1. Elements & Atoms
Section 2.1

2. Learning Objectives
Name the principal chemical elements in living things
Compare the physical properties & locations of electrons, protons, & neutrons. Distinguish between the atomic number & mass number of an atom.
Define orbital & electron shell. Relate electron shells to principal energy levels.

3. Elements
Element = substance that can’t be broken down into simpler things by normal chemical reactions
Each element has its own chemical symbol (Ex. Oxygen is O, Helium is He)
4 elements (O, C, H, & N) make up 96% of most organisms
The smallest unit of an element is an atom

5. Elements Found in All Living Things
Major Elements:
Oxygen
Carbon
Hydrogen
Nitrogen
Important, but not found in as large of amounts:
Calcium
Phosphorous
Potassium
Sulfur
Sodium
Magnesium
Chlorine
Iron

6. Trace Elements
Required by organisms to grow, develop, & function properly but not needed in large amounts
Iodine
Manganese
Copper
Zinc
Cobalt
Fluorine
Molybdenum
Selenium
Boron
Silicon

7. Goiters are caused by a deficiency (not enough) of the trace element iodine

8. Atoms
Atom = the smallest portion of an element that still has its chemical properties
Atoms are matter
Matter = anything that has mass & takes up space
Everything is made up of matter!

10. Atoms Are Made Up of … An atomic nucleus Electrons Protons Neutrons
Have a positive (+) charge
Neutrons
Have a neutral (0) charge
Electrons
Have a negative (-) charge
Found in shells or orbitals around the atomic nucleus

11. Where Electrons Are Found
Electron shell = energy levels (orbitals of similar energy) drawn as rings around the atomic nucleus
Orbital = Areas of 3-D space where electrons are found around the atomic nucleus
1s, 2s, 2p, 3s, 3p, 3d, etc.

12. Valence Shell Valence shell = the outermost electron shell
Valence electrons = Electrons found in the valence shell
Determine the chemical properties of an atom
Usually an atom wants 8 valence electrons
Hydrogen & Helium only want 2

13. Each Element Has An…
Atomic number = the number of protons in the element’s atomic nucleus
Atomic mass = the number of protons & neutrons in one atom of an element
How much matter is in the atom

14. Isotopes
Isotope = Atoms of an element that have more or less neutrons than protons
Same atomic number, but different atomic mass
Radioisotopes = isotopes that emit (give off) particles because they are unstable