ChemistryDr. Michael P. Gillespie

Chemistry

• Chemistry is the study of matter, its chemical and physical properties, the chemical changes it undergoes, and the energy changes that accompany those processes.

• Matter is anything that has mass and occupies space. The changes that matter undergoes always involve either gain or loss of energy.

• Energy is the ability to do work to accomplish some change.

Chemistry

• The study of chemistry involves matter, energy, and their interrelationship.

• Matter and energy are at the heart of chemistry.

Scientific Method

• The scientific method is a systematic approach to the discovery of new information.

• It is a way of gaining information (facts) about the world by forming possible solutions to questions.

• Rigorous testing is employed to determine if the proposed solutions are supported.

Basic Assumptions In Science

• There are specific causes for events observed in the natural world.

• The causes for events in nature can be identified.

• There are general rules or patterns that describe what happens in nature.

Basic Assumptions In Science

• Repeated events probably have the same cause.

• What one person observes can be observed by others.

• The same fundamental rules apply, regardless of when or where they occur.

Cause and Effect

• Some events are correlated (happen together).

• Some events have a cause and effect relationship (an event is a direct result of a previous event).

Components of the Scientific Method

• Observation

• Hypotheses

• Openness to new information and ideas

• Willingness to submit ones ideas to the scrutiny of others

Observation

• Observations are made using our senses or an extension of our senses.

• Observations are careful, thoughtful recognition of an event.

Questioning and Exploration

• Optimal questions lend themselves to experimentation.

• Explore other sources of knowledge relevant to the question.

Hypothesis

• A hypothesis is a statement that provides a possible answer to a question or an explanation for an observation that can be tested.

Characteristics of a Good Hypothesis

• Logical

• Account for all relevant information

• Predict future events

• Testable

• Use the simplest hypothesis with the fewest assumptions

Einstein

• “Make everything as simple as possible, but not simpler.”

Testing a Hypothesis

• A good hypothesis is testable.

• It can be either supported or disproved.

• If a hypothesis cannot be disproved, confidence in it increases.

• New information can encourage scientists to reformulate an hypothesis.

Methods for Testing a Hypothesis

• Collect relevant information.

• Make additional observations.

• Devise an experiment.

Experiment

• An experiment is a re-creation of an event or occurrence in a manner that allows the scientist to support or disprove a hypothesis.

Variables

• Variables are individual factors that help determine the outcome of an event.

Controlled Experiment

• A controlled experiment is one in which only one variable is present.

• Two groups:• Control group – no manipulation of

the variable.• Experimental group – a group in

which one variable is manipulated.

Variables

• Independent variable – is manipulated in the experiment by the scientist.

• Dependent variable – will change as a result of manipulation of the independent variable.

• There should be only one independent variable in an experiment.

• Be careful not to introduce additional variables into the experiment.

Development of Theories and Laws

• If new evidence consistently and repeatedly supports the original hypothesis and other related hypotheses, we begin to see patterns emerge.

• Scientific theories and laws come into existence.

Inductive Reasoning

• The process of developing general principles from the examination of many specific facts is known as inductive reasoning or induction.

Deductive Reasoning

• The process of using general principles to predict the specific facts of a situation is called deductive reasoning or deduction.

Scientific Theory

• A theory is a widely accepted, plausible, general statement about fundamental concepts in science that explain why things happen.

• A theory is a very broad statement, which is the result of years of observation, questioning, experimentation, and data analysis.

Theory Vs. Hypothesis

• A hypothesis provides a possible explanation for a specific question; whereas a theory is a broad concept that shapes how scientists look at the world and how they frame their hypothesis.

Scientific Law

• A scientific law is a uniform or constant fact of nature that describes what happens in nature.

Theory Vs. Law

• Theory

• Describes why things happen

• Examined repeatedly

• Independently verified

• Excellent predictors of how nature behaves

• Law

• Describes what happens in nature

• Examined repeatedly

• Independently verified

• Excellent predictors of how nature behaves

Properties of Matter

• Properties are characteristics of matter and are classified as either physical or chemical.

States of Matter

• Three states (phases) of matter:• Solid state• Liquid state• Gaseous state.

States of Matter

• The phases of matter are determined by the following:• The amount of kinetic energy molecules

have.• The strength of the attractive forces

between molecules.• The arrangement of molecules.

Solid

• A solid consists of molecules with strong attractive forces and low kinetic energy.

• The molecules vibrate in place and are at fixed distances from one another.

Liquid

• A liquid has molecules with enough kinetic energy to overcome the attractive forces that hold the molecules together.

• The molecules are still strongly attracted to one another, but they are slightly farther apart.

Liquid

• The molecules can slide past one another.

• Liquids change shape, but they maintain their volume.

• Liquids flow and are called fluids.

Gas

• A gas is made of molecules that have a great deal of kinetic energy.

• The attraction of the molecules to one another is overcome by the speed with which the individual molecules move.

Gas

• The molecules collide against one another and push each other apart.

• Therefore, gases expand to fit their container.

• Vapor is the gaseous form of a substance that is usually in a liquid phase.

States of Matter

Water

• Water is the most common example of a substance that can exist in all three states over a relatively small temperature range.

States of Water

Physical Change

• A physical change produces a recognizable difference in the appearance of a substance without causing any change in its composition or identity.

• Conversion of water from one state to another constitutes a physical change.

Physical Properties of Matter

• A physical property can be exhibited, observed or measured without changing the composition or identity of a substance.

Physical Properties

• A practical application of this concept is in the separation of materials based upon their physical properties.

Chemical Properties of Matter

• Chemical properties can be observed only through chemical reactions and result in a change in the composition of the material.

• The substances internal structure must be affect to observe chemical properties.

Chemical Reaction

• A chemical reaction is a process that produces a change in matter by rearranging, removing, replacing, or adding atoms to produce new substances.

• This is achieved by either forming or breaking chemical bonds.

• A chemical reaction involves atoms interacting with other atoms to fill their outermost energy shell.

Chemical Reaction

Chemical Reaction

• The interacting atoms become attached or bonded to one another.

• Two types of bonds:• Ionic• Covalent

Ionic Bonds

• A positively or negatively charges atom or molecule is called an ion.

• Ionic bonds are formed after atoms transfer electrons to achieve a full outermost energy level.

• Electrons are donated or received during the transfer to form positive or negative ions (ionization).

Ionic Bonds

Covalent Bonds

• A covalent bond is a chemical bond formed by the sharing of electrons.

• A covalent bond in which a single pair of electrons is shared is called a single covalent bond (single bond).

• Double bond – two pairs of electrons are shared.

• Triple bond – three pairs.

Hydrogen Bonds

• Hydrogen bonds are due to the unequal sharing of electrons and the resulting polar nature of the molecule.

• Hydrogen bonds can be either intermolecular or intramolecular.

• Hydrogen bonds hold molecules together, they do not bond atoms together. Therefore, they are not true chemical bonds.

Intensive Vs. Extensive Properties

• Properties can be classified according to whether or not they depend upon the size of the sample.

Intensive Properties

• An intensive property is a property of matter that is independent of the quantity of the substance.

• Density, boiling and melting points, and specific gravity are intensive properties.

• The boiling point of a single drop of water is exactly the same as the boiling point of a liter of water.

Extensive Properties

• An extensive property depends on the quantity of a substance.

• Mass and volume are extensive properties.

• There is an obvious difference between 1 gram of silver and 1 kg of silver.

Classification of Matter

• Chemists look for similarities in properties among various types of materials.

• The most useful classification systems are based on composition.

• All matter is either a pure substance or a mixture.

Pure Substances

• A pure substance has only one component.

• Elements and compounds are both pure substances.• An element is a pure substance that

cannot be changed into a simpler form of matter by any chemical reaction.

• A compound is a substance resulting from the combination of two or more substances in a definite, reproducible way.

Water

• Pure water is a pure substance.

• The elements hydrogen and oxygen may combine to form the compound water, H20.

Mixture

• A mixture is a combination of two or more pure substances in which each substance retains its own identity.

• Alcohol and water may be combined in a mixture. They coexist as pure substances because they do not undergo a chemical reaction; they exist as thoroughly mixed discrete molecules.

Mixture

• The substances are not in set proportions.

• There are an infinite number of combinations of quantities of alcohol and water that can be mixed.

• You can have a small amount of water and a large amount of alcohol or vice versa.

• Either way, it is still an alcohol-water mixture.

Types of Mixtures

• A homogenous mixture has a uniform composition. It’s particles are well mixed, or thoroughly intermingled. (i.e. alcohol-water)

• A heterogenous mixture has a nonuniform composition. (i.e. salt and pepper or concrete).

Solutions

• A solution is a liquid mixture of ions or molecules of two or more substances.

• The process of making a solution is called dissolving.

• The solvent is the component present in the larger amount.

• The solute is the component that dissolves into the solvent.

Solutions

• Aqueous solution – a solid, liquid, or gas dissolved in water.

• Gaseous solution – a mixture of gasses such as air.

Concentrations

• Concentration is a measure of the number of particles of a substance, or the mass of those particles, that are contained in a specified volume.

• The amounts of solute and solvent are the concentration of a solution.

Data

• A scientific experiment produces data. Each piece of data is the result of a single measurement or observation. Mass, length, volume, time, temperature, and energy are common types of data obtained from chemical experiments.

Data

Results

• Results are the outcome of an experiment. Data and results may be identical; however, typically, several related pieces of data are combined and logic is used to produce a result.

Unit

• A unit of measurement is a definite amount of a physical quality.

• A unit defines the basic quantity of mass, volume, time, or whatever quantity is being measured.

Experimental Quantities

• Mass

• Length

• Volume

• Time

• Temperature

• Energy

Mass Vs. Weight

• Mass describes the quantity of matter in an object.

• Weight and mass are NOT synonymous.

• Weight is the force of gravity on an object.

• Weight = mass * acceleration due to gravity.

Mass Vs. Weight

• When gravity is constant, weight and mass are directly proportional, but gravity is not constant.

• Mass is independent of gravity. It is the result of a comparison of an unknown mass with a known mass called a standard mass.

Atomic Mass Unit

• An atom of a substance has a very tiny mass.

• An atom of hydrogen has a mass of 1.661 X 10-24 g.

• One atomic mass unit is a more convenient way to represent the mass of one hydrogen atom, rather than 1.661 X 10-24 g.

• Units should be chosen to suit the quantity of the item being described.

Length

• Length is the distance between two points.

• The standard metric unit of length is the meter.

• Larger distances are measured in kilometers, smaller distances are measured in centimeters or millimeters. Very small distances such as the distances between atoms are measured in nanometers.

Volume

• Volume is the space occupied by an object.

• The standard metric unit of volume is the liter.

• The volumetric flask is designed to contain a specified volume of liquid.

• The graduated cylinder, pipet, and buret dispense a desired volume of liquid.

Time

• The standard metric unit of time is the second.

• Matter can be characterized by the time required for a certain process to occur.

• The rate of a chemical reaction is a measure of change as a function of time.

Temperature

• Temperature is the degree of “hotness” of an object.

• The common temperature scales are Fahrenheit (⁰F), Celsius (⁰C), and Kelvin (K).

• Two convenient reference points that are used to calibrate a thermometer are the freezing and boiling points of water.

Energy

• Energy is the ability to do work.

• It can be categorized as either kinetic energy or potential energy.

• Kinetic energy is the energy of motion.

• Potential energy is the energy of position. It is stored energy that is not yet doing work.

• All energy is either kinetic or potential.

Forms of Energy

• The principal forms of energy include:• Light• Heat• Electrical• Mechanical• Chemical

Characteristics Of Energy

• Energy cannot be created or destroyed.

• Energy may be converted from one form to another.

• Conversion of energy from one form to another always occurs with less than 100% efficiency.

• All chemical reactions involve either a “gain” or “loss” of energy.

1st Law of Thermodynamics

• The 1st law of thermodynamics is also known as the law of conservation of energy.

• Energy is neither created or destroyed.

• Energy can be converted from one form to another, but the total energy remains constant.

Concentration

• Concentration is a measure of the number of particles of a substance, or the mass of those particles, that are contained in a specified volume.

• Concentration is used to represent m ixtures of different substances.• i.e. concentration of oxygen in the air.

Density

• Density is the ratio of mass to volume.• d = mass / volume = m / V

• It is not dependent upon the quantity of the material present and is therefore an intensive property.

• Each substance has a unique density.

• One milliliter of air and one milliliter of iron do not weigh the same amount.

Specific Gravity

• Values of density are often related to a standard, well-known reference, the density of pure water at 4⁰C.

• This “referenced” density is called the specific gravity, the ratio of the density of the object in question to the density of pure water at 4⁰C.• specific gravity = density of object g/mL) /

density of water (g / mL)

• The density of water at 4⁰Cnis 1.00 g/mL.