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)1

2

3 4 5 6 7 8 9 10

11 12

13

14

15

16

17

18

Alk

ali

Meta

lsA

lkalin

e

Eart

h

Halo

gen

sN

ob

le

Gases

Oxyg

en

Fam

ily

Nit

rog

en

Fam

ily

Carb

on

Fam

ily

Boro

n F

am

ilyB CN O

H

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.

Why?

Group 2 metals

Called Alkaline Earth Metals

They have 2 valence electrons.

They are harder and less reactive than group 1 metals.

Group 17Called halogens

Most reactive nonmetals

They all have 7 valence electronsThey react with metals to form

“salts”

Why?

Group 18

Called Noble gasesThey don’t react

They have 8 valence electrons (except Helium)This is a full outer level (Octet Rule)

Why?

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)

BSiGe

AsSb

TeAtMETALS

METALLO

IDS

MetalsMost 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 MetalsGroups 3 – 12

They have many different propertiesLess reactive than alkaline earth metals

Some are fairly non-reactive (Cu, Ag, Au)Tungsten has the highest melting pointMercury is a liquid with high density

Metals can be mixed together (alloy) to produce desirable properties.

Periodic TrendsAtomic RadiusIonization EnergyElectron AffinityElectronegativity

IonDefinitionIon: an atom that has gained or lost electrons

Cation = Positively charged atom + Anion = negatively charged atom -(anion 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.]

Bigger Atom!

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)