1. TRENDS IN THE PERIODIC TABLE

2. Review Are periods in the periodic table horizontal or vertical?
Are groups in the periodic table horizontal or vertical?
What is another name for ‘group’?
What is the family name of group 1? 2? 17? 18?
What is a unique property of elements in group 18?

3. What is a trend in the periodic table?
Going across a period or down a group, the properties of elements change in a regular way

4. TRENDS IN THE PERIODIC TABLE

5. TRENDS IN THE PERIODIC TABLE
Examine the number of valence electrons for each atom:
What do you notice?

6. Reactivity and Outermost Electrons
Valence electron: an electron in the outermost occupied energy level of an atom
Number of valence electrons determines an element’s properties
Atoms in the same group have the same number of valence electrons  react in similar ways
Valence electrons increase as you go across a period

8. Achieving Full Outer Energy Levels
Atoms other than noble gases undergo chemical reactions to become more stable
They can lose, gain, or share electrons to fill their outermost energy level = more stability
Generally, the closer the element is to a noble gas, the more reactive it is
The alkali metals and halogens are so reactive because they only need to gain or lose one electron to achieve a full outer energy level

9. TRENDS IN THE PERIODIC TABLE
The number of valence electrons can determine reactivity:
Elements become stable by achieving 8 valence electrons (except for hydrogen and helium, which achieve 2 electrons)
Noble gases are non-reactive because they have 8 electrons
This is called the Octet Rule

10. TRENDS IN THE PERIODIC TABLE
How many valence electrons does each atom need to gain or lose to achieve a full octet?
Alkali metals lose 1 electron
Alkali earth metals lose 2 electrons
Group 13 elements lose 3 electrons
Group 14 elements lose or gain 4 electrons 10

11. TRENDS IN THE PERIODIC TABLE
How many valence electrons does each atom need to gain or lose to achieve a full octet?
Group 14 elements lose or gain 4 electrons
Group 15 elements gain 3 electrons
Group 16 elements gain 2 electrons
Halogens gain 1 electron
Noble gases already have a full octet 11

12. TRENDS IN THE PERIODIC TABLE
Examine the number of energy levels of electrons:
Increasing size
TREND:
Atoms in the same period have the same number of energy levels
The lower an atom is on the periodic table, the larger it is

13. Reactivity and Atom Size
The distance from the centre of the nucleus to the valence electrons determines the size of an atom

14. Reactivity and Atom Size
As you go down a group, the valence electrons are in higher energy levels
The higher the energy level, the farther the valence electrons from the nucleus, and the larger the atom
The farther the valence electrons are from the nucleus, the more easily they are lost =  reactive

17. Reactivity and Atom Size
Atoms get larger as you move left across a period
Draw the Bohr-Rutherford diagrams for elements in period 2:

18. Reactivity and Atom Size
All valence electrons for atoms of elements in a period are in the same energy level
As you move towards the left side of a period, the number of protons decreases
Less protons = less attraction of electrons to protons in nucleus =  atom size

19. Homework
Read p
Complete the back of the Periodic Table activity (Due Monday)
Read a procedure and create a table for the lab on page ____ in text (for Friday)

20. TRENDS IN THE PERIODIC TABLE
Alkali metals
Alkali metals have 1 electron in their valence shell
They can achieve a full octet by losing this electron
Thus they lose their valence electron easily to another element, making them very reactive K Na
19P+
11P+
20N
12N

21. TRENDS IN THE PERIODIC TABLE
Halogens
Halogens have 7 valence electrons
They can achieve a full octet by gaining one electron
Thus they readily take an electron from other atoms, making them very reactive Cl F
17P+
9P+
18N
10N