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Atomic Structure and Periodicity. Chemistry Timeline #1. B.C. 400 B.C. Demokritos and Leucippos use the term "atomos”.  2000 years of Alchemy . 1500's Georg Bauer: systematic metallurgy Paracelsus: medicinal application of minerals. 1600's

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Atomic Structure and Periodicity

Chemistry Timeline #1


400 B.C. Demokritos and Leucipposuse the term "atomos”

2000 years of Alchemy

  • 1500's

  • Georg Bauer: systematic metallurgy

  • Paracelsus: medicinal application of minerals


Robert Boyle:The Skeptical Chemist.Quantitative experimentation, identification of


  • 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

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)

  • 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

  • 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

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:

Atoms cannot be subdivided, created, or destroyed

Modern theory states:

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

The law of definite proportions states that a chemical compoundalways contains exactly the same proportion ofelementsby mass. An equivalent statement is the law of constant composition, which states that all samples of a given chemical compound have the same elemental composition by mass.

The Law of Multiple Proportions sometimes called “Dalton’s Law”states that if two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers.

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.

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

  • 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!”


  • The nucleus is small

  • The nucleus is dense

  • The nucleus is positively charged

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

“q” is a particle called a “quark”

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”


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

Atomic Number

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

Mass Number

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

Mass # = p+ + n0













Valence electrons
Valence electrons

  • These are the outer electrons that are involved in bonding. You can know how many valence electrons an atom has by what group number it is in. The group numbers are found in roman numerals on the top of each column.

Predicting Ionic Charges

Group 1:

Lose 1 val. electron to form1+ions





The Properties of a Group: the Alkali Metals

  • Easily lose valence electron

  • (Reducing agents)

  • React violently with water

  • Large hydration energy

  • React with halogens to form salts

Predicting Ionic Charges

Group 2:

Lose 2 val. electron to form2+ions





Alkaline earth metals
Alkaline Earth Metals

  • All alkaline earth metals have 2 valence electrons

  • Alkaline earth metals are less reactive than alkali metals

  • Alkaline earth metals are not found pure in nature; they are too reactive

  • The word “alkaline” means “basic”

    • common bases include salts of the metals

      • Ca(OH)2

      • Mg(OH)2

Properties of metals
Properties of Metals

  • Metals are good conductors of heat and electricity

  • Metals are malleable

  • Metals are ductile

  • Metals have high tensile strength

  • Metals have luster

Predicting Ionic Charges

Group 14:

Loses 4

val. electrons or gains 4 val. electrons

Caution! C22- and C4- are both called carbide

Predicting Ionic Charges



Group 15:

Gains 3

val. electrons to form3-ions





Predicting Ionic Charges



Group 16:

Gains 2

val. electrons to form






Predicting Ionic Charges





Group 17:

Gains 1

Val. electron to form






Predicting Ionic Charges

Predicting Ionic Charges

Group 18:

Stable Noble gasesdo notform ions!

Predicting Ionic Charges

Groups 3 - 12:


have more than one possible oxidation state.

Iron(II) = Fe2+

Iron(III) = Fe3+

Predicting Ionic Charges

Groups 3 - 12:


have only one possible oxidation state.

Zinc = Zn2+

Silver = Ag+

Transition metals
Transition Metals

Copper, Cu, is a relatively soft metal, and a very good electrical conductor.

Mercury, Hg, is the only metal that exists as a liquid at room temperature