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• Check your work on the formula and

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Atomic Structure

Image courtesy of www.lab-initio.com

Chemistry Timeline #1 B.C.

400 B.C. Demokritos and Leucippos use the term "atomos”

1500's

Georg Bauer: systematic metallurgy

Paracelsus: medicinal application of minerals

1600's

Robert 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 #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

Dalton’s Atomic Theory (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 Theory Several 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 #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

Discovery of the Electron In 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 Model

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

J.J. Thomson

Mass of the Electron

1909 – Robert Millikan determines the mass of the electron.

The oil drop apparatus

Mass of the electron is 9.109 x 10-31 kg

Conclusions from the Study of the Electron

Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons Electrons have so little mass that atoms must contain other particles that account for most of the mass

Rutherford’s Gold Foil Experiment

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

Try it Yourself! In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

The Answers

Target #1 Target #2

Rutherford’s Findings

The nucleus is small The nucleus is dense The nucleus is positively charged

Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected

“Like howitzer shells bouncing off of tissue paper!”

Conclusions:

Atomic Particles

Particle 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 Scale

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

Helium-4

Image: User Yzmo Wikimedia Commons.

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”

Images: Arpad Horvath, Wikimedia Commons.

Isotopes 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 Masses

Isotope Symbol Composition of the nucleus

% in nature

Carbon-12 12C 6 protons

6 neutrons

98.89%


7 neutrons

1.11%


8 neutrons

<0.01%

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

Carbon = 12.011

Atomic Number

Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

Element # of protons Atomic # (Z)

Carbon 6 6

Phosphorus 15 15

Gold 79 79

Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope.

Mass # = p+ + n0

Nuclide p+ n0 e- Mass #

Oxygen - 10

- 33 42

- 31 15

8 8 18 18

Arsenic 75 33 75

Phosphorus 15 31 16

Molecules and Ions

Image courtesy of www.lab-initio.com

Ions

Cation: A positive ion Mg2+, NH4

+

Anion: A negative ion Cl-, SO4

2-

Ionic Bonding: Force of attraction between oppositely charged ions.

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

Predicting Ionic Charges

Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+ Cs+


Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+

Predicting Ionic Charges Group 13: Loses 3 electrons to form 3+ ions

B3+ Al3+ Ga3+

Predicting Ionic Charges Group 14: Loses 4 electrons or gains 4 electrons

Caution! C22- and C4-

are both called carbide


Group 15: Gains 3 electrons to form 3- ions

N3-

P3-

As3-

Nitride Phosphide

Arsenide


Group 16: Gains 2 electrons to form 2- ions

O2-

S2-

Se2-

Oxide

Sulfide Selenide


Group 17: Gains 1 electron to form 1- ions

F1-

Cl1-

Br1-

Fluoride

Chloride

Bromide

I1- Iodide


Group 18: Stable Noble gases do not form ions!

Predicting Ionic Charges Groups 3 - 12: Many transition metals have more than one possible oxidation state.

Iron(II) = Fe2+ Iron(III) = Fe3+

Predicting Ionic Charges Groups 3 - 12: Some transition metals have only one possible oxidation state.

Zinc = Zn2+ Silver = Ag+

Writing Ionic Compound Formulas

Example: Barium nitrate

1. Write the formulas for the cation and anion, including CHARGES!

Ba2+ NO3-

2. Check to see if charges are balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced

( ) 2


Example: Ammonium sulfate


NH4+ SO4

2-



Not balanced

( ) 2


Example: Iron(III) chloride


Fe3+ Cl-



Not balanced

3


Example: Aluminum sulfide


Al3+ S2-



Not balanced

2 3


Example: Magnesium carbonate


Mg2+ CO32-


They are balanced


Example: Zinc hydroxide


Zn2+ OH-



Not balanced

( ) 2


Example: Aluminum phosphate


Al3+ PO43-


They ARE balanced

Naming Ionic Compounds Cation first, then anion

Monatomic cation = name of the element

Ca2+ = calcium ion

Monatomic anion = root + -ide

Cl- = chloride

CaCl2 = calcium chloride

Naming Ionic Compounds

some metal forms more than one cation

use Roman numeral in name

PbCl2

Pb2+ is cation

PbCl2 = lead(II) chloride

Metals with multiple oxidation states

Binary Molecular Compounds

Compounds between two nonmetals

First element in the formula is named first.

Keeps its element name

Gets a prefix if there is a subscript on it

Second element is named second

Use the root of the element name plus the -ide suffix

Always use a prefix on the second element

List of Prefixes

1 = mon(o)

2 = di

3 = tri

4 = tetra

5 = penta

6 = hexa

7 = hepta

8 = octa

9 = nona

10 = deka

Naming Binary Compounds

P2O5 =

CO2 =

CO =

N2O =

diphosphorus pentoxide

carbon dioxide

carbon monoxide

dinitrogen monoxide

Practice – Write the Formula Compound Name Compound Formula

Carbon dioxide

Carbon monoxide

Diphosphorus pentoxide

Dinitrogen monoxide

Silicon dioxide

Carbon tetrabromide

Sulfur dioxide

Phosphorus pentabromide

Iodine trichloride

Nitrogen triiodide

Dinitrogen trioxide

Check next slide for answers

Answers – Write the Formula Compound Name Compound Formula

Carbon dioxide CO2

Carbon monoxide CO

Diphosphorus pentoxide P2O5

Dinitrogen monoxide N2O

Silicon dioxide SiO2

Carbon tetrabromide CBr4

Sulfur dioxide SO2

Phosphorus pentabromide PBr5

Iodine trichloride ICl3

Nitrogen triiodide NI3

Dinitrogen trioxide N2O3

Practice – Name the Compounds

Compound Formula Compound Name

N2O4

SO3

NO

NO2

As2O5

PCl3

CCl4

H2O

SeF6

Check next slide for answers

Answers – Name the Compounds

Compound Formula Compound Name

N2O4 dinitrogen tetroxide

SO3 sulfur trioxide

NO nitrogen monoxide

NO2 nitrogen dioxide

As2O5 diarsenic pentoxide

PCl3 phosphorus trichloride

CCl4 carbon tetrachloride

H2O dinitrogen monoxide

SeF6 selenium hexafluoride

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