioneers in the field of physics. In this section, pupils learn about further developments to the atomic model. Bohr and his study of energy levels and James Chadwick with his investigation of the neutron are further examined in this first part of the atomic structure topic.
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Atoms, Isotopes and Ions
Atoms
Atoms are extremely small in size and have a radius of approximately 1 × 10-10 metres. An atom has a nucleus containing protons and neutrons with smaller electrons that circle around the nucleus.
Each particle has its own mass and its own charge:
| Charge | Mass | |
|---|---|---|
| Electron | +1 | 1 |
| Neutron | 0 | 1 |
| Proton | -1 | Almost 0 or (1/2,000) |
Protons and neutrons are the heaviest particles in an atom and the total number of them in an element is known as the mass number and the number of protons by themselves is called the atomic number.
The mass number and atomic number and both essential pieces of information about an atom. Atoms can be represented using the following symbol:
In this symbol A is the mass number, Z is the atomic number and X is the symbol or element. The numbers can be examined on the periodic table of elements which show how many particles are in the nucleus and how many protons each element has.
Isotopes
In this section, students will also discover what exactly isotopes are. They can be defined this way, they are the forms of an element that have the same number of protons but different numbers of neutrons. For example, chlorine has two isotopes and carbon has three.
Ions
Atoms are normally neutral and have the same number of protons in the nucleus as they have electrons spinning around. Nevertheless, there are always exceptions. These exceptions can possibly occur when there is a loss or gain of electrons after a collision. When this happens, little particles are created and are called ions.
Ions can either be positively or negatively charged. They are positively charged if the atom loses one or more electron and they are negatively charged if the atom gains one or more electron.
Radioactive Decay
If nuclei have an incorrect number of neutrons it can quickly fall apart. This is also called radioactive decay.
Attaining Stable Nuclei
The nucleus of an atom can only be stable if it has a certain amount of neutrons for the number of protons it has. Elements that have very few protons and that can be found near the top of the periodic table are stable if they have the same number of neutrons and protons.
Nevertheless, it is important to note that as the number of protons increases, more neutrons are needed to keep the nucleus stable and troubles at bay!
A nucleus that has too few or too many neutrons does exist in nature but will decay and eventually emit radiation.
Ask your physics and maths tutor who pioneered the concept of nuclear decay!
Nuclear Radiation
A nucleus can discharge a package of two protons and two neutrons called an alpha particle. The alpha decay causes the mass number and the atomic number of the nucleus to drop by four and two respectively.
If the poor little nucleus is overwhelmed and has too many neutrons, a proton transforms into a neutron and emits a fast-moving electron. This entire process is known as beta radiation. Beta decay will cause the atomic number of the nucleus to raise by one and the mass number stays the same.
When an alpha or beta particle is discharged, most often than not the nucleus will be too hot and will lose energy. The nucleus will try to cool down and while doing so it will emit a very energetic electromagnetic wave called a gamma ray. The atomic number and mass number remain the same during gamma-ray emission.
We have now analyzed the different types of radiation. They are often compared by the penetrating power, the ionising power and how far they can travel in the air.
There are reliable websites online that help students receive further information about the three types of radiation.
Half life
Radioactive decay is a very random process. Not all nuclei will decay at the same time. Scientists cannot precisely calculate when the particular nucleus will decay but graphs and estimates can be used to arrive at an educated guess.
Half life, which is the time it takes for half of the unstable nuclei to decay or for the activity to halve, can be used to determine the radioactive decay. The count rate is the number of decays recorded each second by a detector such as the Geiger-Muller tube.
In this section students also learn valuable equations to calculate the isotope remaining, the changes experienced by emitting alpha or beta particles.
Uses and Dangers of Radiation
We are all exposed to radiation in one way or another in our everyday life. Radiation can be very useful in certain situations but needs to be handled with a lot of care in order to avoid any serious problems.
Irradiation
Exposing objects to beams of radiation is called irradiation and can damage living cells. Nevertheless, it can be put to good use or become a hazard depending on how it is utilized.
Some of the ways it can be used include the following:
- Sterilizing fruit to preserve it when sold in supermarkets. Do not worry this process of irradiation does not cause the fruit to become radioactive!
- Medical irradiation can be used to sterilize surgical instruments and a tool known as a gamma knife can be used to kill tumours that are deep inside a patient's body.
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Contamination
This occurs when an object has a radioactive material introduced into it. It can be very useful or extremely harmful. The most common uses of contamination radiation are as follows:
- Medical contamination: injected radioactive sources can be used to make soft tissues such as blood vessels or kidneys. Medical image processing and x-rays are possible when an isotope emits gamma rays through the body to a detector outside.
- Checking for leaks: if the local government is suspicious of pipe leaks in the water supply, it can be contaminated with gamma-emitting radioactive isotope to find the leaks. Leaks can be identified when contaminated water seeps into the ground and causes a build-up of gamma emissions. This makes it easier to find the leak.
Students in the section compare irradiation versus contamination due to the fact that they are often mistaken for one another.
Background Radiation
Radioactive materials occur naturally and we are all exposed to a low-level of radiation per day. The most common causes of background radiation are radon gas from the ground, our own foods or drinks, cosmic rays, man-made objects such as microwaves and buildings.
Radiation can be easily calculated by using Becquerel (Bq) which is the measure of the activity and the nucleus.
It is extremely important to note that radiation can be extremely harmful on the human body causing cataracts, skin rashes, sterility, damaged DNA and even leukaemia or cancer in specific cases. Precautions need to be met if you are in regular contact with radiation.
My physics and maths tutor made these concepts graphically, alarmingly clear to me!
Nuclear Fission and Fusion
The nuclei of atoms most definitely contain a lot of energy. If this energy would be realized it would prevent the world from using so many fossil fuels. This can be done by using nuclear fission and nuclear fusion.
Nuclear Fission
Nuclear fission is the splitting of a large atomic nucleus into smaller nuclei. The whole nucleus splits into fragments called "daughter nuclei" and other reactions may occur causing something known as a "chain reaction." The fast-moving neutrons carry most of the energy but before a collision can occur they need to be slowed down.
This happens so that the energy can pass to other parts of the nuclear reactor. A fission reactor has a wide variety of parts that each have their own specific function and this learnt by the pupil in this section of the GCSE Physics Syllabus.
Nuclear Fusion
This is accomplished when two small and light nuclei join together to make one heavy nucleus. There are many different nuclear fusion reactions constantly happening in the Sun.
The simplest of these fusions is when four hydrogen nuclei become one helium nuclei.
It is also important to note that in all nuclear reactions a small amount of the mass changes to energy. It may not be a lot of energy but it is the result of the fusion experienced.
Sample Exam Questions for Atomic Structure
The first four topics of the GCSE Physics Syllabus are tested together and later on the last four are studied to mark the end of this GCSE subject. There are certain questions that can be expected on the assessment. Here are the different types of exam questions:
- Multiple choice questions,
- One and two mark questions,
- Three and four mark questions,
- Maths questions,
- Six mark questions,
- Equations.
The bitesize study guide from the BBC can prepare students for what questions may be on their examination by providing examples and explanations.
Studying the different sections of the atomic structure topic can prove to be very interesting and diverse. A thorough explanation of an atom, radioactive decay or uses of radiation is all covered in the GCSE Physics Syllabus and can be great fun for science enthusiasts!
Atomic structure is just one of the eight topics covered in the GCSE Physics Syllabus, the other seven include energy, electricity, particle model of matter, forces, waves, magnetism and electromagnetism and space physics.
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