I. BASIC CONCEPTS OF CHEMISTRY

Prepared by PhD Halina Falfushynska

Branches of chemistry

Physical chemistryOrganic chemistry

Inorganic chemistryAnalytical chemistryIndustrial chemistry

Bio chemistryNuclear chemistry

Agricultural chemistryGeo chemistry

Uses of chemistry

Abuses of chemistry

A compound is a substance which can be decomposed into two or more dissimilar substances.

2 2 2Compound

Elements

2H O 2H O

Compound and mixture

Mixture contains two or more components.

Homogenous mixture: Same or uniform composition.Air is a mixture of gases like O2, N2, CO2, etc.

Heterogeneous mixture: Different compositions in different phases. Smog.

Law of conservation of mass

Total mass of the product remains equal to the total mass of the reactants.

H2 + Cl2 2 HCl2g 71g 73g

A chemical compound always contains same elements combined together in same proportion of mass.

Law of definite proportions

Ice water H2O 1 : 8

River water H2O 1 : 8

Sea water H2O 1 : 8

Law of Multiple Proportions

• If two elements form more than a single compound, the masses of one element combined with a fixed mass of the second are in the ratio of small whole numbers (John Dalton, 1803).

• It is found elemental iron combines with elemental chlorine to form two different compounds; ferric chloride and ferrous chloride. The definite composition of these two compounds is:

• This data can be used to determine the mass of chlorine per 1.00g of iron needed to produce these compounds.

Dalton’s Atomic Theory

• 1) All matter is made of atoms. Atoms are indivisible and indestructible.

• 2) All atoms of a given element are identical in mass and properties

• 3) Compounds are formed by a combination of two or more different kinds of atoms.

• 4) A chemical reaction is arearrangement of atoms.

Avogadro's Law

• Equal volumes of gases under identical temperature and pressure conditions will (atoms, ion, molecules, electrons, etc.).

Avogadro's Number!How many carbon-12 atoms are needed to have a

mass of exactly 12 g? That number is Na - Avogadro's number.

• Careful measurements yield a value for Na = 6.0221367x10^+23.

• 1 mole = 6.022 x 1023 particles of any substance

Moles

• n = mass (m)/Molar mass (M) n= m/M• n = number of particles (N)/

Avogadro's Number (Na) n= N/Na

.

Simplest and molecular formulaeConsider NaCl (ionic) vs. H2O2 (covalent)

Cl Na

Na Cl

Cl

Cl

Na

Na

• Chemical formulas are either “simplest” (a.k.a. “empirical”) or “molecular”. Ionic compounds are always expressed as simplest formulas.

• Covalent compounds can either be molecular formulas (I.e. H2O2) or simplest (e.g. HO)

Q - Write simplest formulas for propene (C3H6), C2H2, glucose (C6H12O6), octane (C8H14)

Q - Identify these as simplest formula, molecularformula, or both H2O, C4H10, CH, NaCl

HOO

H HOO H H

OO H

Equivalent weight• Molecular weight / Valency

• • Valency is equal to:• - absolute number of ion charge• - number of H+ or OH-• ions that can combine with the ion• - absolute number of change in charge of ion in a

reaction• • Quantity of chemicals equivalent to each other• • One chemical expressed as another• • Same number of equivalents of reactants in a chemical• reaction

Equivalent weight

Equivalent weight

• Example: for the balanced reaction2NaOH + H2SO4 =Na2SO4 +2H2O

- 2 moles NaOH react with 1 mole H2SO4

- 80g NaOH react with 98g H2SO4- 2eq NaOH react with 2 eq H2SO4

Law of Equivalence •

For a chemical reaction:• aA + bB -> cC + dD

•

Equivalent of A = Equivalent of B = Equivalent of C = Equivalent of D where n, and M is n factor, molecular mass of the species

•

• If the reaction is carried out in solution, then NAVA = NBVB = NCVC = NDVD or

nAMAVA = nBMBVB = nCMCVC = nDMDVD

For a given solution, number of equivalents per litre is same as the number of milliequivalents per ml, Moles, millimoles, equivalent, milli equivalent of solute does not change on dilution.