BICOL UNIVERSITY College of Science

Department of Chemistry

CHEM 1

GENERAL CHEMISTRY LECTURE HANDOUT 2

Ver. 1.2 α 20110705

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Anything that occupies space and has mass Exists in three physical states: solid, liquid, gas

MIXTURES a combination of two or more substances in which the substances retain their

distinct identities

HOMOGENEOUS MIXTURE composition of the mixture is

the same throughout

HETEROGENEOUS MIXTURE composition is not uniform

throughout

PURE SUBSTANCES form of matter that has a definite composition

and distinct properties

ELEMENTS Composed of one type of atom

Classified as metal non-metal or metalloid

Simplest type of matter that retains characteristic properties

May occur as individual atoms or as molecules

Atomic mass is average of isotopic masses weighed by abundance

COMPOUNDS

Two or more elements combined in fixed parts by mass

Properties differ from those of component elements

Molecular mass is sum of atomic masses

CHEMICAL CHANGES alters the composition or identity

of the substance(s) involved

PHYSICAL CHANGES does not alter the

composition or identity of a substance Filtration Extraction Distillation

Crystallization Chromatography

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PLASMA the fourth state of

matter

Most of the matter in the universe is in the form

of plasma. Plasma is formed if some of the negatively charged electrons are separated from their host atoms in a gas, leaving the atoms with

a positive charge. The negatively charged electrons and the positively charged atoms

(known as positive ions) are then free to move separately under the influence of an applied

voltage or magnetic field.

The collapse of the atoms into a single quantum state is known as Bose condensation

or Bose-Einstein condensation is now considered a 5th state of matter.

Velocity in a gas of rubidium as it is cooled: the starting material is on the left, and Bose–

Einstein condensate is on the right.

A liquid consists of atoms or molecules in close proximity to each other (usually not as close as in a solid); liquids occupy a definite volume, but flow to assume the shape of their containers. high density

hard to expand or compress

takes shape of container

A gas (vapor) consists of very widely separated atoms or molecules; gases have neither definite volume nor shape, and they expand to fill their containers.

low density

easy to expand or compress

fills container

A solid consists of atoms or molecules in close contact with each other and often in an organized arrangement; solids have a definite shape and volume. high density

hard to expand or compress

rigid shape

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An extensive property of a material depends upon how much matter is being considered (mass or volume) An intensive property of a material does not depend upon how much matter is being considered (temperature or density). A physical property is a characteristic of a substance that can be observed without changing it into another substance. A chemical property is a characteristic of a substance that can be observed only by reacting it to form another substance.

Which of the following properties of gold are chemical and which are physical?

a. Gold metal can be dissolved by reacting it with a mixture of nitric and

hydrochloric acids known as aqua regia; __________________________________

b. Gold melts at 1064°C.

__________________________________

c. Gold can be hammered into gold leaf sheets that are so thin that light passes through them.

__________________________________

d. Gold can be recovered from gold ore by treating the ore with a solution

containing cyanide, which reacts with and dissolves tiny particles of gold in the ore.

__________________________________

matter 5

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A. Classify the following as colloid, suspension, metals, metalloids nonmetals, solution organic or inorganic compound.

a. Seawater

b. Magnesium

c. Gasoline

d. Air

e. Tomato juice

f. Iodine crystals

g. Sand

h. hydrogen gas

i. orange juice

j. carbon dioxide (CO2)

B. Compare and contrast a mixture and a compound. How are they alike? How are they different? Use complete sentences.

C. For each type of mixture draw a picture representing the size and distribution of particles in a liquid.

SOLUTION COLLOID SUSPENSION

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The separation of the components of a mixture is a problem frequently encountered in chemistry. The basis of the separation is the fact that each component has a different set of physical and chemical properties. The components are pure substances that are either elements or compounds. Techniques used to separate mixtures rely on differences in the physical properties of the components. Techniques useful for the

separation of mixtures include the following:

Distillation/Evaporation is the

purification of a liquid by heating it to its boiling point, causing vaporization, and then condensing the vapours into the liquid state and collecting the liquid. Separation of two or more liquids requires that they have different boiling temperatures. Decreasing the pressure on the liquid can reduce all boiling temperatures.

Filtration is the process of removing or “straining” a solid (the chemical term is

precipitate) from a liquid by the use of filter paper or other porous material.

Decanting is the pouring of a liquid from a solid-liquid

mixture, leaving the solid behind.

Sublimation is the physical property of some

substances to pass directly from the solid state to the gaseous state without the appearance of the liquid state. Not all substances possess this characteristic. If one component of a mixture sublimates, this property may be used to separate it from the other components of the mixture. Iodine (I2), Naphthalene (C10H8, mothballs), ammonium chloride (NH4Cl) and dry ice (solid CO2) are some substances that sublime.

Extraction is the removal of one substance from a

mixture because of its greater solubility in a given solvent.

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Centrifuging is the process of separating a suspended solid from a liquid by whirling

the mixture at high speed.

Chromatography is the process of separating a mixture by the distribution of its

components between two phases, one phase stationary and the other phase moving. Some examples of chromatography are gas chromatography, paper chromatography, and thin-layer chromatography.

Crystallization is a process of forming crystals. It is also a method for separating

dissolved solids from a solution. It can be used to purify solids as well. Assume a sample of cane sugar contains a small amount of glucose as impurities. They are both soluble in water. Pure cane sugar can be crystallized and removed from the solution. In the solution, glucose will remain dissolved.

Match the items on the right to the items on the left.

Mixture Technique

Sand and Water Filtration followed by evaporation

Soil and Water Decanting

Salt from sea water Evaporation

Water and alcohol Filtration

Dyes in an ink Distillation

Salt, sand and water chromatography

Sand, alcohol and water Filtration followed by distillation

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The form of the matter changes, but the same atoms, ions, or molecules are present

Take place on the molecular level. A chemical change

produces a new substance

The atoms themselves change, but the total number

of protons and neutrons remains the same

Physical changes typically involve the least amount of energy, while nuclear reactions usually involve the largest amount of energy. Chemical reactions are somewhere in between.

When ice melts, this is a physical change. The form changes, since ice and water look and behave differently. However, the water molecules are still there - instead of being packed together in an ordered arrangement, they are moving randomly. Since the molecules haven't changed, this is a physical change. All changes of state (boiling, freezing, condensing, etc.) are physical changes.

Another example of a physical change is when sugar dissolves in water. If you add a spoonful of sugar to water, a mixture is formed. It looks a little different (the form of the substances has changed), but the basic properties of the water and the sugar are the same. The water still flows and the sugar still tastes sweet. This is because the same

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molecules are present; the same chemical bonds are there. Whenever mixing occurs (without causing a chemical reaction), a physical change has occurred.

PHASE CHANGE –a physical change in which a substance goes from one phase to another; solid, liquid, or gas, by the addition or removal of heat.

Evaporation is the process of changing a liquid into a gas and is an essential

part of the planet’s water cycle. Condensation is the reverse of evaporation. It is the process of changing a gas

into a liquid. Melting is the process by which a solid changes into a liquid, and is the phase

change that allows frozen water on Earth to be taken out of storage.

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Freezing, the opposite of melting, is the process by which a liquid changes into a solid. It is the phase change responsible for creating frozen forms of precipitation.

Sublimation is the process by which a solid changes into a gas without going through the liquid phase. It is the phase change responsible for making snow disappear without melting.

Deposition is the process by which a gas changes into a solid without going through the liquid phase. It is the opposite of sublimation. Deposition is responsible for creating snow at high altitudes and the formation of frost on cold winter days.

An example of a chemical change is an iron nail rusting. Right off you can see that the form has changed – iron is shiny and ductile, while rust is red-orange colored and flaky. The real story comes when you look at the atoms involved. At the beginning, you have iron atoms as individual atoms, and oxygen atoms in diatomic molecules. After the reaction has occurred, you have a compound containing iron and oxygen. Since iron is a metal and oxygen is a nonmetal, this is an ionic compound, made of ions. So the iron atoms have gone from being individual atoms to ions, and the oxygen atoms have gone from being in diatomic molecules to being ions. Since Fe2O3 is a new compound, chemical bonds have been broken and formed, and a chemical reaction has occurred.

Notice, however, that the atoms themselves have not changed. There were iron and oxygen atoms present at the beginning, and iron and oxygen atoms present at the end. Only the connections between them have changed. This is like taking a Lego structure apart and putting it back together again in a different way.

How is a chemical change different from a physical change? In a physical change, you still have the same compounds that you started with; when water melts, the molecules are still there. In a chemical change, new compounds are made when chemical bonds are broken and formed.

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An example of a nuclear reaction is the formation of rutherfordium, one of the artificial elements. When plutonium-241 and neon-20 atoms are smashed together at high velocity in a nuclear accelerator such as the one shown below, some of them combine to form a rutherfordium-261 atom. This equation for this process must include the isotopes for each element.

241Pu + 20Ne --> 261Rf

Since a new element is made, this must be a nuclear reaction. However, notice that the number of protons and neutrons did not change in this process.

plutonium-241 neon-20 rutherfordium-261

94 p+ 10 p+ 104 p+

147 no 10 no 257 no

Other examples of nuclear reactions include the fusing of atoms under intense heat and pressure inside a star, the radioactive decay of unstable atoms to form new elements, and the breaking apart of large, unstable atoms in a fission bomb.

Putting it all together...

Physical change: H2O (ice) --> H2O (water)

The form changes (solid to liquid) but the same molecules are present. No chemical bonds are formed or broken.

Chemical reactions: 4 Fe + 3 O2 --> 2 Fe2O3

The form changes (silvery metal to flaky, brittle, reddish solid) and the individual atoms and molecules change to ions. In order for this to occur, chemical bonds must be broken and formed. However, the same atoms are present at the beginning and the end, and in order to show this, the equation must be balanced.

Nuclear reaction: 241Pu + 20Ne --> 261Rf

The atoms themselves change their identity, but the total number of protons and neutrons present remains the same. The masses of the atoms

matter 13

must be shown, since different isotopes undergo different nuclear reactions.

1. Classify the following as chemical or physical changes.

a. grapes fermenting

b. copper melting

c. recycling aluminum

d. gasoline exploding

e. perspiration

f. sugar dissolving

g. aging

2. Check the appropriate box

Ph

ysi

cal

Ch

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al

N

ucl

ear

a) Involves great amounts of energy

b) Each substance keeps its own set of properties

c) Occurs when dissolving oil based paint in turpentine

d) Involves the release of radiation

e) Occurs in the nucleus of the atom

f) An event which rearranges chemical bonds and forms one or more new substances with different properties

g) Forms a new substance

h) Forms different elements

i) Occurs when burning wood

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ATOMIC THEORY Greek philosophers

Democritus - all matter was made up of tiny particles. These particles are called atoms after the Greek word atomos, which means indivisible Empedocles - all matter was composed of four elements: fire, air, water, and earth. The ratio of these four elements affected the properties of the matter.

Dalton’s Atomic Theory (1808)

1. Elements are composed of

extremely small particles called atoms.

2. All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements.

3. Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction.

4. A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their

Law of Multiple Proportions

Law of Conservation of Mass

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creation or destruction. Discovery of the Electron

In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. (a) The cathode ray tube was used in early experiments to characterize the electron. (b) Cathode rays (electrons) are deflected by an applied electric (magnetic) field.

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

CATHODE RAY TUBE

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In 1909 the American physicist Robert Millikan advanced Thomson's work in an elegant experiment to determine the charge on the electron. Thomson had defined the mass-to-charge ratio of the electron, and if the charge could be determined, the mass could be calculated as well.

e- charge = -1.60 x 10-19 C

Thomson’s charge/mass of e- = -1.76 x 108 C/g

e- mass = 9.10 x 10-28 g

RUTHERFORD’S GOLD FOIL EXPERIMENT

Alpha () particles are helium nuclei

Particles were fired at a thin sheet of gold foil

Particle hits on the detecting screen (film) are recorded

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Rutherford’s Finding Conclusion Most of the particles passed right through The nucleus is small A few particles were deflected The nucleus is dense VERY FEW were greatly deflected The nucleus is positively charged

Particle Charge Mass # Location Weight(grams) amu

Electron -1 0 Electron cloud 9.1083x10-28 0.0005483

Proton +1 1 Nucleus 1.6726x10-24 1.007276

Neutron 0 1 Nucleus 1.6750x10-24 1.008665

In 1913, Bohr published a paper describing a model of the hydrogen atom based on the notion that its electron must reside in one of an array of discrete energy states called allowed energy levels.

The electron in a hydrogen atom occupies a discrete energy level and may exist only in the available energy levels.

The electron may move from one energy level to another by either acquiring or releasing an amount of energy equal to the difference in the energies of the two levels.

Each energy level is designated by a specific value for n, called the principal quantum number. The level closest to the nucleus has the lowest value for n.

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Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

Element # of protons Atomic # (Z)

Carbon 6 6

Phosphorus 15 15

Gold 79 79

Mass number is the number of protons and neutrons in the nucleus of an isotope.

Nuclide p+ n0 e- Mass

number Oxygen

10

33 42

15

31

Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.

Isotope Protons Electrons Neutrons Nucleus Hydrogen–1 (protium)

1 1 0

Hydrogen-2 (deuterium)

1 1 1

Hydrogen-3 (tritium)

1 1 2

Atomic mass is the average of all the naturally occurring isotopes of that element.

Isotope Symbol Composition of

the nucleus % in

nature

Carbon-12 12C 6 protons

6 neutrons 98.89%

Carbon-13 13C 6 protons

7 neutrons 1.11%

Carbon-14 14C 6 protons

8 neutrons <0.01%

Carbon = 12.011

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Complete the table below

Element Atom No.

Mass No. p+ e- n0 charge

𝑯𝟏𝟏 1 1 1

13 6 6 0

17 17 18 -1

197 118 0

𝑺𝒄𝟐𝟏𝟒𝟓

𝑨𝒓𝟏𝟖𝟒𝟎

𝑪𝒓𝟐𝟒𝟓𝟐 + +1

𝑯𝒈𝟖𝟎𝟐𝟎𝟎 𝟐+

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Book References: Chang, Raymond. Chemistry. 9th edn. Digital Content Manager. 2007.

Manning, Phillip. Essential Chemistry: Atoms, Molecules, and Compounds.

Infobase Publishing. New York NY. 2008

Silberberg, Martin S. Chemistry: The molecular nature of matter and change. 5th

edn. The McGraw-Hill Companies, Inc. New York, NY USA. 2009

Internet Resources: http://cactus.dixie.edu/smblack/chem1010/lecture_notes/1H.html

http://antoine.frostburg.edu/chem/senese/101/measurement/

http://www.sciencegeek.net/Chemistry/index.shtml

http://www.visionlearning.com/library/cat_view.php?cid=1

http://www.ccri.edu/chemistry/Courses/CHEM_1030/Flanagan%20Cam

pus/Experiments/Physical_Separation.pdf