Atoms and Bonding Study Guide

Atoms and Bonding Study Guide

Bonding and the Periodic Table:

1. The number of valence electrons determines how an atom can bond with other atoms.
1. The number of valence electrons is the same as ______________________________________________________
2. Lewis dot structures-show _________________________________

2. Octet Rule-____________________________________________________
3. Noble gases are in _______________ and don’t ______________________

Ionic Bonds

1. Ions form when _____________________________________________
1. Lose-________________________________________________
2. Gain-________________________________________________
3. Polyatomic ions­­­­­­­­­­­­­­­­­­­-­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­________________________________________
2. Ionic bonds form when _______________________________________ between ______________ and ______________________
3. Formulas show the _______________and the __________________________
1. Subscript _____________________________________________

                                          i.    MgCl₂-(# and type) __________________________________________

2. Ratio of the elements _______________ out the charges- ionic compounds are __________________________
3. Naming-_____________________ first, change ending of negative ion to ______
1. Exception-do not change the name of _______________ ions

                                          i.    NaCl-___________________________

                                        ii.    Mg₃S₂-___________________________

                                       iii.    (NH4)₂SO₄-___________________________

5. Properties of ionic compounds
1. ____________________________________________________
2. ____________________________________________________
3. ____________________________________________________

Covalent Bonds

1. Covalent bonds form when ___________________________________
1. Form between ___________________________________
2. Each bond is a shared pair (2) of electrons
3. Lewis dot structure can be used to visualize shared electrons

4. Properties
1. ____________________________________________________
2. ____________________________________________________
5. Polarity-________________________________________________

a.    Results in slight negative and positive poles

6. Formulas give ratio of elements-H₂O-_______________________________

Metallic Bonds

1. Alloy-______________________________________________

a.    Get metals that are generally stronger and less reactive

2. Metallic bonding-___________________________________________________
3. Properties

a.    Change shape

                                          i.    ____________________________________________________

                                        ii.    ____________________________________________________

2. ____________________________________________________

4. Luster-____________________________________________________

Heat conductors-____________________________

Naming Ionic Compounds

There are three different types of ions that could be involved in an ionic bond and the rules for naming changes with the type of ion. (Please note,

First, a simple bond between a metal that is NOT a transition metal and a nonmetal. The charges of these elements is always the same, so we don't have to do anything fancy with the names. We simply write the name of the positive ion first. Then, we write the negative ion and change the ending to -ide. Simple! For example, NaCl would be sodium chloride; MgBr2 would be magnesium bromide. There is no need to mention the subscript 2 because it only tells us that we need 2 Br- ions to balance out the Mg+2 ion.

Second, bonds involving transition metals and nonmetals can be a little trickier. This is because many of the transition metals can have different charges. Iron can have a +2 or +3 charge! That means iron can bond with oxygen in two ways. It can be FeO or Fe2O3! So, how are you supposed to clarify that it the name? Simple, we write the charge of iron in parenthesis. FeO would be iron (II) oxide (notice the negative ion still ends in -ide) and Fe2O3 would be iron (III) oxide.

How do you figure out which iron is which using the formula? How about a little reverse formula writing :) Now, FeO has iron and oxygen bonded in a 1:1 ratio; in class we said that is the ratio is 1:1 that means the charges are equal and opposite. We know that oxygen always forms a -2 ion (because it is in family 6 and gains two electrons); that means that iron has to be a +2 ion (opposite and equal). On the other hand, Fe2O3 is a 2:3 ratio, so we'll do the criss-cross method in reverse.

Fe₂O₃

Fe⁺³    O^-2

Since this iron had to have a +3 charge, we write it as iron (III) oxide.

Third, the bond can involve polyatomic ions, which are atoms bonded together and acting as a single ion. Any compound involving polyatomic ions is named with the positive ion first and the negative ion second (as all are and as the formulas are written). BUT, the name of the polyatomic ion is NEVER changed. If the formula is MgSO4 then the name is magnesium sulfate. Mg+2 is the positive ion of magnesium and SO4 -2 is sulfate. There is no change to the ending of the negative ion because it is a polyatomic ion. We haven't had any of these for you to name in class and you aren't expected to memorize the names of polyatomic ions.  

Writing Formulas for Ionic Compounds

Chemical formulas are written to show the ratio of elements in a compound. Ionic bonds are between positive metal ions and negative nonmetal ions. When writing the formula for an ionic compound, the positive ion is written first and the negative ion second. Ions must bond to each other in a ratio that creates a neutral compound. This means your positive and negative charges must balance out.

To get the charges to balance out, we add subscripts to show the number of each type of ion in the compound. If the charges are already equal, but opposite, they will be in a 1:1 ratio. So, Na+1 and Cl -1 combine to form NaCl. Al+3 and N-3 combine to form AlN. However, if the charges are NOT equal (they will still be opposite because like charges won't attract), we use the criss-cross method. For the criss-cross method, we take the number for one element's charge and cross it over to become the other element's subscript.

Image from here

Creating ionic bonds using polyatomic ions would be similar. However, we would have the charge of the entire polyatomic ion cancel out with the other charge. If more the subscript for the polyatomic ion would be more than 1, we would put parenthesis around the polyatomic ion and then write the new subscript. You cannot change anything about the polyatomic ion. It must stay together as if it were a single ion because that's how polyatomic ions work.

Image from here

Periodic Table Project

The 7th grade is creating a periodic table out of every day objects. The purpose of this project is to come up with a way to organize objects into groups based on similar characteristics.

Students will create a table that looks like the periodic table with 8 families (columns) and 4 (7.1) or 5 (7.2) periods (rows). They are skipping the transition elements. Each family should have some characteristic in common and change as you go down the column in some way. The change should be consistent in each family.

For example, the periodic table of colors could be organized by different colors in each family and could get darker from the top to the bottom. However, hydrogen should be different from the other elements in the same column because hydrogen is not truly in the same family.

Each family should have a name based on the characteristics of that family and the project should include a key. The key should explain what each family has in common and how the family changes as you go down the periodic table.

All About Atoms (7th)

Our first unit this year is Chemistry and we start by reviewing what they learned in 5th grade. So, we review the parts of an atom! We then add a little more to it and learn all about atomic models and the atoms of different elements.

In our notebooks, we created a timeline (to scale) for developments of different atomic models. They do have to know the different scientists we discussed and the contributions of each. The timeline includes a foldable we filled out to help them remember the different scientists.

We then reviewed the location and charges for protons, neutrons, and electrons. We filled out another foldable. I found the idea on another teacher's site and then used Publisher to make one for us! We went through everything together and they filled it out. We'll get it glued into our notebooks, but they need it for homework right now.

For their homework, they need to know how to calculate the mass number, atomic number, and the number of protons, neutrons, and electrons. Here are the instructions we went over in class:

• Mass number = # protons + # neutrons
• Atomic number = # protons (they are always the same number!)
• Protons = atomic number (see above) OR Protons = mass number - # neutrons 
• Neutrons = mass number - # protons
• Electrons = # protons OR atomic number

For example: Iodine has a mass number of 127 and an atomic number of 53. So, Iodine has 53 protons (atomic number), 53 electrons (# protons), and 74 neutrons (127 - 53).

We also started learning how to draw Bohr diagrams and Lewis dot structures. A Bohr diagram shows all the electrons that an atom has; whereas, a Lewis dot shows only the valence, or outermost, electrons. In a Bohr diagram the energy levels are shown as rings around the center and the electrons are added to each ring until the energy level is full. This is the Bohr model for an element with 11 protons and 11 electrons. Notice that the first energy level has the only 2 electrons it can hold spaced as far apart as possible because like charges repel. The second energy level will have the electrons spread as far as possible for the first 4, then the electrons start pairing up (this has to do with orbitals-the s, p, and ds that are outside of what we cover in 7th grade). The electrons continue filling the 2nd level until it contains all 8 it can hold, then start filling the 3rd level. We won't have more than 3 energy levels for this class. Also, we have not yet started discussing the periodic table, so students do not need to try to figure out which element this would be.



The Lewis dot structure would be easier to draw because it only shows the valence electrons. These are the outermost electrons an atom has. It is important to be able to tell how many valence electrons an atom has because these are the electrons that are involved in chemical bonds and atoms will react in certain ways with other atoms based on the number of valence electrons. For now, students will determine the number of valence electrons an atom has by looking at the Bohr diagram (we will learn how to do that using the periodic table, but that comes later). For the atom above, it would look like this: