April 26 2011 - Periodic Table

The original sketch of the periodic table by Mendeleev.

- intial copy was published in 1896 by Dmitri Mendeleev
1. The elements, if arranged according to their atomic weights, exhibit an apparent periodicity of properties.
2. Elements which are similar as regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).
3. The arrangement of the elements, or of groups of elements in the order of their atomic weights, corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, Ba, C, N, O, and Sn.
4. The elements which are the most widely diffused have small atomic weights.
5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
6. We must expect the discovery of many yet unknown elements–for example, elements analogous to aluminium and silicon–whose atomic weight would be between 65 and 75.
7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. (This was based on the position of tellurium between antimony and iodine whose atomic weight is 127. However Moseley later explained the position of these elements without revising the atomic weight values — see below.)
8. Certain characteristic properties of elements can be foretold from their atomic weights.


Modern periodic table

April 20 2011 - Electron Configuration

The electron configuration of an atom is a form of notation which shows how the electrons are distributed among the various atomic orbital and energy levels.

Energy level is an amount of energy which electrons in atoms can possess ( "n"= number of energy levels)

Quantum of energy is an energy difference between 2 particular energy levels

Ground state is when electrons of atoms are in their lowest possible energy level

Excited state is when 1 or more of an atom's electrons are in energy levels other than the lowest available level

Orbital is an actual region of space occupied by an electron in particular energy level

Shell is a set of all orbitals having the same "n" value

Subshell is set of orbitals of the same type

The letters s, p, d, f refer to the four different types of orbitals

Each subshell consists of:
1: s-orbital
3: p-orbital
5: d-orbital
7: f-orbital

Due to Pauli Exclusion Principle, maximum of 2 electrons can be placed in each orbit.

For a given value of "n", different types of orbitals are possible for:

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.

Electron Configuration for Neutral Atoms

1. Always start with the lowest energy level.
2. Figure out how many electrons you have

3. Start at the lowest (1s) and keeping adding.
-each electron has an opposite spin designated by upward and downward arrows.

Electronic Configuration for Ions
For negative ion:
Add electrons to the unfilled subshell starting where the neutral atom left off.

For positive ion:
1. Start with neutral atom and remove electrons from outermost shell depending on the charge.
2. If there are electrons in both s and p orbital of the outermost shell, elextrons in the p-orbital are removed first.

Core Notation

the set of electrons for an atom can be divided into two subsets

-the core electrons and the outer electron.
-the core is the set of electron with the configuration of the nearest noble gas that comes before it.
-the outer electron consist of all electron outside the core electron normally take part in chemcal reactions.

Atomic Theory - April 14th

Greek philosophers believed that atomos were the smallest pieces of matter...
- Aristotle believed there were 4 elements : earth, air, fire and water

From this theory marked the beginning towards a greater understanding of matter.

There were many theories regarding this matter:

-Democritus, 300 B.C was a greek philosopher who believed that atoms were invisible particles

-Lavoisier in 1700's, he stated the first version of the law of conservation of mass and law of definite proportions

-Proust in 1799, proved that Lavoisier's law by experiments

-Dalton in 1800's defined atoms as solid and indestructible spheres based on the Law of Conservation of Mass

-J.J. Thomson in 1850's came up with the first theory atoms have either positive or negative charges which proved the existence of electrons using using a cathrode ray tube

-Rutherford in 1905, proved atoms having a positive charge, dense center with electrons outstide it and explains why electrons spun around nucleus and suggested atoms are mostly empty space

-Neils Bohr in 1885-1962, studied gaseous samples of atoms, which were made to glow by passing an electonic current through them

Bohr Diagram

Remember! Project on History of Atomic Theory

DUE: Next Tuesday

Alkanes, Branched Hydrocarbons, and Alkyl groups.

3 types of bonds :
- Single
- Double
- Triple

2 types of chain patterns :
- straight line
- circular pattern
- branched pattern

Alkanes :
- end in '-ane'
- straight/unbranched chains
- formula : CnH2n+2

Branched Hydrocarbons :
- has side branches of hydrocarbon chains

Alkyl group :
- ends in '-yl'
- alkanes which have lost one hydrogen atom


Naming Simple Alkanes.

Apr 04 2011 Percent Yield & Percent Purity

Percent Yield

The ratio of amount of product obtained to amount of product expected by calculation, expressed as a percent.

Ex.

Percent Purity

Percent purity is the ratio of the mass of pure substance to mass of impure sample.

Percent Purity = mass of pure substance/mass of impure sample x 100%

Before we calculate how much product will form, we need to use percent purity to calculate how much reactant that actually is available to react.

Ex . If a 1.00g sample of Iron ore (the rock that the metal is found in) contains 0.60g of Iron metal, what's percent purity?

% purity = 0.60g Fe/1.00g Fe ore x 100% = 60 %