Module 4: Exam 3 Flashcards
Number of atoms in the unit cell of a simple cubic cell
1
Number of atoms in the unit cell of a body centered cubic
2
Number of atoms in the unit cell of a face centered cubic
4
What fraction of a cell is on the corner of a unit cell?
1/8
What fraction of a cell is on the edge of a unit cell?
1/4
What fraction of a cell is on the side of a unit cell?
1/2
Packing efficency of simple cubic
52%
Packing efficiency of body centered cubic
68%
Packing efficiency of face centered cubic
74%
What is a coordination number?
The number of other atoms that are touching a particular atom
Coordination number of simple cubic
6
Coordination number of body centered cubic
8
Coordination number of face centered cubic
12
Edge length formula of simple cubic
2r
Edge length formula of face centered cubic
2(sqrt 2) * r
Edge length formula of body centered cubic
4/(sqrt3) *r
Which cubic model has the least amount of space between the atoms?
Face centered cubic
Crystalline solids
rigidly held in place
Amorphous solids
free to move around
What type of electrons do metals have?
Electrons that are free to move around
This makes them good conductors of electricity since they can transfer kinetic energy
Why are two neutral hydrogen atoms attracted to eachother?
As force of attraction increases, the potential energy decreases
This allows them to move to a state of lower potential energy
What happens to two atoms when they get too close together?
There is repulsion between the two nuclei and there is electron-electron repulsion
On a potential energy curve for the interaction of two atoms, where is change in potential energy 0?
At the bottom of the “sweet spot” dip
On a potential energy curve for the interaction of two atoms, where do repulsive forces overcome the attractive forces?
Once potential energy crosses the x-axis and becomes positive
As force of attraction increases, what happens to potential energy?
It decreases
Until a certain point where force of repulsion overcomes because two atoms are too close
Bond length
the distance(r) that makes change in potential energy 0
Would a deeper potential energy well result in a stronger or weaker bond?
Stronger
less potential energy (deeper) = greater force of attraction
Why does an ionic solid have to be expressed by an empirical formula?
Because it can go on forever
Therefore, need to simplify to ratio because there is no exact amount
Difference between ionic bond and covalent bond
Ionic bond involves the complete transfer of an electron (metal and nonmetal)
Covalent bond involves the sharing of electrons
Percent ionic character
how ionic a bond is
Why is bonding a continuum?
different differences in electronegativies make some bonds and charges stronger than others?
What does electronegativity tell us?
In a polar covalent bond, it will tell us which atom the electron is going to be pulled towards
Example of a pure nonpolar covalent
O2
there is no difference in electronegativities
Example of an ionic bond
NaCl
large difference in electronegativies, complete transfer of electrons
Which type of bond is normally the strongest?
Ionic
How do you determine the most polar covalent?
The greatest difference in electronegativity
How do you determine the most polar covalent?
The greatest difference in electronegativity
Percent ionic character of a complete ionic bond
100%
Percent ionic character of a complete covalent bond
0%
Percent ionic character of Na-Cl
79%
nothing is perfect
Percent ionic character of Na-Cl
79%
nothing is perfect
Is polar or nonpolar covalent a stronger bond?
In general, nonpolar covalent is stronger
However, have to take into consideration things like electron-electron repulsion
Why is bond length of Cl2 longer than H2?
Cl2 has a larger radius, which makes the length longer
also decreases the force of attraction, making the bond between H2 stronger
When does the atomic radius argument for bond length NOT work?
Size argument is negligible within the same period
Relationship between formal charges and force of attraction
Formal charges increase the force of attraction and strengthen the bond
Relationship between lone pairs and force of attraction
Lone pairs weaken the force of attraction and weaken the strength of the bond
it also makes the bond longer, since it is weaker
What can effect the length of a bond?
If the atoms have the same charge, this increases repulsion and resultingly lowers force of attraction, making a longer bond
Is there a greater difference in electronegativity between row or column?
If you move up a column and 2 over, that is normally a greater difference than moving DIRECTLY up a column
Coordination number of ions that are wedged between face centered? Only on edges?
6
