Transcript The Chemistry of Titanium

THE CHEMISTRY OF TITANIUM
1b – Trends in the
Periodic Table
LEARNING INTENTIONS
To examine trends in properties when moving
across or down the periodic table
 To be able to define the terms Co-valent Radius,
1st Ionisation Energy, Electronegativity
 To be able to explain the trends with regard to
atomic structure
 To relate nuclear charge, no.of electrons, effect of
increasing number of electron shells ( energy
levels), size of atom to particular trends

COVALENT RADII OF ELEMENTS
The size of an atom is measured by it’s covalent radius, the distance
between the nucleus and it’s outer electrons.
nucleus
covalent
radius
energy
levels
Values for covalent radii can be found on page
5 of the data book
LOOKING ACROSS A PERIOD
Across a period we can see the covalent radius decreasing.
As we move left to right we are adding a proton to the nucleus and an
electron to the outermost energy level.
So, from lithium to fluorine:
-
-
-
3+
-
9+
Lithium Atom
-
-
Fluorine Atom
LOOKING ACROSS A PERIOD
The lithium atom has a
smaller nuclear charge
than neon and so a larger
covalent radius
Fluorine’s greater nuclear
charge pulls the outer energy
level in closer.
-
-
3+
- -
- - -
9+
-
radius = 134pm
-
-
radius = 71pm
LOOKING DOWN A GROUP
-
Li
-
- - - - - - - - - - Cs
- - - - - - - - - -
single electron
in the
outermost
energy
level isbetween
much further
fromouter
the
The caesium
atom also
has
many more
electrons
the single
nucleus in
caesium.
electron
and
the nucleus.
This screening
causes theeffect
caesium
atom to have
a much larger
covalent
counteracts
the attraction
from the
greaterradius.
nuclear
charge.
ATOMIC SIZE SUMMARY
Decreasing Atomic Size
Across a period from left to right atomic size decreases
This is because of the atom having more electrons & protons and therefore
a greater attraction which pulls the atom closer together hence the smaller
size.
ATOMIC SIZE SUMMARY
Increasing Atomic Size
Decreasing Atomic Size
Down a group atomic size increases
This is because of the extra outer energy levels and the screening effect of
the outer electrons.
IONISATION ENERGY
The ionisation energy is the energy required to remove one mole of
electrons from one mole of atoms in the gaseous state.
The first ionisation energy of magnesium:
Mg (g)
Mg+ (g)
+
e-
744 kJmol-1
Values for ionisation energies can be found on page
10 of the data book
LOOKING ACROSS A PERIOD
From lithium to neon the first ionisation energy increases. Why?
Li
Be
B
C
N
O
F
Li (g)
Li+ (g)
+
e-
526 kJmol-1
Ne (g)
Ne+ (g)
+
e-
2090 kJmol-1
Ne
AN ATOM OF LITHIUM
The lithium atom has 3 protons inside the nucleus
-
3+
The outer electron is attracted by a relatively
small nuclear charge
Li (g)
Li+ (g)
+
e-
526 kJmol-1
AN ATOM OF NEON
The neon atom has 10 protons inside the nucleus
-
-
-
-
10+
-
-
Each of neon’s eight outer electrons is attracted by a
stronger nuclear charge
Ne (g)
Ne+ (g)
+
e-
2090 kJmol-1
LOOKING DOWN
A GROUP
The first ionisation energy decreases down a group in the periodic table.
Why?
Li (g)
Li+ (g)
+
e-
526 kJmol-1
Cs (g)
Cs+ (g)
+
e-
382 kJmol-1
2.
Screening
Effect
1. MORE ENERGY LEVELS
As
we saw with
atomicfor
size,
the single
electron
in the by
outermost
energy level is
Caesium’s
attraction
its outer
electron
is lowered
the screening
much
theitsnucleus
in caesium than in lithium.
effectfurther
causedfrom
by all
other electrons.
-
Li
-
- - - - - - - - - - Cs
- - - - - - - - - -
IONISATION ENERGY SUMMARY
Increasing Ionisation Energy
Across a period from left to right ionisation energy increases
This is due to the increase in atomic charge having a greater pull on the
electrons and therefore more energy is required to remove electrons.
IONISATION ENERGY SUMMARY
Decreasing Ionisation Energy
Increasing Ionisation Energy
Down a group ionisation energy decreases
This is due to the outer electrons being further away from the nucleus and
so the attraction is weaker and they are more easily removed.
ELECTRONEGATIVITY
Electronegativity is a measure of an atom’s attraction
for the shared pair of electrons in a bond
e
C
e
H
Which atom would have a greater
attraction for the electrons in this bond
and why?
LINUS PAULING
Linus
American
chemist (and
TodayPauling,
we still an
measure
electronegativities
winner
of twousing
Nobelthe
prizes!)
came
up with the
of elements
Pauling
scale.
concept of electronegativity in 1932 to help
explain the nature of chemical bonds.
Since fluorine is the most electronegative
element (has the greatest attraction for the
bonding electrons) he assigned it a value
and compared
other elementscan
to fluorine.
Values forall
electronegativity
be
found on page 10 of the data book
ELECTRONEGATIVITIES
Looking across a row or down a group of the
periodic table we can see a trend in values.
We can explain these trends by applying the
same reasoning used for ionisation energies.
LOOKING ACROSS A PERIOD
Increasing Electronegativity
B
Li Be
C
N
O
F
2.0 2.5 3.0 3.5 4.0
1.0 1.5
What are the
electronegativities of
these elements?
Across a period electronegativity increases
The charge in the nucleus increases across a period.
Greater number of protons = Greater attraction for bonding electrons
Decreasing Electronegativity
LOOKING DOWN A GROUP
F
4.0
Cl 3.0
What are the
electronegativities of
these halogens?
Down a group electronegativity decreases
Atoms have a bigger radius (more electron shells)
The positive charge of the nucleus is further away from the bonding
electrons and is shielded by the extra electron shells.
Br 2.8
I
2.6
ATOMIC SIZE SUMMARY
Decreasing Atomic Size
Across a period from left to right atomic size decreases
This is because of the atom having more electrons & protons and therefore
a greater attraction which pulls the atom closer together hence the smaller
size.