Elements & Atoms Section 2.1

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.

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

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

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

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

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!

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

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.

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

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

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