Chapter 4 AtomicStructure IRON ATOMS. Section 4.1 – Defining the Atom All matter is composed of atoms. All matter is composed of atoms. An atom is the.

Chapter 4Chapter 4

AtomicAtomic

StructureStructure

IRON ATOMS

Section 4.1 – Defining the AtomSection 4.1 – Defining the Atom

All All mattermatter is composed of is composed of atomsatoms..An An atomatom is the smallest particle of an is the smallest particle of an

elementelement that retains its that retains its identityidentity in a in a chemical reaction.chemical reaction.

DemocritusDemocritus believed that believed that

atoms were atoms were indivisibleindivisible and and

indestructible.indestructible.

Dalton’s Atomic TheoryDalton’s Atomic Theory All All elementselements are composed of tiny indivisible are composed of tiny indivisible

particles called particles called atomsatoms.. AtomsAtoms of the same element are of the same element are identicalidentical. The . The

atomsatoms of any one element of any one element differdiffer from those of any from those of any other element.other element.

AtomsAtoms of different elements can of different elements can physicallyphysically mix mix together or can together or can chemicallychemically combine in simple combine in simple whole-number ratioswhole-number ratios to form compounds. to form compounds.

Chemical reactionsChemical reactions occur when atoms are occur when atoms are separated, joined, or rearranged. separated, joined, or rearranged. AtomsAtoms of one of one element, however, are element, however, are nevernever changed into atoms of changed into atoms of another element as a result of a another element as a result of a chemical reactionchemical reaction..

Sizing up the AtomSizing up the AtomThe The radiiradii of most atoms fall within the of most atoms fall within the

range of range of 5 x 105 x 10-11-11mm to 2 x 10 to 2 x 10-10-10m.m. If you could line up 100,000,000 copper If you could line up 100,000,000 copper

atoms side by side, they would produce a atoms side by side, they would produce a line only line only 1 cm1 cm long!! long!!

Despite their small size, Despite their small size,

individual individual atomsatoms are are

observable with observable with

instruments such as instruments such as

scanning tunneling microscopesscanning tunneling microscopes..IRON ATOMS

4.1 Section Assessment4.1 Section Assessment

1. In your own words, state the main ideas 1. In your own words, state the main ideas of Dalton’s atomic theory.of Dalton’s atomic theory.

2. According to Dalton’s theory, is it possible 2. According to Dalton’s theory, is it possible to convert atoms of one element into to convert atoms of one element into atoms of another?atoms of another?

3. A sample of copper with a mass of 63.5g 3. A sample of copper with a mass of 63.5g contains 6.02 x 10contains 6.02 x 102323 atoms. Calculate the atoms. Calculate the mass of a single copper atom.mass of a single copper atom.

1 Cu atom x 63.5g = 1.05 x 10-22 g 6.02 x 1023 Cu atoms

Section 4.2 – Structure of the Section 4.2 – Structure of the Nuclear AtomNuclear Atom

Three kinds of subatomic particles are Three kinds of subatomic particles are electrons, protons, and neutronselectrons, protons, and neutrons..

Subatomic Particle

Symbol ChargeRelative

MassLocation

Electron e- -1 1/1840 Electron Cloud

Proton p+ +1 1 Nucleus

Neutron n0 0 1 Nucleus

ElectronsElectrons

In 1897, the English physicist In 1897, the English physicist J. J. ThomsonJ. J. Thomson discovered the discovered the electronelectron..

ElectronsElectrons are are negativelynegatively charged subatomic charged subatomic particles.particles.

Thomson discovered Thomson discovered electronselectrons by studying a by studying a cathode ray tubecathode ray tube. .

A A cathode raycathode ray is a glowing beam that travels is a glowing beam that travels from a from a cathodecathode to an anode. to an anode.

Cathode Ray TubeCathode Ray Tube

ProtonsProtons

AtomsAtoms have no have no netnet electric charge; they electric charge; they are electrically are electrically neutralneutral..

In 1886, In 1886, Eugen GoldsteinEugen Goldstein found evidence found evidence for for positivelypositively charged particles with he charged particles with he found rays traveling in the opposite found rays traveling in the opposite direction of the direction of the cathode raycathode ray..

These These positivelypositively charged particles are charged particles are called called protonsprotons. .

NeutronsNeutrons

In 1932, the English physicist In 1932, the English physicist James James ChadwickChadwick confirmed the confirmed the

existence of existence of neutronsneutrons..NeutronsNeutrons are subatomic are subatomic

particles with particles with no chargeno charge. .

Plum Pudding ModelPlum Pudding Model

The The plum puddingplum pudding model shows electrons model shows electrons dispersed in a large dispersed in a large positively positively charged charged area.area.

Rutherford’s ExperimentRutherford’s ExperimentRutherfordRutherford decided to test the plum decided to test the plum

pudding model by shooting pudding model by shooting alpha particlesalpha particles (helium atoms with no electrons) at a thin (helium atoms with no electrons) at a thin sheet of sheet of gold foilgold foil..

The particles should pass through the foil The particles should pass through the foil with slight with slight deflectiondeflection..

HOWEVER, many HOWEVER, many alpha alpha particlesparticles passed passed straightstraight

through, and some through, and some particles actually particles actually bounced bounced

backback..

Rutherford’s ExperimentRutherford’s Experiment

Rutherford’s ExperimentRutherford’s ExperimentRutherfordRutherford proposed that the atom is proposed that the atom is

mostly mostly empty spaceempty space, thus explaining the , thus explaining the lack of lack of deflectiondeflection of most of the alpha of most of the alpha particles.particles.

He concluded that all the He concluded that all the positive chargepositive charge and most of the and most of the massmass are concentrated in are concentrated in a small region and has a positive charge a small region and has a positive charge called the called the nucleusnucleus..

The The nucleusnucleus is the tiny central core of an is the tiny central core of an atom and is composed of atom and is composed of protons and protons and neutronsneutrons..

Rutherford’s ExperimentRutherford’s Experiment

Atomic StructureAtomic Structure In the nuclear atom, In the nuclear atom,

the the protons and protons and

neutronsneutrons are located are located

in the in the nucleusnucleus..The The electronselectrons are are

distributed around distributed around

the nucleus and the nucleus and

occupy almost all occupy almost all

of the of the volumevolume..

4.2 Section Assessment4.2 Section Assessment

1. What are the three types of subatomic 1. What are the three types of subatomic particles?particles?

2. How does the Rutherford model describe 2. How does the Rutherford model describe the structure of atoms?the structure of atoms?

3. What are the charges and relative 3. What are the charges and relative masses of the three main subatomic masses of the three main subatomic particles?particles?

4. Compare Rutherford’s expected outcome 4. Compare Rutherford’s expected outcome of the gold-foil experiment with the actual of the gold-foil experiment with the actual outcome.outcome.

4.2 Section Assessment4.2 Section Assessment

5. What experimental evidence led 5. What experimental evidence led Rutherford to conclude that an atom is Rutherford to conclude that an atom is mostly empty space?mostly empty space?

6. How did Rutherford’s model of the atom 6. How did Rutherford’s model of the atom differ from Thomson’s plum pudding differ from Thomson’s plum pudding model?model?

Section 4.3 – Distinguishing Among Section 4.3 – Distinguishing Among AtomsAtoms

ElementsElements are different because they are different because they contain different numbers of contain different numbers of protonsprotons..

The The atomic numberatomic number of an element is the of an element is the number of number of protonsprotons in the in the nucleusnucleus of an of an atom of that element.atom of that element.

The The atomic numberatomic number identifies an element. identifies an element.Atoms are electrically Atoms are electrically neutralneutral, so the , so the

number of number of protonsprotons equals the number of equals the number of electronselectrons..

Atomic MassAtomic Mass

Practice ProblemsPractice Problems15. Complete the table.15. Complete the table.

16. How many protons and electrons are in 16. How many protons and electrons are in each atom?each atom?a. fluorinea. fluorineb. calciumb. calciumc. aluminumc. aluminum

Mass NumberMass Number

Most of the Most of the massmass of an atom is of an atom is concentrated in the concentrated in the nucleusnucleus made of made of protons and neutrons.protons and neutrons.

The total number of The total number of protonsprotons and and neutronsneutrons is the is the mass numbermass number..

The number of The number of neutronsneutrons in an atom is the in an atom is the difference between the difference between the mass numbermass number and and the the atomic numberatomic number..

ShorthandShorthandAtomic information can be written in two Atomic information can be written in two

forms of forms of shorthandshorthand..The first form has the symbol of the The first form has the symbol of the

element with the element with the mass numbermass number as a as a superscript and the superscript and the atomic numberatomic number as a as a subscript. subscript.

The second form is the The second form is the

element element namename followed followed

by the by the atomic massatomic mass..

Ex. gold-197Ex. gold-197

Periodic TablePeriodic Table

On the On the periodic tableperiodic table the element symbol the element symbol is in the middle with the is in the middle with the atomic numberatomic number above and the above and the mass numbermass number below. below.

ATOMIC NUMBER

ELEMENT SYMBOL

MASS NUMBER

Number of Subatomic ParticlesNumber of Subatomic Particles

Practice ProblemsPractice Problems

17. How many neutrons are in each atom?17. How many neutrons are in each atom?

18. Express the composition of each atom in 18. Express the composition of each atom in the other type of shorthand form.the other type of shorthand form.a. carbon-12a. carbon-12

b. fluorine-19b. fluorine-19

c. beryllium-9c. beryllium-9

IsotopesIsotopes IsotopesIsotopes are atoms that have the same number are atoms that have the same number

of of protonsprotons but different number of but different number of neutronsneutrons..Because Because isotopesisotopes of an element have different of an element have different

numbers of numbers of neutronsneutrons, they also have different , they also have different mass numbersmass numbers..

Practice ProblemsPractice Problems

19. Three isotopes of oxygen are oxygen-19. Three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18. Write the 16, oxygen-17, and oxygen-18. Write the symbol for each, including the atomic symbol for each, including the atomic number and mass number.number and mass number.

20. Three isotopes of chromium are 20. Three isotopes of chromium are chromium-50, chromium-52, and chromium-50, chromium-52, and chromium-53. How many neutrons are in chromium-53. How many neutrons are in each isotope?each isotope?

Atomic MassAtomic Mass

An An atomic mass unit (amu)atomic mass unit (amu) is defined as is defined as one twelfth of a carbon-12 atom.one twelfth of a carbon-12 atom.

Atomic massAtomic mass is measured in is measured in amusamus.. In nature, most elements occur as a In nature, most elements occur as a

mixture of two or more mixture of two or more isotopesisotopes..The The atomic massatomic mass of an element is the of an element is the

weighted weighted averageaverage mass of the atoms in a mass of the atoms in a naturally occurring sample of the element.naturally occurring sample of the element.

Atomic MassAtomic Mass

Practice ProblemsPractice Problems

21. Boron has two isotopes: boron-10 and 21. Boron has two isotopes: boron-10 and boron-11. Which is more abundant, given boron-11. Which is more abundant, given that the atomic mass of boron is 10.81 that the atomic mass of boron is 10.81 amu?amu?

22. There are three isotopes or silicon; they 22. There are three isotopes or silicon; they have mass numbers of 28, 29, and 30. have mass numbers of 28, 29, and 30. The atomic mass of silicon is 28.086 amu. The atomic mass of silicon is 28.086 amu. Comment on the relative abundance of Comment on the relative abundance of these three isotopes.these three isotopes.

Atomic MassAtomic Mass

To calculate the To calculate the atomic massatomic mass of an of an element, multiply the element, multiply the massmass of each of each isotopeisotope by its by its natural abundancenatural abundance, expressed as a , expressed as a decimal, and then add the products.decimal, and then add the products.

For example, carbon has two stable isotopes: For example, carbon has two stable isotopes: Carbon-12 with a mass of 12.000 amu, which has a Carbon-12 with a mass of 12.000 amu, which has a

natural abundance of 98.89%, andnatural abundance of 98.89%, and Carbon-13 with a mass of 13.003 amu, which has a Carbon-13 with a mass of 13.003 amu, which has a

natural abundance of 1.11%.natural abundance of 1.11%.

Atomic MassAtomic Mass

10.012 amu x 0.1991 = 1.993 amu11.009 amu x 0.8009 = + 8.817 amu 10.810 amu

Practice ProblemsPractice Problems23. The element copper has naturally 23. The element copper has naturally

occurring isotopes with mass numbers of occurring isotopes with mass numbers of 63 and 65. The relative abundance and 63 and 65. The relative abundance and atomic masses are 69.2% for mass = atomic masses are 69.2% for mass = 62.93 amu, and 30.8% for mass = 64.93 62.93 amu, and 30.8% for mass = 64.93 amu. Calculate the average atomic mass amu. Calculate the average atomic mass of copper.of copper.

24. Calculate the atomic mass of bromine. 24. Calculate the atomic mass of bromine. The two isotopes of bromine have atomic The two isotopes of bromine have atomic masses and relative abundance of 78.92 masses and relative abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%).amu (50.69%) and 80.92 amu (49.31%).

The Periodic TableThe Periodic TableThe The periodic tableperiodic table is an arrangement of is an arrangement of

elementselements in which the elements are in which the elements are separated based on a set of separated based on a set of repeating repeating propertiesproperties..

The Periodic TableThe Periodic Table

Notice that the Notice that the elementselements are listed in order are listed in order of increasing of increasing atomic numberatomic number..

Each Each horizontal rowhorizontal row of the periodic table is of the periodic table is called a called a periodperiod..

Each Each vertical columnvertical column of the periodic table of the periodic table is called a is called a groupgroup..

Elements within a Elements within a groupgroup have similar have similar physical and chemical physical and chemical propertiesproperties..

4.3 Section Assessment4.3 Section Assessment

1. What distinguishes the atoms of one 1. What distinguishes the atoms of one element from the atoms of another?element from the atoms of another?

2. What equation tells you how to calculate 2. What equation tells you how to calculate the number of neutrons in an atom?the number of neutrons in an atom?

3. How do the isotopes of a given element 3. How do the isotopes of a given element differ from on another?differ from on another?

4. What does the number represent in the 4. What does the number represent in the isotope platinum-194? Write the symbol isotope platinum-194? Write the symbol for this atom using the other shorthand.for this atom using the other shorthand.

4.3 Section Assessment4.3 Section Assessment

5. The atomic masses of elements are 5. The atomic masses of elements are generally not whole numbers. Explain why.generally not whole numbers. Explain why.

6. List the number of protons, neutrons, and 6. List the number of protons, neutrons, and electrons in each pair of isotopes.electrons in each pair of isotopes.a. a. 66

33Li, Li, 7733LiLi

b. b. 42422020Ca, Ca, 4444

2020CaCa

c. c. 78783434Se, Se, 8080

3434SeSe

7. Name two elements that have properties 7. Name two elements that have properties similar to those of the element calcium.similar to those of the element calcium.

THE ENDTHE END