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8/13/2019 01 LectureOutlines LO

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1 Introduction to Chemistry


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Copyright 2007 Pearson Education, Inc., publishing as Benjamin Cummings

CHAPTER OBJECTIVES

To recognize the breadth, depth, and scope of chemistry

To understand what is meant by the scientific method

To be able to classify matter

To understand the development of the atomic model

To know the meaning of isotopes and atomic masses

To become familiar with the periodic table and to be ableto use it as a predictive tool


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Chemistry: Principles, Patterns,

and Applications, 1e

1.1 Chemistry in the

Modern World


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1.1 Chemistry in the Modern World

Chemistry is the study of matter and the changes thatmaterial substances undergo

Of all the scientific disciplines, it is the most extensivelyconnected to other fields of study

Disciplines that focus on living organisms and theirreactions with the physical world rely heavily onchemistry

Practical applications of chemistry are everywhere

Chemistry affects our daily lives


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1.2 The Scientific

Method


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1.2 The Scientific Method

A procedure that searchesfor answers to questions

and solutions to problems

Consists of makingobservat ions,formulating

hypotheses, and designing

experiments,which leads

to additional observations,hypotheses, and

experiments in repeated

cycles


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Observations

Can be qual i tat ive or quant i tat ive

Qual i tat ive observat ionsDescribe properties or occurrences in

ways that do not rely on numbers

Quant i tat ive observat ions

Measurements that consist of both a

number and a unit



Hypotheses

A tentative explanation for theobservations

May not be correct, but it puts thescientists understanding of the systembeing studied into a form that can betested



Experiments

Tests the validity of the hypothesis

Are systematic observations or measurements

made under controlled conditions, in which the

variable of interest is clearly distinguished from

any others

If experimental results are reproducible, they are

summarized in a law.



Experiments

LawA verbal or mathematical description of a

phenomenon that allows for general predictions

Describes what happens and not why

Unlikely to change greatly over time unless a major

experimental error is discovered

TheoryAttempts to explain why nature behaves as it does

Is incomplete and imperfect, evolving with time to explainnew facts as they are discovered





1.3 A Descriptionof Matter



1.3 A Description of Matter

Matter anything that occupies space and possessesmass

Mass quantity of matter an object contains

does not depend on location of theobject

Weight a force caused by the gravitational

attraction that operates on the object

depends on the location of an object



1.3 A Description of Matter

Three distinct states o f matter:

1. Solids relatively rigid and have fixed shapes and volumes

volumes of solids independent of temperature andpressure

2. Liquidshave fixed volumes but flow to assume the shape oftheir containers

Volumes of liquids independent of

temperature and pressure

3. Gases have neither fixed shapes nor fixed volumes and expandto fill their containers completely

Depend strongly on temperature and pressure



Pure Substances and Mixtures

Pure Chemical Substance any matter that has afixed chemical composition and characteristic properties

Mixture combinations of two or more puresubstances in variable proportions in which the individualsubstances retain their identity

1. Homogeneous mixtures

a. All portions of a material are in the same state, have novisible boundaries, and are uniform throughout

b. Also called solutions

2. Heterogeneous mixtures

a. Composition of a material is not completely uniform




Homogeneous mixtures can be separated into theircomponent substances by physical processes that relyon differences in some physical property

1. Distillation uses differences in volatility, a measure of howeasily a substance is converted to a gas at a giventemperature

2. Crystallization separates mixtures based on differences insolubility, a measure of how much of a solid substanceremains dissolved in a given amount of a specified liquid

Heterogeneous mixtures components can be

separated by simple means such as filtration




Most mixtures can be separated into puresubstances that may be either elements or compounds

Element a substance that cannot be broken downinto simpler ones by chemical changes

Compound contains two or more elements and haschemical and physical properties that are usuallydifferent from those of the elements of which it iscomposed. Can be broken down into their elements bychemical processes




Overall organization of matter and themethods used to separate mixtures are

summarized here



Properties of Matter

Properties used to describe material substances can beclassified as eitherphy sicalor chemical.

Physical properties:

Characteristics that scientists can measure withoutchanging the composition of the sample under study(mass, color, volume, amount of space occupied by thesample).

Chemical properties:

Describe the characteristic ability of a substance to reactto form new substances (flammability and corrosion).



Properties of Matter

Physical properties can be extensive or in tensive1. Extensive propertiesa. Vary with the amount of the substance,

b. Include mass, weight, and volume.

2. Intensive properties

a. Do not depend on the amount of the substance,b. Include color, melting and boiling point, electrical

conductivity, and physical state at a given temperature,

c. Determine a substances identity,

d. Have an important intensive property called density(d),a

ratio of two extensive properties, mass and volume

density = mass d = m

volume V


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1.4 A Brief History

of Chemistry


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In fourth centuryB.C., ancient Greeks proposedthat matter consisted of fundamental particlescalled atoms.

Over the next two millennia, major advances inchemistry were achieved by alchemists. Theirmajor goal was to convert certain elements intoothers by a process called transmutation.

1.4 A Brief History of Chemistry


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Beginnings of modern chemistry were seen in thesixteenth and seventeenth centuries, where great

advances were made in metallurgy, the extraction of

metals from ores.

In the seventeenth century, Boyle described therelationship between the pressure and volume of air and

defined an elementas a substance that cannot be

broken down into two or more simpler substances by

chemical means.

Modern Chemistry


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During the eighteenth century, Priestley discoveredoxygen gas and the process of combustion where

carbon-containing materials burn vigorously in an

oxygen atmosphere.

In the late eighteenth century, Lavoisier discoveredrespiration and wrote the first modern chemistry text.

His most important contribution was the law of

conservation of mass, which states that in any chemical

reaction, the mass of the substances that react equalsthe mass of the products that are formed. He is known

as the father of modern chemistry.

Modern Chemistry


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In 1803, Dalton proposed that elements consist ofindividual particles called atoms. His atom ic theory o fmattercontains four hypotheses:

1. All matter is composed of tiny particles called atoms.

2. All atoms of an element are identical in mass and fundamentalchemical properties.

3. A chemical compound is a substance that always contains thesame atoms in the same ratio.

4. In chemical reactions, atoms from one or more compounds orelements redistribute or rearrange in relation to other atomsto form one or more new compounds.Atoms themselves donot undergo a change of identity in chemical reactions.

The Atomic Theory of Matter


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Daltons atomic theory is essentially correct, with fourminor modifications:

1. Not all atoms of an element must have precisely the samemass.

2. Atoms of one element can be transformed into another throughnuclear reactions.

3. The composition of many solid compounds are somewhatvariable.

4. Under certain circumstances, some atoms can be divided (splitinto smaller particles).

The Atomic Theory of Matter


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The Law of Multiple Proportions

Dalton could not use his theory to determine the

elemental compositions of chemical compounds

because he had no reliable scale of atomic masses.

Daltons data led to a general statement known as thelaw of m ul t ip le propor t ions.

Law states that when two elements form a series of

compounds, the ratios of the masses of the second

element that are present per gram of the first elementcan almost always be expressed as the ratios of

integers.


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Gay-Lussac attempted to establish the formulas ofchemical compounds by measuring, under constanttemperature and pressure conditions, the volumes ofgases that reacted to make a given chemical compound,together with the volumes of the products if they weregases.

Gay-Lussacs results were explained byAvogadroshypothesis, which proposed that equal volumes ofdifferent gases contain equal numbers of gas particleswhen measured at the same temperature and pressure.

Avogadros Hypothesis

Ch i t P i i l P tt


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1.5 The Atom


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1.5 The Atom

Each element is chemically unique. Tounderstand why they are unique, you need

to know the structure of the atom (the

smallest particle of an element) and thecharacteristics of its components.


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1.5 The Atom Atoms consist of electrons, protons, andneutrons.

1. Electrons and protons have electrical charges that are identicalin magnitude but opposite in sign. Relative charges of 1 and+1 are assigned to the electron and proton, respectively.

2. Neutrons have approximately the same mass as protons but nochargethey are electrically neutral.

3. The mass of a proton or a neutron is about 1836 times greaterthan the mass of an electron. Protons and neutrons constitutethe bulk of the mass of the atom.


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1.5 The Atom


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The Electron

In 1897, Thomson demonstrated that cathode rays could bedeflected, or bent, by magnetic or electric fields, which indicated thatthe cathode rays consisted of charged particles.

Measuring the extent of the deflection of the cathode rays, Thomsoncalculated the mass-to-charge ratio of the particles.

Since like charges repel each other and opposite charges attract,Thomson concluded that the particles had a net negative charge.These particles are called electrons.

Millikan calculated the charge on a single electron and determinedthe mass of an electron:

mass X charge = mass

charge


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Radioactivity

1896, Becquerel discovered that certain minerals emitted a new

form of energy.

Becquerels work was extended by Pierre and Marie Curie, whoused the word radioact iv i tyto describe the emission of energy raysby matter.

Rutherford, building on the Curies work, showed that compounds ofelements emitted at least two distinct types of radiation. One wasreadily absorbed by matter and consisted of particles that had apositive charge and were massive compared to electrons. Theseparticles were called particles. Particles in the second type ofradiation were calledparticlesand had the same charge andmass-to-charge ratio as electrons.

A third type of radiation, rays, was discovered later and found tobe similar to a lower energy form of radiation calledX -rays.


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Radioactivity

Three kinds of radiationparticles, particlesand rays

1. Distinguished by the way they are deflected by an electric field

and by the degree to which they penetrate matter

2. particles and particles are deflected in opposite directions;

particles are deflected to a much lesser extent because oftheir higher mass-to-charge ratio.

3. rays have no charge and are not deflected by electric or

magnetic fields.

4. particles have the least penetrating power, and rays are

able to penetrate matter readily.


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The Atomic Model

Rutherfords results strongly suggested that both the mass and

positive charge are concentrated in a tiny fraction of the volume ofthe atom, called the nucleus.

Rutherford established that the nucleus of the hydrogen atom was apositively charged particle, which he called a proton.

Also suggested that the nuclei of elements other than hydrogenmust contain electrically neutral particles with the same mass as theproton.

Theneutronwas discovered in 1932 by Rutherfords studentChadwick.

Because of Rutherfords work, it became clear that an particlecontains two protons and neutronsthe nucleus of a helium atom.

Chemistry: Principles Patterns


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1.6 Isotopes and AtomicMasses


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1.6 Isotopes and Atomic Masses

Atoms of different elements exhibit different chemicalbehavior.

Identity of an element is defined by its atom ic number.

(Z) isthe number of protons in the nucleus of an atom ofthe element.

The atomic number is therefore different for eachelement.

Known elements are arranged in order of increasing Z inthe period ic table.


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The chemistry of each element is determined by its number of

protons and electrons.

In a neutral atom, the number of electrons equals the number ofprotons.

Symbols for elements are derived directly from the elements name.

Nuclei of atoms contain neutrons as well as protons.

The number of neutrons is not fixed for most elements, unlikeprotons.

Atoms that have the same number of protons, and hence the same

atomic number, but different numbers of neutrons are calledisotopes.


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Isotopes1. All isotopes of an element have the same number of

protons and electrons, which means they exhibit the

same chemistry.

2. Isotopes of an element differ only in their atomic mass,

which is given by the mass number (A ),the sum of

the numbers of protons and neutrons.


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Atomic mass1. The mass of any given atom is not simply the

sum of the masses of its electrons,

protons, and neutrons.

2. Atoms are too small to measure

individually and do not have a

charge.

3. The arbitrary standard that has been

established for describing atomic

mass is the atomic mass unit(amu),defined as one-twelfth of the

mass of one atom of 12C.


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4. Most elements exist as mixtures of

several stable isotopes. The

weighted average is of the masses of the

isotopes is called the atomic mass.

5. Electrons added or removed from an

atom produce a charged particle

called an ion,whose charge is

indicated by a superscript after the symbol

for the element.

Chemistry: Principles Patterns


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1.7 Introduction to the

Periodic Table




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1.7 Introduction to the Periodic Table

The single most important learning aid inchemistry

Summarizes huge amounts of information

about the elements so that you can predictmany of their properties and chemicalreactions


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Elements are arranged in seven horizontal rows, in orderof increasing atomic number from left to right and fromtop to bottom.

Rows are calledper iodsand are numbered from 1 to 7.

Elements with similar chemical properties form verticalcolumns, calledgroups,which are numbered from 1 to18.

Groups 1, 2, and 13 through 18 are the main groupelements.

Groups 3 through 12 are in the middle of the periodictable and are the transition elements.

The two rows of 14 elements at the bottom of theperiodic are the lanthanidesand actinides.


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The heavy orange zigzag line running diagonallyfrom the upper left to the lower right through

Groups 1316 divides the elements into metals

( in blue, below and to the left of the line) and

nonmetals(in bronze, above and to the right).

Elements colored in gold that lie along the

diagonal line are semimetalsand exhibit

properties intermediate between metals andnonmetals.

Metals, Nonmetals, and Semimetals


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Metals- Good conductors of electricity and heat- Ductile

- Malleable

- Lustrous

- In chemical reactions, metals lose electrons to form positively

charged ions

- Vast majority of known elements are metals

- All are solids except for mercury, which is a liquid at room

temperature and pressure



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Nonmetals- Poor conductors of heat and electricity- Not lustrous

- Can be gases, liquids, or solids

- Solid nonmetals are brittle

- Tend to gain electrons in reactions with metals to formnegatively charged ions

- Share electrons in reactions with other nonmetals

Semimetals- Exhibit properties intermediate between metals and

nonmetals


C f G


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Chemistry of the Groups

Elements with similar chemical behavior are inthe same group.

Elements of Group 1 are alkali metals.

Elements of Group 2 are the alkaline earths.

Elements of Group 17 are the halogens.

Elements of Group 18 are the noble gases.

Ch i f h G


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The alkali metals (Group 1)

- The alkali metals are lithium (Li), sodium (Na), potassium

(K), rubidium (Rb), cesium (Cs), and francium (Fr).

- Hydrogen is placed in Group 1 but is not a metal.

- The alkali metals react readily with nonmetals to give ions

with a +1 charge.

- Compounds of alkali metals are common in nature and

daily life.

Ch i t f th G


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The alkaline earths (Group 2)

- The alkaline earths are beryllium (Be), magnesium (Mg),

calcium (Ca), strontium (Sr), barium (Ba), and

radium (Ra).

- All are metals that react readily with nonmetals to giveions with a 2 charge.

Ch i t f th G


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The halogens (Group 17)

- The halogens are fluorine (F), chlorine (Cl), bromine (Br)

iodine (), and astatine (At).

- They react readily with metals to form ions with a 1

charge.

Ch i t f th G


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The noble gases (Group 18)

-are helium (He), neon (Ne), argon, (Ar), krypton (Kr), xenon(Xe), and radon (Rn);

- are monatomic;

- are unreactive gases at room temperature and pressure;- are called inert gases.


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1.8 Essential Elements

Elements that are absolutely required in the diets of humans are

called essential elements (highlighted in purple).

Essential elements are restricted to the first four rows of the periodictable with only two exceptions (Mo and ).

An essential element is one that is required for life

and whose absence results in death.

An element is considered to be essential if a deficiency

consistently causes abnormal development or

functioning and if dietary supplementation of that

element and only that element prevents this adverse

effect.

Classification of the Essential Elements


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Classification of the Essential Elements

Most living matter consists primarily of bu lk elements

oxygen, carbon, hydrogen, nitrogen, and sulfur. They arethe building blocks of the compounds that make up ourorgans and muscles; they also constitute the bulk of ourdiet.

Six elementssodium, magnesium, potassium, calcium,chlorine, and phosphorusare called macromineralsand provide essential ions in body fluids and form themajor structural components of the body.

Remaining essential elements called trace elemen tsand are present in small amounts.


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The Trace Elements

It is difficult to detect low levels of some of theessential elements, so the trace elements were

relatively slow to be recognized.

Many compounds of trace elements are toxic.

Dietary intakes of elements range from deficient

to optimum to toxic with increasing quantities;the optimum levels differ greatly for the essential

elements.

A lifi ti


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Amplification

How can elements present in small amountshave such large effects on the health of anorganism?

Trace elements participate in an amplificationmechanismthey are essential components oflarger biological molecules that are capable ofinteracting with or regulating the levels of

relatively large amounts of other molecules.

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