How big is an Atom? • The average size atom (Al) is about 0.00000003 cm. • It would take a stack of 50,000 aluminum atoms to equal the thickness of a sheet of aluminum foil. • That’s Small!!!!
What’s Inside an Atom? • An atom is made up of a team of three players: protons, neutrons, and electrons • They each have a charge, mass, and a location
Protons... • Charge: positive • Mass: 1 amu (atomic mass unit) • Location: Nucleus
Neutrons... • Charge: none • Mass: 1 amu (atomic mass unit) • Location: Nucleus
Electrons... • Charge: negative • Mass: almost zero • Location: electron clouds
Electrons vs Protons • The electron’s negative charge is the same size as a proton’s positive charge. • They cancel each other out: • +1 -1 = 0 • Atoms like to have 0 charge.
Questions... • What particles are in the nucleus? • Explain why atoms are neutral. • Why do scientists say that most of the mass of an atom is located in the nucleus?
How Do Atoms of Different Elements Differ? • Lets compare a Hydrogen atom and a Helium atom…
Hydrogen... • Draw one proton. • Draw a circle around the proton. • Place one electron on the circle. • You have just created a hydrogen atom! • Hydrogen has no neutrons.
Helium • Draw two protons and two neutrons all together. • Draw an electron orbit around them. • Place two electrons on the orbit. • You have just created a helium atom!!!
What is different? • The two different elements have different numbers of electrons, protons, and neutrons. • OK...
Are all atoms of an element the same? • Draw another Hydrogen atom, but this time add a neutron. • It is still Hydrogen because it has only one proton, but it has more mass in the nucleus. • It is called an isotope.
What is an Isotope? • Isotope - atoms that have the same number of protons but have different numbers of neutrons. • Some isotopes are radioactive. • Otherwise they are mostly the same as the regular atom.
How can you tell one isotope from another? • By their mass numbers. • mass number = protons + neutrons. • Different isotopes will have different mass numbers because they have different numbers of neutrons.
Let’s see... • Hydrogen-1 has 1 proton and 0 neutrons. • Mass Number = 1 • Hydrogen-2 has 1 proton and 1 neutron. • Mass Number = 2
Questions… • List the charge, location, and mass of each particle. • Determine the number of protons, electrons, and neutrons in aluminum-27.