1. Physical Science: Ch 5 Notes
A. Organizing the Elements
Dmitri Mendeleev was a Russian chemist and teacher who organized the elements in the 1860s.
Periodic table – an arrangement of elements in columns, based on a set of properties that repeat from row to row
Period: each row in the table of elements is a different period
Group: each column on the periodic table is a different group
Atomic mass units (amu) – the units used to report atomic masses since the mass of an atom is so small in grams
Atomic Mass = the sum of protons and neutrons in an atom

2. Physical Science: Ch 5 Notes
B. Classifying the Elements
1. Classify by state of matter (at room temperature)
Liquids: Mercury and Bromine
Gases: Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Helium, Neon, Argon, Krypton, Xenon, Radon
Solids: all the rest!
2. Classify by general properties
Metals: majority of elements (left side and middle of periodic table)
Metalloids: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Polonium, Astatine
Nonmetals: Elements at the top, right of the periodic table and Hydrogen

3. Physical Science: Ch 5 Notes
classifying continued…
3. Elements can also be divided into those that occur naturally and those that do not
Elements with atomic numbers 43 and 61 do not occur naturally
Elements with atomic numbers 93 and above are also not naturally occurring.
C. Element Characteristics
Metals – elements that are good conductors of electric current and heat (malleable and shiny too!)
Ductile – can be drawn into thin wires
Nonmetals – elements that are poor conductors of heat and electric current (most are gases, some are dull, brittle solids)
Metalloids – elements with properties that fall between those of metals and nonmetals

4. Physical Science: Ch 5 Notes
D. Electron Trends
Valence electron – an electron that is in the highest occupied energy level of an atom
These electrons play a key role in chemical reactions – atoms want to have a full outer energy level so they will gain or lose electrons to make this happen
Properties vary across a period because the number of valence electrons increases from left to right
Elements in a group have similar properties because they have the same number of valence electrons.