1. Atoms, subatomic particles, and isotopes
Units 2.1 – 2.5
Atoms, subatomic particles, and isotopes

2. Unit 2.1 – inside an atom

4. Proton number is the same as atomic number
Proton number is the same as atomic number. It tells the number of protons in an atom
Nucleon number is also known as a mass number (it is the number of protons and neutrons).
The electron shells are the same as energy levels. These contain the electrons.

5. Unit 2.2
Isotopes are atoms that have the same proton number, but a different nucleon number (i.e. the number of neutrons is different).

6. Radioactive isotopes
Radioactive isotope, also called radioisotope, any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.

7. Radioisotopes in Medicine
Nuclear medicine uses radiation to provide diagnostic information about the functioning of a person's specific organs, or to treat them. Diagnostic procedures using radioisotopes are now routine.
Radiotherapy can be used to treat some medical conditions, especially cancer, using radiation to weaken or destroy particular targeted cells.
Tens of millions of nuclear medicine procedures are performed each year, and demand for radioisotopes is increasing rapidly.
Sterilisation of medical equipment is also an important use of radioisotopes.

8. Radioisotopes in Industry
Science and industry use radioisotopes in a variety of ways to improve productivity and, in some cases, to gain information that cannot be obtained in any other way.
Sealed radioactive sources are used in industrial radiography, gauging applications and mineral analysis.
Short-lived radioactive material is used in flow tracing and mixing measurements.
Various radioactive decay series are used to measure the ages of materials incorporating them.
Gamma sterilisation is used for medical supplies, some bulk commodities and, increasingly, for food preservation.

9. Unit 2.3 Electronic structure and the periodic table

10. The diagram shows a section of the periodic table, with the elements arranged as usual in the order of their atomic number, from 2 to 20. The red numbers below each chemical symbol show its electronic structure.

11. Moving across each period, you can see that the number of occupied energy levels is the same as the period number.
As you go across each period from left to right, an energy level gradually becomes filled with electrons. The highest occupied energy level contains just one electron on the left-hand side of the table. It is filled by the time you get to the right-hand side.
Moving down each group, you can see that the number of electrons in the highest occupied energy level is the same as the group number.

12. Unit 2.4 Elements, compounds and mixtures

13. Elements consists of only one kind of atom,
cannot be broken down into a simpler type of matter by either physical or chemical means, and
can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen).

14. Compounds
consists of atoms of two or more different elements bound together
can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means),
has properties that are different from its component elements, and
always contains the same ratio of its component atoms.

15. Mixtures
consists of two or more different elements and/or compounds physically intermingled,
can be separated into its components by physical means, and
often retains many of the properties of its components.

16. Metals and non-metals

17. Calculating density
Density of a substance equals the mass divided by the volume.