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TRENDS OF THE
PERIODIC TABLE
Atomic Radius
Ionization Energy
Electronegativity
VOCAB: ATOMIC RADIUS
 Atomic
Radius of an element is defined as half
the distance between two bonded atoms of the
same element.
A
more simple (but not technically correct)
definition is the distance from the center of
the atom to the outermost electrons
VOCAB: IONIZATION ENERGY
 An
atom’s ionization energy (IE) is the
amount of energy necessary to remove
one of its electrons (make an ion)
 Think
of the ionization energy as strongly an
atom holds onto its outermost electrons
 The
higher the ionization energy, the harder
it is to remove an electron
VOCAB: ELECTRONEGATIVITY
 Electronegativity
shows an atom’s
ability to attract electrons
i.e. How badly does the atom want to gain
electrons
- Electronegativity is expressed as just a
number (like “on a scale of 0-4”)

TRENDS OF THE
PERIODIC TABLE
Atomic Radius
Ionization Energy
Electronegativity
VOCAB: VALANCE ELECTRONS
Valance electrons are the electrons in the last
shell or energy level of an atom
 The number of valance electrons determines
the atom’s properties/reactivity

How many valance
electrons does Ge
have? Cl? Ba?
PERIODIC TREND 1: ATOMIC RADIUS
Radius is the distance from the center of the
atom to the outermost electrons
Remember…
 The
majority of the atom is empty space,
with the electrons orbiting the nucleus
PERIODIC TREND 1: ATOMIC RADIUS
So…
 As
you move down a group (column),
atomic radius increases
 This
should make sense because as you go
down a group, the number increases as
does the number of electrons
NOTE, THAT AS YOU MOVE ACROSS A PERIOD (FROM
LEFT TO RIGHT) ATOMIC RADIUS DECREASES!
WHY?
 As
you move across a period, the outer
electrons are all in the same what?
 What
increases as you move across a period?
 Protons
and electrons have what kind of
charges?
 Positive
and negative charges do what?
PERIODIC TREND 1: ATOMIC RADIUS
So…
 Because
the number of protons increases
across a period, the larger + charge in the
nucleus pulls the electrons further in,
reducing atomic radius
 As
you move across a period (left to
right) atomic radius decreases
SUMMARY:
 As
you move down a group (column), atomic
radius increases
 As you move across a period (left to right)
atomic radius decreases
ION REVIEW…
 Ions
are atoms that have a + or – charge
because they lost or gained electrons
 Positive
ions (cations) have LOST e- and
negitave ions (anions) have GAINED e-
 The
Noble Gases (group 18) are very stable
elements
WHY DO ELEMENTS FORM IONS?
 Remember that atoms like to be stable (i.e.
stable e- configurations) like the noble gases
 Groups
1 & 2 will lose a number of e- (form
cations) to get to a noble gas config
 Groups
15, 16, & 17 will gain a number of e(form anions) to get to a noble gas
 The
other groups vary, and we will ignore them
for now
PERIODIC TREND 2: IONS AND IONIC SIZE
Groups 1 & 2
 When these elements lose e- to form cations,
they eliminate a quantum level (shell)
and create more of a pull towards the +
nucleus.
 So
positive ions (cations) become
smaller than their neutral forms
Group 1 atom and ion size
PERIODIC TREND 2: IONS AND IONIC SIZE
Groups 15,16, and 17
 When these elements gain e- to form anions,
the negative charges of the electrons repel
each other, which increases the size of the
overall ion.
 Negative
ions (anions) are larger than
their neutral atom counterparts
Group 17 atom and ion size
TRENDS OF THE
PERIODIC TABLE
Atomic Radius
Ionization Energy
Electronegativity
PRACTICE
1.
Which has the larger atomic radius:
a) Br or I?
d) Zn or Fe?
b) Ar or K?
e) N or N-3 ?
c) Li or Li+ ?
2. Write the symbol for the ions that form from:
a) Rubidium
c) Phosphorous
b) Fluorine
d) Beryllium
PERIODIC TREND 3: IONIZATION ENERGY
 An
atom’s ionization energy (IE) is the
amount of energy necessary to remove one
of its electrons (make an ion)
 The
higher the ionization energy, the harder it is
to remove an electron
 Which
elements do you think will have high IE?
PERIODIC TREND 3: IONIZATION ENERGY
 What
was, and how did we explain, the
atomic radius trend?
 Ionization
energies decrease as you
move down a group.
 Ionization
energies increase as you
move from left to right across a period.
 Does
this sound familiar?
PERIODIC TREND 4: ELECTRONEGATIVITY
 Electronegativity
shows an atom’s
ability to attract electrons
i.e. How badly does the atom want to gain
electrons
- Electronegativity is expressed as just a number
(like “on a scale of 0-4”)

•
Fluorine the most electronegative element,
while Francium is the least.
PERIODIC TREND 4: ELECTRONEGATIVITY
 Electronegativity
values increase as we go
from left to right across a period
 Electronegativity
values decrease as you
move down a group
 The
cause of these patterns has to do with something
called electron affinity which we will not discuss because
if we did, your heads might explode. So lets just
describe the trend and leave it at that, ok? 