Introduction to Chemistry and Physics
Basic Chemistry Concepts
Common Acids and Formulas
Hydrofluoric acid: HF. Hydrochloric acid: HCl. Hydrobromic acid: HBr. Hydriodic acid: HI. Hydrogen sulfide: H2S. Chromic acid: H2CrO4. Manganic acid: H2MnO4. Permanganic acid: HMnO4. Chloric acid: HClO3.
Formulas of Organic Compounds
Empirical: Represents the simplest relationship between the atoms that form a molecule. (e.g., C2H5)
Molecular: Indicates the exact number of different atoms constituting the molecule of a substance. (e.g., C4H10)
Identifiers: Some details are lacking, normally the intercarbonic ones. (e.g., CH3-CH2-CH2-CH3)
Developed: Shows all the links that form the molecule.
Functional Group
A group of atoms appearing in a molecule that gives it some characteristic properties.
Homologous Series
A set of organic compounds that have the same functional group whose carbon chain is ever-increasing with intermediate groups -CH2– called “methylenes.”
Basic Units and Concepts
- M: Distance traveled by light in 1/299792458s.
- sec: 1/86400 part of the mean solar day.
- Mole: Amount of a substance that contains as many elementary entities as there are atoms in 0.012kg of the carbon isotope 12.
- Atomic Number: Number of protons in the nucleus: Z.
- Mass Number: Sum of the number of protons and neutrons.
Chemical Bonds
- Ionic: An atom of a metallic element binds with an atom of a nonmetallic element, the metal atom yielding one electron.
- Covalent: An atom of a nonmetallic element binds with another nonmetallic element or with hydrogen. Electrons are shared.
- Metallic: Joins atoms of metallic elements.
Isotopes
Atoms of the same element that have a different number of neutrons and therefore a different mass number.
Atomic Models
Dalton
- Elements are constituted by atoms, which are independent, unchanging, and indivisible material particles.
- Atoms of the same element are equal in mass and properties.
- Compounds are formed by the union of the corresponding atoms of the elements in a simple numerical relationship.
- In chemical reactions, atoms are neither created nor destroyed, only redistributed to form new compounds.
Thomson
Proposes an atomic model consisting of a sphere of positive electricity that includes embedded as many electrons as are necessary to neutralize it.
Rutherford
Bombarded a sheet of gold with alpha particles, observing the particles that passed through it behind a screen.
Conclusions
- Matter is mostly empty space.
- The deflections are due to electrostatic repulsions suffered by the particles passing near positive charges.
Postulates
- Existence of neutral particles in the core.
- Suggests that electrons must move around the nucleus.
Limitations
- Any electric charge that has acceleration must emit energy.
- Could not explain atomic spectra with this model.
Bohr
Said that electrons in atoms can only be in certain states, in which they maintain a fixed energy. Electrons can pass from one level to another through absorption. (1/wavelength = R(1/n2-1/n2) where n is a positive integer)
Electromagnetic Spectrum
The set of all electromagnetic radiation. Higher frequency: gamma rays. Lower frequency: radio waves.
Properties of Compounds and Bonds
Properties of Ionic Compounds
Solid, hard at room temperature, forming a crystal lattice, high boiling and melting points, not soluble in water, do not conduct electricity.
Properties of Covalent Compounds
Form networks, can be gas, liquid, or solid at room temperature; low boiling and melting points, do not conduct electricity, soluble in non-polar organic solvents.
Properties of Metallic Bonds
Solid at room temperature except for mercury. Hardness, ductile, malleable, conductive of heat and electricity.
Hydrogen Bridge
Occurs between a hydrogen molecule and an atom that is very electronegative and small. The hydrogen element joined to the element attracts much of the negative charge of the bond, and this provokes the appearance of some positive charge on the hydrogen.
Van der Waals Forces
Electrostatic forces that bind molecules with non-polar bonds or that are not joined by hydrogen bridges. They are weaker.
Mixtures and Solutions
Homogeneous Mixture
Formed by two or more components that cannot be visually distinguished.
Heterogeneous Mixture
Components can be distinguished by the naked eye.
Laws and Principles
Law of Combining Volumes
Gay-Lussac: The volumes of the reactant gases and the obtained gases always keep a simple numerical relationship when they are in normal conditions.
Boyle’s Law
P1/T1 = P2/T2
Charles’s Law
V1/T1 = V2/T2
Chemical Reaction
The process by which one or more substances (reactants) become another (products) by redistribution of their atoms.
Solution
A homogeneous mixture between a solute and a solvent.
Concentration Units
- %: (mass of solute / mass of solution) * 100
- g/L: grams of solute / liters of solution
Types of Reactions
- Exothermic: Energy is released (appears on the right side of the equation).
- Endothermic: Requires external energy input (appears on the left side of the equation).
Empirical Formula
Divide the number of atoms of each element by the sum of its components (e.g., H=1), divide by the smallest result, and multiply to obtain integers.
Molecular Formula
Use the ideal gas law (PV = nRT) to find the molar mass and then relate it to the empirical formula to determine the molecular formula.
Measurement and Errors
Magnitude Scale
When a quantity is perfectly defined with a number and its corresponding unit (e.g., mass of a body, volume of a pool).
Vector Magnitude
Requires knowing the direction and the point of application (e.g., acceleration of an airplane, force hitting a ball).
Vector Expression
Vectors are segments whose origin indicates the point of application; the module or length is equivalent to the value of the magnitude with its corresponding unit; the spatial position indicates the direction; the tip of the arrow indicates its sense.
Motion and Forces
Types of Motion
- Translation: Change of place or position.
- Rotation: When a body rotates around a fixed axis, it moves but does not change position.
- Absolute: An object moving relative to a fixed reference point.
- Relative: An object moving relative to another moving object.
Reference Systems
A reference system is inertial when the origin is at rest or moving with constant speed.
Trajectory
The locus of successive positions that a mobile point occupies in space.
Displacement
If the movement ends at the same point where it starts, there is no displacement.
Distance Traveled
The length of the trajectory followed by a mobile object. It is a scalar magnitude that matches the module of the displacement only in the case of rectilinear motion without change of direction.
Acceleration
The variation of speed with time.
Force
Interaction between two bodies. Measures the strength of the interaction.
Newton’s Laws
1st Law: Principle of Inertia
If no force acts on a body, or the resultant of all forces is zero, the body remains at rest or moves with rectilinear and uniform motion.
2nd Law: Fundamental Principle of Dynamics
The force on a body is directly proportional to the acceleration it experiences.
3rd Law: Principle of Action and Reaction
When an object exerts a force on another, the latter exerts another force of equal magnitude and opposite direction on the first.
Mass
Scalar magnitude of constant value.
Weight
Vector quantity whose value depends on gravity.
Principle of Conservation of Linear Momentum
When the force applied to a body vanishes, the linear momentum of the body remains constant.
Fundamental Interactions
- Strong Nuclear: Responsible for holding the nuclei of atoms together. It has no reach outside the core.
- Electromagnetic: Attractive and repulsive, its range is infinite.
- Weak Nuclear: Acts on particles, responsible for radioactive phenomena.
- Gravity: Attractive, its range is infinite. (These are the most commonly used)
Universal Gravitation
Any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
Errors in Measurement
Accidental Error
Unforeseeable circumstances determined by factors external to the phenomenon being investigated, especially if we do not make enough measurements.
Systematic Error
Produced by the use of poorly calibrated instruments.
Absolute Error
The difference between the exact value and the experimental value (Ea = |X1 – X0|)
Relative Error
The ratio between the absolute error and the considered accurate measure (ER = EA / X).
Work, Energy, and Power
Work
The transfer of energy that occurs when a force produces a displacement.
Mechanical Work
The product of the module of the force and the displacement experienced in the same direction of the force.
Power
The scalar defined as work per unit of time.
Energy
The ability to perform work.
Kinetic Energy
Due to movement: the ability to perform work matches the work that bodies in motion can do.
Potential Energy
Energy a body has due to its position. A body has potential energy if it can perform work by changing its position.
Gravitational Potential Energy
Its value is given by the work necessary to lift a body to a certain height, overcoming its weight.
Elastic Potential Energy
Directly proportional to the square of the shortening or lengthening experienced by the spring.
Mechanical Energy
The sum of the kinetic and potential energies of a system.
Principle of Conservation of Mechanical Energy
In an isolated system without friction, mechanical energy is conserved, i.e., the sum of kinetic and potential energies is constant.
Law of Conservation of Energy
Energy is neither created nor destroyed, only transformed.
Thermodynamics
Thermodynamic Systems
Part of the universe that relates to its environment through the exchange of matter and/or energy through walls.
- Open: Can exchange both matter and energy with the environment.
- Closed: Cannot exchange matter with the environment, but can exchange energy.
- Adiabatic: No exchange of heat, but can exchange matter or work.
- Isolated: Cannot exchange either matter or energy with the environment.
Thermodynamic Variables
- Intensive: Temperature, pressure, concentration…
- Extensive: Volume, mass, moles…
- State Variables: Volume, pressure, temperature…
Temperature
Proportional to the average kinetic energy of the particles that make up a body.
Heat
Energy transferred from one system to another due to a temperature difference between them.
Zeroth Law of Thermodynamics
Two systems that are in thermal equilibrium with a third party are in thermal equilibrium with each other.
Heat Capacity
The amount of heat required to produce a one-degree temperature variation in a body.
Specific Heat
The amount of heat required to produce a one-degree temperature variation in a unit mass of a substance.
Temperature Conversions
- °C to K: +273
- °C to °F: *1.8 + 32
Types of Equilibrium
- Mechanical: Pressure is equal at all points of the system.
- Chemical: The composition of the system does not vary over time.
- Thermal: The temperature is the same in all parts of the system.
Equivalence Between Work and Heat
Heat is transferred when there is a temperature difference between a system and its environment. Work is transferred when forces act between the system and the environment and produce some displacement in either of them.
First Law of Thermodynamics
When a system evolves through a certain process, its internal energy variation is equal to the amount of energy exchanged with the environment in the form of heat and work. ΔU = Q + W.
Work in Thermodynamic Processes
- Isochoric: V = constant
- Isobaric: P = constant
- Isothermal: T = constant
- Adiabatic: Q = 0
Electricity
Properties of Electric Charges
When a body is rubbed, it exerts forces of attraction or repulsion. This means that the body has been electrified or loaded with electricity.
Types of Charges
- Positive: The charge acquired by rubbing glass (protons).
- Negative: The charge acquired by rubbing plastic, amber, etc. (electrons).
Electrification
Consists in the loss or gain of electrons. The charge is conserved. Charges of the same sign repel each other, charges of opposite signs attract each other. Charge is quantized.
Coulomb’s Law
The force of attraction or repulsion between two point charges is directly proportional to the product of said charges and inversely proportional to the square of their distance.
Electric Field
An electric field exists in a region of space if a test charge at rest, placed at a point in that region, experiences an electric force.
Electric Field Intensity
The electric force acting on a unit of positive test charge placed at that point.
Lines of the Electric Field
Properties:
- Always go from positive charges and end in negative charges or close on themselves.
- The number of lines that leave a positive charge or enter a negative charge is proportional to that charge.
- A field is uniform if its lines are parallel to each other.
Electric Potential
The potential energy corresponding to a unit of positive charge. V = Ep / q+
Potential Difference
The variation of potential energy of a unit of positive charge.
Electricity
The orderly and permanent movement of electrons through a conductor when there is a potential difference between its ends.
Current Intensity
The amount of charge that crosses the section of a conductor per unit of time. I = q / t.
Ohm’s Law
I = V / R
Current Generators
- Chemical (battery)
- Photovoltaic (solar panels)
- Thermal (thermopile)
- Mechanical (dynamo)
Measuring Apparatus
- Ammeter: Measures current intensity. Must be connected in series and have very low resistance.
- Voltmeter: Measures voltage drop. Must be connected in parallel.