1. Periodic Trends
Chapter 6 Section 3 pp

2. What is a trend?
1. The general direction in which something tends to move.
2. A general tendency or inclination. See Synonyms at tendency.

3. Things to remember… Nuclear charge
Positively charged nucleus pulls electrons towards it
Atomic radius is measured in picometers
1 x 10^-12 meters = 1 pm

5. Electrostatic repulsion
Ions
An atom or bonded group of atoms that has a positive or negative charge
Occurs when an atom gains or loses an electron
Electrons are charged so you are gaining or losing a negative charge
Affects the overall charge of the atom
Electrostatic repulsion
Remember like charges repel each other…electrons in orbitals repel/push each other away

7. Energy is needed to overcome the attraction between the positive protons and negative electrons
Ionization energy (IE) is the energy required to remove an electron from a gaseous atom (kJ/mol)
IE indicates how strongly a nucleus can hold onto its valence e-
High IE= strong hold on e-; less likely to make positive ions
Low IE= atom can lose valence e- easily; likely to make positive ions

8. More about ionization energy…
After removing the 1st e- it is still possible to remove additional electrons
Second ionization energy:
The IE needed to remove a second electron from a +1 ion
Third ionization energy:
The IE needed to remove a third electron from a +2 ion

9. Electro negativity
Characteristic of an element that indicates the relative ability of its atoms to attract electrons in a chemical bond
Units: Paulings
Values are less than 3.98 or less
Leave out noble gases (they really don’t react)

10. Atomic Radius Electron cloud
Spherical surface in which there is a 90% probability of finding an e-
Not physical
Atomic size is defined by how closely an atom lies to its neighboring atom
Each atom has different properties so there are going to be different sizes…
Different sizes in different blocks…

12. Atomic Radius of a Metal
Metals
Atomic radius
half the distance between adjacent nuclei in a crystal of that element

13. Atomic Radius of a Nonmetal
Usually occur as molecules
Atomic radius:
Half the distance between nuclei of identical atoms that are chemically bonded together
Diatomic molecules
Hydrogen
Bromine
Iodine
Oxygen

14. Ionic Radius Losing/gaining electrons affects size of an atom
Gain an electron atom becomes negative atom becomes larger
Electrostatic repulsion between atom’s outer electrons increase
Forces outer electrons to move further apart
Makes radius bigger
Lose an electron atom becomes positive atom becomes smaller
Electron lost is valence electron
Can lead to completely empty orbital=smaller radius
Electrostatic repulsion between atoms decrease so they can be pulled closer to nucleus

15. Periodic Trend Scramble
Break up into your first group
Find everyone with the same type of card…all kings together, all queens together, etc….
Listen for instructions

16. Atomic Radius: Trends in Periods
DECREASE in atomic radii left-to-right
Increasing positive charge in the nucleus
Principle energy level (n) remains the same throughout the period
Each successive element the atomic # Increase
Add proton and electron
Electron gets added to same Prin. E level (n)
No additional electrons come across valence electrons and nucleus
Val. E- are not shielded from increased nuclear charge
Therefore the increased nuclear charge brings the outermost electrons closer to the nucleus …which means…
Smaller atomic radii going   

17. Atomic Radius: Trends within Groups
INCREASE as you move down a group
Nuclear charge increases
What happens to your principle energy level as you move down a group?
Therefore…Electrons added to higher principle energy levels
Although nuclear charge increased, other factors in play to overpower increased nuclear charge...
Outermost orbital increases in size
Electrons are farther from the nucleus b/c of bigger orbital
More resistant to higher nuclear charge b/c of increased distance
Principle energy level increased
Puts more orbital with electrons between the nucleus and the outermost electrons
These electrons in between shield the outermost electrons from the pull of the nucleus

19. Solve… Which has the largest radius? Which has the smallest radius?
Magnesium (Mg)
Silicon (Si)
Sulfur (S)
Sodium (Na)
Which has the smallest radius?

20. And the answer is…
Largest: Na (sodium)
Smallest: S (sulfur)

21. Ionic Radius: Trends in Period
What type of ions do you think will be formed on the left side of the table?
Smaller positive ions
What type of ions do you think will be formed on the right side of the table?
Larger negative ions
General Rule:
Left-to-right across a period, the size of positive ions gradually decreases
Around 5A and 6A, the size of much larger negative ions gradually decreases

23. Ionic Radius: Trends in Group
What happens to the principle energy level as we move down a group?
Increases
Ion’s outer electrons are in a higher principle level
This means an increase in ionic size
Ionic radii increases as we move down a group for both positive and negative ions

25. Ionization Energy What type of IE does group 1A have? High or low?
Low IE
Likely to form + ions
What type of IE does group 8A have?
High IE
Unlikely to form ions
From left to right, the IE to remove successive electrons always increases
Does not happen smoothly…requires large jump of energy

26. IE continued…. Trends in periods:
First IE generally increases as you move left-to-right
The nuclear charge increases with each successive element…
What does this have to do valence electrons?
Increase the nuclear charge=stronger hold on valence electrons

27. IE continued… Trends within groups…
First IE generally decrease as you move down a group
What happens to the size of an atom as you move down a group?
Increases
This cause decrease in IE
Valence electrons are farther from the nucleus
Easier to remove

28. Octet Rule What is the electron configuration for sodium?
What is the new configuration when a sodium atom becomes a +1 sodium atom?
What noble gas does this configuration look like?
OCTET RULE:
Atoms tend to gain, lose, or share electrons in an order to acquire a full set of valence electrons
First period elements are en exception to the rule
This rule helps to determine what kind of ions will form

29. Food for thought….
Do atoms on the right side of the periodic table tend to gain or lose electrons?
Gain electrons
What type of ions are they likely to form?
Negative ions
Do atoms on the left side of the periodic table tend to gain or lose electrons?
lose e-
What type of ions do they form?
Positive ions

30. Electronegativity (EN)
Fluorine is the most electronegative element
Value: 3.98
Cesium and Francium are the least electronegative
Values: 0.79 and 0.7
Atom with greater electronegativity attracts electrons in a chemical bond the strongest

32. Electronegativity (EN)
Trends in periods and groups:
EN decreases as you move down a group
Increases as you move left to right on table
Where are the lowest electronegatives found?
Lower left side of the periodic table
Where are the highest electronegatives found?
Upper right side of the periodic table

34. What are some things you have an affinity for?

35. Electron Affinity
The energy change that occurs when an electron is acquired by a neutral atom
Measure in kJ/mol
Many atoms release energy when they gain an electron
A + e-  A- + energy
A + e- + energy  A-
Some atoms need energy to be “forced” to gain an electron
Produces unstable ions that lose electron quickly

38. Study for Ch. 6 test!