The Structure of MatterThe Structure of Matter

Atomic ModelsAtomic Models

Subatomic ParticlesSubatomic Particles

Forces Within the AtomForces Within the Atom

Part One: Atomic models past and present

Atomic Models Throughout Atomic Models Throughout HistoryHistory

Greek (~400 BC)Greek (~400 BC) Dalton (1800)Dalton (1800) Thomson (1897)Thomson (1897) Rutherford (1908)Rutherford (1908) Bohr (1913)Bohr (1913) Wave ModelWave Model

Greek (~400 BC)Greek (~400 BC)

Atomos: indivisibleAtomos: indivisible Democritus said the smallest piece of Democritus said the smallest piece of

matter was an atommatter was an atom Theory wasn’t accepted for 2100 Theory wasn’t accepted for 2100

yearsyears

Dalton (1800)Dalton (1800)

All elements are composed of atoms. All elements are composed of atoms. Atoms are indivisible and indestructibleAtoms are indivisible and indestructible

Atoms of the same element are exactly Atoms of the same element are exactly alikealike

Atoms of different elements are differentAtoms of different elements are different Compounds are formed by the joining of Compounds are formed by the joining of

atoms of two or more elementsatoms of two or more elements

Thomson (1897)Thomson (1897)

Discovered negatively charged Discovered negatively charged particlesparticles The atom was divisible!The atom was divisible! Particles discovered are Particles discovered are electronselectrons

““Plum Pudding Model”Plum Pudding Model” Atom consists of positively charged Atom consists of positively charged

material with negative charges material with negative charges spread evenly throughoutspread evenly throughout

Here’s JJ!Here’s JJ!

Rutherford (1908)Rutherford (1908)

Gold Foil ExperimentGold Foil Experiment Positive particles shot at gold Positive particles shot at gold

foil occasionally bounced foil occasionally bounced back!back!

Proposed dense, positively Proposed dense, positively charged center called the charged center called the nucleusnucleus

Thomson’s theoryThomson’s theory

Rutherford’s realityRutherford’s reality

Rutherford’s atomRutherford’s atom

Bohr (1913)Bohr (1913)

Electrons move in definite orbits Electrons move in definite orbits around the nucleusaround the nucleus

Places each electron in a Places each electron in a specific specific energy levelenergy level

The Bohr Atom

Wave ModelWave Model

Modern model based on wave mechanicsModern model based on wave mechanics Nucleus is surrounded by electrons Nucleus is surrounded by electrons Electrons do Electrons do notnot move in orbits move in orbits We can determine the We can determine the probable locationprobable location

of an electron based on the amount of of an electron based on the amount of energyenergy the electron has the electron has

This probable location is called an This probable location is called an orbitalorbital

Part Two: Subatomic particles

Three main subatomic particles

Proton Neutron Electron

Protons

Positively charged Found in nucleus Has a mass of 1 amu The number of protons determines the

identity of the atom The atomic number tells the number of

protons

Elements are made of atoms

Hydrogen-1proton Helium-2 protonsLithium-3 protons

The number of protons determines the identity

of the element!! (atomic number)

What is that other particle found in the nucleus?

It’s a neutron! Neutrons have no charge

– (they’re neutral)

Neutrons have a mass of 1 amu Proton + neutron = mass number

Electrons

Electrons hang out in “orbitals” outside the nucleus of the atom

Electrons have almost no mass The electron cloud is the majority of the

volume of the atom ELECTRONS ARE NEGATIVELY

CHARGED!

More electron info!

In a neutral atom, the number of electrons is equal to the number of protons

When an atom gains or loses electrons, it is called an ion.

Now I’m a happy ion!I’m POSITIVE! And my outer shell is full, without thattroublesome extra electron.

The ionization process

This chloride ion has added an electron. It is a NEGATIVE ion!

(note: the inner 2 electrons are not shown)

Now I’m a happy ion!!!

Sodium chloride-everybody’s happy!

One lost……One gained.

(positive ion) (negative ion)

Quick Review:

• The three subatomic particles are proton, neutron and electron

• Protons are positively charged, electrons are negative, neutrons are neutral

• When an electron is lost or gained, the atom becomes an ion.

IsotopesIsotopes

►Atoms with the same number of Atoms with the same number of protons but different numbers of protons but different numbers of neutrons are called isotopes.neutrons are called isotopes.

► Isotopes are designated by the symbol Isotopes are designated by the symbol and the mass number:and the mass number: H-1: 1 proton, no neutronsH-1: 1 proton, no neutrons H-2: 1 proton, one neutronH-2: 1 proton, one neutron H-3: 1 proton, two neutronsH-3: 1 proton, two neutrons

It’s the Isotopes!It’s the Isotopes!

What symbols represent ions?What symbols represent ions?

Elements on the left side of the Elements on the left side of the periodic table will lose electrons to periodic table will lose electrons to become positive ionsbecome positive ions– Examples: CaExamples: Ca2+2+, Na, Na++,Fe,Fe3+3+,Fe,Fe2+2+,Al,Al3+3+

Elements on the right side of the Elements on the right side of the periodic table will gain electrons to periodic table will gain electrons to become negative ionsbecome negative ions– Examples: FExamples: F--, O, O2-2-, P, P3-3-, Cl, Cl--

How big is the nucleus?How big is the nucleus?

If an atom was as If an atom was as big as a football big as a football field, the electrons field, the electrons would move over would move over the entire field, the entire field, while the nucleus while the nucleus would be the size would be the size of a lima bean in of a lima bean in the middle of the the middle of the field.field.

If an atom was an elephant, the If an atom was an elephant, the nucleus would be as big as a flea nucleus would be as big as a flea

on the elephanton the elephant

How massive is the nucleus?How massive is the nucleus?

Even though the nucleus is VERY Even though the nucleus is VERY small, it is VERY massive. Even small, it is VERY massive. Even though it’s the size of the flea, it though it’s the size of the flea, it would weigh as much as the would weigh as much as the elephant. And though the electrons elephant. And though the electrons take up as much space as the take up as much space as the elephant, they would only weigh as elephant, they would only weigh as much as the flea.much as the flea.

Part Three: Forces Within The Atom

Forces that govern the behavior of subatomic particles:

StrongWeakElectromagneticGravity

Strong force

Opposes electro-

magnetic force of

repulsion between protons“Glues” protons together to form

the nucleusGreatest of the forces, but has very

limited range

Weak force

Responsible for radioactive decay in the atom

Electromagnetic forceRepels positively

charged protons within the nucleus.

Do you remember the force which holds them together so the atom doesn’t explode?

(Yes- strong force!)

Strong force overcomes

electromagnetic repulsion

Electromagnetic forcecauses proton repulsion

GravityWeakest of the forcesForce of attraction between

all objectsEffect seen easily only for

very large objects