Groups (families)  Vertical columns  Group # = # of valence electrons (# of electrons in outer shell)  18 groups or families  Some properties repeat in an orderly way  Example – Li, Na, K, Rb, Cs, and Fr are all soft metals which react violently with water.

Periods  Horizontal rows (7 rows)  Period # = All elements in a period have electrons on the same energy level.

History of the Groupings within Periodic Table ☺ Dmitri Mendeleev looked for patterns within the properties of elements. ☺ Mendeleev organized elements by atomic mass. ☺ He found patterns where the properties were repeated at regular intervals ☺ Mendeleev was able to predict properties of elements not yet discovered in 1871.

History Continued ☺ Arranging the periodic table by atomic mass is not foolproof. Once the protons were discovered 40 years later, Henry Moseley arranged the elements by atomic number. This removed problems in the original table.

Groups (families)

Group 1 metals  Called alkali metals.  They all react violently with nonmetals.  They have 1 valence electron which they lose very easily.  Li is the least reactive, Fr is the most reactive  They are all soft  They are not found in nature because they are so reactive.

Group 2 metals  Called Alkaline Earth Metals  They have 2 valence electrons.  They are harder and less reactive than group 1 metals.

Group 17  Called halogens  Most reactive nonmetals  They all have 7 valence electrons  They react with metals to form “salts”

Group 18  Called Noble gases  They don’t react  They have 8 valence electrons (except Helium)  This is a full outer level (Octet Rule)

Metals, Non-metals, & Metalloids METALS- to the left of the staircase; tend to lose electrons easily; form positive ions NON-METALS- to the right of the staircase; tend to gain electrons easily; form negative ions METALLOIDS- border the staircase (exceptions are Al and Po)

Metals  Most elements are metals  Metals are good conductors of heat and electricity  Metals are ductile (can be squeezed into a wire)  Metals are malleable (can be hammered or bent)

Transition Metals  Groups 3 – 12  They have many different properties  Less reactive than alkaline earth metals  Some are fairly non-reactive (Cu, Ag, Au)  Tungsten has the highest melting point  Mercury is a liquid with high density  Metals can be mixed together (alloy) to produce desirable properties.

Periodic Trends Atomic Radius Ionization Energy Electron Affinity Electronegativity

Ion  Definition Ion: an atom that has gained or lost electrons  Cation = Positively charged atom +  Anion = negatively charged atom - (a n ion has an n like negative)

Atomic Radius  Definition  The distance from the nucleus to the boundary of the surrounding cloud of electrons.  Period Trend  Radius decreases as you go across.  The nucleus become more positive and it pulls the electrons in tighter  Group Trend  Radius increases as you go down.  There are more energy levels so the electrons are at a greater distance from the nucleus

Atomic Radius  Atomic radii decrease from left to right across a period and increase down a group as shown below

Atomic Radius  As you go across the period, there are more protons (greater effective nuclear charge) and therefore a greater attraction pulls the electrons closer to the nucleus and decreases the size of the atom

Ionization Energy  Definition  Energy required to remove an electron from an atom of an element.  If an electron is easy to remove, it takes little energy  Period Trend  Ionization Energy increases as you go across.  The nucleus become more positive and therefore it is harder to pull electrons off.  Group Trend  Ionization Energy decreases as you go down.  As you go down the number of energy levels increases, therefore the electrons are farther away from the nucleus and are more easily removed.

Ionization Energy

Electron Affinity  Definition  Energy change when an atom gains an electron  Period Trend  Electron Affinity increases as you go across.  (The value becomes more negative – meaning more exothermic – electrons are more easily gained)  Group Trend  General trend is to decrease (become more positive) as you go down a group.  It is more difficult to add electrons to larger atoms [outer E levels are farther away from the positive nucleus.]

Electron Affinity

Electronegativity  Definition  The tendency of an atom to attract electrons to itself when it is combined with another atom.  Assigned numbers 0-4  Period Trend  Electronegativity increases as you go across.  Group Trend  Electronegativity decreases as you go down. The most electronegative element is Fluorine (F) The least electronegative element is Cesium (Cs)