Atomos: Not to Be Cut The History of Atomic Theory

Atomic Models This model of the atom may look familiar to you. This is the Bohr model. In this model, the nucleus is orbited by electrons, which are in different energy levels. This model of the atom may look familiar to you. This is the Bohr model. In this model, the nucleus is orbited by electrons, which are in different energy levels. A model uses familiar ideas to explain unfamiliar facts observed in nature. A model uses familiar ideas to explain unfamiliar facts observed in nature. A model can be changed as new information is collected. A model can be changed as new information is collected.

The atomic model has changed throughout the centuries, starting in 400 BC, when it looked like a billiard ball → The atomic model has changed throughout the centuries, starting in 400 BC, when it looked like a billiard ball →

Who are these men? In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.

Democritus This is the Greek philosopher Democritus who began the search for a description of matter more than 2400 years ago. This is the Greek philosopher Democritus who began the search for a description of matter more than 2400 years ago. He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided? He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided? 400 BC

Atomos His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained. His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained. This piece would be indivisible. This piece would be indivisible. He named the smallest piece of matter “atomos,” meaning “not to be cut.” He named the smallest piece of matter “atomos,” meaning “not to be cut.”

Atomos  To Democritus, atoms were small, hard particles that were all made of the same material but were different shapes and sizes.  Atoms were infinite in number, always moving and capable of joining together.

This theory was ignored and forgotten for more than 2000 years! This theory was ignored and forgotten for more than 2000 years!

Why? The eminent philosophers of the time, Aristotle and Plato, had a more respected, (and ultimately wrong) theory. The eminent philosophers of the time, Aristotle and Plato, had a more respected, (and ultimately wrong) theory. Aristotle and Plato favored the earth, fire, air and water approach to the nature of matter. Their ideas held sway because of their eminence as philosophers. The atomos idea was buried for approximately 2000 years.

Dalton’s Model In the early 1800s, the English Chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms. In the early 1800s, the English Chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms.

Dalton’s Theory He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles. He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles. Atoms of the same element are exactly alike. Atoms of the same element are exactly alike. Atoms of different elements are different. Atoms of different elements are different. Compounds are formed by the joining of atoms of two or more elements. Compounds are formed by the joining of atoms of two or more elements.

. This theory became one of the foundations of modern chemistry. This theory became one of the foundations of modern chemistry.

Thomson’s Plum Pudding Model In 1897, the English scientist J.J. Thomson provided the first hint that an atom is made of even smaller particles. In 1897, the English scientist J.J. Thomson provided the first hint that an atom is made of even smaller particles.

Thomson Model He proposed a model of the atom that is sometimes called the “Plum Pudding” model. He proposed a model of the atom that is sometimes called the “Plum Pudding” model. Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding. Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding.

Thomson Model Thomson studied the passage of an electric current through a gas. Thomson studied the passage of an electric current through a gas. As the current passed through the gas, it gave off rays of negatively charged particles. As the current passed through the gas, it gave off rays of negatively charged particles.

Thomson Model This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from? This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from? Where did they come from?

Thomson concluded that the negative charges came from within the atom. A particle smaller than an atom had to exist. The atom was divisible! Thomson called the negatively charged “corpuscles,” today known as electrons. Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom. But he could never find them.

Rutherford’s Gold Foil Experiment In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure. In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure.

Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick) Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick)

Rutherford experiment Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all. Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all. Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges. Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.

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This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material. This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material. Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.” Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.” He called the center of the atom the “nucleus” He called the center of the atom the “nucleus” The nucleus is tiny compared to the atom as a whole. The nucleus is tiny compared to the atom as a whole.

Rutherford Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge. Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge.

Bohr Model In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level. In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level.

Bohr Model According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus. According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.

Wave Model

The Wave Model Today’s atomic model is based on the principles of wave mechanics. Today’s atomic model is based on the principles of wave mechanics. According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun. According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.

The Wave Model In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has. In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has. According to the modern atomic model, at atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral. According to the modern atomic model, at atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral.

Electron Cloud: A space in which electrons are likely to be found. A space in which electrons are likely to be found. Electrons whirl about the nucleus billions of times in one second Electrons whirl about the nucleus billions of times in one second They are not moving around in random patterns. They are not moving around in random patterns. Location of electrons depends upon how much energy the electron has. Location of electrons depends upon how much energy the electron has.

Electron Cloud: Depending on their energy they are locked into a certain area in the cloud. Depending on their energy they are locked into a certain area in the cloud. Electrons with the lowest energy are found in the energy level closest to the nucleus Electrons with the lowest energy are found in the energy level closest to the nucleus Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus. Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

IndivisibleElectronNucleusOrbit Electron Cloud Greek X Dalton X Thomson X Rutherford X X Bohr X X X Wave X X X

The Periodic Table I. History II. Arrangement of Elements III. Electron Configuration Trends IV. Periodic Trends V. Reactivity

A. Johann Dobreiner’s Law of Triads in 1817

B. John Newlands – Law of Octaves

C. Lothar Meyer ( German) P roperties of elements show a P roperties of elements show a repetitive pattern when they are repetitive pattern when they are arranged by atomic mass arranged by atomic mass D.Dimitri Mendeleev ( Russian) (father of modern periodic table) (father of modern periodic table) Published system used today (1869) 2. Elements arranged by increasing mass 3. Left spaces for elements not yet discovered - predicted properties discovered - predicted properties (scandium, gallium, germanium) (scandium, gallium, germanium)

Dimitri Mendelev

Mendeleev’s Table His table re-organized

Mendeleev’s Periodic Table

E. Henry Mosley ( ) English 1.Arrange elements by increasing atomic number – this led to the periodic law by increasing atomic number – this led to the periodic law 2. Periodic Law - properties of elements are periodic of elements are periodic functions of their atomic # functions of their atomic # periodic repetition of periodic repetition of physical and chemical physical and chemical properties properties

II. Arrangement of Elements A. Periodic Table – arrangement of elements in order of increasing atomic number so that elements with similar properties are in the same column period – horizontal row (7) period – horizontal row (7) group(family)- vertical columns (1-18) group(family)- vertical columns (1-18) periodicity – reoccurrence of similar periodicity – reoccurrence of similar properties of elements in groups properties of elements in groups

C. Special Groups on the Periodic Table

D. Periodic Table Showing s,p,d,f Blocks

E. Metals – Metalloids - Nonmetals 1. Metals are on the left side – all are solids except mercury (Hg) except mercury (Hg) a. elements near the left of a period are more metallic than those near the right a. elements near the left of a period are more metallic than those near the right b. elements near the top of a group are more metallic than those near the bottom b. elements near the top of a group are more metallic than those near the bottom 2. Metalloids – group of elements between metals and nonmetals(B,Si,Ge,As,Sb,Te) metals and nonmetals(B,Si,Ge,As,Sb,Te) 3. Nonmetals are on the right side – all are solids or gases except bromine(Br) liquid solids or gases except bromine(Br) liquid

Metals – Metalloids - Nonmetals

PROPERTY METAL NONMETAL Luster highlow Deformability malleablebrittle and ductile and ductile Conductivity good poor Electron gain/lose lose gain Ion formed cation (+) anion(-) Ionization energy lowhigh Electronegativity lowhigh

IV.Periodic Trends(Main Group Elements) A. Atomic Radii 1. atomic radius is ½ the distance 1. atomic radius is ½ the distance between nuclei of identical atoms between nuclei of identical atoms joined in a molecule joined in a molecule 2. decreases across periods (left-right) 2. decreases across periods (left-right) a. caused by increasing attraction a. caused by increasing attraction between protons and electrons between protons and electrons 3. increases from top to bottom 3. increases from top to bottom a. caused by adding electrons to a. caused by adding electrons to new shells new shells

What is the atomic radius? Atomic radii include the region in which electrons are found 90% of the time

Atomic Size Atomic Radius = half the distance between two nuclei of a diatomic molecule. Atomic Radius = half the distance between two nuclei of a diatomic molecule. } Radius

Periodic Trends in Atomic Radii

Trends in Main Groups Trends in Main Groups

Atomic Radii Period Trends

A. Periodic Trends in Atomic Radii

B. Ionization Energy 1. Energy required to remove an electron from an atom of an element (KJ/mol) from an atom of an element (KJ/mol) 2. Increases across periods (left to right) a. result of increased nuclear attraction a. result of increased nuclear attraction 3. Decreases down groups (families) a. electrons added to higher energy levels a. electrons added to higher energy levels b. shielding effect of inner shell electrons b. shielding effect of inner shell electrons c. repulsion of inner shell electrons c. repulsion of inner shell electrons 4. Energy to remove second and third electron is greater

B. Trend in Ionization Energy

B. Periodic Trends in Ionization Energy

SymbolFirstSecond Third H He Li Be B C N O F Ne

C. Electronegativity 1. Measures how strongly one atom attracts the electrons of another atom when they form a compound 2. Increases across periods (left to right) a. Fluorine has greatest value of 4 a. Fluorine has greatest value of 4 3. Decreases down groups a. electrons far from the nucleus in a. electrons far from the nucleus in larger atoms have less attraction larger atoms have less attraction b. Cesium and Francium with large radii b. Cesium and Francium with large radii have the smallest electronegativity have the smallest electronegativity

Periodic Trends in Electronegativity

C. Periodic Trends in Electronegativity

D. Ionic Radii 1. Ion – atom that acquires a charge by gaining or losing electrons gaining or losing electrons a. cation (+) ion anion (-) ion a. cation (+) ion anion (-) ion 2. Period trends a. cation radii decrease across periods a. cation radii decrease across periods b. anion radii increase across periods b. anion radii increase across periods 3. Group trends a. increase in cation and anion radii a. increase in cation and anion radii down groups down groups

Formation of an Anion (- ion)

D. Comparison of Atomic and Ionic Radii

D. Periodic Trends in Ionic Radii

E. Electron Affinity 1. Energy change that occurs when an electron is added to a neutral atom 2. If it is easy to add an electron to an atom the energy value is negative atom the energy value is negative a. halogens have large negative values a. halogens have large negative values 3. If it is difficult to add an electron to an atom the energy value is positive atom the energy value is positive a. atoms in groups 2 and 18 have high a. atoms in groups 2 and 18 have high positive values (due to filled subshells) positive values (due to filled subshells) b. usually higher values in larger atoms b. usually higher values in larger atoms

Electron Affinity for Chlorine

Periodic Trends in Electron Affinity

PERIODIC TRENDS

Periodic Trends in Melting Point

Periodic Trends in Density

V. Reactivity A. Reactivity – measure of the tendency of an element to engage in chemical reactions by losing, gaining or sharing electrons 1. atoms of reactive elements are very 1. atoms of reactive elements are very likely to gain, lose or share electrons likely to gain, lose or share electrons 2. atoms of reactive elements are likely to form chemical bonds with other elements 2. atoms of reactive elements are likely to form chemical bonds with other elements

B. Reactivity and the Periodic Table 1. alkali metals (group 1) most reactive 1. alkali metals (group 1) most reactive metals metals 2. alkaline earth metals (group 2) 2. alkaline earth metals (group 2) second most reactive group of metals second most reactive group of metals 3. halogens (group 17) most reactive 3. halogens (group 17) most reactive nonmetals nonmetals 4. noble gases (group 18) least reactive 4. noble gases (group 18) least reactive C.Ionization Energy and Electronegativity 1. elements with very high and very 1. elements with very high and very low values are very reactive low values are very reactive

Electron Arrangement and Reactivity

Electron Configuration S block [groups 1 and 2] S block [groups 1 and 2] P block [groups 13,14,15,16,17,18] P block [groups 13,14,15,16,17,18] D block [groups 3,4,5,6,7,8,9,10,11,12] D block [groups 3,4,5,6,7,8,9,10,11,12] F block (lanthanide and actinide series) F block (lanthanide and actinide series)

1s 1 group 1 1s 2 2s 1 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 1 H 1 Li 3 Na 11 K 19 Rb 37 Cs 55 Fr 87

Alkali metals all end in s 1 Alkali metals all end in s 1 Alkaline earth metals all end in s 2 Alkaline earth metals all end in s 2 Should include He but helium has the properties of the noble gases. Should include He but helium has the properties of the noble gases. - its outer shell is filled with the - its outer shell is filled with the maximum number of electrons maximum number of electrons allowed for the first shell (2) allowed for the first shell (2) s2s2 s1s1 S- block

He 2 Ne 10 Ar 18 Kr 36 Xe 54 Rn 86 1s 2 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6

The P-block p1p1 p2p2 p3p3 p4p4 p5p5 p6p6

Transition Metals -d block d1d1 d2d2 d3d3 s1d5s1d5 d5d5 d6d6 d7d7 d8d8 s 1 d 10 d 10

F - block inner transition elements- hold a maximum of 14 therefore there are 14 elements in both the actinides and lanthanides inner transition elements- hold a maximum of 14 therefore there are 14 elements in both the actinides and lanthanides

Group Ion Formed Electron Changes Group Ion Formed Electron Changes Group 1X + Group 1X + Group 2X 2+ Group 2X 2+ Group 13X 3+ Group 13X 3+ Group 14X varies Group 14X varies Group 15X 3- Group 15X 3- Group 16X 2- Group 16X 2- Group 17X - Group 17X - Group 18X 0 Group 18X 0 Loses 1 electron Loses 1 electron Loses 2 electrons Loses 2 electrons Loses 3 electrons Loses 3 electrons Varies Varies Gains 3 electrons Gains 3 electrons Gains 2 electrons Gains 2 electrons Gains 1 electron Gains 1 electron Does not gain or lose electrons Does not gain or lose electrons