PSC 4012

Ionic Phenomena: A study of an environmental problem

PSC 4012

Changes in matter can be: (Fig 3.1, page 3.4) Physical (appearance) Chemical (electrons in last shell) Nuclear (nucleus)

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Physical changes:

Superficial change Needs little amount of energy DOES NOT change nature of

element or compound DOES NOT affect the properties

of element or compound Changes state of matter

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Physical changes:

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Nuclear changes:

Most profound change Needs much more energy Involves particles in nucleus! An element is changed into

another ALL involve emission of

radiation (which can be harmless, dangerous, or lethal)

PSC 4012Chemical changes (chemical reactions):

More profound change Needs more energy Involves electrons in last shell NEW SUBSTANCES are formed Evidences of chemical change:_change of color_gas release_formation of precipitate_change of temperature

PSC 4012Chemical changes:

Ionization: when an atom gains or loses one or more electrons, it turns into an ion.

• Thus ions become negatively charged when atoms gain electrons (A-, anion)

• Or positively charged when atoms lose electrons (M+ cation)

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Classification of matter (Fig. 5.1, p 5.5):

Mixtures SeparationMethods:

_Filtration_Decantation_Evaporation_Distillation

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Molecules:Specific combination of atoms (same or different elements) that are united by chemical bonds

Example:_H2O (Water)1 molecule of water contains2 elements (hydrogen and oxygen)Each element has H: 2 atoms, O: 1 atom

PSC 4010: Chapter 4

Molecules:

Practice ExercisePage 3.8, Ex. 3.4

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Compounds:Pure chemical substance whose molecules are made of one or more elements (e.g. Gold, Water, Sulfuric Acid)

Element: A substance made of only one type of atom. For example: Gold (Au)Binary compound: Compound made of two elements. For example: Water (H2O)Complex compound: Compound made of more than two elements. For example: Sulfuric Acid (H2SO4)

PSC 4010: Chapter 4

Compounds:

Practice ExercisePage 3.8, Ex. 3.5

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Chemical bonds:The force that keeps atoms united in chemical compounds.

There are three type of chemical bonds:_Ionic_Covalent_Polar covalent

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Ionic bonds:

Is the transfer of one or more electrons from one atom to another (usually from a metal to a nonmetal)

Metals (low electronegativity, tendency to lose electrons, form Cations, positively-charged ion)

Non-metal (high electronegativity, tendency to gain electrons, form Anions, negatively-charged ion)

Ionic Bond

Be + O Be 2+ O2- (BeO)

4P5N

8P8N

4P5N

8P8N

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Electronegativity:Measurement of the force of attraction exerted by an atoms on the electrons it shares with another atom.

Fig 3.15, page 3.45

Electronegativity difference between bonding atoms

Chemical bond

More than 1.7 Ionic

Between 1.7 and 0.4 Polar covalent

Less than 0.4 Covalent

PSC 4012Covalent bonds:

Is the sharing of one or more pair of electrons between two identical atoms (non metals).

F + F F2

9P10N

9P10N 9P

10N9P

10N

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Polar covalent bond:

Is the sharing of one or more pair of electrons between two different atoms (non metals).

The more electronegative atoms tend to have a stronger attraction for the electron pair (or pairs).

This difference of electronegativity causes a certain degree of polarity, and as a result, the more electronegative atom ends up carrying a slightly negative charge whereas the less electronegative atom ends up with a slightly positive charge.

Slightly charged means a fraction of the actual charge. Do not confuse with ionic bond where the transfer of electrons is complete and so is the charge of the ions or elements involved.

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Polar covalent bond (H2O)

8P8N1P

0N 1P0N

H (δ+) H (δ+)O(δ-)

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Ionic bond Covalent bond Polar covalent bond

Between a metal (cation) and non metal (anion)

Between two identical atoms(non-metals)

Between two different atoms (non-metals)

Transfer of one or more electrons from one atom to another

Sharing of one or more pair of electrons

Sharing of one or more pair of electrons

Results in opposite-charged ions. One positive: cation (metal)One negative: anion (non metal)

No charges

No polarity

Perfect sharing

Results in slightly charged atoms.Less electronegative slightly positiveMore electronegative, slightly negative

NaCl, CaO, Li2O, CaF2 H2, N2, F2, Cl2 NH3, CCl4, PF5, H2O