CH 2: Atoms, CH 2: Atoms, Molecules, and IonsMolecules, and Ions

Chapter OutlineChapter Outline

History of chemistry (2.1 – 2.4)History of chemistry (2.1 – 2.4) Chemical laws – Chemical laws – start with slide 8 for content, 3-7 FYI slidesstart with slide 8 for content, 3-7 FYI slides

Path to the atomPath to the atom Modern atomic structure (2.5)Modern atomic structure (2.5) Molecules vs. Ions (2.6)Molecules vs. Ions (2.6) Naming molecular and ionic compounds Naming molecular and ionic compounds

(2.8)(2.8) Introduction to the periodic table (2.7)Introduction to the periodic table (2.7)

History of ChemistryHistory of Chemistry

Greek Philosophers: 5th Century BCEGreek Philosophers: 5th Century BCE (BCE = before the common era - replaces BC)(BCE = before the common era - replaces BC)

The Greek philosophers were the first to The Greek philosophers were the first to reflect on the nature of matter.  reflect on the nature of matter.  They proposed that all matter is made out of They proposed that all matter is made out of

first 4 elements -- earth, air , water, fire.  first 4 elements -- earth, air , water, fire.  Aristotle added a fifth element, plasma (also Aristotle added a fifth element, plasma (also called ether). called ether). 

Greek PhilosophersGreek Philosophers

Democritus had an alternate view of Democritus had an alternate view of matter.  He proposed that matter was  matter.  He proposed that matter was  made up of tiny particles called atoms.  made up of tiny particles called atoms.  His "theory" was not well accepted at the time. His "theory" was not well accepted at the time.

AlchemyAlchemy

Alchemy: ~600-1600's CEAlchemy: ~600-1600's CE (CE = common era, replaces AD)(CE = common era, replaces AD) Alchemy developed at about the same time in Alchemy developed at about the same time in

China, India, and Greece. It spread into China, India, and Greece. It spread into Europe in the 8th century. Europe in the 8th century.

AlchemyAlchemy

Alchemists had two pursuitsAlchemists had two pursuits1.1. Search for a means to convert “base” metals Search for a means to convert “base” metals

into goldinto gold

2.2. Search for the elixir of lifeSearch for the elixir of life• Substance that would lead to immortalitySubstance that would lead to immortality

AlchemyAlchemy

Advances from AlchemyAdvances from Alchemy Many new substances where identifiedMany new substances where identified

• Plaster of Paris, nitric acid….Plaster of Paris, nitric acid…. New lab techniques and equipment New lab techniques and equipment

developeddeveloped New medicines identifiedNew medicines identified

Modern Chemistry, ~1600 onModern Chemistry, ~1600 on First chemists/physicists to use scientific methodFirst chemists/physicists to use scientific method

Boyle - elementsBoyle - elements Lavoisier – law of conservation of matterLavoisier – law of conservation of matter Proust - law of definite proportionsProust - law of definite proportions Dalton – law of multiple proportions, atomic theoryDalton – law of multiple proportions, atomic theory Avogadro - hypothesisAvogadro - hypothesis Thomson – charge to mass ratio for an electronThomson – charge to mass ratio for an electron Millikan – charge on the electronMillikan – charge on the electron Bequerel and the Curies - radioactivityBequerel and the Curies - radioactivity Rutherford – nuclear atomRutherford – nuclear atom

Modern ChemistryModern Chemistry

Robert Boyle: ~1660Robert Boyle: ~1660 Proposed a substance to be an Proposed a substance to be an elementelement

unless it can be broken down into simpler unless it can be broken down into simpler substances.substances. Proposed one of the gas laws – CH 5Proposed one of the gas laws – CH 5

Lavoisier: ~1760Lavoisier: ~1760

Law of Conservation of MatterLaw of Conservation of Matter Matter is neither created nor destroyed in a Matter is neither created nor destroyed in a

chemical reaction. chemical reaction.

Proust: late 1700sProust: late 1700s

Law of Definite Composition/ProportionsLaw of Definite Composition/Proportions A given compound always contains the same A given compound always contains the same

proportion of elements by mass.proportion of elements by mass.

John John Dalton: ~1800: ~1800

Law of Multiple ProportionsLaw of Multiple Proportions When two elements form more than one When two elements form more than one

compound, the ratios of the masses of the compound, the ratios of the masses of the second element that combines with one gram second element that combines with one gram of the first element can always be reduced to of the first element can always be reduced to small whole numbers. small whole numbers.

Law of Multiple Proportions Law of Multiple Proportions ExampleExample

Consider two 100.0 g samples 2 different Consider two 100.0 g samples 2 different compounds containing only C and H. compounds containing only C and H. Compound A: 27.2 g of CCompound A: 27.2 g of C

Compound B: 42.9 g of C. Compound B: 42.9 g of C.

Show how this data illustrates the law of Show how this data illustrates the law of multiple proportions.multiple proportions.

Dalton also proposed the first table of Dalton also proposed the first table of atomic massesatomic masses Most masses later need revisionMost masses later need revision

Dalton is best known for proposing Dalton is best known for proposing Atomic Atomic TheoryTheory

Dalton’s Atomic TheoryDalton’s Atomic Theory

1.1. Elements are made up of tiny particles Elements are made up of tiny particles called atoms.called atoms.

• Atoms are indivisible and indestructibleAtoms are indivisible and indestructible

2.2. Atoms of a given element are identicalAtoms of a given element are identical Atoms of different elements differ in some Atoms of different elements differ in some

fundamental way(s)fundamental way(s)

Dalton’s Atomic TheoryDalton’s Atomic Theory

3.3. Compounds form when atoms of Compounds form when atoms of different elements combine with each different elements combine with each other.other.

A given compound always has the same A given compound always has the same relative number and types of elements.relative number and types of elements.

Dalton’s Atomic TheoryDalton’s Atomic Theory

4.4. Chemical reactions occur when atoms Chemical reactions occur when atoms change how they are bound to each change how they are bound to each other.other.

Individual atoms are not changed, just Individual atoms are not changed, just rearrangedrearranged

Avogadro: 1811Avogadro: 1811

Avogadro's Avogadro's HypothesisHypothesis At the same temperature and pressure equal At the same temperature and pressure equal

volumes of gases contain the same number of volumes of gases contain the same number of particles.particles.• Based on Guy-Lussac’s dataBased on Guy-Lussac’s data• See page 41/42See page 41/42

From Dalton to Atomic StructureFrom Dalton to Atomic Structure

Dalton’s atomic theory lead to much Dalton’s atomic theory lead to much research on the nature of the atom.research on the nature of the atom.

This research showed the atom to made This research showed the atom to made up of smaller particles.up of smaller particles.

J.J. ThomsonJ.J. Thomson

Thomson measured the deflection of a Thomson measured the deflection of a cathode ray beam in electrical and cathode ray beam in electrical and magnetic fields of known strengths. magnetic fields of known strengths.

+

-

(+)

Metal electrode

(-)Metal electrode

Cathode ray tube experiment, pg 43

Cathode ray Applied electrical field

Thomson found the cathode rays were Thomson found the cathode rays were attracted by the positive charge and repelled attracted by the positive charge and repelled by negativeby negative

These findings clearly indicated that the rays These findings clearly indicated that the rays consisted of negatively charged particles. consisted of negatively charged particles. • Today we know these particles as electrons. Today we know these particles as electrons.

Thomson measured the deflection of the beam Thomson measured the deflection of the beam in a magnetic field and more! From his data he in a magnetic field and more! From his data he determined the charge:mass ratio for an electrondetermined the charge:mass ratio for an electron

e e = - 1.76 x 10 = - 1.76 x 1088 C/g C/gmm

e = charge on the electron in coulombse = charge on the electron in coulombs

M = mass of an electron in gramsM = mass of an electron in grams

Cathode ray tube experiment

Thomson also found that the cathode ray Thomson also found that the cathode ray particles were identical regardless of particles were identical regardless of source. source. Concluded all elements contain these Concluded all elements contain these

negative particles (electrons)negative particles (electrons)

J.J. ThomsonJ.J. Thomson

Thomson: Thomson: identified cathode ray beams as a stream of identified cathode ray beams as a stream of

negatively charged particles negatively charged particles calculated the charge to mass ratio for these calculated the charge to mass ratio for these

negatively charged particles negatively charged particles proposed the existence of positively charged proposed the existence of positively charged

particles particles • To balance the negative charge of the electronsTo balance the negative charge of the electrons

Millikan ~1909Millikan ~1909

Millikan’s oil drop experiment allowed him allowed him to determine the charge on an electronto determine the charge on an electron This charge can be plugged into Thomson’s This charge can be plugged into Thomson’s

formula and the mass of the electron formula and the mass of the electron calculatedcalculated• Mass electron = 9.11 x 10Mass electron = 9.11 x 10-31-31 kg kg

• Page 44Page 44

RadioactivityRadioactivity

Becquerel, Marie and Pierre Curie: ~1896Becquerel, Marie and Pierre Curie: ~1896 Henri Becquerel - observed the natural emission Henri Becquerel - observed the natural emission

of energy/rays by uranium. of energy/rays by uranium.

Marie and Pierre Curie studied “Becquerel's Marie and Pierre Curie studied “Becquerel's rays”. rays”. The Curies’ findings suggested that matter was The Curies’ findings suggested that matter was

composed of smaller particles than atoms.composed of smaller particles than atoms. The Curies coined the term radioactivity to describe The Curies coined the term radioactivity to describe

the rays emitted. the rays emitted.

RadioactivityRadioactivity

Three types of radioactivity were identified:Three types of radioactivity were identified: gamma rays - very high energy lightgamma rays - very high energy light beta particles - high energy electronsbeta particles - high energy electrons alpha particles - Healpha particles - He+2+2 particles particles

• 2 protons and 2 neutrons2 protons and 2 neutrons

Plum Pudding Model of the AtomPlum Pudding Model of the Atom

In the early 1900’s the accepted model of In the early 1900’s the accepted model of the atom was called the plum pudding the atom was called the plum pudding model of the atommodel of the atom Electrons (tiny and negatively charged) were Electrons (tiny and negatively charged) were

pictured to be dispersed in a ‘cloud’ of positive pictured to be dispersed in a ‘cloud’ of positive charge. charge. • Proposed by JJ Thomson and Lord Kelvin in 1904Proposed by JJ Thomson and Lord Kelvin in 1904

Rutherford and the Nuclear AtomRutherford and the Nuclear Atom

In 1911 an experiment conducted in Ernest In 1911 an experiment conducted in Ernest Rutherford’s lab showed the “plum pudding” Rutherford’s lab showed the “plum pudding” model to be incorrect.model to be incorrect. Experiment was conducted by Geiger and Experiment was conducted by Geiger and

Marsden and the findings interpreted by Marsden and the findings interpreted by Rutherford.Rutherford.

See page 45See page 45

Rutherford’s AtomRutherford’s Atom

First to propose a First to propose a nuclearnuclear atom. atom. An atom has a dense positive center An atom has a dense positive center

containing all of positive charge and most of containing all of positive charge and most of the mass of the atom – the nucleusthe mass of the atom – the nucleus

Electrons are scattered in the empty space Electrons are scattered in the empty space around the nucleusaround the nucleus• Electrons occupy a volume that is huge as Electrons occupy a volume that is huge as

compared to the size of the nucleus. compared to the size of the nucleus.

A New Model of the AtomA New Model of the Atom

Expected based onExpected based on

Plum pudding modelPlum pudding model

Rutherford’s modelRutherford’s model

Based on ”his” resultsBased on ”his” results

Modern Atomic StructureModern Atomic Structure

Rutherford continued to study the atom Rutherford continued to study the atom and the positive matter of the atom.and the positive matter of the atom. 1919, + particle named the proton1919, + particle named the proton

~1932 James Chadwick proposed the ~1932 James Chadwick proposed the existence of a third subatomic particle, the existence of a third subatomic particle, the neutron.neutron.

Subatomic ParticlesSubatomic Particles

Subatomic Particle

Charge Mass, amu Location in atom

Electron (e-)

-1 0 amu Outside of nucleus

Proton (p) +1 ~1 amu Nucleus

Neutron (n) 0 ~1 amu Nucleus

Mass of Subatomic ParticlesMass of Subatomic Particles

Protons and neutrons have ~ the same Protons and neutrons have ~ the same mass mass (in the range of 10 (in the range of 10 -27-27 kg). kg). Mass of each and of individual atoms is often Mass of each and of individual atoms is often

expressed in amu rather than gramsexpressed in amu rather than grams• Atomic mass unit (amu) – 1/12 the mass of a Atomic mass unit (amu) – 1/12 the mass of a

carbon-12 atomcarbon-12 atom

Mass of Subatomic ParticlesMass of Subatomic Particles

The mass of the electron The mass of the electron (10(10-31-31 kg) kg) is tiny as is tiny as compared to that of the proton and compared to that of the proton and neutron neutron (10(10-27-27 kg) kg) . . Therefore, the electron’s mass is considered Therefore, the electron’s mass is considered

to be ~0 amu when calculating the mass of an to be ~0 amu when calculating the mass of an atom.atom.

Subatomic Particles and the Subatomic Particles and the Elements Elements

Each element has a unique number of Each element has a unique number of protons.protons. Number of protons defines the element.Number of protons defines the element.

6

C

Atomic # = # protons

Subatomic ParticlesSubatomic Particles

Since atoms are neutral, for every proton Since atoms are neutral, for every proton there is a/n _________.there is a/n _________.

When atoms interact to form compounds, When atoms interact to form compounds, it is their ___________ that interact.it is their ___________ that interact.

TermsTerms

Mass number = sum of the # of protons Mass number = sum of the # of protons and the # neutrons in the nucleus of an and the # neutrons in the nucleus of an atomatom FOR MOST ELEMENTS THE MASS FOR MOST ELEMENTS THE MASS

NUMBER IF NOT ON THE PERIODIC NUMBER IF NOT ON THE PERIODIC TABLE.TABLE.• You will be given enough information to determine You will be given enough information to determine

mass number or number of neutrons.mass number or number of neutrons.

TermsTerms

Isotopes = atoms of a given element that Isotopes = atoms of a given element that differ in mass numberdiffer in mass number Isotopes have the same number of Isotopes have the same number of

_____________._____________. Isotopes differ in the number of _______.Isotopes differ in the number of _______.

IsotopesIsotopes

Writing atomic symbols for isotopesWriting atomic symbols for isotopes pg 46pg 46

B5

11

Atomic #

Mass # Symbol for element

FAQ - IsotopesFAQ - Isotopes

When is mass number found on the When is mass number found on the periodic table?periodic table?

What’s the atomic mass? Is it the same What’s the atomic mass? Is it the same as the mass number? as the mass number?

Po

84 (209)

C

6 12.0107

Molecules and Ions Molecules and Ions (2.6)(2.6)

Atoms of different elements combine to Atoms of different elements combine to form compoundsform compounds Atoms in compounds are held together by Atoms in compounds are held together by

chemical bonds.chemical bonds.• Bonds involve interactions of the bonding atoms’ Bonds involve interactions of the bonding atoms’

________________

BondingBonding

There are two types of bonds:There are two types of bonds:1.1. Covalent bonds – bonding atoms share Covalent bonds – bonding atoms share

electronselectrons• Atoms are always nonmetal atomsAtoms are always nonmetal atoms• Covalently bonded atoms form moleculesCovalently bonded atoms form molecules• Ways to represent moleculesWays to represent molecules

Chemical formula; HChemical formula; H22OO Structural formulaStructural formula

OO

H HH H

BondingBonding

2.2. Ionic bonds – attractive force among Ionic bonds – attractive force among oppositely charged ionsoppositely charged ions

• Bond formed between metal cations and Bond formed between metal cations and nonmetal anionsnonmetal anions

• No molecules involvedNo molecules involved

Ions - TermsIons - Terms

Ion – charged atom or group of atomsIon – charged atom or group of atoms Formed when atoms gain or lose electronsFormed when atoms gain or lose electrons

Cation – positively charged ionCation – positively charged ion Formed when an atom _______ electronsFormed when an atom _______ electrons

Anion – negatively charged ionAnion – negatively charged ion Formed when an atom ______ electronsFormed when an atom ______ electrons

IonsIons

Describing ion formationDescribing ion formation Cation example: Cation example:

Anion example:Anion example:

Naming Binary CompoundsNaming Binary Compounds

Binary compounds – compound composed Binary compounds – compound composed of 2 elementsof 2 elements NaClNaCl

COCO

COCO22

Types of Binary CompoundsTypes of Binary Compounds

Type I binary ionic compoundsType I binary ionic compounds Metal forms only one ionMetal forms only one ion

Type II binary ionic compoundsType II binary ionic compounds Metal forms more than one ionMetal forms more than one ion Use roman numerals to indicate the charge Use roman numerals to indicate the charge

on the ionon the ion Type III binary covalent compoundsType III binary covalent compounds

Compound between 2 nonmetalsCompound between 2 nonmetals

Types I Binary CompoundsTypes I Binary Compounds

Compound between a metal and a Compound between a metal and a nonmetalnonmetal Metal forms only one ionMetal forms only one ion

Name the cation and then the anion.Name the cation and then the anion. Name of the cation is the name of the elementName of the cation is the name of the element Name of the anion is the name of the Name of the anion is the name of the

nonmetal with the ending changed to “ide”nonmetal with the ending changed to “ide”

Monoatomic cations to knowMonoatomic cations to know

Group #Group # Charge on ionCharge on ion examplesexamples

IAIA +1+1 NaNa1+1+ sodium (ion) sodium (ion)

KK1+1+ potassium (ion) potassium (ion)

IIAIIA +2+2 MgMg2+2+ magnesium (ion) magnesium (ion)

IIIA IIIA metalsmetals

+3+3 AlAl3+3+ aluminum (ion) aluminum (ion)

Monoatomic anions to knowMonoatomic anions to knowGroup #Group # Charge on ionCharge on ion examplesexamples

VAVA -3-3 NN3-3- nitride (ion) nitride (ion)

PP3-3- phosphide (ion) phosphide (ion)

VIAVIA -2-2 OO2-2- oxide (ion) oxide (ion)

SS2- 2- sulfidesulfide

VIIAVIIA -1-1 FF1-1- fluoride (ion) fluoride (ion)

ClCl1-1- chloride (ion) chloride (ion)

BrBr1-1- bromide (ion) bromide (ion)

II1-1- iodide (ion) iodide (ion)

PracticePractice

Name Name chemical formula chemical formula

Chemical formula Chemical formula name name