Element : a substance that cannot be broken down by chemical reaction eg carbon, gold. Everything in the universe is made of 92 different elements. Living things contain a maximum of 25 elements.
Important biological elements :
These four are the most important, making up about 96% of the body: Carbon C Oxygen O Hydrogen H Nitrogen N Most of the rest of the body is made up of the next 4 elements: Calcium Ca Phosphorus P Potassium K Sulfur S
Compound - two or more elements joined by chemical bonds eg salt, water, plastic.
Atom - the smallest unit of an element. An atom is made up of three particles:
Particle Location Weight Charge Proton Nucleus 1 dalton (amu) + 1 Neutron Nucleus 1 dalton (amu) 0 Electron Shells 1/2000 dalton (amu) - 1
Atomic number = Number of Protons per atom. Atomic number also equals the number of electrons. Elements are often shown in the Periodic Table which arranges them in order of the atomic number (Hydrogen = 1, Helium = 2 etc).
Example : Carbon (atomic number of 6) has 6 protons and 6 electrons.
Atomic mass = Number of Protons + Neutrons.
Example: carbon 14 has 8 neutrons (14 minus 6 )
Isotopes - atoms of the same element that differ in the number of neutrons.
Radioactive atoms : large isotopes that break apart, releasing energy. The energy is either:
Alpha particles : weak, cannot penetrate paper
Beta particles : stronger, can penetrate paper but not metal
Gamma rays : very strong, can penetrate metal and harm living things
Radioactive atoms can be used to:
a) Track chemicals in the body
b) Work out the age of fossils. Radiocarbon dating method
c) Track the movement of individual animals (eg butterflies). Murder
Chemical bonds only involve electrons. Valence electrons are the electrons in the outer shell of an atom. When they form chemical bonds, all atoms try to fill their valence shell of electrons.
Maximum number of electrons per shell :
Strong acid : pH 0 - 3 Weak acid : pH 4 - 6 Neutral : ph 7 Weak base : pH 8 - 11 Strong base : pH 12 - 14Examples :
Rainfall: Natural (unpolluted) rain : pH 5.5 Florida rain : pH 4.5 NE US rain : pH 3.5Last edited January 2015, by David Byres, David.Byres@fscj.edu