Atoms

Atom smallest part of element that has all properties of the element If you break an atom apart into sub-atomic particles, they no longer have the properties of the element For example, if you take a lump of coal (the element carbon), and break it into smaller and smaller pieces, the smallest piece that still acts like coal is one atom of carbon.

Parts of an Atom 2 main parts nucleus electron cloud. Most space between nucleus and electron cloud is empty Electron Cloud

Nucleus Nucleus is located in the center of the atom 2 subatomic particles: Protons Neutrons

+ Protons + Charge = + (positive) Mass = 1 amu Location = nucleus Sub-atomic particle Charge = + (positive) Mass = 1 amu Location = nucleus Every atom of an element has the same number of protons NOTE: amu = atomic mass unit; it is also abbreviated u FYI: From the National Institute of Standards and Technology (http://physics.nist.gov/Pubs/SP811/sec05.html#5.1.3): The unified atomic mass unit (u) is equal to 1/12 times the mass of a free carbon 12 atom, at rest and in its ground state, 1.660 538 782(83) × 10-27 kg

= Neutrons = Charge = 0 (neutral) mass = 1 amu Location = nucleus Sub-atomic particle Charge = 0 (neutral) mass = 1 amu Location = nucleus Number of neutrons in an element can vary FYI: the number of neutrons can change from the normal; when it does, it is called an Isotope. From Chem4kids (http://www.chem4kids.com/files/atom_isotopes.html): NEUTRON MADNESS We have already learned that ions are atoms that are either missing or have extra electrons. Let's say an atom is missing a neutron or has an extra neutron. That type of atom is called an isotope. An atom is still the same element if it is missing an electron. The same goes for isotopes. They are still the same element. They are just a little different from every other atom of the same element. There are a lot of carbon atoms in the universe. The normal ones are carbon-12. Those atoms have 6 neutrons. There are a few straggler atoms that don't have 6. Those odd ones may have 7 or even 8 neutrons. As you learn more chemistry, you will probably hear about carbon-14. Carbon-14 actually has 8 neutrons (2 extra). C-14 is considered an isotope of the element carbon. MESSING WITH THE MASS If you have looked at a periodic table you may have noticed that the atomic mass of an element is rarely an even number. That happens because of the isotopes. If you are an atom with an extra electron, it is no big deal. Electrons don't have much of a mass when compared to a neutron or proton. Atomic masses are calculated by figuring out how many atoms of each type are out there in the universe. For carbon, there are a lot of C-12, a couple C-13, and a few C-14 atoms. When you average out all of the masses, you get a number that is a little bit higher than 12 (the weight of a C-12 atom). The mass for element is actually 12.011. Since you never really know which C atom you are using in calculations, you should use the mass of an average C atom.

- Electron - Charge = - (negative) mass  0.005 amu Sub-atomic particle Charge = - (negative) mass  0.005 amu 1836 electrons = mass 1 proton Location = electron cloud outside & around nucleus

Parts of an Atom Electron Cloud Protons Neutrons Ask a student to identify what the line is pointing at, (nucleus) click and the answer will appear. Ask a student what two particles are found in the nucleus, (protons and neutrons) click and the answer will appear. Ask a student what the arrow is pointing at (electron cloud)

Electron Cloud...

Electrons are what determines how an atom reacts But where exactly are the electrons inside an atom? atom

where there is a high probability Orbitals areas within atoms where there is a high probability of finding electrons

Orbital Levels closest to nucleus – max 2 electrons 2nd shell – max 8 electrons 3rd shell – max 8 electrons fill shells closest to nucleus first TEACHER NOTE: the term “shell” is used here to demonstrate there are various terms for the orbitals. We recommend that you use orbital, electron shell, electron cloud and circle, interchangeable throughout this unit so students are familiar with all the terms. Since electrons can be anywhere in the electron cloud, we use a model of circles (Bohr Model) to demonstrate the orbitals. This might be a good point to talk about the limitations of this model…electrons don’t travel in circular orbits; they are found somewhere in the cloud at any given moment. It s3d, not 2d, etc.

Hydrogen - NUCLEUS Have students locate the elements on the periodic table as you go through the next several slides. They should come to the conclusion that the period numbers indicate the number of electron shells and that the group numbers indicate the number of electrons in the last shell.

Helium - - NUCLEUS

Lithium - - - NUCLEUS

Beryllium - - - NUCLEUS -

Boron - - - NUCLEUS - -

Carbon - - - - NUCLEUS - -

Nitrogen - - - - - NUCLEUS - -

Oxygen - - - - - NUCLEUS - - -

Fluorine - - - - - - NUCLEUS - - -

Neon - - - - - - NUCLEUS - - - -

Sodium - - - - - - - NUCLEUS - - - -

Magnesium - - - - - - - NUCLEUS - - - - -

Aluminum - - - - - - - - NUCLEUS - - - - -

Silicon - - - - - - - - NUCLEUS - - - - - -

Phosphorus - - - - - - - - - NUCLEUS - - - - - -

Sulfer - - - - - - - - - NUCLEUS - - - - - - -

Chlorine - - - - - - - - - - NUCLEUS - - - - - - -

Argon - - - - - - - - - - NUCLEUS - - - - - - - -

Science has determined where the orbitals are inside an atom, but it is never known precisely where the electrons are inside the orbitals If students are struggling to understand this, have one student walk around the classroom in one large circle. Instruct the student not to stop walking until you direct them to. Have another student point to the exact location of the student. (You may need to get real specific and instruct them to point to the exact tile on the floor the student is on) As students realize this is not possible because as soon as they have located the place the walking student is the student has moved, have the walking student stop and then allow the other student to identify the exact location. Just as we can know that the person walking around the room is on a specific path, but not know exactly where on the path, we know that electrons are in specific orbits but we can not identify exactly where on the orbit. Because of this unknown we call the orbitals an “electron cloud”

Knowing how electrons are arranged in an atom is important because that controls how atoms react with each other to form molecules

HAPPY ATOMS valence number – number of electrons in outer most shell of atom Atoms want outer most shell to be full, will lose or gain extra electrons Make sure to point out that atoms with only one shell will be “happy” with 2 electrons.

What does that have to do with anything?? Putting it all together

Sodium - - - - - - - - - - - NUCLEUS VALENCE Ask students how many electrons an atom of Sodium should have – 11 How many of the electrons will fit in the first orbital? – 2 How many electrons will fit in the second orbital? 8 How many electrons will be in the third orbital? 1 What is the valence number for Sodium? 1 Ask students what would need to occur for this atom to be “happy”. They should come up with gain 7 electrons or lose 1 electron. Explain that it takes the same amount of energy for an atom to gain or lose electrons. Would it be easier for Sodium to gain 7 electrons or lose 1 electron? – lose 1 - - -

Chlorine - - - - - - - - - - - - - - - - - NUCLEUS Ask students how many electrons an atom of Chlorine should have – 17 How many of the electrons will fit in the first orbital? – 2 How many electrons will fit in the second orbital? 8 How many electrons will be in the third orbital? 7 What is the valence number for Sodium? 7 Ask students what would need to occur for this atom to be “happy”. They should come up with lose 7 electrons or gain 1 electron. Would it be easier for Chlorine to lose 7 electrons or gain 1 electron? – lose 1 - - - - - -

Sodium Chloride “SALT” Chlorine - - - - - - - - - - - - - - NUCLEUS NUCLEUS - - - - - On the first click Sodium’s valence electron will move to Chlorine and it’s outer orbital will disappear. On the second click the names will combine. Have students explain how this makes both atoms in the molecule “happy”. - - - - - - - - -

NaCl H2O O2 SO4 H2 CO2 N2 O3 Molecule two or more atoms that are chemically bonded Compound two or more different elements that are chemically bonded H2O O2 SO4 H2 CO2 Go over the definitions of molecule and compound with students. Have students predict if the each of the formulas in the middle is a molecule, compound or both. As you click the answers will appear. Make sure to point out that every is compound a molecule but not every molecule is a compound. Just like all squares are rectangles but not all rectangles are squares. N2 O3