structure of atom lecture

8/3/2019 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

-

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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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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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

structure of atom lecture

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