Understanding Laws, States of Matter, and Chemical Reactions
A law is a brief statement of a general nature about regularities in nature observed experimentally. Boyle’s Law states that for a mass of gas at constant temperature, the product of the gas pressure exerted by the volume it occupies is constant.
States of Matter
- Gaseous State: It has no fixed shape or volume, is compressible, and flows easily.
- Liquid State: It adapts to the container, is difficult to compress, and flows.
- Solid State: It has its own rigid shape and volume and is hardly compressible.
Temperature: T (K) = t (°C) + 273
Atomic Structure
Interior of Atoms:
- Protons (p): Have a positive electric charge. This is called the elementary charge because it is the smallest known.
- Neutrons (n): Have no electric charge and have the same mass as the proton. Protons and neutrons are called nucleons.
- Electrons (e-): Have a negative electrical charge equal in magnitude to the proton’s positive charge but opposite in sign.
Isotopes and Ions
The isotope is placed at the top left of the symbol, and the atomic mass is placed below the symbol. The number of neutrons is found by subtracting the two numbers.
The relative atomic mass of an element is the ratio of the average mass of an atom of the element to one-twelfth of the mass of a carbon-12 atom.
If an atom loses one or more electrons, it becomes a positive ion, called a cation. If an atom gains one or more electrons, it becomes a negative ion, called an anion.
Isotopic mass is the ratio between the mass of an atom of a particular isotope and one-twelfth of the mass of a carbon-12 atom.
If atoms of different elements combine to form a molecule, the molecule forms a chemical compound called a molecular compound.
The Mole Concept
A mole is the amount of substance containing 6.02 x 10^23 particles. This number is called Avogadro’s constant and is denoted by L.
Volume occupied by one mole of gas at standard conditions: 22.4 dm3.
Avogadro’s Law states that equal volumes of gases under the same conditions of pressure and temperature have the same number of molecules.
The molar volume of a gas whose pressure is standard and its temperature is zero is 22.7 dm3.
Valence and Chemical Compounds
Valence is the number of hydrogen atoms that an atom of that element combines with.
Hydroxides are compounds formed by the combination of a metal cation with the hydroxide ion (OH-).
Oxides are binary compounds consisting of oxygen and another element (except fluorine).
Mixtures and Solubility
A homogeneous mixture presents the same properties and composition at all points of its mass.
Solubility in a given solvent is the composition of the saturated solution.
Chemical Reactions
A chemical reaction occurs when one or more pure substances are transformed into other substances with different properties than the initial substances.
In a chemical reaction, the initial pure substances that react are called reactants, and the pure substances obtained from the reaction are called products.
Lavoisier’s Law states that in any chemical reaction, the total mass of the reactants equals the total mass of the products obtained.
A chemical reaction involves a rearrangement of atoms, arranged in a different way to form new pure substances.
Exothermic reactions are reactions that take place with the evolution of energy as heat.
Endothermic reactions are chemical reactions that take place with the absorption of energy as heat.