Download Chem Basics

POGIL-ish: Chemistry Basics
Integrated Science (H)
Model 1: Atoms are composed of neutrons, electrons, and protons. The number of neutrons
varies in the different isotopes of an element, and the number of electrons varies when ions
form, but the number of protons is constant and so defines an atom. Protons and neutrons are
located in the nucleus of the atom, while electrons surround them in a ‘cloud’. Each particle in
the atomic nucleus has a mass of 1.0 atomic mass units (amu). An electron is very small, with a
mass of just 0.0005 amu, and so the mass of the electrons is not included in the atomic mass.
atomic
number
element
symbol
atomic
mass (amu)
2
He
Helium
4.003
First use the information above to complete the Model 1 data table.
1. What is the convention used for element symbols?
2. What is the relationship between atomic number and the number of protons?
3. What is the relationship between atomic mass, atomic number, and neutrons?
Model 2: Although an atom is defined by it’s protons, it’s the electrons that determine how
it will behave. In a neutral atom (no charge), the number of protons and electrons is equal. The
electrons move within ‘shells’ or ‘orbits’ about the nucleus; those in the outermost shell are
called valence electrons. A stable atom has its outer shell ‘full’; in all but two cases, an outer
orbit with 8 e- is ‘full’. (Hydrogen and helium are so small they have but a single orbit, which
holds a maximum of two e-). Any atom with a less-than-full outer orbit will share, gain, or lose
electrons to other atoms and in the process form chemical bonds. The number of electrons of
an atom involved in forming bonds is the oxidation number; an atom may have multiple
oxidation numbers. One oxidation number can be found from the valence: the atom is ‘short’ a
few e- (i.e. oxygen is -2), or has a few to donate to another atom (Li +1).
Use the information from Model 1 and above to complete the Model 2 data table.
4. What’s the relationship between the valence number and the oxidation number?
5. Which atoms are likely to gain electrons from other atoms?
6. Which atoms will readily donate electrons?
7. Look at the dot diagrams you drew. Which atom pairs could bond in order to both have full
outer orbits?
8. Look at the orbital models you drew. Which atoms are not likely to form bonds?
9. What can you predict about H and C based on their oxidation numbers?
10.
What can you predict about C and Si based on their oxidation number?
Model 3: The periodic table is the most important chemistry reference there is. The rows of
elements on the table are called periods; the columns are called groups. By examining an
element's position on the periodic table, one can infer the relative mass, the number of
electron shells, the number of valence electrons, and the oxidation number, as well as a variety
of other properties that are better covered in a chemistry class.
11. Read the periodic table from left to right, and top to bottom. What is the numerical
pattern?
12. What accounts for the fact that the other informative number does not always follow the
same pattern?
13. What do the elements in any group (column) have in common?
14. What do the noble gases, Group 18, have in common as a result?
15. What do the periods (rows) have in common?
Model 4: Create another table listing the molecules below and the type and number of
atoms in each. Draw an electron dot model of the molecule. (Use a different color for each
atom type & associated electrons)
NF3
SrO
CCl4
CH4
CaCl2
HCCl3
H2O
NaCl
Teacher notes:
• whiteboards and poker chips!
• electron-dot diagram
organize the valence electrons (represent each with a dot)
above, below, to the left and to the right of the atom symbol. Pairs okay.
The rules for determining whether or not two atoms will form an ionic or covalent bond are as
follows:
IONIC: A bond is ionic only if BOTH of the following criteria are satisfied:
1. The absolute difference in charge between the two ions is 3 or less. For
example, in NaCl, Na is +1 and Cl is -1. The difference in charge is 2,
therefore satisfying this criterion.
2. The positive ion (or cation) is larger than the negative ion (anion). You can tell
by looking at their covalent radii which are listed on certain versions of the
periodic table.
COVALENT: A bond is covalent if BOTH of the following criteria are satisfied:
1. The absolute difference in charge between the two ions is 4 or more.
2. The positive ion (cation) is smaller than the negative ion (anion). Again, check
their covalent radii.
If you examine a bond to fulfill only one of the criteria for either bond, then it is
POLAR COVALENT. Most bonds are polar covalent.
Ionic bond forms between a metal and a nonmetal. Metals have 1,2 or 3 valance electrons(or
+1, +2, +3 charges) and nonmetals have 5,6 or 7 valance(in other words -1, -2, -3 charges)
electrons. In ionic bonds, there is an electron transfer. Metals give their extra valance electrons
to nonmetals. When metals give and nonmetals receive electrons, they become stable like the
noble gases. This electron transfer process forms ionic bonds between metals and nonmetals.
On the other hand, covalent bonds form between nonmetals- nonmetals. A nonmetal with 5,6
or 7 valance electrons shares their valance electrons with another nonmetal with 5,6 or 7
valance electrons. This way they have a stable structure by electron sharing. By the way,
valance electrons are electrons in the last shell.
It is through the This is how molecules and compounds are formed. In ionic bonding, atoms
that have donated or received electrons become charged and attract one another. In covalent
bonding, two non-metal atoms will share electrons.