• The science of the composition and structure
of materials and the changes that materials
undergo. The biosphere
Atomic Theory of Matter (John Dalton)
• All matter is composed of atoms, which retains its
identity during chemical reaction.
• An element is a type of matter composed of only one
kind of atom, each atom of a given kind having the
same properties (e.g. mass).
• A compound is a type of matter composed of atoms of
two or more elements combined in fixed proportions.
• a chemical reaction consists of the rearrangement of
the atoms present in the reacting substances to give
new chemical combinations present in the substances
formed by the reaction.
Nuclear Model of the Atom
All nuclei of atoms of a particular element have the same atomic number, but they may have
different mass number
Isotopes: same number of protons but different number of neutrons: O-16 99.759%, O-17
0,037% and O-18 0,204% useful for biomolecules labeling
Atomic mass unit (dalton): a mass unit equal to exactly 1/12 the mass of C-12 relative.
(1,993X10-26/12= 1,6605402X10-27 Kg).
Atomic weight: is the average atomic mass for the naturally occurring element, expressed in
atomic mass units.
The sum of Isotopic massesX corresbonding fractional abundances
• 1 mole = 6.02X1023 of anything Avogadro’s number.
• Coins counting in a bank.
• Mass of dozen of eggs ≠ dozen of cars.
• In chemistry: 1 mole = 6.02X1023 particles = formula
weight in grams
• Molar mass - the mass of a single atom of an element
(in amu) is numerically equal to the mass of one mole
of those atoms (in grams).
• Molar mass of C-12 = 6.02X1023 X 12 amu X
1,6605402X10-27 Kg/amu = 12 g
Molarity and Molality
• Molarity: The number of moles of solute
divided by the volume of the solution
measured in liters.
• Moles of solutes/L of solution
• Molality: The number of moles of solute
divided by the weight measured in Kg.
• Molality=Moles of solutes/Kg
• Mole= mass/Mwt
• From moles and volume:
– What is the molarity of a solution containing 0.32 moles of NaCl in 3.4
– 0.32 mole/3,4L= 0.094 M
• From Mass and Volume:
– What is the molarity of a solution made by dissolving 2.5 g of NaCl in
enough water to make 125 ml of solution?
– Moles= mass/mwt 2,5g/58.5g/mole= 0.0427 mole
– M= 0.0427 mole/ 0.125= 0.34 M
• Calculating Mass of Solute from Molarity:
– How would you prepare 400. ml of 1.20 M solution of sodium
– Moles = V*M 0.4L*1.2 mole/L= 0.48 moles
– Mass = mwt*moles 58.5*0.48 = 28.1 g
• moles = M*V, but moles are equal before and
• Which one is the highest concentration?
• How can we make them equally concentrated
without adding more atoms?
1. A sample of 0.0256 mole of FeCl3 was dissolved in water to give 25
2. What volume of 0.12M CuSO4 is required to give 0.15 mole of
3. How many grams of Na2Cr2O7, should be added to 50 ml flask to
prepare 0.025? Given that the Mwt of Na is 23, Cr is 104 and O is
4. A 4 g sugar cube (sucrose: C12H22O11) is dissolved in a 350 ml
teacup filled with hot water. What is the molarity of the sugar
solution? Given that Mwt of C is 12, H is 1 and O is 16.
5. How many mL of 14.8 M NH3 solution you need to prepare 100 ml
of 1 M NH3?
6. How many mL of 15.8 M HNO3 solution you need to prepare 1 L of
0.12 M HNO3?