The Periodic Table

History u Russian scientist Dmitri Mendeleev was given credit for developing the first periodic table u Mid 1800 – atomic masses of elements were known u Wrote down the elements in order of increasing mass u Found a pattern of repeating properties

Mendeleev’s Table u Grouped elements in columns by similar properties in order of increasing atomic mass u Found some inconsistencies - felt that the properties were more important than the mass, so switched order. u Found some gaps u Must be undiscovered elements u Predicted their properties before they were found

The Modern Table u Elements are still grouped by properties u Similar properties are in the same column u Order is in increasing atomic number u Added a column of elements Mendeleev didn’t know about (The Noble Gases) and we keep adding elements that are discovered.

u Horizontal rows are called periods u There are 7 periods

u Vertical columns are called groups or families. u Elements are placed in columns by similar properties.

The Different Groups of Elements

Metals

l Luster – shiny. l Ductile – drawn into wires. l Malleable – hammered into sheets. l Conductors of heat and electricity.

Transition metals

u These are called the inner transition elements and they belong here

Non-metals l Dull l Brittle l Nonconductors - insulators

Metalloids or Semimetals l Properties of both l Semiconductors B Si GeAs SbTe PoAt

u Group 1 are the alkali metalsalkali metals u Group 2 are the alkaline earth metals

u Group 17 is called the halogens u Group 18 are the noble gases

Why do we have a periodic table? u Organizes the properties of atoms u Tells us information about elements that make up compounds

Answer the Following: u Write down the element symbols on the index card and indicate whether they are metals (M), nonmetals (NM) or metalloids (ME). 1. H 2. Se 3. Zn 4. Si 5. Al 1.NM 2.NM 3.M 4.ME 5.M

Numbers of electrons u Atoms of different elements have different numbers of electrons but they may have the same number of electrons in the outer most energy level u The outer most electrons help determine the chemical properties of elements u So how does the periodic table help us figure out the number of outer electrons?

u We use the group number to determine the number of electrons in the outermost energy level of an atom.