Chapter 4 The Structure of the Atom. Section 4.1—Early Theories of Matter Science as we know it did not exist several thousand years ago. Curiosity sparked

Chapter 4Chapter 4

The Structure of the The Structure of the AtomAtom

Section 4.1—Early Section 4.1—Early Theories of MatterTheories of Matter

Science as we know it did not exist Science as we know it did not exist several thousand years ago. several thousand years ago. Curiosity sparked the Curiosity sparked the investigations of most scholarly investigations of most scholarly thinkers and they based their thinkers and they based their thoughts on life experiences.thoughts on life experiences.

The prefix The prefix ““philphil”” means means lovingloving or or deardear & is seen in many science & & is seen in many science & non-science words. non-science words. ““PhilosophyPhilosophy”” refers to a love of knowledge.refers to a love of knowledge.

DemocritusDemocritus

Section 4.1—Early Section 4.1—Early Theories of MatterTheories of Matter Democritus was a Greek philosopher Democritus was a Greek philosopher

and the 1and the 1stst person to propose the idea person to propose the idea that matter was not infinitely divisible. that matter was not infinitely divisible. He also thought that:He also thought that: Matter is composed of empty space through which atoms Matter is composed of empty space through which atoms

movemove Atoms are solid, homogeneous, indestructible, & indivisibleAtoms are solid, homogeneous, indestructible, & indivisible Different kinds of atoms have different sizes & shapesDifferent kinds of atoms have different sizes & shapes Apparent changes in matter result from changes in the Apparent changes in matter result from changes in the

atoms themselvesatoms themselves The differing properties of matter are due to the size, shape, The differing properties of matter are due to the size, shape,

& movement of the atoms& movement of the atoms


Democritus idea of the atomic Democritus idea of the atomic ““theorytheory”” was rejected because he could not was rejected because he could not answer the question of what held the answer the question of what held the atoms together. Also, the most atoms together. Also, the most influential Greek philosopher Aristotle influential Greek philosopher Aristotle rejected Democritusrejected Democritus’’ theory just theory just because it did not agree with his own because it did not agree with his own ideas of nature. ideas of nature.


In 1808, another atomic theory In 1808, another atomic theory was published by John Dalton, a was published by John Dalton, a schoolteacher in England. schoolteacher in England.

DaltonDalton’’s theory marks s theory marks

the beginning of the the beginning of the

development of moderndevelopment of modern

atomic theory. atomic theory.

Section 4.1—Early Section 4.1—Early Theories of MatterTheories of Matter Dalton revised DemocritusDalton revised Democritus ’’s ideas based s ideas based

upon the results of scientific research he upon the results of scientific research he conducted. Dalton thought that:conducted. Dalton thought that: All matter is composed of extremely small particles called All matter is composed of extremely small particles called

atomsatoms All atoms of a given element are identical, having the same All atoms of a given element are identical, having the same

size, mass, & chemical properties. Atoms of a specific element size, mass, & chemical properties. Atoms of a specific element are different from those of any other element are different from those of any other element

Atoms cannot be created, divided into smaller particles, or Atoms cannot be created, divided into smaller particles, or destroyed destroyed

Different atoms combine in simple whole-number ratios to Different atoms combine in simple whole-number ratios to form compounds form compounds

In a chemical reaction, atoms are separated, combined, or In a chemical reaction, atoms are separated, combined, or rearranged rearranged


DaltonDalton’’s theory easily explained s theory easily explained the law of conservation of massthe law of conservation of mass

DaltonDalton’’s theory has received 2 s theory has received 2 revisions over timerevisions over time atoms are divisible into several atoms are divisible into several

subatomic particlessubatomic particles atoms of an element may have atoms of an element may have

slightly different massesslightly different masses


Atom—smallest particle of an element Atom—smallest particle of an element that retains the properties of the elementthat retains the properties of the element

Scanning tunneling microscope allows us Scanning tunneling microscope allows us to see atoms and to actually move atoms to see atoms and to actually move atoms to form shapes, patterns, & simple to form shapes, patterns, & simple machines. This has lead to the discovery machines. This has lead to the discovery of of nanotechnologynanotechnology—the atom-by-atom —the atom-by-atom building of machines the size of building of machines the size of molecules. molecules.

Scanning tunneling Scanning tunneling microscopemicroscope


Molecule—is a group of atoms that Molecule—is a group of atoms that are bonded together & act as a are bonded together & act as a unitunit


**Draw a double bubble map of **Draw a double bubble map of DaltonDalton’’s & Democrituss & Democritus’’s atomic s atomic theory.theory.

Section 4.2—Subatomic Section 4.2—Subatomic Particles & the Nuclear AtomParticles & the Nuclear Atom

In the 1800s, scientists were looking for In the 1800s, scientists were looking for a relationship between matter & electric a relationship between matter & electric charge.charge.

Cathode ray tube—glass tube of which Cathode ray tube—glass tube of which most of the air and matter had been most of the air and matter had been sealed out of with electrodes connected sealed out of with electrodes connected to the ends of the tube and then to a to the ends of the tube and then to a battery discovered by William Crookesbattery discovered by William Crookes negative terminal end—cathodenegative terminal end—cathode positive terminal end—anodepositive terminal end—anode


As a result of continued research, As a result of continued research, Crookes was convinced thatCrookes was convinced that cathode rays were actually a stream of cathode rays were actually a stream of

charged particlescharged particles the particles carried a negative chargethe particles carried a negative charge

These negatively charged particles These negatively charged particles were found to be in all matter and were found to be in all matter and were called electrons.were called electrons.


As a result of William Crookes cathode ray As a result of William Crookes cathode ray tube, one of the most important tube, one of the most important technological & social developments was technological & social developments was discovered—the television.discovered—the television.


J.J. Thomson, an English physicist, J.J. Thomson, an English physicist, began to run cathode ray experiments began to run cathode ray experiments to measure the ratio of the electronto measure the ratio of the electron’’s s charge to its mass. After obtaining the charge to its mass. After obtaining the ratio, he compared it to other known ratio, he compared it to other known ratios, for instance the hydrogen atom. ratios, for instance the hydrogen atom. Thomson found that the mass of the Thomson found that the mass of the electron was lighter than that of electron was lighter than that of hydrogen, which disproved part of hydrogen, which disproved part of DaltonDalton’’s atomic theory (atoms cans atomic theory (atoms can’’t be t be divided into smaller particles).divided into smaller particles).


In 1909, American physicist Robert In 1909, American physicist Robert Millikan determined the actual charge Millikan determined the actual charge of an electron, of an electron, -1-1. Knowing the mass . Knowing the mass to charge ratio and the charge of an to charge ratio and the charge of an electron, Millikan was able to electron, Millikan was able to determine the mass of a single electrondetermine the mass of a single electron—9.1x10—9.1x10-28-28 g or 1/1840 mass of a g or 1/1840 mass of a hydrogen atom. hydrogen atom.


It was known that matter is neutral It was known that matter is neutral because you donbecause you don’’t go around getting t go around getting shocked when you touch any object. shocked when you touch any object. So it was proposed that electrons were So it was proposed that electrons were evenly spaced within a uniformly evenly spaced within a uniformly distributed positive charged. This was distributed positive charged. This was known as the known as the ““plum puddingplum pudding”” model. model. AKA chocolate-chip cookie dough AKA chocolate-chip cookie dough model.model.


In 1911, Ernest Rutherford conducted an In 1911, Ernest Rutherford conducted an experiment which led to the rejection of the experiment which led to the rejection of the ““plum puddingplum pudding”” model. Using gold and an model. Using gold and an alpha particle emitting source, Rutherford alpha particle emitting source, Rutherford calculated that an atom consisted mostly of calculated that an atom consisted mostly of empty space through which the electrons empty space through which the electrons move. He also coined the term nucleus--the move. He also coined the term nucleus--the tiny, dense region in the center of the atom tiny, dense region in the center of the atom that contained most of the atomthat contained most of the atom’’s positive s positive charge & virtually all of its mass. charge & virtually all of its mass. RutherfordRutherford’’s new theory was called the s new theory was called the nuclear atomic theory. nuclear atomic theory.

Gold foil experimentGold foil experiment


In 1919, Rutherford fine-tuned his concept In 1919, Rutherford fine-tuned his concept of the nucleus, stating that it contained of the nucleus, stating that it contained positively charged subatomic particles positively charged subatomic particles equal to but opposite that of an electron equal to but opposite that of an electron (+1 charge)—proton. (+1 charge)—proton.

In 1932, Rutherford & his co-worker, James In 1932, Rutherford & his co-worker, James Chadwick, concluded that the nucleus Chadwick, concluded that the nucleus contained yet another subatomic particle, a contained yet another subatomic particle, a neutral particle called the neutron, having a neutral particle called the neutron, having a mass nearly equal to that of a proton. mass nearly equal to that of a proton.


The mass of the nucleus (protons The mass of the nucleus (protons & neutrons) is about 99.7% of the & neutrons) is about 99.7% of the atomatom’’s total mass.s total mass.

**Draw a double bubble map about **Draw a double bubble map about ThomsonThomson’’s s ““plum puddingplum pudding”” atomic atomic model and Rutherfordmodel and Rutherford’’s nuclear s nuclear atomic model.atomic model.

Section 4.3—How Atoms Section 4.3—How Atoms DifferDiffer

Not long after RutherfordNot long after Rutherford ’’s gold foil s gold foil experiment, Henry Moseley discovered experiment, Henry Moseley discovered that atoms of each element contain a that atoms of each element contain a unique positive charge in their nuclei. unique positive charge in their nuclei. The number of protons in an atom is The number of protons in an atom is referred to as the elementreferred to as the element ’’s atomic s atomic number. number.

The periodic table is arranged left-to-The periodic table is arranged left-to-right, top-to-bottom by increasing atomic right, top-to-bottom by increasing atomic number. number.


Remember that all atoms are neutral—Remember that all atoms are neutral—SO, if Atomic SO, if Atomic number = number of protons = number number = number of protons = number

of electronsof electrons How many protons are in each type of How many protons are in each type of

atom?atom?

Gold (Au) _______Gold (Au) _______

Silver (Ag) _________Silver (Ag) _________

Potassium (K) ________Potassium (K) ________

exampleexample

elemenelementt

AtomiAtomic #c #

ProtonProtonss

electroelectronsns

AA PbPb 8282

BB 88

CC 3030

Practice problemsPractice problems

1.1. How many protons & electrons are in How many protons & electrons are in each of the following atoms?each of the following atoms?

a.a. BoronBoron c. c. Platinum Platinum b.b. RadonRadon d. d. MagnesiumMagnesium

2.2. An atom of an element contains 66 An atom of an element contains 66 electrons. What element is it?electrons. What element is it?

3.3. An atom of an element contains 14 An atom of an element contains 14

protons. What element is it?protons. What element is it?

**worksheet **worksheet Determine the element, symbol, # of Determine the element, symbol, # of

p, n, e, atomic #, or atomic mass p, n, e, atomic #, or atomic mass where needed.where needed.


Isotopes have the same number of protons & Isotopes have the same number of protons & electrons but different numbers of neutrons.electrons but different numbers of neutrons.

Most elements in nature are a mixture of Most elements in nature are a mixture of isotopes. Isotopes with more neutrons have isotopes. Isotopes with more neutrons have higher mass numbers—sum of the number of higher mass numbers—sum of the number of protons & the number of neutrons in the protons & the number of neutrons in the nucleus. To make it easier to identify each of nucleus. To make it easier to identify each of the various isotopes of the elements, chemists the various isotopes of the elements, chemists add the mass number after the name. add the mass number after the name. Chemists also use abbreviations to represent Chemists also use abbreviations to represent isotopes also. isotopes also.

Fig 4-15, p 100Fig 4-15, p 100


Mass number – atomic number = Mass number – atomic number = number of neutronsnumber of neutrons

107107 109109

47 47 ArAr 47 47 ArAr

Example 4-2Example 4-2 & practice b-f & practice b-f

Determine the number of protons, Determine the number of protons, electrons, & neutrons in the electrons, & neutrons in the isotope of neon. Also, name the isotope of neon. Also, name the isotope given.isotope given. element Atomic # Mass

number

a. neon 10 22

b. calcium 20 46

c. oxygen 8 17

d. iron 26 57

e. zinc 30 64

f. mercury 80 204


You can calculate the atomic mass You can calculate the atomic mass of any element if you know its of any element if you know its number of isotopes, their masses, number of isotopes, their masses, & their % abundances. & their % abundances.

Example 4-3Example 4-3

Calculate the atomic mass of Calculate the atomic mass of unknown element X. Then identify unknown element X. Then identify the unknown element, which is the unknown element, which is used medically to treat some used medically to treat some mental disorders.mental disorders. IsotopeIsotope Mass Mass

(amu)(amu)Percent Percent abundanceabundance

66XX 6.0156.015 7.5%7.5%

77XX 7.0167.016 92.5%92.5%

PracticePractice

1. Boron has 2 naturally occurring isotopes: Boron-10 (abundance= 19.8%, mass= 10.013 amu), boron-11 (abundance= 80.2%, mass= 11.009 amu). Calculate the atomic mass of boron

2. Helium has 2 naturally occurring isotopes, helium-3 & helium-4. The atomic mass of helium is 4.003 amu. Which isotope is more abundant in nature?

3. Calculate the atomic mass of magnesium. The 3 magnesium isotopes have atomic masses & relative abundances of 23.985 amu (78.99%), 24.986 amu (10.00%), & 25.982 amu (11.01%).

Section 4.4—Unstable Nuclei Section 4.4—Unstable Nuclei & Radioactive Decay& Radioactive Decay

In a chemical reaction, only the electrons are In a chemical reaction, only the electrons are involved in the reaction—NOT the particles of involved in the reaction—NOT the particles of the nucleus. This is the reason that an atoms the nucleus. This is the reason that an atoms identity does not change during a chemical identity does not change during a chemical reaction. reaction.

However, there are some reactions that DO However, there are some reactions that DO involve the changing of an atoms nucleus—involve the changing of an atoms nucleus—nuclear reactions. In the late 1890s, nuclear reactions. In the late 1890s, scientists noticed that some substances scientists noticed that some substances spontaneously emitted radiation in a process spontaneously emitted radiation in a process called radioactivity. The actual rays & called radioactivity. The actual rays & particles emitted were called radiation. particles emitted were called radiation.


Radioactive atoms emit Radioactive atoms emit radiation because their radiation because their nuclei are unstable. To nuclei are unstable. To gain stability, they emit gain stability, they emit radiation so that they radiation so that they can lose energy, trying can lose energy, trying to gain stability—a to gain stability—a process called process called radioactive decay. radioactive decay.

There are 3 types of There are 3 types of radiation:radiation:

Radiation Type

Symbol Mass (amu)

Charge

Alpha α 4 2+

Beta β 1/1840 1-

Gamma γ 0 0


A nuclear equation shows the atomic number A nuclear equation shows the atomic number & mass number of the particles involved. It is & mass number of the particles involved. It is important to note that in a nuclear equation, important to note that in a nuclear equation, both mass number & atomic number are both mass number & atomic number are conserved.conserved.

The primary reason that atoms are not stable The primary reason that atoms are not stable is the neutron-to-proton ratio. Eventually, is the neutron-to-proton ratio. Eventually, radioactive atoms undergo enough radioactive radioactive atoms undergo enough radioactive decay to form stable, non-reactive atoms—decay to form stable, non-reactive atoms—this explains their rare existence in nature.this explains their rare existence in nature.

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Chapter 4 The Structure of the Atom. Section 4.1—Early Theories of Matter Science as we know it did not exist several thousand years ago. Curiosity sparked