UNIT 3UNIT 3

STRUCTURE OF STRUCTURE OF MATTER MATTER

CUTTING EDGE OF THE CUTTING EDGE OF THE SCIENTIFIC RESEARCHSCIENTIFIC RESEARCH

STRING THEORYSTRING THEORY Is our most recent attempt to answer the Is our most recent attempt to answer the

following questions: following questions:

What is the world made of?What is the world made of? How does our Univers work?How does our Univers work?

STRING THEORYSTRING THEORY The essential idea behind string theory is The essential idea behind string theory is

this: all of the different 'fundamental ' this: all of the different 'fundamental ' particles of the Univers are really just particles of the Univers are really just different manifestations of one basic different manifestations of one basic object: a object: a STRINGSTRING ..

SPACESPACE --TIMETIME So, under an extremely powerful So, under an extremely powerful

'microscope' (that, it still doesn’t exist) we 'microscope' (that, it still doesn’t exist) we would realize that the space-time is not would realize that the space-time is not really formed by points, but tiny loops of really formed by points, but tiny loops of strings. Such as this:strings. Such as this:

So, if str ing theory is correct, the entire world is made of strings!

Perhaps the most remarkable thing about string theory is that such a simple idea works.

But it should also be said that, to date, there is no direct experimental evidence that string theory itself is the correct description of Nature.

A important part has been verified experimentally with incredible precision but not the whole theory as it is still under development.

ALL THE STRINGS ALL THE STRINGS VIBRATEVIBRATE

Such the guitar strings do it!!Such the guitar strings do it!! They can do it in a different ways!! They can do it in a different ways!!

Every way Every way STRINGSSTRINGS oscillate produces oscillate produces different exhibition ways:different exhibition ways:

FORCEFORCE ENERGY MATTERENERGY MATTER

The The THEORYTHEORY describes both the describes both the fundamental building blocks out of which fundamental building blocks out of which the world is made, and the forces through the world is made, and the forces through which these blocks interact.which these blocks interact.

FORCE:FORCE:

- Each of these is produced by fundamental - Each of these is produced by fundamental particles that act as carriers of the forceparticles that act as carriers of the force ::

GRAVITYGRAVITY FORCEFORCE

Particle: Particle: GRAVITONGRAVITON

ELECTROMAGNETIC FORCE ELECTROMAGNETIC FORCE

Particle:Particle: PHOTONPHOTON

STRONG NUCLEAR FORCESTRONG NUCLEAR FORCE

Particles:Particles: eight particles known

as GLUONSGLUONS

WEAK NUCLEAR FORCEWEAK NUCLEAR FORCE

Particles:Particles: - - the the W+W+- the - the W-W- - the - the ZZ

ENERGYENERGY

ELECTRIC E. ELECTRIC E.

POTENTIAL E. POTENTIAL E.

KINETIC E. KINETIC E.

HEAT E. HEAT E.

MATTERMATTER

Something that occupies space and has Something that occupies space and has mass.mass.

We will study matter this courseWe will study matter this course

How matter is built How matter is built up?up?

Due to the different oscillations of the Due to the different oscillations of the strings, we have differents kinds of strings, we have differents kinds of particles.particles.

The most important and basic ones are:The most important and basic ones are:

QUARKSQUARKS ELECTRONSELECTRONS

This particles join together building:This particles join together building:

ATOMSATOMSThey are formed by:They are formed by:- Nucleus: - Nucleus: - PROTONSPROTONS : is made of 3 quarks:: is made of 3 quarks:

(2 ups and 1 down)(2 ups and 1 down) - - NEUTRONSNEUTRONS : is made of 3 quarks:: is made of 3 quarks:

(2 down i 1 up)(2 down i 1 up)

- Shell: - - Shell: - ELECTRONSELECTRONS

Atoms bonded together in groups Atoms bonded together in groups to form:to form:

MOLeCULESMOLeCULES

Crystal latticesCrystal lattices

With all the differents With all the differents combinations amongs combinations amongs

atoms...atoms... All the substances we know are formed, not only:All the substances we know are formed, not only:

- The - The naturalnatural onesones: :

- But also the - But also the artificialartificial ones ones::

AToMIC MODELSAToMIC MODELS Human beings always have been trying to Human beings always have been trying to

explain the nature…explain the nature… Along the History, many models were Along the History, many models were

suggested in order to explain how all the suggested in order to explain how all the material substances are made… material substances are made…

ANCIENT GREEK PHILOSOPHY SCHOOLS

EMPEDOCLES & ARISTOTLE All matter is a combination of 4 elements:

earth, water, air & fire

DEMOCRITUSDEMOCRITUS (460 b.c. – 370 b.c)(460 b.c. – 370 b.c)

Proposed that matter was composed of tiny indivisible particles = atoms

ATOM → from the greek a=without + tomus = division

Not based on experimental data

Alchemy (next 2000 years) Mixture of science and mysticism. Lab procedures were developed, but

alchemists did not perform controlled experiments like true scientists.

DALTONDALTON(1808)(1808)

British Schoolteacher– based his theory on others’ experimental data

Bill iard Ball Model– atom is a

uniform, solid sphere

(protons, neutron & electrons not discovered yet!!!)

Dalton’s Four Postulates

1. Elements are composed of small indivisible particles called atoms. (*** not true)

2. Atoms of the same element are identical. Atoms of different 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.

THOMSONTHOMSON18971897

Discovered Electrons = negative particles within the atom → so atom divisible Plum-pudding Model“plum cake”

Plum-pudding Model– positive sphere (pudding) with

negative electrons (plums) dispersed throughout

– So, atom = neutral

RUTHERFORDRUTHERFORD19111911

Gold Foil Experiment Discovered the nucleus

– Small, dense, positivecharge in the center of the atom = nucleus– Most of the atom is empty

Nuclear Model

Nuclear Model Small, dense, positive nucleus (with

protons) surrounded by negative electrons (where?? not clear)

BOHRBOHR19131913

- Energy Levels– electrons can only exist in specific energy

states → Planetary Model: electrons orbit the

nucleus, like planets orbiting the Sun.

Planetary ModelElectrons move in circular orbits with specific energy

levels

SCHRÖDINGER1926

Quantum mechanics – electrons can only exist in specified energy

states Electron cloud model

– ORBITAL: region around the nucleus where e- arelikely to be found

CHADWICK 1932

Discovered neutrons– neutral particles in the nucleus of an atom

ATOMIC STRUCTURE

So the ATOMIC STRUCTURE is: made up of a central nucleus (containing

protons and neutrons), surrounded by electrons in diferent shells. Most of the atom is empty space.

ATOMIC SCALE

HOW CAN WE WEIGHT THE ATOMS MASS?

Because of the very small mass of atoms, their mass is measured in atomic mass units (u). 1 u = 1,67 × 10−24 g

CHARGE SUBATOMIC PARTICLES

QUANTUM MECHANICQUANTUM MECHANIC(current model)(current model)

PARTICLES(symbol)(symbol)

MASSMASS

(u)(u)CHARGECHARGE

PROTONPROTON

(p(p++))11 ++

NEUTRONNEUTRON

(n(n00))11 00

ELECTRONELECTRON

(e(e--))1/20001/2000 --

NUCLINUCLI The central nucleus contains protons

and neutrons

The atomic number (Z) is the number of protons in an atom.

Atomic numberAtomic number Z = pZ = p++

The The atomic mass numberatomic mass number (A) is the (A) is the number of protons and neutrons in the number of protons and neutrons in the nucleus of an atom.nucleus of an atom.

Mass numberMass numberA = pA = p++ + n + n00

The standard notation that is used to write an element, where X is the element symbol, A is the atomic mass number and Z is the atomic number.

Every element is distinguished from the orders because of it atomic Every element is distinguished from the orders because of it atomic number, therefore because of it number of protons.number, therefore because of it number of protons.

ISOTOPES The isotope of a particular element is made up of atoms which

have the same number of protons as the atoms in the original element, but a different number of neutrons. This means that not all atoms of an element will have the same atomic mass.

They have = Z i ǂ A

The relative atomic mass of an element is the average mass of all the naturally occurring isotopes of that element.

The units for relative atomic mass are atomic mass units.

The relative atomic mass is written under the elements' symbol on the periodic table.

So, the relative atomic mass has “comes”

Carbon-14 dating is a way of determining the age of certain archeological artifacts of a biological Origin up to about 50,000years old. It is used in dating things such as bone, cloth, wood and plant fibers that

were created in the relatively recent past by human activities.

ELECTRONSELECTRONS Electrons move around the nucleus of the atom in a region of space Electrons move around the nucleus of the atom in a region of space

in which the exact positions of the electrons cannot be determined in which the exact positions of the electrons cannot be determined at any one time, and each shell consist of:at any one time, and each shell consist of:

AToMICS ORBITALSAToMICS ORBITALS

- An orbital defines the space in which an electron is most likely to be An orbital defines the space in which an electron is most likely to be found.found.

- There are 4 kinds of orbitals in 7 shells, increasing in radius whith There are 4 kinds of orbitals in 7 shells, increasing in radius whith distance from the nucleus: s, p, d, fdistance from the nucleus: s, p, d, f

(To remember them: “(To remember them: “ssooppa a dde e ffideus”)ideus”)

- They have different shapes.- They have different shapes.- They can hold up to a certain number of They can hold up to a certain number of

electrons.electrons.

- There is only 1 “There is only 1 “ss” spherically shaped” spherically shaped - There are 3 of “There are 3 of “pp” dumbbell shaped” dumbbell shaped - There are 5 of “There are 5 of “dd” ” - There are 7 of “There are 7 of “ff” ”

- Which are these shapes?Which are these shapes?

ORBITALS ORBITALS ATÒMICSATÒMICS

ff

dd

pp

ss

Each orbital only can hold up 2 eEach orbital only can hold up 2 e --

So:So:- Orbitals “Orbitals “ss ” can hold up: 2 x 1 = ” can hold up: 2 x 1 = 22- Orbitals “Orbitals “pp ” can hold up: 2 x 3 = ” can hold up: 2 x 3 = 66- Orbitals “Orbitals “dd ” can hold up: 2 x 5 = ” can hold up: 2 x 5 = 1010- Orbitals “Orbitals “ff ” can hold up: 2 x 7 = ” can hold up: 2 x 7 = 1414 The arrangement of electrons in an atomThe arrangement of electrons in an atom is

ELECTRON CONFIGURATIONELECTRON CONFIGURATION

MÖELLER MÖELLER RULERULE

The arrangement The arrangement starts from the starts from the innermost shell to theinnermost shell to theoutermost shell outermost shell following the arrows.following the arrows.

ATOM IS ATOM IS ELECTRICALLY ELECTRICALLY

NEUTRALNEUTRAL

Atom has the same number of protons Atom has the same number of protons and electrons, so, the number of positive and electrons, so, the number of positive charges is equal to of negative charges charges is equal to of negative charges and therefore atom is electrically neutral.and therefore atom is electrically neutral.

+ = -+ = -

The electrons in the outermost energy level are called valence electrons .

The electrons in an atom that are not valence electrons are called core electrons .

But, however, the atom sometimes can gain or But, however, the atom sometimes can gain or lose some electrons, so now the atom is lose some electrons, so now the atom is electrically charged, it is called: electrically charged, it is called: IONION ..

An ion with a positive charge, formed when an An ion with a positive charge, formed when an atom loses electrons, is called: atom loses electrons, is called: CATIONCATION ..

An ion with a negative charge, formed when an An ion with a negative charge, formed when an atom gains electrons, is called: atom gains electrons, is called: ANIONANION ..

Atoms whose outermost energy level is full, are less chemically reactive and therefore more stable, than those atoms whose outermost energy level is not full.

These are the NOBLE GASOS

The other elements are unstable and need to gain, lose or share valence electron in order to be more energetically stable.

THE OCTET RULE

Rosa Mª Rodríguez García-Caro

Physics and Chemistry Departament

IES ALCÚDIA