(CHAPTER 2) Matter is anything that takes up space and has mass.
An element is a substance that cannot be broken down into other substances by chemical reactions. (E.g. gold, copper, carbon, oxygen)
A compound is a substance consisting of two or more elements combined in a fixed ratio. (e.g. H2o and table salt NaCI)
C, H, O, N make up 96% of living matter.
Trace elements are those required by an organism in only minute quantities (e.g. iron and iodine)
**Matter consists of chemical elements in pure form and in combos called compounds**

Atoms are the smallest unit of an element; made up of neutrons, protons, and electrons.
Protons are positively charged; found in the nucleus.
Electrons are negatively charged; found in electron shells around the nucleus.
Neutrons have no charge and are found in the nucleus.
Atomic number is the number of protons an element possesses.
Mass number is the sum of protons and neutrons.
**An element’s properties depend on the structure of its atoms**

Chemical bonds are interactions between the valence electrons of different atoms.
Covalent bonds are when valence electrons are shared by two atoms.
An ion is the resulting charged atom or molecule.
Ionic bonds occur because ions will be either positively or negatively charged, and will be attracted to each other by these opposite charges.
Hydrogen bonds are weak bonds that form between the positively charged hydrogen atom of one molecule and the strongly electronegative