Law of Definite Proportions

• General Chemistry CHG101 (2025) is an introduction to Chemistry, covering terms 1 and 2.

Chemistry as a Science

• Humans have observed natural phenomena since the dawn of mankind, leading to the development of natural sciences
• Natural sciences evolved as separate subjects starting in the 17th-19th centuries
• These include botany, zoology, physiology, geo-sciences, physics, and chemistry
• Botany focuses on plants and vegetation, including systematics and characterization
• Zoology deals with animals, their systematics, and characterization
• Physiology studies the human body, its structure, and processes
• Geo-sciences focuses on the construction of our planet and the mechanisms that shape it
• Physics is concerned with the quantitative changes matter experiences, specifically mass and energy
• Chemistry emphasizes synthesizing new materials and identifying structure-property relationships
• Natural scientific fields overlap and require basic understanding across the board.
• Chemistry is essential for understanding life-sustaining processes in plants, animals, and the human body
• Physics is needed to explain the forces behind earthquakes
• Mathematics is needed for predicting the motion of planets and stars

Chemistry - From Past to Present

• People have "done chemistry" unconsciously for ages
• Examples include burning wood, producing metals, cooking, baking, and brewing beer
• Arabian scholars in the 7th and 8th centuries were the first to venture into alchemy, the predecessor to chemistry
• Distillations were a chemical operation first described at this time
• Terms such as 'alkaline', 'alcohol', and 'elixir' have possible connections Arabic world
• 'Alchemy' roughly translates to 'changing metals' or 'black soil'
• Alchemy entailed magic and witchcraft trying to solve the alchemists' main goal; to find the Philosopher's Stone
• The Philosopher's Stone is a compound shrouded in legend that was said to dissolve compounds, turn metals into gold, and provide eternal life
• Alchemists never succeeded in finding the Stone but they discovered many working techniques, synthesis methods, and properties of chemical compounds
• Alchemy developed from the 18th century onward with the rise of quantitative measurements from Antoine Lavoisier

Sub-Disciplines of Chemistry

• General Chemistry presents a basic overview of inorganic, organic, analytical, and physical chemistry
• Inorganic Chemistry deals with all compounds except hydrocarbons (compounds not containing only carbon and hydrogen)
• Organic Chemistry deals with hydrocarbons and related compounds
• Physical Chemistry studies the quantitative and energetic changes in chemical reactions and the physical principles of matter's structure
• Analytical Chemistry studies the quantitative/qualitative composition of compounds and their spectroscopic characteristics
• Biochemistry focuses on processes in living creatures
• Radiochemistry deals with the disintegration and transmutation of elements and compounds with radioactive atoms also known as "Hot Chemistry"
• Macromolecular Chemistry focuses on molecules of high molecular mass, natural and artificial (Polymer Chemistry)
• Theoretical Chemistry seeks to describe matter and chemistry "as such" by mathematical methods
• Computational Chemistry applies mathematical methods to predict the properties of compounds by simulations
• Technical Chemistry focuses on scaling up reactions and procedures from laboratory to industrial dimensions also known as "Industrial Chemistry"
• Pharmaceutical Chemistry specializes in synthesizing new drugs applying structure-property relationships
• The "classical split" in chemistry involves inorganic, organic, and physical chemistry
• Boundaries between fields are not strict to promote better collaboration

Basic Concepts

Each natural science can be approached quantitatively with numerical statements about amounts (masses, energy, etc.) based on reproducible measurements

• Lavoisier's quantifying step of using a balance in the laboratory uplifted alchemy to chemistry
• It is essential to understand basic chemical rules to pursue chemistry

Accuracy and Precision

• Measurements in natural sciences and real life have random and systematic errors
• Repeating a measurement multiple times and averaging the results can cancel out random errors
• The quality of measurements is judged using 'accurate' and 'precise'.
• Accuracy refers to how close a measured value is to the true value
• Precision refers to the reproducibility of a measurement

The SI System

• Natural scientists discovered that quantification is defined by limited properties
• Seven basic properties are known as the SI Units and they are identified with standard equations

SI Base Units

• Length is measured in meters (m)
• Mass is measured in kilograms (kg)
• Time is measured in seconds (s)
• Temperature is measured in Kelvin (K)
• Electric current is measured in Ampère (A)
• Amount of substance is measured in mole (mol)
• Luminous intensity is measured in candela (cd)

Prefixes

• The metric system has prefixes for smaller and larger values related to the base unit
• Examples include kilo (10^3), mega (10^6), giga (10^9), and tera (10^12)
• These prefixes work due to their metric system of multiplication

Conversions

• Careful handling is needed when converting derived properties
• The correct calculation takes milimeters squared into account rather than simple milimeters
• Examples of these converstions are area/volume, not just length

Additional Units

• Despite the SI system, some old units have survived like liters (volumes) and Å (short distances)
• Roman numerals are preferably used for oxidation states in chemistry
• The metric system is encouraged overall, but these exceptions exist

Logarithims and Significant Figures

• Logarithmic scales are useful with the very large and very small numbers
• loga(b) is the mathematical operation: "Which number has to be used as the exponent for a to yield b?"
• A logarithm with a base a is to raise the basis to the power a
• A base "10" logarithm has the short name "lg"
• "In" (natural logarithm or logarithmus naturalis) using Euler's number "e" as the base

Logarithm Arithmetical Rules

• log(ab) = log(a) + log(b)
• log(a/b) = log(a) – log(b)
• log(ab) = b × log(a)

Significant Figures

• All natural sciences strive for perfection in predicting descriptions
• Experimental sciences have measurements to obtain values impacting accuracy
• Different measurement methods lead to calculation based on such values offer different degrees of accuracy which prevents infinite precision
• Numerical statements are limited to lowest number of significant figures given
• Rules for significant figures determination

Rules for Significant Figures

• All non-zero digits are significant.
• Zeros between non-zero digits are significant.
• Zeros beyond the decimal point at the end of a number are significant.
• Zeros preceding the first non-zero digit in a number are not significant.

States of Matter

• Chemists deal with compounds i.e. types of substances comprised of matter with volume
• Compounds can be grouped into solids, liquids, and gases
• A potential fourth state is the super-fluid one
• Each compound exists in all 3 states of aggregation, depending on the temperature and pressure

Phase Diagrams

• Graphs plotting a compound state versus temperature/pressure
• It is quickly assessed what phase the substance will be in depending on factors
• Increasing the pressure on solid water at constant temperature will turn it into liquid
• The opposite holds true for carbon-dioxide
• As you heat compounds at a given pressure, they melt if solid, and vaporize if liquid
• All three phases coexist at the triple point at one specific set of pressure and temperature
• Phase diagrams end at high temperature and pressure, at a point known as the critical point where there is no liquid/gas difference

Mixtures

• Many substances encountered in nature form mixtures of multiple compounds, occurring between substances in all states of aggregation
• Homogeneous mixtures are where one cannot tell that the substance is under investigation as it looks uniform
• Heterogeneous mixtures appear visibly as a mixture wth different components

Mixture Overview

• All homogeneous mixtures are called solutions regardless of phases combined
• Specific terminology used to describe multiple phases combined heterogeneously

Solid-Solid Seperation

• Manual sorting is possible if visibly different (Pasteur's tartaric acid)
• Sifting is possible with solids differing in size
• Magnets are possible for magnetic compounds
• Electrostatics is possible in charging solids electrostatically
• Winnowing separates heavy and light particles by streaming air
• Flotation uses medium density liquid that floats lighter solids on top of the heavier particles
• Sublimation allows evaporation of of the solid components
• Extraction dissolves one of the solid compounds in a solvent

Solid-Liquid Seperation

• Sedimentation allows solid particles in liquid to settle by gravity
• Centrifugation accelerates settling of particles
• Filtration involves a filter holding back solid material
• Filters can also hold back bacteria

Liquid-Liquid Seperation

• Using sedimentation and subsequent decantation will cause the gravity, over time, make the liquids separate according to their density
• Centifugation sorts liquids accoding to density

Solid-Gas and Liquid-Gas Seperation

• Filtration is where aerosols are passed through a filter holding back everything but the gas
• Washing is when aerosols are bubbled theough a liquid that will hold the gas

Homogenous Mixture Seperation

• One separates homogeneous solutions through physical ways

Evaporation/Extraction/Distillation/Chromatography

• Evaporation involves isolating a dissolved solid from solution by evaporating the solvent
• Extraction moves a substance from one solvent to another more amenable substance
• Distillation separates two liquids boiling their solution
• Chromatography uses materials that attract each other but to differing degrees

Properties of Pure Compounds

• Once isolated in pure form, properties can be measured uniquely.
• Measurement involves color, smell, taste, state, melting/boiling points, electrical conductivity, magnetic behavior, heat conductivity, speed of sound, a refractoy index and spectrescopy.

Decomposing Properties

• A substance that decomposes breaks into new chemical and physical conditions from intense heat, radiation and electricity
• Substances may or may not break into new compounds.
• In this case one of the types is element versus compound

Early Atomic Theory

• An early atomic theory comes from philosopher Demokrit in thinking and dividing that all matter must be comprised of some very small unit that cannot be chopped down
• The first atomic theory was shunned until English philosophers like Newton and Boyle revivied this idea
• Lavoisier made the fundamental laws that proved the smallest particles existed.

Family Tree

• Each group is then divided between homogeneous/heterogeneous, and compounds/elements by splitting up the different components.

Old Atomic Concept/Historic Roots

• The greek Philosopher Demokrit pondered whether the "division of a rock" went on, and the answer led to Atoms
• "Atoms" is an old term for uncuttable smaller pieces
• This theory was not looked at by other prominent philosophers and scientists during the time of the Greeks
• English scholars in the 17th century brought back this theory, and with Newton/Boyle in the picture
• In 1808 Dalton stated that elements consisted of small particles of matter with laws

Mass in Chemistry

• Alchemy was never a real science, and it altered chemistry in the sense matter comes from no where such as the Stone
• Lavosier was able to make the Alchemists disproven through mass by making it evident
• Scientists were quickly able to allow other scientists to implement fundamental laws

Coneservation of Mass

• Alchemists thought that matter could vanish due to changes in the experiment that did not take into account surrounding properties

Einsteins Famous Law

• E = mc²
• Energy
• Mass
• Speed of Light

Law of Conservation of Mass:

• In the wake of a chemical reaction, the sum of the masses of all products equals the sum of the masses of all starting materials.
• Mass changed in a large chemical reaction

Heating the Elements

• When scientists started to charactertize pure properties to describe matter the scientists discovered 2 products being colorful gas and shiny metallic liquid
• Upon heating, the scientist discover mercury oxide composes two elements from experiment

Law of Constant Proportions: In Compound

• Law of Constant Proportions: In any specific compound, always the same elements are combined in always the same ratio of their masses.

Analyzing Compounds

• An analysis shows both carbon and oxygen composition

Law Of Multiple Proportions: If 2 compounds are created between properties of the element will have certain numbers

• Both of those cannot be exclusive of the other and have to be tested

Dalton's and Rutherford's Model

• Constant Proportions (espeically, Multiple Proportions) the chemists thought in the the matter
• The first detail set was to be told about the findings of the experiments of john dalton
• Elements consist of small particles(atoms) and atoms of one element are identical
• If there is at least more than one element atoms cannot be created
• Cheimcal reactions separate with each other
• It is important to recognize chemical relations in order to find properties

Particle Discovery

• Dalton claimed that experiments had the lowest form of the existence of atoms, which could not be composed of anything
• Experiments regarding particles in evacuated tunnels performed by Stoney and Johnson resulted in the discovery of radiation
• While the particles could not be split that way the particles that did form ended up having new properties

Particles Named

• The negative particles are electrons and the proitive particles from Rutherford would be protons
• Rutherford showed the postively charge had a spot in the charge known today as the the nucleon. The empty charge is filled by electrons

Atomic Design

• Third particle was neutron, original set was proposed by Rutherford and discovered in Chaldwicks
• The nucleus containing proton is made of neutrons
• Daltons atoms can be taken as atoms of the varoous elements where the numbers of atom is present inside the atoms

Basic Information

• All matters know will be nothing
• Dalton stated certain things about elements and it became a postiate after knowing the variation inside of that
• All atoms are named qualitative or qualative, there is also an element for which there neutrons and protions is present
• When a neutral atom exists in its form will be equal to the number of protons in the atom

Neutrons

• Determine the number of protons and their relations
• Atoms is called as "ions" and the number of electrons is simialr or lower rather than more protons
• The first statement with Dalton is "elements consist of" is very incorecte

Different Atoms

• For quita large number of protons, and in case of neutral atoms there are different variations known as "isotopese
• There are hydrogen/chorine variations of isotope molecules

More Isotope Example

• Cl and 37Cl atoms which vary in proton mass by the number of neutrons known as isotones atoms
• The result of experiment will show hwo small atom parts actually are and how the particle affects
• The law of multiple proportions can affect compounds is how compounds composed will have some value
• Each reference affects masses of atoms and change their unit
• The mass of each molecule is found in the sub atomic particles
• The mass will be calculated through the subatomic blocks they have

Mass Unit

• The mass of any atom is less/more than the starting element of it
• This is known as mass defect where one element has high mass due to the atom

Masses of Atoms and Isotopes

• The average will not be resorted because those particles has
• Whenever someone has deals with it is important to recognize that is

Average Example

• Bromine will occur naturally and the abundance value is 78 or 79 with some numbers to it
• The natural mass is 78/79. The equation finds total mass from percentages of the atoms within it

Average Calculation

• As a consequence is must show one to recongzie is not the mases and that it is only the total mass

Questions about the Law of Definite Proportions. Includes calculations of mass ratios and discussion of constant composition. Identifying deviations from the law in experimental data.