1. 2.3 Periodic Table & Atomic Theory

2. Bohr Models
Elements with similar properties have similar electron arrangements
Bohr models show electron arrangement in shells
See page

3. How to draw a Bohr model:
Examples:
Helium
Boron

4. Oxygen
Magnesium

5. Bohr model patterns
Chemical families have the same number of valence electrons
Valence electrons = electrons in the outermost shell; they are involved in chemical reactions
Elements in the same period have the same number of shells
Period number = the number of electron shells
See page 66

6. Atom Stability Noble gases:
very unreactive because their atoms have filled valence shells
Atoms with filled shells do not easily trade or share electrons.
See pages

7. Other atoms: gain or lose electrons in to achieve stability
Full valence shell (outermost shell) = stability
gaining or losing electrons makes atoms into ions
Metals lose electrons & form positive ions
Non-metals gain electrons & form negative ions
Ions have a similar electron arrangement to the nearest noble gas
See pages

9. Examples of Ion Formation

10. For example: Sodium has one valence electron
For example: Sodium has one valence electron. It will lose this electron & form the sodium ion (Na+). The sodium ion will then have 11 protons (11+) and 10 electrons (10-) for a total charge of 1+ Think mathematically: (-10) = +1

11. Take the Section 2.3 Quiz