Chemistry PDF

# Chemistry ## Definition of Chemistry Chemistry is the science that studies the composition, structure and properties of matter, as well as the changes it undergoes during chemical reactions and its relation to energy. ### Matter Everything that has mass and occupies space (volume). It is impene...

# Chemistry ## Definition of Chemistry Chemistry is the science that studies the composition, structure and properties of matter, as well as the changes it undergoes during chemical reactions and its relation to energy. ### Matter Everything that has mass and occupies space (volume). It is impenetrable and is classified according to its composition. ### Body Limited portion of matter with shape, characterized by having mass (in kg) and volume (in L). ### Mass Amount of matter. Measured in kilograms (kg). ### Volume Space occupied by an object. Measured in liters (L). ### Substances ### Simple A single type of element. ### Compound More than one type of element. ### Pure Substance Invariant composition, not separable into other substances. ### Mixtures Variable composition, separable by physical methods. ### Phases and Components A phase is a homogeneous portion of a material system. It can be visualized and distinguished from the other phases. All phases of a system material have the same intensive properties. A component is a substance that is part of a material system. ### Material Systems Portion of the material isolated for study. ### Classification of Material Systems #### Homogeneous Systems present the same intensive properties at all points. They have the same chemical composition and a single phase. ##### Homogeneous systems can be divided into: - Pure substances: Water or gold - Solutions: Combinations of two or more substances (e.g., water and salt) A solvent is the component that usually has the highest proportion in the solution. A solute is the component that has the lowest proportion. Solutions can be solid, liquid, or gas. #### Heterogeneous Systems present variations in at least one intensive property. They are formed by two or more phases. ### Properties of matter #### Intensive Characteristics that help us identify substances. They are independent of the amount of matter. Examples: - Density: m(gr) / v(ml) - Boiling point - Solubility - Conductivity - Melting Point - Viscosity #### Extensive Properties that depend on the amount of matter. Examples: - Mass - Volume - Area - Inertia - Weight - Divisibility - Length ### Solubility Solubility = grams of solute/ grams of solvent ### Phenomena of matter #### Physical Temporary changes that do not affect the molecular structure. They are reversible and preserve intensive properties. Examples: Melting ice, Dissolving alcohol in water. #### Chemical Permanent changes that affect the molecular structure. They can be reversible or not. Their intensive properties change. Examples: Iron oxidation; Burning paper. ### Melting Point (Pf) and Boiling Point (Peb) Melting point (Pf) is the temperature at which a substance changes from solid to liquid state. Boiling point (Peb) is the temperature at which a substance changes from the liquid to gaseous state. ### States of Aggregation of Matter The states of aggregation depend on the force of interaction between particles and the thermal agitation of the particles. The three states are: #### Solid Solids have their own shape and volume. They are compact with a lot of attraction between them, meaning they are difficult to compress. #### Liquid Liquids have their own volume but not their own shape. They have a free horizontal surface. Their particles are disordered but still have strong forces of attraction between them. They are almost incompressible. #### Gaseous Gases do not have their own shape nor volume. They have disordered and mobile particles. They are easily compressible. ### Process of Change of State #### Vaporization From liquid to gas. - If it occurs in the entire mass of the liquid, it is called boiling, and it occurs at the boiling point. - When it occurs on the liquid surface at any temperature, it is called evaporation. #### Condensation From gas to liquid. This occurs when there is a decrease in temperature #### Liquefaction From gas to liquid. It occurs when there is an increase in pressure, a decrease of temperature, or both. #### Volatilisation From solid to gas without going through the liquid state. Ex. Dry ice #### Sublimation From gas to solid. Ex. Iodine vapor when it cools. ### Methods of Separation of Phases of Heterogeneous Systems #### Physical Methods ##### Mechanical - **Sieving:** Separating two solids of different sizes, using a sieve or metallic mesh. - **Filtration:** Separating solids dispersed in liquids using a barrier. - **Sedimentation and Decantation:** Separating components with a large density difference. - **Centrifugation:** Accelerating sedimentation using centrifugal force when there is not a large density difference between phases. - **Dissolving :** Separating solid phases by dissolving one in a solvent. - **Magnetization:** Separate magnetic solids from nonmagnetic solids. - **Distillation:** Separating liquids with different boiling points by heating the solution and condensing the vapors by passing them through a refrigerant tube. ## Methods for Fractionation of Homogeneous Systems #### Physical Methods - **Simple:** For liquids dissolved in salts - **Fractional:** For liquids with different boiling points. #### Chemical Methods - **Evaporation or crystallization:** To separate solids dissolved in liquid solvents. - **Chromatography:** ## Definition of Atom The atom is the smallest portion of matter, indivisible, and capable of conserving its properties. It can combine to form molecules. ## Definition of Molecule The molecule is the smallest portion of matter that exists in a free state. It is formed by atoms. ## Atomic-Molecular Theory Matter is discontinuous and composed of small particles called molecules, which may be composed of one or more atoms. ## Atomic Models ### First model (Dalton) Dalton proposed that matter is formed by small particles called atoms that are indivisible. He proposed the existence of simple substances (only one type of atom, joined or not) and compound substances (atoms of different types joined). Reactions between particles are reactions of joining or separating atoms. A molecule is the union of two or more atoms. ### Second Model (Thomson) Thomson proposed the "plum pudding model", where the atom is a uniform and solid positive sphere with embedded electrons. ### Third Model (Rutherford) Rutherford found through experiments that the atom is mostly empty and has a nucleus with a positive charge surrounded by electrons with negative charge. The positive charge is concentrated in the nucleus. The atom is electrically neutral: the amount of positive charge is the same as the amount of negative charge. ### Fourth Model (Bohr) Bohr proposed that electrons have a certain amount of energy called a quantum. He said that these move around the positive nucleus in certain energy levels or atomic orbitals, in an elliptical form. They can jump between levels when they absorb or emit energy. ### Actual Model (Schrödinger) - Schrodinger proposed that electrons are around the nucleus in orbitals, but their specific location is unknown; only the probability of finding them is known. ## Parts of an atom ### Nucleus Small volume, contains almost all of the mass of the atom, and contains nucleons: protons and neutrons. ### Cortex or Extra-Nuclear Zone Large volume but negligible mass. It contains electrons. ## Atomic and Mass Numbers ### Atomic Number (Z) Number of protons in the nucleus. It indicates the position of an atom in the periodic table. It is written as: Z C. ### Mass Number (A) Sum of protons and neutrons. It is written as: A C. ## Protons, Neutrons, and Electrons - Protons have a positive charge, have a mass and size similar to neutrons. - Neutrons are neutral, have a mass and size similar to protons. - Electrons have a negative charge, and they are found in atomic orbitals with negligible mass. ## Isotopes Atoms with the same atomic number (Z) but different mass number (A). They have the same chemical but different physical properties. Isotopes do not have special names and are named by the element followed by the mass number. Example: Hydrogen, Deuterium, Tritium ## Types of Isotopes - **Natural Isotopes:** Most prevalent in nature. They are usually found in the periodic table. - **Artificial Isotopes:** They are manufactured in nuclear laboratories by bombarding particles with subatomic particles. Artificial isotopes usually have a short life due to instability and radioactivity. ### Stability of Isotopes - **Stable:** They have a long half-life. - **Unstable:** They are radioisotopes. They emit energy and particles to transform into a more stable isotope. ## Isobars Atoms from different elements with the same mass number (A) but different atomic number (Z). ## Ions - **Cations:** Ions with a positive charge. They lose electrons. - **Anions:** Ions with a negative charge. They gain electrons. ## Ionic Strength It measures the amount of ions in solution. It accounts for the strength of attraction/repulsion between ions and the charges they possess. ## Schrödinger’s Atomic Model This model describes electrons rotating around the nucleus in defined atomic orbitals. The probability of finding them there is high. Four quantum numbers help describe the location and behavior of electrons. ### Principal Quantum Number (n) Indicates how many energy levels are in the atom. It also gives us an idea of the atom size. There are seven energy levels (N). To know how many electrons can fit in each energy level, use this formula: 2 x (Energy level N)^2 = 2 x N^2 ### Azimuthal or Secondary Quantum Number (l) Describes the shape of an orbital. There are four types of orbitals: -**S or spherical:** L=0 - **P or double helix:** L=1 - **D or complex:** L=2 - **F or more complex:** L=3 To know which suborbital belongs to an orbital L, calculate (N-1). For example, if N=2: (2-1)=1 sub-orbital within the L orbital. ### Magnetic Quantum Number (m) Indicates the direction of the orbital in space. The value of quantum number (m) depends on the azimuthal quantum number (L). - **S:** L=0, M=0 - **P:** L=1, M= 1, 0, -1 - **D:** L=2, M= 2, 1, 0, -1, -2 - **F:** L=3, M=3, 2, 1, 0, -1, -2, -3 ### Spin Quantum Number (s) Describes the rotation of the electron on its own axis. It can take two values (1/2 or -1/2) depending on the direction of the electron spin. - 1/2 is an upward facing spin on the electron. - -1/2 is a downward spin of the electron. ## Types of Levels and their Capacities - **S level:** 1 level, up to 2 electrons - **P level:** 3 levels, up to 6 electrons - **D level:** 5 levels, up to 10 electrons - **F level:** 7 levels, up to 14 electrons ## Electronic Configuration Describes the distribution of electrons in an atom ## Centesimal Composition It shows the relationship between the mass of a component and the total mass of the system, expressed as a percentage. ## History of the Periodic Table ### Dimitri Mendeliev(1869) He created the first periodic table by organizing elements according to their atomic masses (A). He noticed that the properties of elements (except Hydrogen), repeat every eight elements. ### Henry Moseley(1913) He showed that elements could be arranged by their atomic number (Z), which is the number of protons. ## Periodic Table The periodic table is a classification of known elements organized by their atomic numbers (Z) according to their properties. It has 7 periods and 18 groups. ### Periods The periodic table is divided into seven rows called periods. The period number indicates the number of energy levels or atomic orbitals present in each element. The first period contains two elements, hydrogen, and helium, and the next two periods contain eight elements each, called short periods. The remaining periods are called long periods. They contain eighteen elements in periods 4 and 5, and 32 elements in period 6. The seventh period contains elements called actinides, which are synthesized artificially through radioactive processes. ### Groups The periodic table is divided into 18 columns called groups. The elements in the same group have similar physical and chemical properties. The first two columns and the last six columns are considered to be representative elements because they show a smooth trend in their properties. Groups 3-12 are called transition metals. They are located in the center of the periodic table. The elements that belong to the lanthanide and actinide series are considered internal transition metals. ## Classification of Elements ### Metals They have good conductivity, are shiny, have high malleability and ductility, are solid at room temperature (except for mercury), and are located on the left and center of the periodic table. They easily lose electrons to form cations. ### Metalloids or Semi-metals They have properties that lie between metals and nonmetals, and are found on the right side of metals. They form cations with difficulty, conduct electricity only unidirectionally, and have some properties of metals and some of nonmetals. ### Nonmetals They do not conduct electricity or heat, are not shiny, are solid, liquid, or gaseous at room temperature. They are found in the right side of the periodic table and are found in the solid, liquids, and gaseous states. They easily gain electrons forming anions. ## Properties of the Periodic Table ### Atomic Number (Z) Represents the number of protons in the atom's nucleus. ### Atomic Radius It is the distance from the atom's nucleus to its outermost electron, indicating the atom's size. It increases from right to left and from top to bottom. ### Ionization Energy It is the energy needed to remove an electron from a gaseous element. It indicates the strength of the attraction between the nucleus and the outermost electron. The lower the ionization energy, the easier it is to remove an electron. It increases from left to right and from top to bottom. ### Electronegativity It is the ability of an atom to attract electrons in a chemical bond. It indicates the strength of an atom's pull on electrons. It increases from left to right and from bottom to top. ### Electropositivity It is the tendency of an atom to lose electrons. It increases from right to left and from top to bottom. ### Ionic Radius It is the size of an ion, not the neutral atom. Cations are smaller than neutral atoms because they have lost electrons, and anions are larger than neutral atoms because they gained electrons.