1. What is true about all substances?
Every substance is either an element or a compound.
All substances are “pure”, by definition.

2. What is true about compounds?
A compound consists of more than one kind of atom.
The elements in a compound exist in a definite proportion by mass.

3. Where would the elements in a molecular compound be found on the periodic table?
Molecular compounds consist of elements from the nonmetal portion of the periodic table.

4. Where would the elements in an ionic compound be found on the periodic table?
Ionic compounds consist of elements from both the metal and nonmetal portions of the periodic table.

5. What are the two types of compounds?
A compound is either molecular or ionic in nature.

6. What information is given by a molecular formula?
A molecular formula shows the number and kinds of atoms present in a molecule of a compound.

7. What information is given by the molecular formulas listed below: CO and CO2?
CO means one carbon and one oxygen;
CO2 means one carbon and two oxygen.

8. Why do ionic compounds conduct current when part of an aqueous solution?
Ionic compounds are composed of oppositely charged ions combined in electrically neutral groupings. Because they are composed of ions, they easily dissolve in water and conduct electricity.

9. NaCl crystals are composed of alternating units of Na and Cl
NaCl crystals are composed of alternating units of Na and Cl. Why isn’t the formula something like Na124Cl124?
A formula unit gives the lowest whole-number ratio of ions in the compound. Since we don’t know how many units of each atom, it makes sense to use the least common multiple.

10. The charges of the ions of the representative elements can be determined by the position of these elements in the periodic table. ?

11. Most transition metals have more than one common ionic charge.
Why do we not predict the charges of
transition metals
from their positions in the periodic table?

12. What is an ion such as OH1- or SO42-?
A polyatomic ion is a group of atoms that behaves as a unit and has a charge.

13. Why do both iron(II) and iron (III) appear on our list of cations?
When a cation can have more than one ionic charge, a Roman numeral is used in the name.

14. There are simple rules for naming ionic and molecular compounds
There are simple rules for naming ionic and molecular compounds. The first rule is listed below. What is different about naming an ionic compound than a molecular compound?
For both, we write the least electronegative (most positive) first, followed the less electronegative atom.
For ionic compounds, we just list the cation, then the anion. For molecular compounds, you use prefixes. The less electronegative atom only gets a prefix if there is more than one. For the more electronegative ion, you always use a prefix, then you use the – ide ending. Ex: Carbon monoxide, carbon dioxide, dinitrogen pentoxide.

15. What do you know about the electron configuration and
chemical reactivity of an atom
based on this picture?
Elements that have similar properties also have similar electron configurations and are members of the same group.

16. Since Li has the electron configuration 1s22s1
and sodium has the electron
configuration 1s22s22p63s1
Which would lose electrons more
easily?
Sodium would lose electrons more easily because there is more shielding.

17. Since Li has the electron configuration 1s22s1
and beryllium has the electron
configuration 1s22s2
Which would lose electrons more
easily?
Lithium would lose electrons more easily than beryllium because there is less shielding.

18. As we go down a group, the density increases.
We found the density
of silicon, tin, and lead.
As we went down a group
we noticed a periodic trend.
What trend did we notice?
As we go down a group, the density increases.

19. As we go down a group, the chemical reactivity increases.
Magnesium metal can
be purchased in pure form.
Calcium metal can be purchased,
but usually oxidizes soon after.
Strontium can only be purchased (by
a high school teacher) in the oxidized
form. What periodic trend does this
illustrate?
As we go down a group, the chemical reactivity increases.

20. What does this graph show?
Regular changes in the electron configuration of the elements cause gradual changes in both the physical and chemical properties within a group and within a period. And, as a result, the
atomic radii decrease as you move from left to right in a given period.

21. What does this picture show?
Regular changes in the electron configuration of the elements cause gradual changes in both the physical and chemical properties within a group and within a period. And, as a result, the
atomic radii generally increase as you go down a group, and decrease as you go across a period.

22. What does this graph show?
The graph shows that electronegativity increases across a period and decreases down a group.

23. What do the red dots represent?
The red dots represent valence electrons

24. What do the red dots represent
What do the red dots represent? How do they vary with position on the periodic table?
The red dots represent valence electrons
The number of dots is the same as the group number (except for helium)

25. Summary of goals for Unit 5
Every substance is either an element or a compound.
A compound consists of more than one kind of atom.
A compound is either molecular or ionic in nature.
Molecular compounds are composed of two or more nonmetals.
A molecular formula shows the number and kinds of atoms present in a molecule of a compound.
Ionic compounds are composed of oppositely charged ions combined in electrically neutral groupings.
A formula unit gives the lowest whole-number ratio of ions in the compound.
The charges of the ions of the representative elements can be determined by the position of these elements in the periodic table.
Most transition metals have more than one common ionic charge.
A polyatomic ion is a group of atoms that behaves as a unit and has a charge.
When a cation can have more than one ionic charge, a Roman numeral is used in the name.
There are simple rules for naming ionic and molecular compounds.
Elements that have similar properties also have similar electron configurations and are members of the same group.
Regular changes in the electron configuration of the elements cause gradual changes in both the physical and chemical properties within a group and within a period.
Atomic radii decrease as you move from left to right in a given period.
Ionization energy increases as you move from left to right in a given period.
Atomic radii increase within a given group because the outer electrons are farther from the nucleus as you go down the group.
Ionization energy decreases as you move down through a group.