1. Chapter 4
Section 2 and 3

2. Periodic Trends How are elements arranged on the table?
Order of increasing atomic number
What is a trend?
Predictable change in a particular direction
Trends on the periodic table allow us to make predictions about chemical behavior

3. Atomic Radii Do we know the exact size of an atom?
No it is difficult to determine
It is determined by the volume occupied by the electrons surrounding the nucleus
Radii are usually determined for atoms that are chemically bonded or close together in the solid state

4. Atomic Radii What is bond radius? Van der Waals radius:
½ the distance between the nuclei of the atoms in each molecule
Line A represents twice the bond radius
Van der Waals radius:
Distance between the nuclei in adjacent nonbonded molecules, which is equal to twice the distance called the Van der Waals radius

5. Atomic Radii Which radius is used in this book? Bond radius
Van der Waals are not very precise
Measuring bond radius is a useful way to compare the size of atoms

6. Atomic Radius
What is the trend for atomic radius on the periodic table?
The radii increases as you go down a group
Due to the addition of another energy level from one period to the next

7. Atomic Radius Electron shielding:
Electrons in the inner energy level are between the nucleus and the outermost electrons
The inner electrons shield the outer electrons from the full charge of the nucleus
Since they are not subject to the full charge of the nucleus they are not held as close to the nucleus

8. Atomic Radius What happens to the radius as you go across a period?
The radius decreases as you go across a period
The radius decreases because the positive charge of the nucleus increases
This causes the nucleus to pull the electrons closer
This reduces the size of the atom
Eventually the electrons will not come any closer and the size of the atom tends to level off

9. Ionization Energy, Electron Affinity, and Melting Points
Are atoms neutral or do they have a charge?
Electrically neutral
Protons = Electrons
Ionization energy:
Energy used to remove an outer electron

10. Ionization Energy, Electron Affinity, and Melting Points
If an atom loses an electron it becomes a _________ ion
Positive ion
Alkali metals lose 1 electron
If you lose an electron the ion is smaller than the atom
Figure 4-25 page 138

11. Ionization Energy, Electron Affinity, and Melting Points
Which way does ionization energy increase?
Increases across a period
The electrons are held more tightly to the nucleus
Decreases down a group
The outer electrons are held less tightly to the nucleus and less energy is required to remove one
Attractive forces between the nucleus and the electrons decreases and the energy required to remove an electron decreases

12. Electron Affinity Electron Affinity:
Ability of an atom to attract and hold an electron
An approaching element could feel the net pull and enter the vacant orbital
When Fluorine gains an extra electron it becomes a ___________ ion.
Negative ion
Figure 4-28

13. Electron Affinity What does a negative electron affinity indicate?
Energy is released when an atom gains an electron
What does a positive electron affinity indicate?
Energy is needed to add the electron to an atom

14. Electron Affinity What is the trend for electron affinity?
It becomes more negative across a period
Decreases from top to bottom in a group
There are exceptions to these general trends

15. Trends in Melting and Boiling Point
What is the trend for melting and boiling point?
At first, as the # of electrons increases the melting and boiling points increases
This indicates stronger bonding
However, when the d orbital becomes half-filled the melting and boiling points decrease

16. Homework
Page 142
1-14 due before notes

17. Section 2 - Metals
What one property distinguishes metals from nonmetals?
Metals are excellent conductors of electricity
The most widely used metal to conduct electricity is copper

18. Metals In general, poor electrical conductors are poor heat conductors
The mechanism by which electricity is conducted must be closely connected with the mechanism for conduction of heat

19. Other Properties of Metals
Tungsten has the highest melting point
Most are strong and durable
Aluminum and magnesium have a high strength-to-weight ratio making them useful in construction
Some are ductile and can be squeezed into a wire
Some are malleable and can be hammered into sheets
Gold
2 or more can be mixed together to make an alloy