Introduction to Chemistry

• Chemistry is the study of matter and its properties as well as how matter changes
• Physical chemistry is the study of macroscopic, and particulate phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics and chemical equilibrium
• Thermochemistry is the study of the heat evolved or absorbed in a chemical reaction
• Chemical kinetics is the study of reaction rates, factors affecting them and reaction mechanism, while photochemistry is the study of chemical reactions caused by absorption of light or ultraviolet radiation
• Surface chemistry is the study of phenomena occurring at surfaces or interfaces, while electrochemistry is the study of chemical processes that cause electrons to move
• Spectroscopy is the study of the interaction between matter and electromagnetic radiation

Matter and its classification

• Matter is anything that has mass and occupies space
• Matter can exist in three physical states: solid, liquid and gas
• Solids have definite volume and definite shape
• Liquids have definite volume but no definite shape and take the shape of the container
• Gases have neither definite volume nor definite shape, they occupy completely the space in the container
• Matter can also be classified as mixtures or pure substances
• A mixture contains two or more substances present in it in any ratio, which are called its components
• Mixtures can be homogeneous or heterogeneous
• Homogeneous mixtures have uniform composition throughout, for example, sugar solution and air
• Heterogeneous mixtures have non-uniform composition throughout, for example, sand and water
• Pure substances have fixed composition and distinct properties
• Pure substances can be elements or compounds
• Elements consist of only one type of atoms and cannot be broken down into simpler substances by chemical means, for example, hydrogen and oxygen
• Compounds are formed when two or more atoms of different elements combine in a fixed ratio, for example, water and carbon dioxide
• Properties of matter can be physical or chemical
• Physical properties are those that can be measured or observed without changing the identity or the composition of the substance, for example, color and boiling point
• Chemical properties are those that describe the ability of a substance to undergo change to form new substances, for example, flammability and acidity

Measurements in Chemistry

• Mass is the amount of matter present in a substance, while weight is the force exerted by gravity on an object
• Volume is the amount of space occupied by matter
• The SI unit of length is meter (m), the SI unit of mass is kilogram (kg), the SI unit of time is second (s), the SI unit of electric current is ampere (A), the SI unit of temperature is kelvin (K), the SI unit of amount of substance is mole (mol), and the SI unit of luminous intensity is candela (cd)
• The prefixes used to denote multiples or submultiples of SI units are: deca (10), hecto (10^2), kilo (10^3), mega (10^6), giga (10^9), tera (10^12), deci (10^-1), centi (10^-2), milli (10^-3), micro (10^-6), nano (10^-9), pico (10^-12)
• Temperature is a measure of the hotness or coldness of an object
• There are three common scales to measure temperature: Celsius (°C), Fahrenheit (°F) and Kelvin (K)
• The relationship between Celsius and Fahrenheit is: °F = (9/5)°C + 32
• The relationship between Celsius and Kelvin is: K = °C + 273.15
• Density is the amount of mass per unit volume: density = mass/volume
• Significant figures are meaningful digits in a measured or calculated value
• Rules for determining the number of significant figures:
  • All non-zero digits are significant
  • Zeros preceding the first non-zero digit are not significant
  • Zeros between two non-zero digits are significant
  • Zeros at the end of a number are significant only if they are to the right of the decimal point
• Rules for rounding off numbers:
  • If the digit to be dropped is greater than 5, the preceding digit is raised by one
  • If the digit to be dropped is less than 5, the preceding digit is left unchanged
  • If the digit to be dropped is 5, the preceding digit is raised by one if it is odd and left unchanged if it is even
• Dimensional analysis is a method used to convert measurements from one unit to another

Laws of Chemical Combinations

• Law of Conservation of Mass: mass can neither be created nor destroyed
• Law of Definite Proportions: a given compound always contains exactly the same proportion of elements by weight
• Law of Multiple Proportions: if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers
• Gay Lussac's Law of Gaseous Volumes: when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at the same temperature and pressure
• Avogadro's Law: equal volumes of all gases at the same temperature and pressure contain equal number of molecules

Dalton’s Atomic Theory

• Matter is made up of extremely small particles called atoms
• Atoms of a given element are identical in mass and properties
• Atoms of different elements are different
• Compounds are formed by a combination of two or more different kinds of atoms
• A chemical reaction involves only the rearrangement of atoms; atoms are neither created nor destroyed during a chemical reaction

Atomic and Molecular Masses

• Atomic mass is the mass of an atom
• Atomic mass unit (amu) is used to express atomic mass
• One atomic mass unit (amu) is equal to exactly one-twelfth (1/12) the mass of one carbon-12 atom
• Average atomic mass is the weighted average of the masses of the isotopes of an element
• Molecular mass is the sum of the atomic masses of the elements present in a molecule
• Formula mass is the sum of the atomic masses of the elements present in a formula unit of an ionic compound

Mole Concept and Molar Masses

• One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012 kg) of the 12C isotope
• The number of particles in one mole is called Avogadro constant or Avogadro number (NA = 6.022 × 10^23)
• Molar mass is the mass of one mole of a substance in grams
• Molar mass of an element is numerically equal to atomic mass in grams
• Molar mass of a compound is numerically equal to molecular mass or formula mass in grams

Percentage Composition

• Percentage composition is the percentage by mass of each element in a compound
• Percentage of an element = (mass of that element in the compound / molar mass of the compound) x 100

Stoichiometry and Stoichiometric Calculations

• Stoichiometry deals with the quantitative relationships between reactants and products in a balanced chemical equation
• Stoichiometric coefficients are the numbers placed before the formulas of reactants and products in a balanced chemical equation
• Limiting reagent is the reactant that is completely consumed in a reaction and determines the amount of product formed
• Excess reagent is the reactant that is not completely consumed in a reaction
• Theoretical yield is the amount of product that can be produced in a reaction based on the stoichiometry
• Actual yield is the amount of product actually obtained in a reaction
• Percentage yield = (actual yield / theoretical yield) x 100

Concentration in Solutions

• Solution is a homogeneous mixture of two or more substances
• Solute is the substance that is dissolved in a solvent
• Solvent is the substance in which a solute is dissolved
• Molarity (M) is the number of moles of solute per liter of solution: M = moles of solute / volume of solution in liters
• Molality (m) is the number of moles of solute per kilogram of solvent: m = moles of solute / mass of solvent in kilograms
• Mole fraction (x) is the ratio of the number of moles of one component to the total number of moles of all components: xA = moles of A / (moles of A + moles of B)
• Mass percentage is the mass of the solute in grams present in 100 g of the solution
• Volume percentage is the volume of the solute in mL present in 100 mL of the solution
• Parts per million (ppm) is the number of parts of a component per million parts of the solution
• Normality (N) is the number of gram equivalents of solute per liter of solution: N = gram equivalents of solute / volume of solution in liters