Science, Chemistry and You

Chemistry

• Definition – study of the composition and properties of matter and the energy transformations accompanying changes in the structure of matter

Major Branches of Chemistry

• Inorganic Chemistry – Study of all the elements other than Carbon

• Organic Chemistry – Study of compounds containing carbon

• Biochemistry – study of chemical processes in living things

• Nuclear Chemistry – study of radioactivity, the nucleus and the changes that the nucleus undergoes

Aristotle

Early Greek Theories

• 400 B.C. - Democritus thought matter could not be divided indefinitely.

• 350 B.C - Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air.

Democritus

• Aristotle was wrong. However, his theory persisted for 2000 years.

• This led to the idea of atoms in a void.

The Rise of Modern Chemistry• The Greek idea of the 4 basic elements

was not disputed until the mid 1600s• Robert Boyle proposed that elements

are substances that cannot be chemically decomposed into simpler substances. Earth, air, fire and water could not be called elements

• In 1774 Joseph Priestly discovered a gas in which substances burned easily, Antoine Lavoisier named the gas Oxygen

Boyle

Priestly

John Dalton• 1800 -Dalton proposed a modern atomic model

based on experimentation not on pure reason.• All matter is made of atoms.• Atoms of an element are identical.• Each element has different atoms.• Atoms of different elements combine

in constant ratios to form compounds.• Atoms are rearranged in reactions.

• His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).

Reaction of the Day 9/9/10

Table sugar + sulfuric acid Carbon + H20

H2SO4

C12H22011 (s) 12 C (s) + 11 H2O (g)

Ch 2 - MatterMatter – anything that takes up space and has mass

Chemical and Physical Properties of Matter

Physical properties – color, shape, texture, odor, taste, electrical conductivity, and densitydensity – how closely packed the molecules are malleable – substances that can be easily hammered into shapesductility – substances that can be stretched into wiresconductivity – substances that can transfer heat or electricity

Chemical properties – describe how matter acts in the presence of other materials

What is each picture modeling?

Density, malleability, ductility, conductivity

Physical or Chemical Change

Physical vs. Chemical ChangePhysical Change• Atoms do not rearrange• Only physical properties change. Chemical properties do not

change.• Physical changes are generally easy to reverse.• No energy is produced by the substance.

Chemical Change• Atoms are rearranged into different molecules• Both physical and chemical properties are changed• Changes are not reversible without another reaction• Energy is often produced ( fire or heat, for example)

Identify each of the following as a Physical or Chemical Change.Put a P next to Physical Changes and a C next to Chemical Changes

1. A piece of wood burns to form ash.

2. Water evaporates into steam. 3. A piece of cork is cut in half.4. A bicycle chain rusts. 5. Food is digested in the

stomach. 6. Water is absorbed by a paper

towel. 7. Hydrochloric Acid reacts with

zinc. 8. A piece of an apple rots on the

ground.

9. A tire is inflated with air. 10. A plant turns sunlight, CO2,

and water into sugar and oxygen.

11. Sugar dissolves in water. 12. Eggs turn into an omelette. 13. Milk sours. 14. A popsicle melts. 15. Turning brownie mix into

brownies.

Homework

• Read pgs 21 - 28• http://www.quia.com/quiz/303980.html

The Division of Matter

Two major categories:1) pure substances - consists of only one type of matter, which cannot be separated into other kinds of matter by any physical processes. Ex: Olive oil2) mixtures – material that can be separated by physical means into two or more pure substances. Ex: Oil and vinegar salad dressing

Two Types of Mixtures• Heterogeneous – physical

combinations of pure substances that show two or more distinct phases. Ex: oil & vinegar dressing, granite has quartz & mica

• Homogeneous – (solution) physical combinations of pure substances that show one distinct phase, the physical properties appear to be the same throughout. Ex: dough & air

Elements and Their SymbolsElement - pure substance that cannot be broken

down into simpler substances

Elements and Their Symbols• Atoms – smallest particles that maintain the

physical and chemical characteristics of an element

• Monoatomic elements – elements that do not naturally combine or bond together. Ex: Ne, He, Ar

• Diatomic elements - elements that bond into two-atom units. Ex: O2, H2

• Polyatomic elements – elements composed of multi-atom units. Ex: S8

Elements and Their SymbolsSymbol – letter given to represent the name of

each elementH – hydrogenO – OxygenCa – CalciumMg – MagnesiumMn – ManganeseNa - Sodium

Compounds and Their Formulas• Compounds are made up of atoms from two

or more different elements, chemically bonded together

• Formulas tell the type and number of atoms that are present in compoundsCommon Compounds and Their FormulasCompound Formula Atoms

Ammonia NH3 1 nitrogen, 3 hydrogen

Rust Fe2O3 2 iron, 3 oxygen

Salt NaCl 1 sodium, 1 chlorine

Sucrose C12H22O11 12 carbon, 22 hydrogen, 11 oxygen

Sample Problems

How many atoms of each element are present in each of the following groups?

a. Na2S2O3

b. Mg(NO3)2

c. 5 Fe2O3

Molecule

• The smallest independent units of compounds • Consist of two or more atoms that are

chemically bonded together• Ex: H20, NH3, H2SO4

• Homework: Section Review Questions 2A, pg 29, #1-3

2B Energy in Matter

• Every chemical reaction either releases or absorbs energy

• Exothermic reactions – release energy (get hot) Ex: lighting a match

• Endothermic reactions – absorb energy (get cold) Ex: ice pack

Energy – the ability to do work• There are many forms of energy• Chemistry is concerned with the relationship among

chemical, thermal, electrical and nuclear energy

Energy Conservation• Thermodynamics – the study of energy flow• First Law of Thermodynamics or Law of

Conservation of Mass-Energy –matter and energy can neither be created nor destroyed, simply changed from one form to another

• Second Law of Thermodynamics – during any energy transformation, some energy goes to an unusable form

Energy Conservation

• Entropy – randomness or disorder of a system

• There is a tendency for all natural processes to increase in entropy (disorder)

Heat, Energy & Temperature• Kinetic Energy – energy of motion

All matter contains particles that are moving• Thermal Energy – sum of all the kinetic energy

of an object• Temperature measures the average kinetic

energy of all the particles in a sample• Heat – thermal energy that is transferred from

one object to another• Amount of heat transfered between objects is determined by

the temperature difference between then and the mass of the hotter object

Which contains more thermal energy?

A teaspoon of boiling water or a bathtub full of lukewarm water

The Measurement of Energy• Joule – standard unit of measurement for

energy• BTU – English unit of measurement for

thermal energy, the amount of heat required to raise one pound of water by one degree Fahrenheit

• Calorie – amount of energy required to raise the temperature of one gram of water one degree Celsius

• 1 cal = 4.184 J

Temperature Scales

Celsius scale – freezing point of water is 0◦ Cboiling point of water is 100 ◦

CKelvin scale – uses absolute zero (point at which

molecules no longer move) as the zero pointfreezing point of water is 273

Kboiling point of water is 373 K

Fahrenheit scale – freezing point of water is 32◦Fboiling point of water is 212 ◦F

Conversion between scalesK = ◦ C + 273 ◦ C = K - 273 ◦ F = (1.8 x ◦ C) ◦ C = (◦ F-32)/1.8

Sample Problem: The weatherman announces that the high for the day is expected to be 33 ◦ C What is this temperature on the Kelvin scale and the Fahrenheit scale?

Homework: Section Review Questions 2BPg 36, questions 1 - 4

Phase Changes of Matter

• Condensation –gas to liquid• Vaporization – liquid to gas• Freezing – liquid to solid• Melting –solid to liquid• Sublimation – solid to gas• Deposition – gas to solid