1. Molecules and Solutions
Grade 10 ST

2. Molecule A molecule is a group of two or more chemically bonded atoms
Few elements exist naturally…
Can you name a few?
Gold
Helium
The atoms of most elements bond with other elements to form molecules.

3. A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
2.5

4. Elements All elements of the periodic table are neutral
Their atomic number is equal to the number of protons and electrons of the element
Therefore they have no charge!

5. Reminder The noble gases are extremely stable Why?
The shell containing the valence electrons is complete!

6. Atomic Bonding
Atoms seek to have a similar configuration to that of the noble gases.
Elements are said to follow the octet rule
Wanting to follow suit of the closest noble gas with eight electrons
Exception: Lithium, beryllium and boron which follow helium: following the duet rule

7. Electron Tendency Lithium Beryllium Boron Carbon Nitrogen Oxygen
Group Number IA
IIA
IIIA
IVA VA
VIA
VIIA
VIIIA
Example of Element
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Valence Electrons 1 2 3 4 5 6 7
8 (except He)
Tendency
Lose 1 e-
Lose 2 e-
Lose 3 e-
Gain or Lose 4 e-
Gain 3 e-
Gain 2 e-
Gain 1 e-
None
Stable

8. Facts
All Alkali metals have one valence electron, therefore they tend to lose the electron
Halogens have 7 valence electrons, tendency to gain one electron
Hydrogen is Special
It can gain or lose, depending on the circumstances

9. Ions
An ion is an atom, or group of atoms, that has a positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons it becomes a cation
anion – ion with a negative charge
If a neutral atom gains one or more electrons it becomes an anion.

10. Sodium and Chlorine Sodium is neutral Sodium has 1 valence electron
Chlorine is neutral
Chlorine has 7 valence electrons Na
11 protons
11 electrons Cl
17 protons
17 electrons

11. Ionic Bonding
=Na+
2,8
2,8, 1
2,8,7
Cl-
2,8,8

13. Ions
Ions are formed when an atom becomes electrically charged by gaining or losing electrons
When an ion is formed the number of protons remains unchanged!
When an atom gains one or more electrons it forms a negative ion
When an atom loses one or more electron it forms a positive ion.

14. Most Probable form of ion
Most Probable Ions
Group Number IA
IIA
IIIA
IVA VA
VIA
VIIA
VIIIA
Most Probable form of ion E+
E2+
E3+
E4+ or E4-
E3-
E2- E-
None
Example
Li+
Be2+
B3+
C4+ or C4-
N3-
O2- F- He

15. Polyatomic Ions
A group of two or more chemically bonded atoms that has become electrically charged by losing or gaining one or more electrons

16. Refresher...
Solute: The minor component in a solution, dissolved in the solvent
Solvent: The liquid in which a solute is dissolved to form a solution

17. Solutions
A solution is a homogenous mixture whose component substances cannot be distinguished, even with the aid of a magnifying instrument
In a solution, the solute is dispersed uniformly throughout the solvent.
Tap water, air and steel are everyday examples of solutions

18. Aqueous Many substances can be dissolved in water=aqueous solution
The polarity of water allows for this

19. Properties: Concentration
The concentration of a solution is the amount of solute present in a given quantity of solution.
Change
Effect on the Concentration
Dilution (addition of solvent)
Reduced concentration
Dissolution (addition of solute)
Increased concentration
Evaporation (reduction of solvent)

20. Expressing Concentration
g/L - grams of solute per litre of solution
%m/V - grams of solute per 100mL of solution
%m/m - grams of solute per 100g of solution
%V/V – millilitres of solute per 100mL of solution

21. Formula
C is the concentration (in g/L) m is the mass of the solute (in g) V is the volume of the solution (in L)

22. Concentration in PPM
Parts per million – the number of parts of solute in a million parts of solution
1 ppm = 1 g of solute in g of solution or to 1 mg of solute in 1000g of solution
In an aqueous solution 1 ppm  1 mg of solute per litre