The AtomThe Atom

How big is an How big is an Atom?Atom?

The average size atom (Al) is The average size atom (Al) is about 0.00000003 cm.about 0.00000003 cm.

It would take a stack of 50,000 It would take a stack of 50,000 aluminum atoms to equal the aluminum atoms to equal the thickness of a sheet of aluminum thickness of a sheet of aluminum foil.foil.

That’s Small!!!!That’s Small!!!!

What’s Inside an What’s Inside an Atom?Atom?

An atom is made up of a An atom is made up of a team of three players: team of three players: protons, neutrons, and protons, neutrons, and electronselectrons

They each have a They each have a charge, charge, mass, and a locationmass, and a location

Protons...Protons... Charge: Charge: positivepositive Mass: Mass: 1 amu 1 amu (atomic mass (atomic mass

unit)unit) Location: Location: NucleusNucleus

Neutrons...Neutrons... Charge: Charge: nonenone Mass: Mass: 1 amu 1 amu (atomic mass (atomic mass

unit)unit) Location: Location: NucleusNucleus

Electrons...Electrons... Charge: Charge: negativenegative Mass: Mass: almost zero almost zero Location: Location: electron cloudselectron clouds

Electrons vs ProtonsElectrons vs Protons

The electron’s negative The electron’s negative charge is the same size as a charge is the same size as a proton’s positive charge.proton’s positive charge.

They cancel each other out: They cancel each other out: +1 -1 = 0+1 -1 = 0 Atoms like to have 0 charge.Atoms like to have 0 charge.

Questions...Questions... What particles are in the What particles are in the

nucleus?nucleus? Explain why atoms are Explain why atoms are

neutral.neutral. Why do scientists say that Why do scientists say that

most of the mass of an atom most of the mass of an atom is located in the nucleus?is located in the nucleus?

How Do Atoms of How Do Atoms of Different Elements Different Elements

Differ?Differ?

Lets compare a Hydrogen Lets compare a Hydrogen atom and a Helium atom…atom and a Helium atom…

Hydrogen...Hydrogen... Draw one proton.Draw one proton. Draw a circle around the proton.Draw a circle around the proton. Place one electron on the circle.Place one electron on the circle. You have just created a You have just created a

hydrogen atom!hydrogen atom! Hydrogen has no neutrons.Hydrogen has no neutrons.

HeliumHelium Draw two protons and two Draw two protons and two

neutrons all together.neutrons all together. Draw an electron orbit around Draw an electron orbit around

them.them. Place two electrons on the orbit.Place two electrons on the orbit. You have just created a helium You have just created a helium

atom!!!atom!!!

What is different?What is different? The two different elements The two different elements

have different numbers of have different numbers of electrons, protons, and electrons, protons, and neutrons.neutrons.

OK...OK...

Are all atoms of an Are all atoms of an element the same?element the same?

Draw another Hydrogen atom, Draw another Hydrogen atom, but this time but this time add a neutronadd a neutron..

It is still Hydrogen because it It is still Hydrogen because it has only one proton, but it has has only one proton, but it has more mass in the nucleus.more mass in the nucleus.

It is called an It is called an isotope.isotope.

What is an Isotope?What is an Isotope? Isotope - atoms that have the Isotope - atoms that have the

same number of protonssame number of protons but but have have different numbers of different numbers of neutronsneutrons..

Some isotopes are Some isotopes are radioactiveradioactive.. Otherwise they are mostly the Otherwise they are mostly the

same as the regular atom.same as the regular atom.

How can you tell one How can you tell one isotope from isotope from

another?another? By their By their mass numbersmass numbers.. mass numbermass number = protons + neutrons. = protons + neutrons.

Different isotopes will have Different isotopes will have different mass numbers different mass numbers because they have different because they have different numbers of neutrons.numbers of neutrons.

Let’s see...Let’s see...

Hydrogen-1 has 1 proton Hydrogen-1 has 1 proton and 0 neutrons.and 0 neutrons.

Mass Number = 1Mass Number = 1 Hydrogen-2 has 1 proton Hydrogen-2 has 1 proton

and 1 neutron.and 1 neutron. Mass Number = 2Mass Number = 2

Questions…Questions…

List the charge, location, List the charge, location, and mass of each particle.and mass of each particle.

Determine the number of Determine the number of protons, electrons, and protons, electrons, and neutrons in aluminum-27.neutrons in aluminum-27.