Crossword Puzzle

1. an ion with a negative electrical charge
4. a simple molecule that can combine with other molecules to form a polymer
6. particle the nucleus of a helium atom that is produced by some radioactive substances
8. a type of particle in an atom that has the opposite electrical charge to the charge that a normal particle has
12. an ion that has a positive electrical charge
13. the part of the nucleus of an atom that has a positive electrical charge
14. the valency of an atom
17. the central part of an atom, consisting of protons and neutrons
18. the smallest unit of any substance

2. the part of the nucleus of an atom that has no electrical charge
3. a particle that is the same size as an electron but has a positive electrical charge
5. the smallest part of an element or compound that is capable of independent existence
7. the path that is taken by an electron around the nucleus of an atom
8. number the number of protons in the nucleus of an atom
9. an extremely small piece of matter that is part of an atom, for example an electron, proton, or neutron
10. a part of an atom that moves around the nucleus and has a negative electrical charge
11. an atom with an electrical force created by adding or removing an electron
15. a part of a molecule consisting of a series of atoms connected in a line
16. a very small unit of matter that the particles of an atom consist of radical
19. a unit for measuring the number of molecules in a substance