CHAPTER 3 Chemical Foundations

3.1 THE ELEMENTS • 118 elements

•92 occur naturally, the rest are synthesized

•All matter in the universe can be chemically broken down into elements

•Compounds are made by combining atoms of elements like words are formed from letters of the alphabet.

Words Compounds

in

ABUNDANCE OF ELEMENTS • 9 elements make up about 98% of Earth

• Elements of the human body: CHNOPS

THE WORD ELEMENT CAN HAVE SEVERAL MEANINGS

Element

Element

Microscopic form Single atom of that element

Macroscopic form Sample of that element large enough to weigh on a balance

Element

Generic form When we say the human body contains the element sodium or lithium, we do not mean that free elemental sodium or lithium is present. Rather we mean that atoms of these elements are present in some form.

NAME AND SYMBOLS FOR THE ELEMENTS • Each element has a unique name and symbol

• Symbol usually consists of first one or two letters of elements name • Oxygen = O • Krypton = Kr

• Sometimes the symbol is taken from the original Latin or Greek name

FORMULAS OF COMPOUNDS • The types of atoms and the number of each type is shown using chemical symbols and subscripts.

• Write the formula for each of the following, listing the elements in the order given

• One atom of sulfur and three atoms of oxygen

• Two atoms of nitrogen and five atoms of oxygen

-

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• give the number of each atom in the following: • Ca(NO3)2

• AlPO4

• Al2(SO4)3

• 2H2O

eCa= I N=2 0=6

Ali I P=1 0=4

to+1=4 0=2

3.2 EARLY IDEAS ABOUT MATTER • Greek philosophers – formed explanations based on life experiences

•Proposed four ‘elements’

DEMOCRITUS – 400 BC

•Believed matter was made of tiny particles called atomos • Cannot be created, destroyed, or divided

•Aristotle disagreed

ALCHEMY

• Origin of the word Chemistry

• Tried to make gold out of abundant elements

• Invented many of the techniques still used today like filtration and distillation

ANTOINE LAVOISIER

• 1743-1794

• French scientist known as the “Father of Chemistry”

• Made Chemistry quantitative by taking accurate measurements

• Wrote 1st chemistry textbook

• Beheaded in 1794 for being funded by taxes

PROUST (1754-1826)

• Proposed the Law of Constant Composition (1794): • A given compound always contains the same proportion by mass of

the elements of which it is composed.

JOHN DALTON (1803)

• Revived and Revised Democritus’ idea

• Came up with his own Atomic Theory • All elements are composed of tiny particles called atoms

which cannot be broken into smaller parts.

• All atoms of the same element are identical, atoms of different elements are different

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• Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms

• Chemical reactions take place when atoms rearrange. Atoms are not created or destroyed during chemical reactions.

3

↳ law of constant Comp .

4

← Dalton 's Model of atom

Solid sphere of

matter

3.3 DEFINING THE ATOM

• The smallest particle of an element that retains the properties of the element

•Atoms are very small � One Cu atom = 1.28 x 10-10 m � Solid copper penny = 2.9 x 1022 atoms � If 1 atom = size of an orange, an orange would be as big as

the earth!

= 00000001 m

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• Scanning tunneling microscope (STM) allows individual atoms to be seen � Scans across the surface of atoms � silicon

x

J.J. THOMSON – 1897

Worked with a cathode ray tube

Discovered cathode ray was attracted to positively charged plate

What 2 things did Thomson learn from this experiment?

By measuring the effects of both magnetic and electric fields on a cathode ray, Thomson determined the mass of the charged particle is less than the hydrogen atom (the lightest atom known)

Why is this significant?

.

What subatomic particle did Thomson discover?

•Thomson’s model � Matter is neutral so some positive charge needs to balance

out the negative electrons � Plum pudding model

ERNEST RUTHERFORD - 1911

• In 1911, Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil.

• Based on Thomson’s model of the atom he expected the alpha particles to pass through the foil but not all did!

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What conclusion can Rutherford draw from this result?

Rutherford concluded: � Atom consists of mostly empty space

� If an atom had a diameter of 2 football fields the nucleus would be the size of a nickel

� Almost all + charge & mass are found in nucleus

-

Rutherford Model of the atom

ATOMIC STRUCTURE Ernest Rutherford showed that atoms have internal structure. � The nucleus, which is at the center of the

atom, contains protons (positively charged) and neutrons (uncharged).

– Electrons move around the nucleus.

×

JAMES CHADWICK - 1932

What we knew

1. Electrons & Protons have opposite charges

2. Neutral atom has same number of electrons as protons

3. Mass of atom was too much to just be made of protons & electrons

.

I

Showed nucleus contained a particle with the same mass as a proton but no charge – neutron

orbits = Bohr

Particle Symbol Location Charge Mass

Electron

Proton

Neutron

The number of protons in an atom identifies it as a particular element

Number of protons = atomic number

Periodic table is organized in order of increasing atomic number

All atoms are electrically neutral therefore

# of protons =

Determine the number of protons and electrons in an atom of Molybdenum

MASS NUMBER

Mass number = protons + neutrons

Neutrons =

Mass numbers are given in atomic mass units (amu) � 1 amu = 1/12 mass of Carbon-12 atom

ATOMIC SHORTHAND

• Beryllium- - -atomic number 4

mass number 9

The atomic number is written as a subscript.

The mass number is written as a superscript.

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Element Atomic Number

Protons Electrons Neutrons Mass number

19 20

35 80

10 20

ISOTOPES

Atoms with the same number of protons but different number of neutrons

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, and mass #

• Most naturally occurring elements have two or more stable isotopes � One is usually more common than the others � Oxygen – 16, oxygen – 17, oxygen - 18

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• mass number vs. atomic mass • Mass number = protons + neutrons • Atomic mass (on periodic table) = weighted average of all

the isotopes of an element

1 whole # )1 decimal )

CALCULATING ATOMIC MASS

Unknown element X has two isotopes. 6X has an atomic mass of 6.015 amu and a 7.59 % abundance. 7X has an atomic mass of 7.016 amu and a 92.41% abundance. What is the atomic mass of the unknown element? What is the identity of the unknown element?

÷oboI 1 6 .

015 ) = 0 .4 57

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IONS •Atoms can form ions by gaining or losing electrons. � Metals tend to lose one or more electrons to form positive ions called

cations.

– Cations are generally named by using the name of the parent atom.

My atom Mg ion

IONS • Nonmetals tend to gain one or more electrons to form negative ions called anions.

• Anions are named by using the root of the atom name followed by the suffix –ide.

Chlorine atom Chloride ion

Element Atomic #

Protons Electrons Neutrons Mass number

O2-

Al3+

19 18

146C

Potassium - 41

M - P Ptn

YO8 8 10 8 16

: 13 B 10 14 27

Yakt19 20 39

•

6 6 6 8 14

019 19 19 22 41

Ion charges can be predicted from the periodic table

WHAT CAN CHANGE IN AN ATOM? Protons – NEVER!!!

Neutrons – if changed an isotope is formed

Electrons – if changed an ion is formed

.

PROTON CHANGED

Whole new atom!!!

Oxygen loses a proton it becomes Nitrogen

Oxygen gains a proton it becomes Fluorine

NEUTRON CHANGED

Different version of the same atom is formed (isotope)

Oxygen – 16 has 8 Neutrons

Oxygen – 17 has 9 Neutrons

Oxygen – 18 has 10 Neutrons

ELECTRONS CHANGED

Charged version of the same atom is formed (ion)

Oxygen gains 2 electrons – 10 electrons & 8 protons � Anion

Oxygen loses 2 electrons – 6 electrons & 8 protons � Cation

COMPOUNDS THAT CONTAIN IONS

•Ions combine to form ionic compounds.

•Properties of ionic compounds � High melting points � Conduct electricity

� If melted � If dissolved in water

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Ionic compounds are electrically neutral � Total positive charge must cancel out total negative charge

Nat Cl-

= Nau

FORMULAS FOR IONIC COMPOUNDS Write cation symbol followed by anion symbol

The number of cations and ions must be correct so their charge sums to zero

• Write the formula for compounds containing the following ions: � Potassium and oxygen

� Calcium and sulfur

� Magnesium and nitrogen

kt 02-

= K2O

cast 5 : Ca

: 6- 6=0

Mg2t N3'

= My } Nd

3.4 INTRODUCTION TO THE PERIODIC TABLE • In 1913 our current periodic table was developed by Henry Moseley who arranged the atoms by atomic number

• Periodic law – when elements are arranged according to increasing atomic number, there is a periodic repetition of chemical and physical properties

THE MODERN PERIODIC TABLE •Columns = groups � Numbered 1 – 18 � Correspond to the number of outermost electrons • Have similar properties � Some have special names

•Rows = periods � Numbered 1 – 7 � Correspond to outermost energy level

/ families

1 valence electrons )

PHYSICAL STATES AND CLASSES OF ELEMENTS •Most elements are solid at room temperature

•Br & Hg are liquid

•N, O, F, Cl, and Noble gases are gas t.it

METALS

•Shiny

•Solid at room temperature

•Good conductors of heat & electricity

•Malleable

•Ductile

•Found to the left of the staircase • 1 exception =

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shaped

H

Alkali metals – group 1 elements � Except for � Very reactive � # of valence electrons =

H

I ( +1 ion )

.

Alkaline earth metals – group 2 elements � Also highly reactive � # of valence electrons = 2 ltd ion )

Transition metals – group 3 – 12 (d block) � Number of valence electrons varies

to

Inner transition metals – f block � Number of valence electrons varies � Lanthanide & actinide series

E

NONMETALS

•Gasses or dull looking solids • 1 exception =

•Poor conductors of heat and electricity

•Found to the right of the staircase

Br is liquid

Halogens – group 17 � Highly reactive � # of valence electrons = 7 1- lion )

Nobel gases – group 18 � Extremely unreactive � # of valence electrons = 8 ( no ion )

METALLOIDS

Border the staircase

Have properties of both metals and nonmetals

Semi-conductors = conduct electricity only under certain conditions

exception = Al is ametal

NATURAL STATES OF THE ELEMENTS

Most elements are very reactive.

Elements are not generally found in uncombined form. � Exceptions are:

� Noble metals – gold, platinum and silver � Noble gases – Group 8

µ 18

NATURAL STATES OF THE ELEMENTS

Diatomic Molecules

Nitrogen gas contains N2 molecules.

Oxygen gas contains O2 molecules.

NATURAL STATES OF THE ELEMENTS

Diatomic Molecules

NATURAL STATES OF THE ELEMENTS

Elemental Solids

Diamond Graphite Buckminsterfullerene

Carbon atoms