Chapter 1- Lecture 1
Instructor : Dr. Manomi Perera
Why Chemistry?
Essential Ideas
 Chemistry in context
 Phases and classification of matter
 Physical and chemical properties
 Measurements
 Measurement uncertainty, Accuracy, and Precision
 Mathematical treatment of measurement results
Chemistry
• Chemistry is the study of matter, its properties, and the changes it undergoes.
• It is central to our fundamental understanding of many science-related fields.
Chemistry the Central Science
•
Chemistry is interconnected to a vast array of other STEM disciplines.
Knowledge of chemistry is central to understanding a wide range of scientific disciplines. This diagram shows just some of the
interrelationships between chemistry and other fields.
Chemistry and Everyday Life
•
Examples of chemistry in everyday life:
• Digesting food
• Synthesizing polymers for clothing, cookware, and credit cards
• Refining crude oil into gasoline and other products
•
As you proceed through this course, you will discover:
• Many different examples of changes in the composition and structure of matter.
• How to classify these changes in matter and understand how they occur.
• The changes in energy that accompany these changes in matter.
Phases and Classification of Matter
•
Matter: Anything that occupies space and has mass.
•
The three most common states or phases of matter:
1) A solid is rigid and possesses a definite shape.
2) A liquid flows and takes the shape of its container.
3) A gas takes both the shape and volume of its
container.
Law of Conservation of Matter (Mass)
The Law of Conservation of Matter states that matter cannot be created or destroyed in a chemical reaction. It can only
be rearranged from one form to another.
If you burn wood: The ash, smoke, and gases produced together have the same total mass as the wood and oxygen before burning (even though gases may
escape into the air).
Classification of Matter Based on Composition
Pure Substances and Mixtures
Mixture: two or more different substances sharing the same space or volume. Mixtures can be separated based on
differences in physical properties.
Mixtures can be:
Homogeneous: every sample of the mixture is the same, no matter what part of the mixture it’s taken from. A
homogeneous mixture is also called a solution (homo = same) E.g., salt water. Gatorade
Heterogeneous: samples taken from different parts of the mixture may be different. Composition varies from point to point
(hetero = different) E.g., chocolate chip cookies, and orange juice.
a) Oil and vinegar salad dressing is a heterogeneous mixture because its composition is not uniform
throughout. (b) A commercial sports drink is a homogeneous mixture because its composition is
uniform throughout.
Classification of Matter Based on Composition
Pure Substances and Mixtures
 Pure substance: a substance that cannot be separated or broken down by any physical change. All specimens in a pure
substance have exactly the same makeup and properties. Eg, color, boiling point, melting point…..
Pure Substance
Compound: a substance made out of different kinds of atoms that
are chemically bonded together. Compounds can be broken down
through chemical changes. Anything that can be described by a
chemical formula is a compound. E.g., H2O, NaCl (table salt), C3H8O
(rubbing alcohol).
Element: a substance made out of only one kind of
atom. Elements cannot be broken down through chemical
changes. The periodic table lists all of the known
elements according to their properties, which means any
substance on the periodic table is an element. E.g., iron,
gold, oxygen, and aluminum.
Classification of Matter Based on Composition
Atoms and Molecules
•
Atom: The smallest particle of an element that has the properties of that element and can enter into a chemical
combination.
• Idea first proposed by Greek philosophers, Leucippus and Democritus, in the 5th century BCE.
• 19th century, John Dalton of England supported this hypothesis with quantitative measurements.
•
Molecule: Consists of two or more atoms connected by strong forces known as chemical bonds.
(a) This photograph shows a gold nugget. (b) A scanning-tunneling microscope (STM) can generate views of the surfaces of
solids, such as the image of a gold crystal. Each sphere represents one gold atom
Classification of Matter Based on Composition
Atoms and Molecules
Molecules
•
Only a few elements exist as individual atoms.
•
There are currently 118 named elements.
•
Most elements exist as molecules in which two or more atoms of the same element are bonded together.
•
Many molecules consist of two or more atoms of different elements.
•
Atoms in all types of molecules move as a unit.
The elements hydrogen, oxygen, phosphorus, and sulfur form molecules consisting of two or more atoms of the same element. The compounds water,
carbon dioxide, and glucose consist of combinations of atoms of different elements.
Classification of Matter Based on Composition
•
If you follow this scheme, you
can determine how to classify
any type of matter.
 Homogeneous mixture
 Heterogeneous mixture
 Element
 Compound
Classification of Matter Based on Composition
Identify the following as a compound, element, heterogeneous mixture, or a homogeneous mixture
1. Copper
2. Sucrose
3. magnesium
4. soil
5. pizza
6. pancake syrup
7. carbon dioxide
Physical and Chemical Properties
•
The characteristics that enable us to distinguish one substance from another are called properties.
•
A physical property is a characteristic of matter that is not associated with a change in its chemical composition.
•
•
Examples: density, color, hardness, melting and boiling points, and electrical conductivity
Physical properties can be observed without changing a substance into another substance
a) Butter undergoes a physical change when solid butter is heated and forms liquid melted butter. (b) Steam condensing inside a cooking pot is a
physical change, as water vapor is changed into liquid water.
Physical and Chemical Properties
•
The change of one type of matter into another type (or the inability to change) is a chemical property.
•
Examples: flammability, toxicity, acidity, reactivity, and heat of combustion.
(a) One of the chemical properties of iron is that it rusts; (b) one of the chemical properties of chromium is that it does not.
Physical and Chemical changes
• Physical changes are changes in matter that do not change the composition of a substance.
– Examples include changes in state, temperature, and volume.
• Chemical changes result in new substances.
– Examples include combustion, oxidation, and decomposition.
• Converting between the three states of matter is a
physical change.
• When ice melts or water evaporates, there are still 2 H
atoms and 1 O atom in each molecule.
Physical and Chemical changes
In the course of a chemical reaction, the reacting substances are converted to new substances. Here, the copper penny reacts
with nitric acid; it gives a blue solution of copper(II) nitrate and a brown gas called nitrogen dioxide.
NOTE: Physical properties, like color, often helps us
SEE that chemical change has occurred.
Physical and Chemical changes
(a)Copper and nitric acid undergo a chemical change to form copper nitrate and brown, gaseous nitrogen dioxide.
(b) During the combustion of a match, cellulose in the match and oxygen from the air undergo a chemical change to form
carbon dioxide and water vapor.
(c) Cooking red meat causes a number of chemical changes, including the oxidation of iron in myoglobin that results in the
familiar red-to-brown color change.
(d) A banana turning brown is a chemical change as new, darker (and less tasty) substances form.
Extensive Properties and Intensive Properties
 In chemistry and physics, properties of matter are classified as extensive or intensive based on whether they depend
on the amount of substance present.
Extensive property
•
Depends on the amount of matter present.
•
Examples: mass, volume, heat
Intensive property
•
Does not depend on the amount of matter present.
•
Examples: density, temperature, color
Separating Mixtures
• Mixtures can be separated based on the physical properties of the components of the mixture. Eg: A heterogeneous
mixture of iron fillings and gold fillings could be sorted by color into iron and gold.
• Some methods used in laboratories to separate mixtures are,
– filtration
– distillation
– chromatography
Filtration
• In filtration, solid substances are separated from liquids
and solutions.
Separating Mixtures
Distillation
• Distillation uses differences in the boiling points of
substances to separate a homogeneous mixture
into its components.
• Eg; If we boil a solution of Salt and Water, the
water evaporates forming gas, and the salt is left
behind. The gaseous water can be converted back
to a liquid on the walls of a condenser
Separating Mixtures
Chromatography
• This technique separates substances on the basis
of differences in the ability of substances to
adhere to the solid surface, ( paper silica etc..)
Summary Questions
1. How does an atom differ from a molecule
2. A sulfur atom and a sulfur molecule are not identical. What is the difference
3. Classify each of the following changes as physical or chemical
1. Souring of milk
2. Dissolving sugar in water
3. Melting of gold
4. Condensation of steam
5. Coal burning
4. What is an intensive property
Provide 3 examples
5. What is an extensive property
Provide 3 examples
6. Is the separation method used in brewing a cup of coffee best described as distillation, Filtration or chromatography