2. Ions  An ion is a charged atom. That means that the number of protons does not equal the number of electrons, as it does in a neutral atom

3. Remember the charges of subatomic particles:

4. To calculate charge:  charge = # of protons – # electrons  Example: If an atom of fluorine(atomic # 9) has 10 electrons, its charge is 9 - 10 = -1

5. Ions are chemically different from their neutral counterparts.  Example:  F - (fluoride: in naming negative ions, we change the suffix of the neutral element's name to ide.) can be used in toothpaste to prevent cavities.  F (fluorine) however, is extremely poisonous.  In fact it is the most poisonous gas of the periodic table.

6. Characteristics of ions  Negative ion  # of electrons > # of protons  Overall charge is negative  Positive ion  # of electrons < # of protons  Overall charge is positive

7. Rutherford-Bohr model  Protons are located in the nucleus (center)  Electrons orbit the shells

8. Lewis notation  The Lewis notation is a simplified representation of the atom where only the valence electrons are illustrated (using dots)

9. Gaining/Losing electrons  The octet rule says that atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell  They all want to be like the noble(inert) gases (who have 8 valence electrons) so they will either gain or lose electrons to accomplish this task  ***Remember valence electrons are the number of electrons in the outermost shell***

10. Tendency to gain/lose electrons for the elements in Group A Family number IAII AIII AIV AV AVI AVII AVIII A Example of element LiBeBCNOFNe Number of valence electrons 12345678 Tendency Lose 1 electron Lose 2 electrons Lose 3 electrons Gain or lose 4 electrons Gain 3 electrons Gain 2 electrons Gain 1 electron Nothing

11. MOLECULE  Definition:  A molecule is the combination of two or more atoms that are chemically bonded together

12. Solutions  A solution is a homogeneous mixture (1 phase) where we can’t distinguish the substances that compose it even with the aid of observation instruments

13. Aqueous solution  An aqueous solution is a solution where the solvent is water

14. Concentration  The concentration of a solution corresponds to the quantity of solute over the quantity of solution

15. Dilution/Dissolution Dilution : add solvent to the solution Dilution = decrease in concentration Dissolution: add solute to the solution Dissolution = increase in concentration

16. Ways of expressing concentration  In number of grams of solute per litre of solution (g/L)  In number of grams of solute per 100 ml of solution ( % m/v )  In number of millilitres of solute per 100 ml of solution ( % v/v)  In number of grams of solute per 100 g of solution ( % m/m)

17. Calculating Concentration To calculate concentration in g/L we can use this formula  C = m V  C (concentration g/L)  m ( mass in g)  V (volume in L)

18. Concentration in ppm  Concentration in ppm corresponds to the number of parts of solute dissolved in one million parts of solution  1 ppm = 1 g = 1 mg = 1 mg/kg 1 000 000 g 1000 g In aqueous solutions: 1 ppm = 1 g = 1 mg/L 1000L

19. Questions  1. What are 2 ways that we can change the concentration of a solution?  2. Which of the following is most concentrated? A. 24 g solute in 150 ml solution B. 21 g solute in 125 ml solution C. 32 g solute in 250 ml solution _____________________________ Mostleast

20. Questions  3. Fill in the table NameLewis notation Atomic number Number of protons Number of electrons Charge Sodium10 chloride oxide Potassium18 Argon Calcium18