Atoms-Molecules-Ions

Dr. Ron RusayDr. Ron Rusay

Spring 2008Spring 2008

© Copyright 2008 R.J. Rusay© Copyright 2008 R.J. Rusay

Aspects of Matter

•Elements, Compounds, and Mixtures (Part 1)•Atomic Theory Today•Elements: The Periodic Table•Ions & Compounds•Compounds: Introduction to Ionic Bonding•Compounds: Formulas & Names (Part 2)•Mixtures: Separation Techniques (Part 3)•Atomic & Molar Masses (Part 4)

Modern History of the Atom 1909: Millikan determines charge and mass of e-1909: Millikan determines charge and mass of e-

1913-19: Rutherford & Bohr’s atom;1913-19: Rutherford & Bohr’s atom;

The proton. The proton. http://www.http://www.yrbeyrbe.edu.on.ca/~.edu.on.ca/~mdhsmdhs/science/chemistry/ch2_2./science/chemistry/ch2_2.htmhtm

1927: Waves & Particles, Quantum Mechanics1927: Waves & Particles, Quantum Mechanicshttp://www.http://www.nmsinmsi.ac.uk/on-line/electron/section3/1927.html.ac.uk/on-line/electron/section3/1927.html

1932: James Chadwick “discovers” the neutron1932: James Chadwick “discovers” the neutronhttp://www.http://www.nmsinmsi.ac.uk/on-line/electron/section3/1932a.html.ac.uk/on-line/electron/section3/1932a.html

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CHEMISTRY of the AtomErnest Rutherford (1871-1937)

Modern History of the Atom1897: J.J. Thomson “discovers” the electron:1897: J.J. Thomson “discovers” the electron:

http://www.http://www.nmsinmsi.ac.uk/on-line/electron/section2/.ac.uk/on-line/electron/section2/

Photo © The Nobel FoundationPhoto © The Nobel Foundation

http://pl.nobel.se/laureates/physics-1906-1-bio.htmlhttp://pl.nobel.se/laureates/physics-1906-1-bio.html

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Milliken Oil Drop Experiment

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

How does an atom relate to nanotechnology?

Consider Powers of 10 (10 x)http://www.eamesoffice.com/powers_of_ten/powers_of_ten.html

http://www.powersof10.com/

Earth = 12,760,000 meters wide (12.76 x 10 6), 12.76 million meters (megameters)

Plant Cell = 0.00001276 meters wide (12.76 x 10 -6) (12.76 millionths of a meter) (12,760 nanometers!)

Nano scale is regarded as < 1,000 nanometers ~1/50 the diameter of a human hair (anything less than a micron (10-6 m). Chemists typically think in views and images of < 1 nanometer (eg. bond lengths and atomic sizes).

• 1 nm = 10 Å• An atom vs. a nucleus ~10,000 x larger

~ 0.1 nm

Nucleus =1/10,000of the atom

Anders Jöns Ångström(1814-1874)

1 Å = 10 picometers = 0.1 nanometers = 10-4 microns = 10-8 centimeters

• 1 nm = 10 Å• An atom vs. a nucleus ~10,000 x larger

Can we “see” and Can we “see” and manipulate atoms manipulate atoms using a microscope?using a microscope?

Yes, using atomic force microscopy (AFM) and Yes, using atomic force microscopy (AFM) and a variety of instruments such as Scanning a variety of instruments such as Scanning Transmission Electron Microscopes.Transmission Electron Microscopes.

TEAM 0.5:TEAM 0.5:LBL’s Latest (2008) LBL’s Latest (2008) TTransmission ransmission EElectron lectron AAberration-corrected berration-corrected MMicroscopeicroscopeResolution:Resolution: +/- 0.5 +/- 0.5 Å

Xe atoms on Ni(110)

Atomic/molecular structures atom-by-atom

STM images courtesy of Don Eigler, IBM, San Jose

Building of a quantum “corral” with Fe atoms on Cu

C

C

H

H

Calculated image (Philippe Sautet)

orbital

pz

TIP

H

O+

Imaging: acetylene on Pd(111) at 28 K

Molecular Image Tip cruising altitude ~700 pmΔz = 20 pm

Surface atomic profile

Tip cruising altitude ~500 pm

Δz = 2 pm

1 cm(± 1 μm)

The STM image is a map of the pi-orbital of distorted acetylene

Why don’t we see the Pd atoms?Because the tip needs to be very close to image the Pd atoms and would knock the molecule away

If the tip was made as big as an airplane, it would be flying at 1 cm from the surface and waving up an down by 1 micrometer

M. Salmeron (LBL)

Excitation of frustrated rotational modes in acetylene molecules on Pd(111) at T = 30 K

Tip

e-

((( ) ( )))

M. Salmeron (LBL)

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CHEMISTRY of the Atom

FUNDAMENTAL PARTICLES:FUNDAMENTAL PARTICLES: MassMass ChargeCharge SymbolSymbol

Nucleus:Nucleus: PROTON PROTON 1 amu 1 amu +1 +1 H+, H, p H+, H, p

• 1.67 x 10 1.67 x 10 -27-27 kg kg

NEUTRON NEUTRON 1 amu 1 amu 0 0 n n• 1.67 x 10 1.67 x 10 -27-27 kg kg

__________________________________________________________________________________ ELECTRON very small -1ELECTRON very small -1 e e - -

• 2000 x smaller than a proton or neutron2000 x smaller than a proton or neutron

The particle is said to “hold” or “bond” atoms together in molecules.

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Periodic Table1

© Copyright 1998-2008 R.J. Rusay© Copyright 1998-2008 R.J. Rusay

• Mendeleev’s Table 1868-1871Mendeleev’s Table 1868-1871Mural at St.Petersburg University, RussiaMural at St.Petersburg University, Russia

QUESTIONThe element found in the 6A family (or group 16) and period four can be toxic and a micronutrient. What is the symbol for that element? You can use any help aid to answer this question except a breathing resource.

1. Sb2. As3. Se4. Te

ANSWERChoice 3 pinpoints an element in both the 6A column and row four. Remember to include the first row of Hydrogen and Helium when counting rows.

Section 2.7: An Introduction to the Periodic Table

Chemical Symbols & Historical Names1

What is the symbol for gold and what was its What is the symbol for gold and what was its original name?original name?

QUESTIONWhich of the following are incorrectly paired?1) Phosphorus, Ph2) Palladium, Pd3) Platinum, Pt4) Lead, Pb5) Potassium, K

ANSWER1) Phosphorus, Pr Section 2.7 An Introduction to the Periodic Table

)

(p. 55

Phosphorus has a symbol of P.

1) Phosphorus, Ph

Section An Introduction to the Periodic Table

QUESTIONOf the following which would not be considered a metalloid?

1. Ge2. Sb3. Se4. Spockonium, element #182 in the Star Trek Periodic Table.

ANSWERChoice 3, Se, is the only element (without considering the possibility of the fictional Spockonium) listed that is not on the accepted Periodic Table’s “stairway” between metals and nonmetals, therefore it is the only non-metalloid listed.

Section 2.7: An Introduction to the Periodic Table

Periodic TablePeriodic TablePeriodic TablePeriodic Table Elements are classified by:Elements are classified by:

properties & atomic numberproperties & atomic number

metals, non-metals, metalloidsmetals, non-metals, metalloids

Groups Groups or or Families Families (vertical)(vertical) 1A = alkali metals1A = alkali metals

2A = alkaline earth metals2A = alkaline earth metals

6A (16) = chalcogens6A (16) = chalcogens

7A (17) = halogens7A (17) = halogens

8A (18) = noble gases8A (18) = noble gases

Periods Periods (horizontal) (horizontal) numbers 1-7numbers 1-7

Group 1 and Group 2 Metals

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Using the Periodic Table

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Atoms, Molecules & Ions

Atoms Atoms (neutral electrostatic charge: (neutral electrostatic charge: # protons# protons = = # electrons# electrons )) • # Protons # Protons = = Atomic NumberAtomic Number• Atomic MassAtomic Mass = = # Protons# Protons + + # of Neutrons# of Neutrons• Isotope: same atomic number but different atomic Isotope: same atomic number but different atomic

mass (different # of neutrons)mass (different # of neutrons)

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QUESTIONWhich among the following represent a set of isotopes? Atomic nuclei containing:

a. 20 protons and 20 neutrons. b. 21 protons and 19 neutrons. c. 22 neutrons and 18 protons. d. 20 protons and 22 neutrons. e. 21 protons and 20 neutrons.

1) a, b, c

2) c, d 3) a, e 4) a, d and b, e 5) No isotopes are indicated.

ANSWER

)

4) a, d and b, e

Section 2.5 The Modern View of Atomic Structure: An Introduction (p. 49

Isotopes have the same number of protons and different numbers of neutrons, so they can be organized by atomic number.

Atoms, Molecules & Ions• Isotopes vary in their relative natural Isotopes vary in their relative natural

abundance.abundance.• Periodic Table’s atomic mass is a Periodic Table’s atomic mass is a

weighted average of all isotopic massesweighted average of all isotopic masses• The mass of sodium, Na, element #11 is The mass of sodium, Na, element #11 is

listed as 22.99 amu. Which isotope is listed as 22.99 amu. Which isotope is naturally present in the larger amount: naturally present in the larger amount: the isotope with 12 neutrons or with 13 the isotope with 12 neutrons or with 13 neutrons? (There is a small percentage neutrons? (There is a small percentage of the isotope with 11 neutrons.)of the isotope with 11 neutrons.)

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Atoms, Molecules & Ions

Atomic Mass of Carbon:Atomic Mass of Carbon:

What is the “weighted” atomic mass?What is the “weighted” atomic mass?

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Exact Mass % Occurence

12.00000 98.98

13.00335 1.011

14.00 negligible

12.00000 x 98.98/100 + 13.00335 x 1.011 =12.00000 x 98.98/100 + 13.00335 x 1.011 =11.8776 + 0.13146 = 12.009011.8776 + 0.13146 = 12.0090

12.0112.01

Atoms, Molecules and Ions1

© Copyright 1998-2008 R.J. Rusay© Copyright 1998-2008 R.J. Rusay

• Atomic Number = 6 (atom’s identity)Atomic Number = 6 (atom’s identity)• CarbonCarbon• Atomic Mass = 13 (isotope 13)Atomic Mass = 13 (isotope 13)• 6 protons; # neutrons = 13 - 66 protons; # neutrons = 13 - 6• neutral atom has 6 electronsneutral atom has 6 electrons

QUESTIONThe average mass of a carbon atom is 12.011. Assuming you were able to pick up only one carbon unit, the chances that you would randomly get one with a mass of 12.011 is 1) 0%. 2) 0.011%. 3) about 12%. 4) 12.011%. 5) greater than 50%.

ANSWER

1) 0%.

Section 3.1 Atomic Mass (p. 77)

The 12.011 is an average of the isotopic masses. None of the isotopes has an exact mass of 12.011.

Atomic SymbolsAtomic Symbols

K Element Symbol

39

19

Mass number

Atomic number

Also written as 39K

Atoms, Molecules and Ions1

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• Atomic Number = 12 (atom’s identity)Atomic Number = 12 (atom’s identity)• Atomic Mass = 24Atomic Mass = 24• 12 protons; # neutrons = 24 - 1212 protons; # neutrons = 24 - 12• neutral atom has 12 electronsneutral atom has 12 electrons• Ion contains 10 electrons: symbol?Ion contains 10 electrons: symbol?

• 12 p12 p++ + 10e + 10e-- = +2 = +2

Mg12

24 +2

Atoms, Molecules and Ions1

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• Atomic Number = 17 (atom’s identity)Atomic Number = 17 (atom’s identity)• Atomic Mass = ?Atomic Mass = ?• # protons = ? ; # neutrons = ?# protons = ? ; # neutrons = ?• neutral atom has ? electronsneutral atom has ? electrons• Ion contains 18 electrons: symbol?Ion contains 18 electrons: symbol?

• 17 p17 p++ + 18e + 18e-- = -1 = -1

Cl17

35 -1

IonsIons

CationCation: A positive ion: A positive ion MgMg2+2+, NH, NH44

++

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

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

QUESTIONCalcium plays several critical roles in the functioning of human cells. However, this form of calcium is the ion made with 20 protons and 18 electrons. Therefore the ion would be…

1. positive and called an anion.2. positive and called a cation.3. negative and called an anion.4. negative and called a cation.

ANSWERChoice 2 provides the correct relationship and name for an atom of calcium (20 protons = 20+) that has lost two electrons (now with 18–). The ion would have a +2 charge. Positive ions are called cations.

Section 2.6: Molecules and Ions

QUESTIONOf the following, which would NOT qualify as an isotope of 35Cl?

1. 36Cl2. 35Cl–

3. 37Cl–

4. 37Cl

ANSWERChoice 2 is NOT an isotope of 35Cl. All three choices represent a form of chlorine but choice 2 has the same number of neutrons as the atom in the question, therefore it does not fit the criteria for isotopes (i.e. variable neutron number with constant proton number). Isotopes can be ions as well as neutral atoms. 37Cl–

and 37Cl are also not isotopes.

Section 2.5: The Modern View of Atomic Structure: An Introduction

NuclearSymbol

Number ofProtons

Number ofNeutrons

Number ofElectrons

AtomicNumber (Z)

MassNumber (A)

12  6 C

6 6 6 6 12

14  7 N

7

7 8 7

18 20 40

17O2– 8

56Fe 26

19F– 9

Worksheet: Atoms IWorksheet: Atoms I Lab Manual: Pg. 157Lab Manual: Pg. 157

Polyatomic Ionshttp://chemconnections.llnl.gov/general/Chem120/polyatomics.html

Molecules

Neutrally ChargedNeutrally Charged Eg. Salt: NaCl -> 1 NaEg. Salt: NaCl -> 1 Na++ and 1 Cl and 1 Cl -- What is the proportion of ions for a What is the proportion of ions for a

compound formed from Mg ion and compound formed from Mg ion and chlorine?chlorine?

MgMg2+2+ andand Cl Cl

11 Mg Mg2+2+ combines with combines with 22 Cl Cl

Ionic vs. Covalent

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Ionic vs. Covalent

Metals generally combine with non- metals to form Metals generally combine with non- metals to form ionic compounds. Electrons are “lost” by the metal ionic compounds. Electrons are “lost” by the metal and “gained” by the non-metal following the octet and “gained” by the non-metal following the octet rule.rule.

Non-metals generally combine with non-metals to Non-metals generally combine with non-metals to form covalent compounds where electrons are form covalent compounds where electrons are “shared”. Each pair of electrons ia a covalent “shared”. Each pair of electrons ia a covalent bond. Eg. Hbond. Eg. H22OO

Polyatomic ions have both covalent and ionic Polyatomic ions have both covalent and ionic properties. Eg. hydroxide, OHproperties. Eg. hydroxide, OH--

QUESTIONAll of the following are true except: 1) Ions are formed by adding electrons to a

neutral atom. 2) Ions are formed by changing the number of

protons in an atom’s nucleus. 3) Ions are formed by removing electrons from

a neutral atom. 4) An ion has a positive or negative charge. 5) Metals tend to form positive ions.

ANSWER

2.6 )

2) Ions are formed by changing the number of protons in an atom’s nucleus.

Section Molecules and Ions (p. 52

The removal of a proton from the nucleus requires extraordinary amounts of energy. It will only happen during a nuclear reaction.

Chemical FormulasChemical Formulas Molecular Formula:Molecular Formula:

Elements’ SymbolsElements’ Symbols = atoms = atoms

SubscriptsSubscripts = relative numbers of atoms = relative numbers of atoms How many atoms of each element are in How many atoms of each element are in

the following componds?the following componds?

MgClMgCl2 2 CClCCl4 4 NaOHNaOH (NH(NH4 4 ))22COCO33

CC20 20 HH26 26 NN2 2 OO (Ibogaine, not ionic)(Ibogaine, not ionic)

QUESTIONHow many oxygen atoms are there in one formula unit of Ca3(PO4)2? 1) 2 2) 4 3) 6 4) 8 5) None of these

ANSWER4) 8 Section 2.8 Naming Simple Compounds (p. 57) Remember to multiply the number of oxygen atoms in the parentheses by the subscript outside of the parentheses.

4) 8

Section 2.8 Naming Simple Compounds (p. 57

Remember to multiply the number of oxygen atoms in the parentheses by the subscript outside of the parentheses.