History of the Atom - By Sally Chen

Aristotle

- Democritus:  suggested that the differences between substances were the direct result of differences in the size and shape of tiny, uniform, unbreakable particles.

- Aristotle:  4 basic elements:  water, air, fire and earth.

- Antoine Lavoisier:  created the first law of the conservation of mass.

- John Dalton:  created Dalton’s Atomic Theory, which is a combination of all discoveries about atoms.
- J. J. Thomson:  He discovered the existence of electron in 1897.  He found it was about 2000 times less than the mass of hydrogen.

- Ernest Rutherford:  He discovered the atomic nucleus and presumed the nuclear structure of the atom and predicted the existence of the neutron.

- Robert Millikan:  He accurately determined the charge carried by an electron, using “falling-drop method”.  He also demonstrated that this quantity was a constant for all electrons.

- Marie Curie:  She and her husband Pierre Curie isolated the elements polonium and radium.  She also developed methods for the separation of radium from radioactive residues.

Albert Einstein

- James Chadwick:  He discovered the neutron, and that it had about the same mass as a hydrogen atom.

- Max Planck:  He discovered that light was released by heat sources in a particular pattern of frequencies for different elements.  Each frequency of light corresponded to different sets of colors of lights seen by our eyes (lowest to highest:  red, orange, yellow, green, blue, purple, and violet).

- Albert Einstein:  In 1905 Einstein projected a theory that light was made up of localized particles.  He also defined detailed equations on light wavelengths and frequency differences within the same light.  He named packets of light energy photons.  Einstein believed that each atom oscillates independently instead of joining to others.

Joseph Louis Proust

- Niels Bohr:  electric fields between negatively charged electrons and a positively charged nucleus must hold electrons in their orbits.  He thought that electrons could circle at different orbit levels above the nucleus depending on how much energy they had.  When electrons jumped to lower levels, Bohr suggested that energy would be released as light.  The diagram of his version of atom is called the Bohr Diagram.

- Louis De Broglie:  He discovered the wave nature of electrons.  He had a theory that the behavior of the electron could also be better understood not just as a particle, but as both a particle and a wave.

- Erwin Schrodinger:  He created an equation describing how Broglie’s theory would be possible, not only for atoms and parts of the atom, but even for large objects – maybe even for the entire universe.

- Joseph Louis Proust:  He discovered the law of definite proportions, also known as Proust’s law, which states that chemical compounds always have the same fraction of each element in them by mass.

- Henri Becquerel:  He was the first person who discovered radiation.

History of Periodic Table--Nemo Jin

Long time ago, a group of people believed that they could turn metals into pure gold. These people were called alchemists. Although they were not successful, many different elements were discovered by these alchemists, including gold, silver, tin, copper, lead and mercury. However, the first scientific discovery of an element was in 1649, the discovery of phosphorous by Hennig Brand.

In the next 200 years, a total of 63 elements had been discovered, and scientists began to recognize patterns in properties and began to develop classification schemes.


In 1863, John Newlands, a English chemist divided 56 elements into 11 groups, based on their characteristics. He also proposed the Law of Octaves,which stated that any given element will exhibit analogous behavior to the eighth element following it in the table.

                                             (John Newlands' Periodic Table)

(Meyer's 1864 textbook included a rather abbreviated version of a periodic table used to classify the elements, but unfortunately for Meyer, Mendeleev's table was the first one available to the scientific community)


      “Father of Periodic Table"
In 1869, Russian chemist Dimitri Mendeleev arranged chemical elements by their atomic masses.  He also accurately predicted the properties of some undiscovered elements, leaving spaces open in his periodic table for them. His contribution to the development of periodic table was usually considered as the foundation of modern periodic table. 

In 1894, Sir William Ramsay and Lord Rayleigh discovered the noble gases which did not fit any of the known periodic groups. Because of the zero valency of the elements, noble gases were added to the periodic table as group 0

In 1911, A. van den Broek proposed that the atomic weight of an element was approximately equal to the charge on an atom. This charge, later termed the atomic number, could be used to number the elements within the periodic table.

The last major changes to the periodic table was in the middle of the 20th Century.


Glenn Seaborg 
--discovery of elements from 94 to 102 
--rearrangement of the periodic table (placing the actinide series below the lanthanide series) 
He was awarded the Nobel Prize in chemistry for his work. Element 106 has been named seaborgium (Sg) in his honor.

Electronic Structure of the Atom--By Tina Zhao

Electronic Structure of the Atom
- The electronic configuration of an atom is notation that describes the orbitals in which the electrons occupy and the total number of electrons in each orbital
-Helps to understand the structure of the periodic table of elements

Energy Level
- is the amount of energy, which an electron in an atom can possess "n" is the number of the energy level
- the energy difference two particular energy levels are called the quantum of energy


Ground State: When all the electrons of an atom are in their lowest possible energy level
Excited State: When one or more of an atoms's electrons are in energy
An orbital is the actually region of space occupied by an electron in a particular energy level
A shell is the set off all orbital having the same n-value
A sub-shell is a set orbital in same level

For a given value of "n", different types of orbitals are possible:
n=1; only the s-type
n=2; s and p- types
n=3; s,p,and d-types
n=4; s,p,d,and f-types

* A maximum of 2 electrons place in one orbital

Writing Electronic configurations for Neutral Atoms

- Always start with lowest energy level first 

- Figure out how many electron you have (neutral number= atomic number) then start  at the lowest energy level (1s)

- Each electrons has an opposite spin

* the 2 electron in the 2p occupy separate suborbitals and are not paired up 

Writing Electronic configurations for ion

Negative ion: Add electrons (equal to the charge) to the last unfilled sub-shell, starting where the neutral atom left off

Positive ion: Start with the neutral configuration, and then remove electrons from the outmost shell first

Core Nation

- The set of electrons for an atom can be divided into two subsets; the core electrons and the outer eletrons

- The core of an atom is the set of electrons with the configuration of the noble gas

- The outer electrons consist of all elections outside of core. Core electrons  normally take part in chemical reaction

- Locate the atom and not the noble gas at the end of the row above the element

Predicting the number of Valence Electrons

- are electrons which can take part in chemical reactions 

- or are all the electrons in an atom EXCEPT those in CORE AND IN FILLED d OR f -sub-shells

Atomic Structure -- by Ria Park

Atomic Structure


Subatomic Particles

• Neutron = Large with no charge; location=nucleus
• Proton = Large with positive charge; location=nucleus
• Electron = small with negative charge; location=cloud surrounding the nucleus - A neutral atom has no overall net charge.

    Atomic Number: The Proton Number

• found in the nucleus of an atom
• has no overall electric charge

Atomic Number = # of protons - # of electrons

Ions

• Atoms that have gained or lost electrons are called Ions
• Most atoms are capable of either gaining or losing electrons. A few elements, like hydrogen, are able to do both -- by accepting electrons from or giving electrons to, either atoms.
• An ion is an electrically charged atom.
• Negatively-charged ion: anion = when electron are added to a neutral atom
• Positively-charged ion: cation = when electron are subtracted to a neutral atom

Mass Number

• is the number of protons and neutrons or atomic mass number since atomic # = the # of neutrons
• Atomic mass ≠ # of protons + #of neutrons
• Number of neutrons = Mass number - protons

Atomic Mass

• The average mass of an element's isotopes
• since most of the mass of an atoms is concentrated in the protons and neutrons located in the nucleus.
• If a neutron is added to an element's nucleus, a heavier version of the same element (isotope) will be produced.

Isotopes

• are atomic species having the same atomic number (protons) but different atomic masses/mass numbers (neutrons)

Periodic Trends - By Sally Chen

Density Graph
Density:  the mass of a substance per unit volume.
Down a group:  increase
Across a period:  increase then decrease

General Shape

Down each group (from left to right)

Melting and Boiling Point
Melting point:  the temperature at which a substance changes from a solid to a liquid.
Boiling point:  the temperature at which a substance changes from a liquid to a gas.
Down a group:  increase
Across a period:  increase then decrease

General Shape

Down some groups

Ionization Energy
Ionization Energy:  the energy required to remove electrons from gaseous atoms or ions.
Down a group:  decrease
Across a period:  increase

General Shape

Down each group (from left to right)

Electronegativity
Electronegativity:  a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself.
Down a group:  decrease
Across a period:  increase

General Shape

Down each group (from left to right)

Atomic Radius
Atomic Radius:  a measure of the size of the atom.
Down a group:  increase
Across a period:  decrease

General Shape

Down each group (from left to right)