Periodic Table - History

A necessary step to the construction of the periodic table was the discovery of the individual elements. All of elements including copper, lead, silver, gold, and mercury have been known for a while, Henning Brand's discovery of phosphporous was the first scientific discovery.

As 200 years passed by, chemists started regarding the properties of the elements. By 1869, 63 elements had been discovered. 

As the number of known elements grew, scientists began to recognize patterns in properties and began to develop classification schemes.

Law of Triads

In 1817 Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties.

After the discovery of the halogen triad (chlorine, bromine, and iodine); and the dicovery of the alkali metal triad (lithium, potassium, and sodium); he proposed that the nature of the triads allowed the middle element to be the average of the two elements (atomic mass). This si known as the Law of Triads.

 

 

First Attempts At Designing the Periodic Table

The periodic table demonstrates the order of chemical elements based on their chemical and physical properties. The credit to the first "draft" of the periodic table has to be given to Beguyer de Chancourtois that positioned a cylinder based on increasing atomic weight which then led to the conclusion that the properties of elements are the properties of numbers and they should be organised based on that.

Law of Octaves

In 1863, John Newland classified 56 elements into 11 groups based on their properties; physical and chemical. He said that after every 8 elements, the properties re-appear. He then propsed his version of the periodic table and the Law of Octaves. This law stated that any given element will exhibit analogous behavior to the eighth element following it in the table.

 

Demetri Mendeleev 

Russian chemist that arranged te periodic table based on the atomic mass of elements; and he put the elements with similar characteristics and properties under eaach other. He left some gaps for elements that are yet to be dicoverred and he did note that they will be discoverred to fit in the gaps that share the same properties. Examples of elements include gallium, scandium and germanium.

Mendleev's periodic table was important because it possessed the means of "periodic law" which states the elements vary periodically with their atomic weight.

 

Discovery of the Noble Gases

Argon was discoverred in 1895 by Lord Rayleigh. He noted that this element did not fit any of the groups previously organized by Mendeleev and Newlands. 3 years after that, Ramsey suggested it should be put in the group between chlorine and potassium in one family with helium. The referred to it as the "zero group" because they had no valence electrons. Ramsey then predicted the discovery of the properties of the element neon.

 

The Modern Periodic Table

After the disovery of plutonium by in 1940 by Seaborg, and the discovery of elements from 94 to 102, he made some changes during the 20th century. He also placed the actinide series below the lanthinide series in 1951. He was awarded the Nobel Prize in chemistry and an element was named after him (seaborgium).

 

Periodic Table - Families

Scientists group families of elements by their chemical properties.  Each family reacts a different way with the outside world.  Metals behave differently than gases and there are even different types of metals.  Some don't react, others are very reactive, and some are metallic.

Usually, the colums of the periodic table are used to define families.  The inert gases are all located in the far right column of the table.

Families

- Alkali Metals

They are found in group 1 of the periodic table:

• Highly reactive metals that do not occur freely in nature.
• These metals have only one electron in their outer shell.  Therefore, they are ready to lose that one electron in ionic bonding with other elements.
• Malleable, ductile, good conductors of heat and electricity.
• Softer than most other metals.

Sodium

- Alkaline Earth Metals

They are found in group 2 of the periodic table:

• Same properties as alkali metals but an ionization number of +2, making them very reactive, but less reactive than the alkali metals.

Magnesium

- Transition Metals

• Transition elements are ductile and malleable, they conduct electricity and heat.
• Their valence electrons are present in more than one shell.  This is why they often exhibit several common oxidation states

Gold

- Halogen Gases

• Non-metallic elements are found in group 17 of the periodic table.
• All halogens have 7 electrons in their outer shells, giving them an ionization number of -1.

Bromine

- Noble Gases

• Group 18 of the periodic table.
• Ionization number of 0.  This prevents them from forming compounds readily.
• All noble gases have 8 electrons in their outer shells, making them stable.

- Lanthanide and Actinide series

• All of them are found in group 3 of the periodic table, 6th and 7th periods.
• most of them are man-made (synthetic)
• Same properties as other metals

Electronic Structure

 Electronic Structure(configuration) is the arrangement of electrons in energy level  around an atomic nucleus. It tells us how many electrons are in each orbital.
 For example, Electronic structure for Na(sodium) is 1s2 2s2 2p6 3s1.
It looks complicated right? But as long as you get the rules, it will be really easy.

First there are four types of shell. There are s,p,d,and f. Like u can see from the periodic table below those shells are based on periodic table.

  To write electronic configuration, you just needed to find location of the element that you want, and write down orderly from left to right.
 Let's use Na for the example, Na has 11 electrons,and it's at 3rd period fist group. Fisrt we start with left top. there are two elements are in 1s(1 simply represent the  period). Thus, you write 1s2, and there are nothing on the 1period on the right side, so we go to period 2. They have two elements as well, thus you write 2s2, then there are 6 elements in 2p, thus you write 2p6, got it? So,over all we have 1s2 2s2 2p6 and finally where Na is 3s1. Thus,  answer is 1s2 2s2 2p6 3s1.
Just be aware of d d start wih row 3 instead of  4









Core Notation
 Some Scentists are really lazy thus, they found the easiler way to write elecronic configuration. It's easy you just need to find the near noble gas and start the electronic configuration from there. Thus, for Na, Ar is the closest noble gas, thus u write (Ar)3s1.

Valence Electrons
They are electrons that are located most outer shell, if we have core notation we just simply need to count the numbers of elecrons exept d and f. For example,Na has 1 valence eletrons
 Here is the video that will help

                                         

Atomic Structure

Atoms are composed of three type of particles: protons, neutrons, and electrons.

Protons and neutrons are responsible for most of the atomic mass.
The mass of an electron is very small (9.108 X 10^-28 grams).

1 - Now let's start with Neutral Atoms:

Both the protons and neutrons reside in the nucleus. Protons have a postive (+) charge, neutrons have no charge, ie they are neutral. Electrons reside in orbitals around the nucleus. They have a negative charge (-).

The number of protons determines the atomic number, e.g., H = 1. The number of protons in an element is constant (e.g., H=1, Ur=92) but the neutron number may vary, so the mass number (protons + neutrons) may vary.

Helium Atom

 2 - Ions:

- In an ion, number of electrons =/ number of protons, but protons = atomic number.
- Electrons are either lost or gained, making the ion either positive or negative.






3 - Isotopes:

The same element may contain varying numbers of neutrons; these forms of an element are called isotopes. The chemical properties of isotopes are the same, although the physical properties of some isotopes may be different. Some isotopes are radioactive-meaning they "radiate" energy as they decay to a more stable form, perhaps another element half-life: time required for half of the atoms of an element to decay into stable form. Another example is oxygen, with atomic number of 8 can have 8, 9, or 10 neutrons. 

To sum this up:

- Isotopes are atoms with same number of electrons and protons, but different numbers of neutrons.
- Different numbers of neutrons means different atomic masses.
- Different amounts of isotopes exist for different elements.








The mass number of elements can be calculated by getting the averages of the atomic masses of isotopes. For example:

potassium has three main isotopes; potassium-39 (93.26%), potassium-40 (0.0117%), potassium-41 (6.73%), so to get the average you multiply the percentages by their atomic masses, then add them together.

(39*0.9326) + (40*0.000117) + (41*0.0673) = 39.13538g/mol

*Always; # neutrons = mass # - atomic #, electron's mass = 1, neutron mass = 1837, proton mass = 1836

April 14

History of Chemistry

The theories of Aristotle, which lasted two thousand years, were that matter was made of atomos, the smallest pieces of matter.  Everything was made of a combo of earth, air, fire, and water.

In the late 1700s, Lavoisier introduced the first version of the Law of Conservation of Mass and the Law of Definite Proportions

In 1799, Proust stated that if a compound was broken down into its constituents, the products would exist in the same ratio as in the compound

Dalton (1800s) discovered that atoms were solid, indestructable spheres. His 5 main points of the Atomic Theory were:

-Elements are of tiny particles called atoms

-Atoms of a given element are identical 

-Atoms of different elements are different by weights
-Atoms from different elements combine to form chemical compounds

-Atoms cant be destroyed, created, or divided.

JJ Thomson

- Thomson introduced the Raisin Bun diagram.  ( solid positive spheres with negative particles embedded in them)

April 6th- Percent Purity

Percent Purity is the percent of a specified compound or element in an impure sample.

Example:

Chalk is almost pure calcium carbonate. We can work out its purity by measuring how much carbon dioxide is given off. 10 g of chalk was reacted with an excess of dilute hydrochloric acid. 2.128 liters of carbon dioxide gas was collected at standard temperature and pressure (STP).
The equation for the reaction is
CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)

 

Solution:

Step 1: Calculate the grams from the volume

1 mole of CaCO₃ gives 1 mole of CO₂
1 mole of gas has a volume of 22.4 liters at STP.
22.4 liters of gas of gas is produced by 100 g of calcium carbonate
and 2.128 liters is produced by 2.128 ÷ 22.4 × 100 = 9.5 g

Step 2: Calculate the percent purity

There is 9.5 g of calcium carbonate in the 10 g of chalk.
Percent purity = 9.5 ÷ 10 × 100% = 95%

April 4th - Percent Yield

Percent Yield

• The percentage yield is the ratio between the actual yield and the theoretical yield multiplied by 100%.  It indicates the percent of theoretical yield that was obtained from the final product in an experiment. 

• The percentage yield can be calculated using the mass of the actual product obtained and the theoretical mass of the product calculated using the balanced equation of the reaction.

Percentage Yield =     Mass of Actual Yield       x   100%

                  Mass of Theoretical Yield

Theoretical Yield

• this is how much product will be synthesized in ideal conditions.

• To determine theoretical yield, multiply the amount of moles of the limiting reagent by the ratio of the limiting reagent and the synthesized product and by the molecular weight of the product.

 Actual Yield

• this is how much product was actually synthesized in the experiment.
  
• Example:  0.135 g acetylsalicylic acid 

Practice Problem

In the following reaction, 0.157g of p-acetaminophenol was used to react with 0.486 g of acetic anhydride to produce acetaminophen and acetic acid.  The product was purified and acetimophen was extracted.  The actual mass of acetaminophen produced was 0.198 g.  Determine the theoretical yield and the percent yield of isopentyl acetate. p-Aminophenol     +     Acetic anhydride     à     Acetaminophen      +    Acetic acid     C6H7NO                                 C4H6O3                    C8H9NO2                  CH3COOH Solution   molar mass of p-aminophenol =109.1g/mol molar mass of acetic anhydride = 102.1 g/mol moles of p-aminophenol = mass/molar mass                                   = 0.157g/(109.1g/mol)                                   = 0.00144 mol moles of acetic anhydride = mass/molar mass                                          = 0.486g/(102.1g/mol)                                          = 0.00476 mol Theoretical Yield = moles of acetamiophen x molar mass of acetaminophen                          = 0.00144 mol x 151.2g/mol                          = 0.217 g Percent Yield =         Actual Yield        x 100%                             Theoretical Yield                     =            0.198g      x 100 %                                   0.217g                     =  91.2 %