Structure of Atom Lecture
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Transcript of Structure of Atom Lecture
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Essentials of Chemical Structure Bondingand Reactivity
CT1508M
Fundamentals of Chemical Structure Bondingand Reactivity
CT1003D
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Dr Tasnim Munshi [email protected] Analytical Centre, IPI building
Dr William Martin [email protected] Building L26c
Dr Ian Scowen [email protected] Analytical Centre, IPI building
Teaching Staff
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CT1508M is a single module worth 10 creditsChemical Engineering students
CT1003D is a double module worth 20 creditsChemistry4, Forensic Science and CPFS students
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Assessment
CT1508M 1.5 hour exam Multiple and short answer questions
Assessment
CT1003D 3 hour exam Multiple and short answer questions
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How are atoms studied?
Atoms are the building blocks of matter
Atoms are too small in size to study easily
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Who studied the atom?
Studied by many scientists for centuries
Democritus (400 BC) phrase atomos Rutherford (1911) nucleus (gold foil expt)
Moseley (1913) X-rays to find atomic #
*Bohr (1913) planetary model of the atom *Schrdinger (1923) electron cloud model
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Atomic Structure Timeline
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Democritus (400 B.C.)
Proposed that matter was composedof tiny indivisible particles
Not based on experimental data
His theory: Matter could not bedivided into smaller and smaller
pieces forever, eventually the smallestpossible piece would be obtained.
This piece would be indivisible.
He named the smallest piece ofmatter atomos, meaning not to becut.
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Alchemy (next 2000 years)
Mixture of science and mysticism.
Lab procedures were developed, but alchemists did notperform controlled experiments like true scientists.
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John Dalton (1807) British Schoolteacher
based his theory on others
experimental data In the early 1800s, the English
Chemist John Dalton performeda number of experiments thateventually led to the acceptanceof the idea of atoms.
Billiard Ball Model
atom is auniform,solid sphere
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Daltons Four Postulates
1. Elements are composed of small indivisible particlescalled atoms.
2. Atoms of the same element are identical. Atoms ofdifferent elements are different.
3. Atoms of different elements combine together in
simple proportions to create a compound.
4. In a chemical reaction, atoms are rearranged, but not
changed.
This theory became one of the foundations of modern chemistry.
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Thomsons Plum Pudding Model
In 1897, the English
scientist J.J.Thomson providedthe first hint that an
atom is made of evensmaller particles.
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Thomson Model (1903)
He proposed a model of
the atom that issometimes called thePlum Pudding model
Atoms were made from apositively chargedsubstance with negativelycharged electrons
scattered about, likeraisins in a pudding.
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Thomson Model
Thomson studied thepassage of an electric
current through a gas
As the current passedthrough the gas, it gave
off rays of negativelycharged particles.
This surprised Thomson,
because the atoms of thegas were uncharged.Where had the negativecharges come from?
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Thomson concluded that the negative charges came from within
the atom.
A particle smaller than an atom had to exist.
The atom was divisible!
Thomson called the negatively charged corpuscles, today known as
electrons.
Since the gas was known to be neutral, having no charge, he reasonedthat there must be positively charged particles in the atom.
But he could never find them.
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Ernest Rutherford (1911)
Gold Foil Experiment
Rutherfords experiment Involved firing a stream oftiny positively charged particles at a thin sheet of
gold foil (2000 atoms thick)
Most of the positively charged bulletspassed right through the gold atoms in thesheet of gold foil without changing course at
all. Some of the positively charged bullets,however, did bounce away from the goldsheet as if they had hit something solid. Heknew that positive charges repel positivecharges.
Discovered the nucleusdense, positive charge in the center of the atom - Nuclear Model
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Ernest Rutherford (1911)
Nuclear Model
dense, positive nucleus surrounded by
negative electrons
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This could only mean that the gold atoms in the sheet were mostlyopen space. Atoms were not a pudding filled with a positively
charged material
Rutherford concluded that an atom had a small, dense, positivelycharged center that repelled his positively charged bullets.
He called the center of the atom the nucleus
The nucleus is tiny compared to the atom as a whole
Rutherford reasoned that all of an atomspositively charged particles were contained in
the nucleus. The negatively charged particleswere scattered outside the nucleus around theatoms edge.
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Bohr (1913)
Planetary Model
According to Bohrs atomic model,electrons move in definite orbitsaround the nucleus, much like
planets circle the sun. Theseorbits, or energy levels, arelocated at certain distances fromthe nucleus.
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Niels Bohr (1913)
Planetary Model
electrons move in circularorbits within specific energylevels
Bright-line spectrum
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The Wave Model
Todays atomic model isbased on the principles of
wave mechanics.
According to the theory ofwave mechanics,
electrons do not moveabout an atom in adefinite path, like theplanets around the sun.
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The Wave Model
In fact, it is impossible to determine the exact location ofan electron. The probable location of an electron isbased on how much energy the electron has
According to the modern atomic model, at atom has a
small positively charged nucleus surrounded by a largeregion in which there are enough electrons to make anatom neutral.
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Electron Cloud
A space in whichelectrons are likely to be
found. Electrons whirl about the
nucleus billions of timesin one second
They are not movingaround in randompatterns.
Location of electrons
depends upon how muchenergy the electron has.
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Erwin Schrdinger (1926)
Quantum mechanics
electrons can only exist inspecified energy states
Electron cloud model
orbital: region around the
nucleus where e
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are likely tobe found
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Erwin Schrdinger (1926)
Electron Cloud Model (orbital)
dots represent probability of finding an e-
not actual electrons
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James Chadwick (1932)
Discovered neutrons
neutral particles in the nucleusof an atom
Joliot-Curie Experiments
based his theory on their
experimental evidence
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James Chadwick (1932)
Neutron Model
revision of Rutherfords Nuclear Model
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What is the structure of an atom?
Nucleus center of the atom
Home of Protons and Neutrons
Proton
Has a positive (+) charge
Has a relative mass of 1
Determines the atomic number
Found inside the nucleus
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What is the structure of an atom?
Neutron
Has no (0) charge Has a relative mass of 1
Determines the isotope
Isotopes are two of the sameelement with different masses
Found inside the nucleus
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What is the structure of an atom?
Electron
Has a negative (-) charge
Has a relative mass of 0 (zero)
Determines the ion
Found outside the nucleus
Bohr model electrons are in specific energylevels
Electron cloud model electrons are in a
random cloud
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How are P, N, e- related?
# protons = atomic number 8O
# electrons = # protons in a neutral atom
# protons + # neutrons = atomic mass O = 16
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What is a chemical symbol?
Chemical symbol tells us what atom it is
Always a CAPITAL LETTER, sometimes followed bya lower case letter
Ex: Oxygen O Nitrogen N Sodium Na
*Cobalt Co *Carbon Monoxide CO
(Co is an element, CO is a compound)
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Chemical Symbols
Capitals matter!
Element symbols contain ONE capital letter followed bylowercase letter(s) if necessary.
Metal thatforms brightblue solid
compounds.
Poisonous
gas.Co vs CO