atoms and molecules parts of the atom. what is an atom? democritus democritus, a greek philosopher...

AtomsAtoms and and MoleculesMolecules

Parts of the AtomParts of the Atom

What is an atom?DemocritusDemocritus, a Greek philosopher theorized that at some point a substance can no longer be divided. He called this atomos, greek for indivisible.

AtomAtom = the smallest part, indivisible.

What is Atomic Theory?

Atomic theory states that atoms are the building blocks of all matter.

• Matter is any material substance that occupies space and has weight.– Matter makes up ALL the observable

universe

Parts of the atomParts of the atomAtoms have a nucleus and an

outer cloud that are made up of smaller parts called subatomic subatomic particles.particles.

ProtonsProtonsIn the NucleusIn the Nucleus

NeutronsNeutrons

In the electron cloudIn the electron cloud ElectronsElectrons

Subatomic ParticlesSubatomic Particles• ProtonProton = the

ppositive “+”“+” charged particle in the nucleus of an atom.– Protons have mass.

• NeutronNeutron = the nneutral (no charge) particle in the nucleus of an atom.– Neutrons have mass

• ElectronElectron = the negative “-”“-” charged particle orbiting around the nucleus of an atom.– Electrons have very

little mass.

What do atoms look like?

What is matter?

Subatomic Particle Comparison

Relative Relative MassMass

Electrical Electrical ChargeCharge

Location in Location in the atomthe atom

ProtonProton 1 amu 1 + Part of the nucleus

NeutroNeutronn

1 amu None Part of the nucleus

ElectroElectronn

0.0005 amu 1 - Moves around the nucleus in the electron cloud

Models: Why use them?

• Models are used to help us see, and understand, something that can not be observed directly, or easily.

• Models help us understand how something is built or how something works.

What is a model?

What is a model?

• A model is a description or physical A model is a description or physical representation of something.representation of something.

• We must make mental models for We must make mental models for things that we can not see.things that we can not see.

Scientific ModelsScientific Models

Early Models of the Atom

John DaltonJ. J. Thomson

Ernest RutherfordNeils Bohr

Early Models of the Atom

John Dalton J. J. Thomson

Ernest Rutherford Neils Bohr

Evolution of Atom Models

The Electron Cloud Model

Atomic NumberAtomic Number• Atomic numberAtomic number is the number of protonsnumber of protons in

the atom of an element.• The atomic number of an element is found

using the Periodic Table of the Elements.

Atomic MassAtomic Mass

• Atomic massAtomic mass is the mass of the atom, or how much the atom weighs. – Different atoms have different masses

because of the different number of protons and neutrons.

• Atomic massAtomic mass is equal to the number of protons plus the number of neutrons

Atomic massAtomic mass = protons + neutrons = protons + neutrons

Atom TermsAtom Terms

Atoms Form Atoms Form ElementsElements

• An elementelement is the simplest form of a substance.

• If we break an element down any smaller we get protons, neutrons and electrons in known proportions. If we do this we lose the characteristics of the substance.

Atoms of Elements Combine to Atoms of Elements Combine to Form MoleculesForm Molecules

• Atoms will combine with other atoms and Atoms will combine with other atoms and form molecules.form molecules.

• Examples are:Examples are:

Oxygen + Oxygen = OOxygen + Oxygen = O22 (oxygen molecule) (oxygen molecule)

Hydrogen + Oxygen = HHydrogen + Oxygen = H22O (water molecule)O (water molecule)

Carbon + Hydrogen + Oxygen = CCarbon + Hydrogen + Oxygen = C66HH1212OO66 (sugar (sugar

molecule)molecule)

What are Molecules?What are Molecules?• A A moleculemolecule is two or is two or

more atoms joined more atoms joined together.together.– Example is water, Example is water,

HH22OO

What do molecules look like?

Salt Molecule

What Are Subatomic Forces?What Are Subatomic Forces?

• Subatomic forces are forces within the atom that are responsible for holding the atom together.

• Subatomic forces explain the behavior of the subatomic particles.

• The four subatomic forces are:– Electromagnetic force– Strong force– Weak force – Gravity

What is What is Electromagnetic ForceElectromagnetic Force??

• Electromagnetic forceElectromagnetic force is a force of attraction.– It can either attract or repel the particles on

which it acts.– If the particles have opposite chargesopposite charges, such

as a proton (+) and an electron (-), the electromagnetic force is a force of attractionattraction.

– If the particles have the same chargessame charges, such as two protons (+) (+), the electromagnetic force is a force of repulsionrepulsion.

What is Strong Force?What is Strong Force?

• Strong forceStrong force is the force that “glues” the protons together to form the nucleus of an atom.

• The strong forcestrong force opposes the electromagnetic force.

What is What is Weak ForceWeak Force??

• The weak forceweak force is the key to the power of the sun, it is responsible for a process called radioactive decay.– During radioactive decay a neutron in the

nucleus changes into a proton and an electron.

What is What is GravityGravity??

• GravityGravity is the force of attraction exerted between all objects in nature.

• GravityGravity is the weakest force known in nature.

Atomic Structure Review

• Parts of the atom:• Subatomic particles

– ProtonProton: “+”“+” charge found in the nucleus

– NeutronNeutron: nono charge found in the nucleus

– ElectronElectron: “-”“-” charge found outside nucleus in electron cloud

• Atomic numberAtomic number = # of protons

• Atomic massAtomic mass = protons + neutrons

• Models of the atom:– DaltonDalton– ThomsonThomson– RutherfordRutherford– BohrBohr– Electron CloudElectron Cloud