Chemistry 11

Periodic Table History

Our modern-day periodic table would not be what it is if it weren't for the contributions made by a few scientists in the 1800's.

The first one was William Odling.

William Odling

Odling seperated the 52 discovered elements into 13 groups based on their physical and chemical properties.

But new discoveries were being made and from 1863-1866, John Newlands stated that if hydrogen had a mass of 1, then every 8th element had common properties, which was named "the Law of Octaves".

John Newlands

But this was not the end of the periodic table. Our modern periodic table is based on the work of Dmitri Mendeleev, who arranged the elements by their masses and properties. He found that properties of elements recur periodically. So he split his table into periods and groups (or families). He made very accurate predictions on the undiscovered elements, which is why he left gaps in his table.

Dmitri Mendeleev

In the modern periodic table as shown below, the elements are arranged by atomic number, not by atomic mass as it was before.

Modern Periodic Table

You can see that the table is split up into the following sections:
1) Alkali metals
2) Alkaline earth metals
3) Lanthanoids
4) Actinoids
5) Noble gases
6) Other non-metals and
7) Poor metals

As you will notice, hydrogen is in its in group. This is because hydrogen behaves unlike any other element, although it has characteristics of groups 1 and 17.

There are other ways of displaying the periodic table, like this:

Circular Periodic Table

If you click here, you'll find some more useful information on the background of the periodic table.

Periodic Trends

Periodic Trends for Electronegativity

Electronegativity is a chemical property that attempts to describe the attraction between a bonding electron and an atom.

The electronegativity of the elements within a period increases from left to right. When the valence shell of an atom is less than half full, it requires less energy to lose an electron than gain one and thus, it is easier to lose an electron. Conversely, when the valence shell is more than half full, it is easier to pull an electron into the valence shell than to donate one.
Down a group, the electronegativity decreases from element to element. This is because the atomic number increases down a group and thus there is an increased distance between the valence electrons and nucleus, or a greater atomic radius.
Important exceptions of the above rules include the noble gases and transition metals. The noble gases possess a complete valence shell and do not usually attract electrons. The transition metals possess a more complicated chemistry that does not generally follow any trends

Periodic Trends for Ionization Energy

Ionization Energy is the amount of energy required to remove an electron from a neutral atom in its gaseous phase.

The ionization energy of the elements within a period generally increases from left to right. This is due to valence shell stability.
The ionization energy of the elements within a group generally decreases from top to bottom. This is due to electron shielding.
The noble gases possess very high ionization energies because of their full valence shell as indicated in the graph. Note that Helium has the highest ionization energy of all the elements.

Periodic Trends for Electron Affinity

Electron affinity describes the ability of an atom to accept an electron.

Electron affinity increases from left to right within a period. This is caused by the decrease in atomic radius.
Electron affinity decreases from top to bottom within a group. This is caused by the increase in atomic radius.

Periodic Trends for Atomic Radius

For atoms, one-half the distance between the nuclei of two atoms is called the atomic radius.

Atomic size gradually decreases from left to right across a period of elements. This is because, within a period or family of elements, all electrons are being added to the same shell. But at the same time, protons are being added to the nucleus, making it more positively charged. The effect of increasing proton number is greater than that of the increasing electron number therefore there is a greater nuclear attraction. This means the nucleus attracts the electrons more strongly and therefore, the shell is pulled closer to the nucleus. The outermost electrons are held closer towards the nucleus of the atom. As a result, the atomic radius decreases.
Going down a group, it can be seen that atomic radius increases. The outermost electrons occupy higher levels due to the higher quantum number (n). As a result, the outermost electrons are further away from the nucleus as the ‘n’ increases. Electron shielding prevents these outer electrons from being attracted by the nucleus, thus they are loosely held and the atomic radius is large.
Atomic radius decreases from left to right within a period. This is caused by the increase in protons and electrons across a period. One proton has a greater effect than one electron and thus a lot of electrons will get pulled towards the nucleus and thus a smaller radius.
Atomic radius increases from top to bottom within a group. This is caused by electron shielding.

Periodic Trends for Melting Point

Generally, the stronger the bonds between the atoms of an element, the higher the energy requirement in breaking that bond.

Metals generally possess a high melting point.
Most non-metals possess low melting points.
The non-metal carbon possesses the highest boiling point of all the elements. The semi-metal boron also possesses a high melting point.

Periodic Trends for Metallic Character

The ease of losing an electron is a measure of an element's metallic character.

Metallic characteristics decrease from left to right across a period. Metallic characteristics increase down a group. Electron shielding causes the atomic radius to increase thus the outer eletrons ionizes more readily than electrons in smaller atoms.
Metallic character relates to the ability to lose electrons, and nonmetallic character relates to the ability to gain electrons.

Overall, these charts can be simpled into this picture:

Here is a video found on YouTuBe about the periodic trends:

Outside Links

Problems

The following series of problems will review your general understanding of the aforementioned material.

1.) Based on the periodic trends for ionization energy, which do you except to have the highest ionization energy?

A.) Fluorine (F)
B.) Nitrogen (N)
C.) Helium (He)

2.) Nitrogen has a larger atomic radius than Oxygen.

A.) True
B.) False

3.) Which do you expect to have more metallic character, Lead (Pb) or Tin (Sn)?
4.) Which element do you expect to have the higher melting point: chlorine (Cl) or bromine (Br)?
5.) Which element do you expect to be more electronegative, sulfur (S) or selenium (Se)?
6) Why is the electronegativity value of most noble gases equal to zero?
7) Arrange the following atoms according to decreasing effective nuclear charge experienced by their valence electrons: S, Mg, Al, Si
8) Rewrite the following list in order of decreasing electron affinity: Fluorine (F), Phosphorous (P), Sulfur (S), Boron (B).
9) An atom with an atomic radius smaller than that of Sulfur (S) is __________.

A.) Oxygen (O)
B.) Chlorine (Cl)
C.) Calcium (Ca)
D.) Lithium (Li)
E.) None of the above

10) A nonmetal will have a smaller ionic radius when compared to a metal of the same period.

A.) True B.) False

11) Which one of the following has the lowest first ionization energy?

A. Element A
B. Element B
C. Element C
D. Element D

Solutions

1. Answer: C.) Helium (He)

Explanation: Helium (He) has the highest ionization energy because, like other noble gases, Helium's valence shell is full. Because of this, Helium is stable and does not readily lose or gain electrons.

2. Answer: A.) True

Explanation: According to periodic trends, atomic radius increases from right to left on the periodic table. Therefore, we would expect Nitrogen to be larger than Oxygen.

3. Answer: Lead (Pb)

Explanation: Lead and Tin share the same column. According to periodic trends, metallic character increases as you go down a column. Lead is underneath Tin therefore we would expect Lead to possess more metallic character.

4. Answer: Bromine (Br)

Explanation: According to periodic trends, in non-metals, melting point increases down a column. Since chlorine and bromine share the same column, we would expect bromine to possess the higher melting point.

5. Answer: Sulfur (S)

Explanation: Note that sulfur and selenium share the same column. Periodic trends tell us that electronegativity increases up a column. This indicates that sulfur is more electronegative than selenium.

6. Answer: Most noble gases have full valence shells.

Explanation: Because of their full valence electron shell, the noble gases are extremely stable and do not readily lose or gain electrons.

7. Answer: S > Si > Al > Mg.

Explanation: The electrons above a closed shell are shielded by the closed shell. S has 6 electrons above a closed shell, so each one feels the pull of 6 prontons in the nucleus.

8. Answer: Fluorine (F)>Sulfur (S)>Phosphorous (P)>Boron (B)

Explanation: According to periodic trends, the electron affinity generally increases from left to right and from bottom to top.

9. Answer: C.) Oxygen (O)

Explanation: Periodic trends indicate that atomic radius increases up a group and from left to right across a period. Therefore, oxygen is expect to have a smaller atomic radius than of sulfur.

10. Answer: B.) False

Explanation: The reasoning behind this lies in understanding that a metal usually loses an electron in becoming an ion while a non-metal gains an electron. This results in a smaller ionic radius for the metal ion and a larger ionic radius for the non-metal ion.

11. Element D

Explanation: Element A, B and D have the same number of elentrons in the inner shell, but element D has the least number of eletrons in the outer shell which requires the lowest ionization energy.

Electronic Structure of the Atom

Electronic Configuration is the arrangement of electrons and atoms.It can help us to understand the periodic table of elements.

Orbital:It is the actual region of space occupied by an electron in a particular energy level.
There are 4 letters which are s,p,d,f refer to the 4 different kinds of orbitals.Look at the picture, each circle represents one orbitals.

An s-type subshell consists of ONE s-orbital
A p-type subshell consists of THREE p-orbitals
A d-type subshell consists of FIVE d-orbitals
An f-type subshell consists of SEVEN f-orbitals.

How to write electronic configurations for neutral atoms?
Aufbau principle told us we should always start with the lowest energy level.
First, you should know how many electrons you have. Next, start at the lowest energy level(1s) and keep adding until you have no left.

How to write electron configurations for IONS?

1.For a negative ion:Add the electron(s) which equal(s) to the charge to the last subshell if it is unfilled.

2.For a positive ion:You should do neutral configuration first, remove the electrons which is in the most out shell.

Orbital Box Notation

Orbital Box Notation is the way shown in the orbital diagram below

Spectroscopic notation (more commonly used, but the "long way")

this is the was it is written under the electron configuration below on the right.

Core Notation

It is a short way to show the electron configuration by using core and the outer elements.You can write out just the ones since the last noble gas.

For example, find carbon in the periodic table, then go backwards till you find the noble gas.For C, the noble gas is He.So the core notation of carbon is [He]2s²2p².

C: 1s²2s²2p²

For C, box notation is also easy for you!

Here is a picture can make you easier to understand the relationship between the periodic table and Electronic Configuration.

BUT NOTICE!!!!

Predicting the Number of Valence Electrons

Valence electrons: Outermost electrons of an atom (in highest energy level). These determine the chemical properties of an element.

Valence Electrons are all the electrons in an atom EXCEPT those in the core, or in the filled d- or f- subshells.

Example.

O 1s²2s²2p⁶

core notation:[He]2s²2p⁶

So the Valence Electrons of O is 8.

YOU UNDERSTAND?

Atomic Theory

We all know that atoms are the smallest particles of an element and they have the same properties of the element. But thousands of years ago, scientists were experimenting and proposing different theories before the modern atomic theory was proven.

Aristotle proposed the Four Elemenrs Theory, which basically stated that matter was made of earth, air, water, and fire. This theory lasted for 2000 years but was rejected because it couldn't be tested and proven.

Lavoisier stated the first version of the Law of Conservation and Mass and the Law of Definite Proportions.
Proust later proved Lavoidier's Laws to be true.

These are the 5 points of Dalton's Theory:
1) elements are made of atoms, which are tiny particles
2) atoms of the same element are the same
3) atoms in different elements are different and can be distinguished by their weights
4) chemical bonds are formed by the joining of atoms
5) atoms cannot be created, divided into smaller parts, or destroyed

Dalton also found out that water was always made up of 11% hydrogen and 88%oxygen, no matter how many atoms of water there were.

J.J. Thomson's theory was the first to have positive and negative charges. He proved the existence of electrons with a cathode ray tube and measured the charge to mass (e/m) ratio of electrons.

Rutherford thought atoms had a dense, positive center with electrons surrounding the center. He figured out that atoms are mostly empty space.

Niels Bohr proposed that electrons surround the nucleus in different energy levels and that when an electron jumped to the next energy level, the atom released light.

The Modern Atom Theory
The atom is the smallest particle of an element and it has the properties of that element. There are 3 subatomic particles: protons (positive), electrons (negative), and neutrons (no charge).

Here is a detailed timeline of scientists that used their observations and experiments to come up with their own theories of the atom before our modern day atom theory was proposed:
http://www.timelineindex.com/content/view/1228

Enjoy this fun, but educational video!
The Atom Song :)

** Note: Remember our Atomic Theory Timeline assignment is due on Wednesday!**

Percent Yield

Percent Yield is the amount of product obtained in a chemical reaction
It can be determined by the masses used in a reaction and the mole ratios in the balanced equation.

A good website for self study:
http://www.chemcollective.org/stoich/percentyield.php

Example 1:

For the balanced equation shown below, if the reaction of 50.6 grams of Pb(NO₃)₂ produces a 74.2% yield, how many grams of PbO would be produced ?
2Pb(NO₃)₂=>2PbO+4NO₂+O₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of PbO:(mass of PbO)/(mass of Pb(NO₃)₂)*given mass
93.94/310*50.6=15.3
Multiplying the theoretical yield by the percent (and dividing by 100), provides the actual yield.
(theory*%yield)/100=actual yield
(15.3*74.2)/100=11.4

Example 2:

For the balanced equation shown below, if the reaction of 57.4 grams of N₂ produces 107 grams of Mg₃N₂, what is the percent yield?
3Mg+N₂=>Mg₃N₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of Mg₃N₂:(mass of Mg₃N₂)/(mass of N₂)*given mass
100.9/28.01*57.4=207
The percent yield is determined as follows:
(actual/theory)*100=%yield
(107/207)*100=51.5%

Example 3:

For the balanced equation shown below, if the reaction of 54.9 grams of C₂H₃O₂Cl produces 32.6 grams of CO₂, what is the percent yield?
4C₂H₃O₂Cl+7O₂=>8CO₂+6H₂O+2Cl₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of CO₂:(mass of CO₂)/(mass of C₂H₃O₂Cl)*given mass
352.08/378*54.9=51.1
The percent yield is determined as follows:
(actual/theory)*100=%yield
(32.6/51.1)*100=63.8%

Here is video about the percent yield found on YouTuBe

Volume @ STP

All of the problems in this set are stoichiometry problems with at least one equation participant as a gas at STP. These questions always refer to chemical reaction.So before we calculating,we must write and balance the equation.You will be given an amount of one of the equation to calculate how much another one of the equation.We know:1 mol of gas=22.4 liters at STP.If the question refer to the mass of one of the equation, we must use the formula weight of the material to change from mass to mols.Then we can work out the volume of the gas of that equation.Here is an example.

10 grams of calcium carbonate,CaCO₃_,was produced when carbon dioxide was added to lime water (calcium hydroxide in solution). What volume of carbon dioxide at STP was needed?

Given:10 grams of CaCO₃ (the mass of CaCO₃)
Find:the volume of carbon dioxide(in liters at STP)

CO₂ + Ca(OH)₂

CaCO₃ + H₂O

Look~we work out the question!

BUT!NOTICE!IT'S At STP only!

Now let's look the map,it's the relationship between mass,moles&volume.

Then you can deal with all this kind of questions,can't you?

Stoichiometry Calculations!

Today, we learned how to do stoichiometry calculations involving particles, moles, and mass. These calculations are somewhat similar to mole conversions except, instead of converting between particles, moles, or mass of just one element in the problem, you can convert between particles, moles, or mass of more than one element.
*But remember, they are much harder than mole conversioins because you have to use your knowledge of all the mole conversions we've learned in the past, plus what we learned last day about the mole ratio to do these stoichiometry calculations.

Here is a helpful website with worksheets, pratice questions, and facts about stoichiometry calculations:
http://www.science.uwaterloo.ca/~cchieh/cact/c120/stoichio.html

Remember to use a concept map like this to organize the pathway of your conversions. You don't want to make silly mistakes!!!

^Road map for stoichiometry calculations^

Here is a video example that takes us through each step we must take in order to reach the answer:

Stoichiometry

Stoichiometry
a branch of chemistry that deals with the quantitative relationships that exist between the reactants and products in chemical reactions.
In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers. For example, in a reaction that forms ammonia (NH3), exactly one molecule of nitrogen (N2) reacts with three molecules of hydrogen (H2) to produce two molecules of NH3:

N2 + 3H2 → 2NH3

A chemical equation is an expression of a chemical process. For example:

AgNO₃(aq) + NaCl(aq) ---> AgCl(s) + NaNO₃(aq) In this equation, AgNO₃ is mixed with NaCl. The equation shows that the reactants (AgNO₃ and NaCl) react through some process (--->) to form the products (AgCl and NaNO₃). Since they undergo a chemical process, they are changed fundamentally.
Often chemical equations are written showing the state that each substance is in. The (s) sign means that the compound is a solid. The (l) sign means the substance is a liquid. The (aq) sign stands for aqueous in water and means the compound is dissolved in water. Finally, the (g) sign means that the compound is a gas.
Coefficients are used in all chemical equations to show the relative amounts of each substance present. This amount can represent either the relative number of molecules, or the relative number of moles (described below). If no coefficient is shown, a one (1) is assumed.

To solve questions as conversions, you need to have conversion factors. Conversion factors relate units to one another. For example, there are 100 cents in 1 dollar, or 100 cents = $1. To use this as a conversion factor, write it as a fraction:

Since 100 cents = 1 dollar, this fraction is equal to 1. That means you can multiply it by anything else, and still have the same quantity that you started with. For example, if you want to convert $5.27 to cents, you can multiply it by the fraction. The dollars cancel out, leaving you with 525 cents:

We can also flip the fraction to get a new conversion factor:

As long as the top and bottom are equal to one another, and we're careful to cancel out units to see what we have left, we can string conversion factors like this together to convert from a starting number to a final answer.

That brings us to stoichiometry. Stoichiometry is the study of relationships in chemical reactions. in other words, it's the study of what amounts of things are equal to amounts of other things in chemical reactions.

Stoichiometry Tutorial website: http://www.chemical-stoichiometry.net/

Endothermic and Exothermic Reactions

We all know that an exothermic reaction gives off energy in the form of heat, light, or sound, and that an endothermic reaction absorbs energy. If the reaction takes more energy to break the bonds that hold molecules together, it is endothermic. If it takes less energy, the reaction is exothermic.

ENTHALPY, or "H", is the sum of all kinetic and potential energies in a system. You will see this term used many times.

Change in enthalpy is denoted as 'delta' H.

Exothermic reactions result in a negative enthalpy, or negative "H". Also, endothermic reactions are characterized by a positive heat flow, or positive "H".

An example of an endothermic reaction is photosynthesis. Plants convert CO2 and water into oxygen and glucose from the energy from the sun.
The general formula of an endothermic reaction is:
A + B + Energy --> AB

The burning of any substance is an example of an exothermic reaction.
The general form of an exothermic reaction is:
A + B --> AB + Energy

Energy diagrams tell us about the relative rate of a chemical reaction. They are also called potential energy diagrams or chemical reaction energy reactions.
Here is an energy diagram of a exothermic reaction:

This is an energy diagram of an endothermic reaction:

where: (a) is the activation energy, which is the energy required to initiate a chemical reaction,
(b) is the change between the reactants and products,
and (c) is the change in energy, or enthalpy

Check out this video! I hope it helps!

Here is a FUN quiz about exothermic and endothermic that you can do :)http://www.softschools.com/quizzes/science/chemical_reactions/quiz380.html

Chemical Reaction Lab

Today, we did a lab about chemical reactions.

The purpose of the lab is to observe a variety of chemical reactions and to interpret and explain obsevations with balanced chemical equations and classify each reactions asa one of the four main types.

There was a reaction where we added solid copper(II) sulfate pentahydrate to a test tube and heated it over a Bunsen burner. Over time, the copper(II) sulfate pentahydrate changed colors (blue to white)

In this reaction, we took the results of the reaction above and added drops of water to it. The copper (II) sulfate pentahydrate changed from white to blue color.

Basically, there are four types of reactions in this lab: synthesis, decomposition, single replacement and double replacement.

There is an interesting website showing the flash of combustion, if you are interested, click the link:
http://www.pbs.org/wgbh/nova/fireworks/fire.html