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.
1
Groups
(families)
2
3
4
5
6
7
8
9
10
11
18
13
12
14
15
16
17
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
They
They
Alkaline Earth Metals
have 2 valence electrons.
are harder and less reactive than
group 1 metals.
Group 17
Called
Most
halogens
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
 They
3 – 12
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 (anion has an n like negative)
Atomic Radius

Definition


Period Trend



The distance from the nucleus to the boundary of the
surrounding cloud of electrons.
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


Electron Affinity increases as you go across.
(The value becomes more negative – meaning more
exothermic – electrons are more easily gained)
 Group


Trend
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

Electronegativity increases as you go across.
 Group

Trend
Trend
Electronegativity decreases as you go down.
The most electronegative element is Fluorine (F)
The least electronegative element is Cesium (Cs)