(B) Periodicity
Trends in the periodic table and bonding
Overview
This section studies
•how the elements are arranged in
the Periodic Table,
•the structure and bonding of the
first twenty elements,
•Helps you explain key periodic
trends in physical properties and
relate these to the bonding
continuum.
(B) Periodicity
THE ATOMIC WORLD
After completing this topic you should be able to :
• Be familiar with atomic structure and how atoms are
structured ( N5 revision).
• Be able to describe electrostatic force of attraction (also
known as Coulomb’s force) holding electrons in orbitals.
• Understand the scale of measurement required when
exploring the depth of atomic structure.
• Know that the radius of a typical atom is one trillionth of a
meter and the units of distance at this scale is the
picometer 1 x10-12 meters .
1pm = 0.000000000001m
N5 Revision
Uncertainty principle
The methods we use to visualize the position of electrons are not suitable to find the
exact location of an electron.
This is because, in-order to visualise the electron, we need to project some energy on
the electron, which in turn makes the electron go to a higher energy state.
For Ex: If you want to capture the location of an electron using some
photography/microscopy you need to use some photons(light particles), when
electron gets hit by them, they get activated and change their location, so the
captured location is not the original location of electron.
We can just find the probability of finding the electron around the nucleus which is the
electron density distribution. I assumed electrons as particles here, if they are are
considered as waves there is another explanation electrons cannot be at the same
place at the same time.
A calculation shows that the electron is traveling at about 2,200 kilometers per
second. That's less than 1% of the speed of light, but it's fast enough to get it around
the Earth in just over 18 seconds.
Coulomb force or more commonly known as
electrostatic force
• The Standard International Unit used to measure
electric charge is the Coulomb (abbreviation C).
• The actual definition of this unit cannot be
explained fully until advanced higher.
• The charge of a proton is equal to e = 1.602x1019 C. The charge of an electron is the negative
of that.
Charles-Augustin de Coulomb
1736 - 1806
Coulombs Law
• Increased charge  increased
force of attraction
• Increased distance between
charged particles  decreased
force of attraction
What implications could this have for the chemistry of elements and periodicity ?
https://whitburnscience.wikispaces.com/%28B%29+PERIODICITY
Unit of length
• 1 meter, symbol m.
• 1 decimetre, symbol dm
• 1 centimetre, symbol cm
1m
1/10 of a
meter
1/100 of
a meter
The picometre (International spelling as used by the International Bureau of
Weights and Measures; SI symbol: pm) or picometer(American spelling) is
a unit of length in the metric system, equal to one trillionth (i.e., 1/1,000,000,000,000) of
a metre, which is the SI base unit of length. It can be written in scientific
notation as 1×10−12 m, in engineering notation as 1 E−12 m, and is simply1 m /
1,000,000,000,000.
It is also one hundredth of an angstrom, an internationally recognised (but non-SI)
unit of length.
1 angstrom = 1.0 ×
10-10 metres
Transmission Electron Microscope
Transmission electron
microscope - The first
experimental image of
lithium atoms from a
transmission electron
microscope. Typically
micro and nano meter
scale.
Lux
Microscopy uses the EM spectrum
Problem is wavelength, in principle you can't resolve things that are closer
together than the wavelength of light.
Micrographia
Robert Hooke (1665)
“But Nature is not to be limited by
our narrow comprehension; future
improvements of glasses may yet further
enlighten our understanding, and ocular
inspection may demonstrate that which as
yet we may think too extravagant either to
feign or suppose.”
User Operated - CCD
Detector
~$200K
X-Ray
Tube
~$350K
Image Plate
"Seeing" Individual
Molecules, Atoms,
and Bonds?
Problem:
l
What IS light?
Accelerated Electrons “Scatter”
Light
direct beam
Why don’t protons or other nuclei scatter light?
Too heavy!
By refocussing, a lens
can reassemble the
information
from the scattered wave into
an image of the scatterers.
But a lens for x-rays
is hard to come by.