Atom - The smallest unit of matter that can exist of an element.

Compound - A molecule containing two or more different atoms bound together.

Element - A fundamental substance that has a unique atomic number on the periodic table.

Isotope - A different form of an element that varies by the number of neutrons in the nucleus.
Neutron - An uncharged atomic particle of mass 1.67493x10-27 . It resides in the nucleus.

Nucleus - The small, dense central region of an atom around which electrons orbit. The nucleus is made up of protons and neutrons.
Proton - A positively charged particle of mass 1.6726x10-27 . Protons reside in the nucleus.
Valence electrons - The electrons in the outermost energy shell of an atom. The configuration of these electrons determine the chemical properties of the element.

Valence shell - The highest energy shell in an atom, containing valence electrons. All interactions between atoms take place through the electrons of the valence shell.

	Created by Xiang Lin Goh over 8 years ago

Secondary 1 Science (Chemistry) Note on Chemistry:Atoms and Molecules Notes, created by Xiang Lin Goh on 30/04/2016.