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Inorganic compounds 2
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3. Organic and inorganic compounds
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Organic and inorganic compounds
Chemical compounds are divided into two main categories:
organic compounds that contain carbon;
inorganic compounds that contain all other elements. 3
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Oxidation number
The oxidation number indicates the actual or formal charge assigned to each atom or ion in the formula of a substance. A sign and a numerical value are assigned based on specific rules.
The oxidation number’s value depends on the number of acquired or lost electrons.
In the case of a molecular substance, the oxidation number indicates the formal charge. Atoms of a pure element have an oxidation number of zero, while the ion corresponds to the charge. +1 –2
K2O 4
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5. Binary compounds: formulas
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Binary compounds: formulas
How to write the formulas of binary compounds:
first write the less electronegative element, followed by the most electronegative element;
if the oxidation numbers are different in value and sign, assign to each element the oxidation number of the other element, without signs;
if the oxidation numbers are multiples (e.g. –2 and +6), simplify them. +6 –2
S O
S2O6
SO3 5
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6. Binary compounds: IUPAC names
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Binary compounds: IUPAC names
The IUPAC names of binary compounds are assigned before
naming the element to the right, which is the most electronegative.
If in the formula there are more atoms of an element, their
number is specified by a prefix. 6
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7. Classes of binary compounds
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Classes of binary compounds
The most important classes of binary compounds that do not
contain oxygen are binary salts, hydrides and hydracids.
Binary salts derive from the union of one or more atoms of a metal and a non-metal.
The IUPAC name is slightly different from the traditional one.
Hydrides are all compounds of hydrogen in which there is an oxidation number –1.
Hydracids are compounds of hydrogen with halogens and elements of group VIA (excluding oxygen). In these compounds hydrogen has an oxidation number +1. 7
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Oxides and peroxides
The most important classes of binary oxygen compounds are oxides and peroxides.
Oxides are compounds which contain oxygen with an oxidation number –2. They comprise oxides of the metal
elements and oxides of non-metals.
Peroxides contain two oxygen atoms linked by a covalent simple bond: in this case the oxidation number of oxygen is –1. 8
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Ternary compounds
Compounds formed by three elements are called ternary.
The most important ternary compounds contain oxygen combined with two other elements:
hydroxides contain a metal joined to one or more hydroxyl groups (-OH);
oxyacids are formed by a non-metal, oxygen and hydrogen;
oxygenated salts contain a metal, oxygen and a non-metal. 9
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Oxyanions and salts
Anions that are created by removing one or more H+ ions from the formula of an oxyacid are known as oxyanions.
In water, oxyacids can become oxyanions.
Combining oxyanions and metal ions or polyatomic ions yields ternary salts.
If the ionic compound contains four elements, it yields quaternary salts. 10
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11. Reactions and chemical equations
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Reactions and chemical equations
In chemical reactions, atoms and ions break the bonds that keep them together to form new ones.
A balanced chemical equation allows us to know:
the changes in the composition of molecules in the system;
the numerical ratios between the particles of reagents and products. 11
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12. Reactions of inorganic compounds /1
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Reactions of inorganic compounds /1
In synthesis reactions, two reagents are combined to form a single product. Reagents can be elements or compounds.
2Cu + O2
2CuO
In breakdown reactions, a compound is separated into two or more products. The products of the breakdown can be elements or compounds.
CaCO3
CaO + CO2 12
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13. Reactions of inorganic compounds /2
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Reactions of inorganic compounds /2
In replacement reactions, one atom or ion in a compound is replaced with a more reactive atom or ion.
H2 + CuO
H2O + Cu
In double displacement reactions, two compounds swap atoms or ions, therefore forming different compounds.
Zn + 2HCl
ZnCl2 + H2 13
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14. Stoichiometric coefficients
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Stoichiometric coefficients
Stoichiometric coefficients express numerical ratios between particles, moles, molar masses of consumed reagents and products.
N2 + 3H2 → 2NH3
By multiplying the molar masses and the stoichiometric coefficients we can determine the ratios (in grams) between reagents and products. 14
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15. ratio between molar masses
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Stoichiometric calculations
molar ratio
Stoichiometric calculations are the mathematical procedures used to calculate the number of moles or the mass of a substance that is consumed or produced in a chemical reaction.
ratio between molar masses
ratio between masses 15
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The limiting reagent
In same cases, the masses of the reagents do not follow the ratios indicated by the stoichiometric coefficients.
The exceding reagent remains unchanged and only the limiting reagent is fully consumed. The limiting reagent determines the quantity of product that can be obtained in the reaction. +
4 molecules of HCl
3 molecules of H2
2 molecules of Cl2 16
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17. Gases and Avogadro’s law
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Gases and Avogadro’s law
According to Avogadro’s law, equal volumes of different gases, measured in the same conditions of temperature and pressure, have the same number of molecules.
The volume of a gas does not depend on the size, composition and mass of its molecules. 17
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The molar volume
At standard conditions, using a temperature of 0 °C and a pressure of 1 atm, one mole of gas occupies a volume of L.
This is called the standard molar volume and it does not depend on the molar mass of the subtance. 18
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19. Gases and stoichiometry
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Gases and stoichiometry
Avogadro’s law is also applied to the gaseous reagents and products in reactions, so that the stoichiometric coefficients of the equation also indicate the numerical ratio between the molar volumes of the gases.
N2 + 3H2 → 2NH3 +
1 volume of N2
3 volume of H2
2 volumes of NH3 19
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