Atoms, Molecules, and Ions

Atoms, Molecules, and Atoms, Molecules, and IonsIons

Chemistry Timeline #1Chemistry Timeline #1B.C. 400 B.C. Demokritos and Leucippos use the term "atomos”

1500's Georg Bauer: systematic metallurgy Paracelsus: medicinal application of minerals

1600'sRobert Boyle:The Skeptical Chemist. Quantitative experimentation, identification of elements

1700s'Georg Stahl: Phlogiston Theory Joseph Priestly: Discovery of oxygen Antoine Lavoisier: The role of oxygen in combustion, law of conservation of mass, first modern chemistry textbook

2000 years of Alchemy

Chemistry Timeline #2Chemistry Timeline #2

1800's Joseph Proust: The law of definite proportion (composition) John Dalton: The Atomic Theory, The law of multiple proportions Joseph Gay-Lussac: Combining volumes of gases, existence of diatomic molecules Amadeo Avogadro: Molar volumes of gases Jons Jakob Berzelius: Relative atomic masses, modern symbols for the elements Dmitri Mendeleyev: The periodic table J.J. Thomson: discovery of the electron Henri Becquerel: Discovery of radioactivity

1900's Robert Millikan: Charge and mass of the electron Ernest Rutherford: Existence of the nucleus, and its relative size Meitner & Fermi: Sustained nuclear fission Ernest Lawrence: The cyclotron and trans-uranium elements

Laws• Conservation of Mass• Law of Definite Proportion –

– compounds have a constant composition.

– They react in specific ratios by mass.• Multiple Proportions-

– When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers.

Proof• Mercury has two oxides.

– One is 96.2 % mercury by mass, the other is 92.6 % mercury by mass.

• Show that these compounds follow the law of multiple proportion.

• Speculate on the formula of the two oxides.

Dalton’s Atomic Theory Dalton’s Atomic Theory (1808)(1808)

Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged

All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties

John Dalton

Modern Atomic TheoryModern Atomic TheorySeveral changes have been made to Dalton’s theory.

Dalton said:

Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties

Modern theory states:Atoms of an element have a

characteristic average mass which is unique to that element.

Modern Atomic Theory #2Modern Atomic Theory #2

Dalton said:

Modern theory states:

Atoms cannot be subdivided, created, or destroyed

Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions!

Atomic ParticlesAtomic ParticlesParticle Charge Mass (kg) Location

Electron

-1 9.109 x 10-31 Electron cloud

Proton +1 1.673 x 10-27 Nucleus

Neutron

0 1.675 x 10-27 Nucleus

The Atomic The Atomic ScaleScale

Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud) Most of the volume of the atom is empty space

“q” is a particle called a “quark”

About Quarks…About Quarks…Protons and neutrons are NOT fundamental particles.Protons are made of two “up” quarks and one “down” quark.Neutrons are made of one “up” quark and two “down” quarks.

Quarks are held together by “gluons”

IsotopesIsotopes Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.

Isotope Protons

Electrons

Neutrons

Nucleus

Hydrogen–1

(protium)

1 1 0

Hydrogen-2 (deuterium

)

1 1 1

Hydrogen-3 (tritium)

1 1 2

Atomic Atomic MassesMasses

Isotope Symbol Composition of the nucleus

% in nature

Carbon-12

12C 6 protons 6 neutrons

98.89%

Carbon-13

13C 6 protons 7 neutrons

1.11%

Carbon-14

14C 6 protons 8 neutrons

<0.01%

Atomic mass is the average of all the naturally isotopes of that element.Carbon = 12.011

MoleculesMolecules

Two or more atoms of the same or different elements, covalently bonded together.

Molecules are discrete structures, and their formulas represent each atom present in the molecule.

Benzene, C6H6

Covalent Network Covalent Network SubstancesSubstances

Covalent network substances have covalently bonded atoms, but do not have discrete formulas.

Why Not??

Graphite Diamond

IonsIonsIonsIons Cation: A positive ion Cation: A positive ion

• MgMg2+2+, NH, NH44++

Anion: A negative ion Anion: A negative ion ClCl, SO, SO44

22

Ionic Bonding: Force of attraction Ionic Bonding: Force of attraction between oppositely charged ions. between oppositely charged ions.

Ionic compounds form Ionic compounds form crystalscrystals, so their , so their formulas are written empirically (lowest formulas are written empirically (lowest whole number ratio of ions).whole number ratio of ions).

Periodic Table with Group Names

This slide contains This slide contains classified material and classified material and

cannot be shown to high cannot be shown to high school students. Please school students. Please

continue as if everything is continue as if everything is normal.normal.

Discovery of the ElectronDiscovery of the ElectronIn 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

Thomson’s Atomic Thomson’s Atomic ModelModel

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Rutherford’s Gold Foil Rutherford’s Gold Foil ExperimentExperiment

Alpha particles are helium nuclei Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recorded

The Puzzle of the AtomThe Puzzle of the Atom Protons and electrons are attracted to each other because of opposite charges

Electrically charged particles moving in a curved path give off energy

Despite these facts, atoms don’t collapse

c = C = speed of light, a constant (3.00 x 108 m/s)

= frequency, in units of hertz (hz, sec-1)

= wavelength, in meters

Electromagnetic radiation Electromagnetic radiation propagates through space as a wave propagates through space as a wave moving at the speed of light.moving at the speed of light.

Types of electromagnetic radiation:Types of electromagnetic radiation:

Long Wavelength

= Low Frequency

= Low ENERGY

Short Wavelength

= High Frequency

= High ENERGY

Wavelength TableWavelength Table

The Wave-like ElectronThe Wave-like Electron

Louis deBroglie

The electron propagates through space on an energy

wave. To understand the atom, one must

understand the behavior of

electromagnetic waves.

Toupee?

The Great The Great Niels Bohr (1885 - 1962)

…produces all of the colors in a continuous spectrum

Spectroscopic analysis of the visible Spectroscopic analysis of the visible spectrum…spectrum…

…produces a “bright line” spectrum

Spectroscopic analysis of the Spectroscopic analysis of the hydrogen spectrum…hydrogen spectrum…

This produces bands of light with definite wavelengths.

Electron Electron transitionstransitionsinvolve jumps of involve jumps of definite amounts definite amounts ofofenergy.energy.

Bohr Model Energy Levels

Schrodinger Wave EquationSchrodinger Wave Equation

22

2 2

8dh EV

m dx

Equation for probabilityprobability of a single electron being found along a single axis (x-axis)Erwin Schrodinger

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple

You can find out where the electron is, but not where it is going.

OR…

You can find out where the electron is going, but not where it is!

“One cannot simultaneously determine both the position and momentum of an electron.”

Werner Heisenberg

Quantum NumbersQuantum Numbers

Each electron in an atom has a unique set of 4 quantum numbers which describe it.

Principal quantum number Angular momentum quantum number Magnetic quantum number Spin quantum number

(n)(l)

(m)(s)

Principal Quantum NumberPrincipal Quantum NumberGenerally symbolized by n, it denotes the shell (energy level) in which the electron is located.

Number of electrons that can fit in a shell:

2n2

Angular Momentum Quantum Angular Momentum Quantum NumberNumber

The angular momentum quantum number, generally symbolized by l, denotes the orbital (subshell) in which the electron is located.

l =3f

Magnetic Quantum NumberMagnetic Quantum NumberThe magnetic quantum number, generally symbolized by m, denotes the orientation of the electron’s orbital with respect to the three axes in space.

Assigning the NumbersAssigning the Numbers The three quantum numbers (n, l, and m) are integers. The principal quantum number (n) cannot be zero. n must be 1, 2, 3, etc. The angular momentum quantum number (l ) can be any integer between 0 and n - 1. For n = 3, l can be either 0, 1, or 2. The magnetic quantum number (ml) can be any integer between -l and +l. For l = 2, m can be either -2, -1, 0, +1, +2.

Principle, angular momentum, and Principle, angular momentum, and magnetic quantum numbers: magnetic quantum numbers: nn, , ll, and , and mmll

Pauli Exclusion PrinciplePauli Exclusion Principle

No two electrons in an atom can have the same four quantum numbers.

Wolfgang Pauli

Spin Quantum NumberSpin Quantum NumberSpin quantum number denotes the behavior (direction of spin) of an electron within a magnetic field.

Possibilities for electron spin:

1

2

1

2

Orbital shapes are defined as the surface that contains 90% of the total electron probability.

An orbital is a region within an atom where thereAn orbital is a region within an atom where thereis a probability of finding an electron. This is a is a probability of finding an electron. This is a probability diagram for the s orbital in the probability diagram for the s orbital in the first first energy level…energy level…

Orbitals of the same shape (s, for instance) grow larger as n increases…

Nodes are regions of low probability within an orbital.

Sizes of Sizes of ss orbitals orbitals

Orbitals in outer energy levels DO penetrate into lower energy levels.

This is a probability Distribution for a 3s orbital.

What parts of the diagram correspond to “nodes” – regions of zero probability?

Penetration #1

The s orbital has a spherical shape centered around the origin of the three axes in space.

s orbital shape

There are three peanut-shaped p orbitals in each energy level above n = 1, each assigned to its own axis (x, y and z) in space.

PP orbital shape orbital shape

Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of:

…and a “peanut with a donut”!

d orbital shapes

“double peanut”

Shape of f orbitalsShape of f orbitals

Things get even more complicated with the seven f orbitals that are found in the f sublevels beginning with n = 4. To remember the shapes, think of:

Flower

Orbital filling tableOrbital filling table

Element Configuration notation

Orbital notation Noble gas notation

Lithium 1s22s1 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s1

Beryllium 1s22s2 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2

Boron 1s22s2p1 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p1

Carbon 1s22s2p2 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p2

Nitrogen 1s22s2p3 ____ ____ ____ ____ ____

1s 2s 2p

[He]2s2p3

Oxygen 1s22s2p4 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p4

Fluorine 1s22s2p5 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p5

Neon 1s22s2p6 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p6

Electron configuration of the Electron configuration of the elements of the first three elements of the first three

seriesseries

Irregular confirmations of Cr and CuIrregular confirmations of Cr and Cu

Chromium steals a 4s electron to half fill its 3d sublevel

Copper steals a 4s electron to FILL its 3d sublevel

0% 0% 0%0%0%

1. energy is emitted2. energy is absorbed3. no change in energy

occurs4. light is emitted5. none of these

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32

gamma ra

ys

micr

owaves

radio w

aves

infra

red ra

dia...

x-ray

s

0% 0% 0%0%0%

1. gamma rays2. microwaves3. radio waves4. infrared radiation5. x-rays

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32

2 5 10 18 6

0% 0% 0%0%0%

1. 22. 53. 104. 185. 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32

0% 0% 0%0%0%0%

n l m s

1. 1 1 0 ½2. 3 0 0 –½3. 2 1 –1 ½4. 4 3 –2 –½5. 4 2 0 ½

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32

1s22s2

2p63s23p...

1s22s2

2p63s23p...

1s23s2

2p63s23p...

1s22s2

2p63s23p...

none of these

0% 0% 0%0%0%

1. 1s22s22p63s23p64s23d104p65s24d105p15d10

2. 1s22s22p63s23p64s23d104d104p1

3. 1s23s22p63s23p64s24d104p65s25d105p1

4. 1s22s22p63s23p64s23d104p65s24d105p1

5. none of these

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32

Periodicity

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

}Radius

Influenced by three factors. Energy Level

› Higher energy level is further away. Charge on nucleus

› More charge pulls electrons in closer. Shielding

› Layers of electrons shield from nuclear pull.

The electron on the outside energy level has to look through all the other energy levels to see the nucleus

The electron on the outside energy level has to look through all the other energy levels to see the nucleus.

A second electron has the same shielding.

As we go down a group

Each atom has another energy level,

So the atoms get bigger.

HLi

Na

K

Rb

As you go across a period the radius gets smaller.

Same energy level. More nuclear charge. Outermost electrons are closer.

Na Mg Al Si P S Cl Ar

Table of Table of

Atomic Atomic RadiiRadii

Cations form by losing electrons. Cations are smaller that the atom they

come from. Metals form cations. Cations of representative elements

have noble gas configuration.

Anions form by gaining electrons. Anions are bigger that the atom they

come from. Nonmetals form anions. Anions of representative elements

have noble gas configuration.

Atomic Number

Ato

mic

Radiu

s (n

m)

H

Li

Ne

Ar

10

Na

K

Kr

Rb

The amount of energy required to completely remove an electron from a gaseous atom.

Removing one electron makes a +1 ion.

The energy required is called the first ionization energy.

The second ionization energy is the energy required to remove the second electron.

Always greater than first IE. The third IE is the energy required to

remove a third electron. Greater than 1st of 2nd IE.

Symbol First Second ThirdH

HeLiBeBCNOF Ne

1312 2731 520 900 800 1086 1402 1314 1681 2080

5247 7297 1757 2430 2352 2857 3391 3375 3963

11810 14840 3569 4619 4577 5301 6045 6276

The greater the nuclear charge the greater IE.

Distance from nucleus increases IE Filled and half filled orbitals have lower

energy, so achieving them is easier, lower IE.

Shielding

As you go down a group first IE decreases because

The electron is further away. More shielding.

All the atoms in the same period have the same energy level.

Same shielding. Increasing nuclear charge So IE generally increases from left to

right. Exceptions at full and 1/2 fill orbitals.

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

He He has a greater IE

than H. same shielding greater nuclear

charge H

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He Li has lower IE than H more shielding further away outweighs greater nuclear

charge

Li

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He Be has higher IE than Li same shielding greater nuclear charge

Li

Be

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He B has lower IE than Be same shielding greater nuclear charge By removing an electron we

make s orbital half filled

Li

Be

B

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He

Li

Be

B

C

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He

Li

Be

B

C

N

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He

Li

Be

B

C

N

O

Breaks the pattern because removing an electron gets to 1/2 filled p orbital

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He

Li

Be

B

C

N

O

F

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He

Li

Be

B

C

N

O

F

Ne Ne has a lower

IE than He Both are full, Ne has more

shielding Greater distance

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

H

He

Li

Be

B

C

N

O

F

Ne Na has a lower

IE than Li Both are s1

Na has more shielding

Greater distance

Na

Firs

t Io

niz

ati

on e

nerg

y

Atomic number

Full Energy Levels are very low energy. Noble Gases have full orbitals. Atoms behave in ways to achieve noble

gas configuration.

Affinity tends to increase across a period

Affinity tends to decrease as you go down in a period

Electrons farther from the nucleus experience less nuclear attraction

Some irregularities due to repulsive forces in the relatively small p orbitals

Electron AffinityElectron Affinity - the energy change - the energy change associated with the addition of an electronassociated with the addition of an electron

Table of Electron AffinitiesTable of Electron Affinities

The tendency for an atom to attract electrons to itself when it is chemically combined with another element.

How fair it shares. Big electronegativity means it pulls the

electron toward it. Atoms with large negative electron

affinity have larger electronegativity.

The further down a group the farther the electron is away and the more electrons an atom has.

More willing to share. Low electronegativity.

Metals are at the left end. They let their electrons go easily Low electronegativity At the right end are the nonmetals. They want more electrons. Try to take them away. High electronegativity.

Ionization energy, electronegativityElectron affinity INCREASE

Atomic size increases, shielding constant

Ionic size increases

Another Way to Look at Ionization Energy

Yet Another Way to Look at Ionization Energy

Summary of Periodic Summary of Periodic TrendsTrends