Introduction to Chemistry

Introduction to Chemistry

• Chemistry is the study of matter and its properties
• Chemistry also studies the processes and changes matter undergoes

Branches of Chemistry

• Organic chemistry covers chemical substances containing carbon-carbon bonds, like plastics and pharmaceuticals
• Inorganic chemistry studies chemical substances lacking carbon-carbon bonds, such as metals, minerals, and semiconductors
• Physical chemistry studies the behavior and changes of matter, including reaction rates and mechanisms, along with energy changes
• Analytical chemistry involves analyzing the components and composition of substances like food nutrients
• Biochemistry focuses on matter and processes in living organisms

Significant Figures

• Nonzero integers are always significant
• Leading zeros are not significant
• Captive (embedded) zeros are always significant
• Trailing zeros are significant only with a decimal point
• 2.5000 has 5 significant figures
• 1400 has 2 significant figures
• 0.005201 has 4 significant figures
• 1.500 x 10^-3 has 4 significant figures

Significant Figures: Addition and Subtraction

• The result of addition and subtraction is limited by the number with the smallest number of significant decimal places
• Examples of adding and subtracting with significant figure rules

Significant Figures: Multiplication and Division

• The result has the same number of significant figures as the measurement with the fewest significant figures
• Round the result to match the smallest number of significant figures in the initial measurements
• Examples of multiplying and dividing using significant figures rules

Matter

• Matter is anything with mass that occupies space
• Matter can be classified as a pure substance or a mixture
• Pure substances can be elements or compounds
• Mixtures can be homogenous or heterogenous
• Homogenous mixtures can be solutions
• Heterogenous mixtures can be suspensions or colloids

States of Matter

• The three common states of matter are solid, liquid, and gas
• Plasma is similar to gases, consisting of free electrons and ions
• Bose-Einstein Condensate (BEC) is the most recent state of matter discovered in 1995 by Cornell and Weiman

Phase Changes

• Phase changes can include recombination, ionization, vaporization, condensation, freezing, melting, deposition, and sublimation

Properties of Matter

• Physical properties can be measured without altering the substance’s composition, such as mass, color, odor, size, freezing/boiling point, and density
• Chemical properties are observed or measured after chemically changing the substance, such as conductivity, malleability, reactivity, flammability, toxicity, radioactivity, and oxidation

Measurable Properties: Extensive vs Intensive

• Extensive properties are dependent on the amount of substance, including mass, volume, length, weight, area, width, and energy
• Intensive properties are independent of the amount of substance, including boiling/freezing point, density, temperature, pressure, melting point, and color

Fundamental Chemical Laws

• The Law of Conservation of Mass states that mass cannot be created nor destroyed
• The Law of Definite Proportion establishes that a given compound always contains the same proportion of elements by mass
• The Law of Multiple Proportions says if elements A and B form multiple compounds, the ratio of masses of B that combine with 1 gram of A can be reduced to small whole numbers

The Atom

• An atom is the basic structural and functional unit of matter
• It is comprised of electrons, protons, and neutrons

Subatomic Particles

• Protons have a charge of +1.6 x 10^-19 Coulombs, a mass of 1.6726 x 10^-27 kg, and are located in the nucleus
• Neutrons have no charge, a mass of 1.6749 x 10^-27 kg, and reside in the nucleus
• Electrons have a charge of -1.6 x 10^-19 Coulombs, a mass of 9.1094 x 10^-31 kg, and are located outside the nucleus

Atomic Models

• Thompson Model: positive charge + electrons inside
• Rutherford Model: + charge in center, electrons outside
• Bohr Model: electrons exist in specific orbits

Atomic Number and Mass

• The atomic number indicates the number of protons in the nucleus of an element
• Atomic mass is the total number of protons and neutrons in an atom's nucleus
• Atomic Mass = No. of Protons + No. of Neutrons
• Isotopes are atoms with identical proton counts but varying neutron counts

Atomic Weight

• Atomic weight is the average mass of an element, calculated using the relative abundance of its naturally occurring isotopes.
• Atomic Weight is defined by the equation m1p1 + m2p2 + m3p3 + …, where $m_n$ refers to the mass of isotopes 1, 2, 3… and $p_n$ is the corresponding percent abundance of isotopes 1, 2, 3…

Mole concept

• Mole represents the amount of a substance that contains the same number of chemical units as the number of atoms in exactly 12 grams of carbon-12
• Avogadro’s Number refers to the count of particles in one mole, ≈ 6.02 x 10^23 particles/mole

Mole Mass Conversions

• The number of moles is calculated by the equation n = m/M, where m is the mass of a substance in grams and M represents the molar mass in grams per mole

Designations of Molecules and Compounds

• Molecular Formula presents the exact quantity of atoms from each element in a molecule or compound
• Empirical Formula shows the simplified ratio of elements in a molecule or compound

Steps in Finding the Empirical Formula:

• Start with the number of grams of each element
• If only percentages are given, consider the total mass to be 100 grams
• Convert the mass of each element to moles
• Divide each mole number by the smallest number of moles calculated
• Round off the nearest whole number to get the mole ratio, and this is what you must input in the empirical formula as subscripts

Steps in Finding the Molecular Formula:

• Determine the empirical formula
• Calculate the mass of the empirical unit
• Divide the molecular mass by the mass of the empirical formula
• Multiply subscripts in the empirical formula to find the molecular formula

Example Problems

• Calculate the moles of Magnesium present in 93.5g given the atomic mass is 24.31g/mol
• Find the grams in Lead (Pb), given a Pb atomic mass is 207.2g/mol
• Determine how many grams exists within 4.57 x 10^21 amu
• Calculate the moles of chloroform with the information about the amu for each element
• Find how many moles of sodium chlorate are present in a solution with a given percentage
• Determine the number of protons and neutrons in Pb
• Determine how many moles exist in a single atom
• Determine the molecular formula of a compound given the grams of elements, element amu, and molar mass

Chemical Bonding

• In Ionic Bonding, one atom donates valence electrons
• It involves a metal and non-metal
• In Covalent Bonding, atoms share atoms
• It involves two or more non-metals
• In Metallic Bonding, uses force of attraction within elemental metals

Chemical Reactions

• A chemical reaction is when a substance undergoes a change in appearance or properties which leads to transformation into a different substance

Classification of Chemical Reactions

• In Direct Combination or Synthesis, two reactants create one product using the formula A + B --> AB
• Decomposition is when one reactant is broken up into multiple products using the formula AB --> A + B
• Single-Replacement is when elements replace another in a compound following the formula A + BC --> AC + B
• Double-Replacement Reactions occurs when elements in separate compounds switch, using the formula AB + CD --> AD + CB

Solutions

• Solutions refers to a homogenous mixture in one phase
• Solubility refers to the maximum amount of a substance dissolves in a given amount of solve
• Solute is the substance that is being dissolved
• Solvent refers to what another substance is dissolved into

Types of Solutions

• Saturated solutions have the maximum amount of solutes dissolved
• Unsaturated solutions have less a solvent can dissolve
• Supersaturated solutions have solutes more than the solvent can dissolve
• Crystals possibly form

Methods of Expressing Concentrations of Solutions

• Mole fraction is the number of moles of solute / the number of moles of solvent + all solutes
• Shown via Xa = na / na + nb, where n = number of moles of each component
• Normality is gram equivalent weights of solute per liter
• Shown via Normality= Equivalent Weight in grams / V solution in Liters
• Molarity is the number of moles of solute dissolved in 1 liter of solution
• Shown via M = n solute / V solution in Liters
• Molalityis defined as the number of moles of solute dissolved in 1 kg of solvent
• Shown via m = n solute / kg solvent
• Percent volume refers to the number of millimeters of solute dissolved in 100 ml of solution
• Shown via %volume = volume solute / volume solution x 100

Dilution

• Dilution occurs when solvent is added to concentrated solution with the formula Nafter = Nbefore and MVafter = MVbefore

Sample Problems

• What is the percent composition by mass of Oxygen?
• Determine how many grams of sucrose is needed
• Calculate the molality of a solution
• Determine mole fraction of the solute
• Calculate the molarity of a solution

Acids

• Acids refer to compounds that release H+ ions when dissolved in water
• They conduct electricity in aqueous solutions and have a sour taste
• Acids turn blue litmus paper to red and have a pH between 0 and 7
• Acids neutralize bases and react with active metals to produce hydrogen
• Acids also react with oxides and hydroxides to form salts and water

pH Equations

• The measure of acidity and alkalinity
• pH = log(1/H+), where H+ is the molar concentration of hydrogen ions
• pOH = log(1/OH-), where OH- is the molar concentration of hydroxide ions
• pH + pOH = 14 in aqueous solutions at 25°C

Bases

• Bases refer to compounds that release OH- ions when dissolved in water
• Properties of bases include a bitter taste and the ability to turn red litmus paper blue
• Bases has a pH between 7 and 14
• Bases react with acids to for salts and water

Sample MCQs

• Identify contents of energy
• Understand different principles