basic chemistry 03

8/14/2019 Basic Chemistry 03

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CH1200 UNIT 5 PART A

5.1 SUBATOMIC PARTICLES

All atoms (except Hydrogen) are composedof three subatomic particles:

- ELECTRONS - PROTONS

- NEUTRONS


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5.1.1 ELECTRON PROPERTIES

Electrons are found in the regions of spacesurrounding a nucleus and have the

following properties:

Have a negative electric charge of - 1

Have a negligible mass when compared tothe mass of a proton or neutron.


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5.1.2 PROTON PROPERTIES

Protons are found in the nucleus of atomsand have the following properties:

Have a +1 Positive Charge Have a relative mass of 1.0 Atomic Mass

unit (AMU)


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5.1.3 NEUTRON PROPERTIES

Neutrons are found in the nucleus of atomsand have the following properties:

Have a Zero Electrical charge Have a relative mass of 1.0 Atomic Mass

unit (AMU)


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5.1.3 ATOMIC NEUTRALITY

All atoms in their normal state areelectrically neutral - that is, they do not

have an overall electrical charge.

This arises from the fact that atoms have the

same number of Protons (+s) asElectrons (-s).


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5.1 - The Atom

Electrons are negatively charged, havealmost no mass and are found outsidethe nucleus of an atom

Protons are positively charged, have arelative mass of 1, and are foundinside the nucleus of an atom

Neutrons are electrically neutral (nocharge), have a relative mass of 1 andare found inside the nucleus of anatom


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5.2.1 DALTON MODEL

Atomic Theories Daltons Atomic Theory andBilliard Ball Model


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5.2.1 Daltons Billiard Ball Model

John Dalton viewed the atom as asolid sphere or a billiard ball


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5.2.1 Daltons Atomic

Theory All elements are composed of atoms. Atoms are indivisible, invisible particles. Atoms of the same element are the same. Atoms of different elements are different. Compounds are formed by 2 or more atoms

joined together.


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5.2.2 Daltons Atomic Theory

Daltons theory correctly predicted the Law of Multiple Proportions.

LAW OF MULTIPLE PROPORTIONS: A givencompound always has the same numbers &types of atoms (and thus always contains thesame proportions by mass).

H2O contain 2 H atoms and 1 Oxygen atom andthe H:O mass ratio is 1:8 (2 Hydrogens = 2.016gm and 1 Oxygen = 16.00 gm)


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5.2.2 Daltons Atomic

Theory All atoms of a particular element are all the same. The atoms of different Elements are made of tiny

particles called atoms. All atoms of a given element elements have

different masses (eg. hydrogen has a differentmass than carbon).

Atoms of one element can combine with atoms of other elements to form compounds (in small,whole number ratios such as 1:1, 1:2, 2:3 etc).

Atoms cannot be divided, created or destroyed inchemical reactions.


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5.2.3 Thompson Model

Atomic Theories

Thomsons Raisin-Bun Model


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5.2.4 RUTHERFORD MODEL

Atomic Theories

Rutherfords Gold Foil Experiment


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5.2.4 Rutherfords Gold Foil Experiment

Rutherford shot +ve charged particles called alpha ( ) particles (helium nuclei) at thin gold foil (element gold or Au).

If Thomsons model was correct, most of the particlesshould have been passed straight through the foil.Q: Why? (Think of Thomsons model)

However, some of the particles were reflected or scattered.Q: What does this imply about the atom?


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5.2.4 Rutherfords Gold FoilExperiment

What Rutherford Saw


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Most particles flew right through the goldfoil as if there was nothing there.

Q: Why?Atoms are mostly empty space.

A small # of particles were bounced back to their source.

Q: Why?There must be a small, dense nucleus in

the atom with a positive charge.


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5.2.4 RUTHERFORDS MODEL

The Nucleus of an atom is the dense centralcore of an atom which contains all the

atoms Protons and Neutrons.

The overall charge on a nucleus is positive

due to the presence of Protons. The nucleus is surrounded by electrons


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5.2.4 Rutherfords Model

Atomic Theories

Rutherfords Nuclear Model


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5.2.4 Rutherfords Nuclear Model

Rutherford proposed that most of the atom is

empty space occupied by moving electrons The positive charge and mass were believed to be

a small dense centre or nucleus Rutherfords model is called the Nuclear Model

because electrons revolved around a positivenucleus


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5.2.4 - The Atom

Electrons account for little of the mass of anatom, but effectively occupy most of thespace or volume

Protons and neutrons occupy little of thespace or volume of an atom but accountfor most of its mass.


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5.2.5 ATOMIC NUMBER

The Atomic Number of an atom is thenumber of protons in an atom of that

element. Each atom has a unique Atomic Number Ex: Hydrogen has Atomic Number = 1

Ex: Carbon has Atomic Number = 6


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5.2.5 ATOMIC NUMBERS ON

THE PERIODIC TABLE The Atomic Number of an element can be

found on the Periodic Table of Elements.

All the elements are arranged in order of increasing Atomic Number.

The Atomic Number is usually found in the

top left hand corner of the space for eachelement.


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5.2.6 CALCULATIONS WITH ATOMIC NUMBERS AND MASS NUMBERS

Formula to determine the Number of Neutrons in an atom:

# Neutrons = Atomic Mass # - Atomic #


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5.2.7 Bohrs Model

Atomic Theories

Bohrs Orbit Model


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5.2.7 Bohrs Orbit Model

Bohr proposed that electrons orbited thenucleus of the atom (same as the planetswhich orbit the sun)

In this model, electrons are assumed to orbitthe nucleus at fixed radii (orbits).


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5.2.7 - Bohrs Orbit Model

Bohrs model showed that electrons orbitedthe nucleus of the atom


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5.2.7 - Bohrs Orbit Model

Electrons can jump from a low-energy orbit near thenucleus to orbits of higher energy by absorbing energy(purple trails).

When the electrons return to a lower energy level (blue

trails), they release the excess energy in the form of radiation of a characteristic wavelength, such as visiblelight.

Bohrs Model is calledthe Orbit Model


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5.2.8 AVERAGE ATOMIC MASS

Average Atomic Mass represents the massof an atom which takes into account the

existence of isotopes. Isotopes are forms of an atom which differ

in Atomic Mass and the Number of Neutrons in the nucleus.

The Atomic Mass reported on the PeriodicTable is an average of the mass of allisotopes of the element.


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CH 1200 UNIT 5 PART B

5.2.10 ELECTROMAGNETIC RADIATION

Electromagnetic Radiation is a form of radiation which requires NO medium to

transport it. Examples: Radio Waves

Satellite Transmissions

X RaysMicrowavesSunlight


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5.2.10 Electromagnetic Spectrum

The full electromagneticspectrum contains allwavelengths andfrequencies

The visible part of thespectrum is shown

below.


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5.2.11 PROPERTIES OF WAVES

Definition: A wave is a means by whichenergy moves from place to place

Examples: Water wavesSound WavesRadio Waves

Some waves require a medium to transportthem ( Water & Sound Waves)

Electromagnetic waves require no medium


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5.2.11 Waves in Nature


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5.2.11 Typical Wave Form


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5.2.11 WAVE RELATED CALCULATIONS

Universal Wave Equation : This equationapplies to all forms of waves

V = f x where v = velocity

f = frequency

= wavelength


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5.2.12 PLANCKS QUANTUM THEORY

Max Planck proposed a theory that energyemitted from an object comes in discrete

amounts called quanta The amount of Energy released is directlyrelated to the frequency of the energyemitted. E = h x f

where E = energyh = Plancks Constantf = frequency


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5.2.13 PHOTOELETRIC EFFECT

PHOTOELETRIC EFFECT: AlbertEinstein proposed that Quanta of Light

called photons striking a metal surfacecause electrons to be dislodged fromatoms . These electrons can form a tinycurrent.

Examples: Photocells in calculatorsPhotoelectric switches


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5.2.14 BOHRS HYDROGEN ATOM

Neils Bohr saw the Hydrogen atom ashaving a series of concentric orbits

around the nucleus. - Each orbit was circular (Solar System) - Each orbit was a discrete distance from

the nucleus. - Electrons on each orbit acquired theenergy value associated with that orbit.


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Electrons on a lower level could absorbenergy and move to a higher level.

These excited electrons would quickly fall back to their own orbit and give outenergy.

The energy given out = the energyabsorbed.


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Electrons in a Bohr atom absorbing andreleasing energy.


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5.2.15 WAVE PROPERTIES OF ANELECTRON

Bohrs Theory did not apply to atoms morecomplex than Hydrogen.

De Broglie and Schrodinger proposed thatelectrons behaved like particles and waves.

The position of any given electron is more afunction of a mathematical probabilitythan a function of a given location


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5.2.16 QUANTUM MECHANICAL MODEL

The Quantum Model of the atom is basedon Mathematical Probability Functions

called Wave Equations. These Equations give us the probability

of finding an electron in a particular

location.


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5.2.16 ELECTRON LOCATION AS APROBABILITY

The location of anelectron at any time isshown as a

probability only.

Each dot shows a possible location for

an electron.


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5.2.16 Quantum Mechanical Model

One image of aQuantum MechanicalAtom is shown

below.


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5.2.17 ELECTRON QUANTUM NUMBERS

Energy Levels are identified by PrincipleQuantum Numbers or n

First Energy Level n = 1 Second Energy level n = 2 Third Energy level n = 3


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5.2.17 QUANTUM NUMBERS

The number of possible orbitals on eachEnergy level is given by n 2

For n = 1 n 2

= 1 For n= 2 n 2 = 4 For n = 3 n 2 = 9

For n = 4 n 2 = 16


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5.2.17 QUANTUM NUMBES

For n = 1 n 2 = 1 For 1 st Energy Level one 1 s Orbital

For n= 2 n 2= 4 For the 2 nd Energy Level one 2 s Orbital

& three 2 p Orbitals

For n =3

n2

=9

For the 3 rd Energy Level one 3 sOrbital,

three 3 p Orbitals & five 3 d Orbitals.


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As we move up EnergyLevels the electronsmove farther from thenucleus.

This image shows howthe 1s orbitalcompares in size to2s.


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CH UNIT PART B


The 3 s orbital is larger than 2s or 1s.


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5.2.18 ELECTRONIC CONFIGURATIONOF AN ATOM

Electronic Configuration of an atom showsthe exact number of electrons present

AND the location of each electron.

Hydrogen H 1 s 1

Helium He 1 s 2 Lithium Li 1 s 2 2 s 1

Beryllium Be 1 s 2 2 s 2


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5.2.18 ELECTRONIC CONFIGURATION

After filling 1s and2s we move to fill the porbitals on the secondEnergy Level.

The p orbitals aremutually

perpendicular on thex, y & z axis.


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5.2.19 DRAW ORBITAL DIAGRAMS

After filling the 2 porbitals we must starton the 3s , 3p and3d orbitals.

The shapes of the 3dorbitals are shownhere.


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5.2.20 ELECTRONIC CONFIGURATIONAND THE PERIODIC TABLE

The elements on the Periodic Table arearranged according to increasing Atomic

Number. Each element has one more electron thanthe element preceding it.

The Atomic Orbitals must be filled insequence: 1s , 2s , 2p , 3s , 3p etc.


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The orbitals being filledfor the first 20elements are shownhere.


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