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Ionic radius, rion, is a measure of the size of an atom's ion in a crystal lattice. It is measured in either picometres (pm) or Angstrom (Ã…), with 1 Ã… = 100 pm. Typical values range from 30 pm (0.3 Ã…) to over 200 pm (2 Ã…).
The concept of ionic radius was developed independently by Victor Goldschmidt and Linus Pauling in the 1920s to summarize the data being generated by the (at the time) new technique of X-ray crystallography: it is Pauling's approach which proved to be the more influential. X-ray crystallography can readily give the length of the side of the unit cell of a crystal, but it is much more difficult (in most cases impossible, even with more modern techniques) to distinguish a boundary between two ions. For example, it can be readily determined that each side of the unit cell of sodium chloride is 564.02 pm in length, and that this length is twice the distance between the centre of a sodium ion and the centre of a chloride ion:
- 2[rion(Na+) + rion(Clâˆ’)] = 564.02 pm
However, it is not apparent what proportion of this distance is due to the size of the sodium ion and what proportion is due to the size of the chloride ion. By comparing many different compounds, and with a certain amount of chemical intuition, Pauling decided to assign a radius of 140 pm to the oxide ion O2âˆ’, at which point he was able to calculate the radii of the other ions by subtraction.
A major review of crystallographic data led to the publication of a revised set of ionic radii in 1976, and these are preferred to Pauling's original values. Some sources have retained Pauling's reference of rion(O2âˆ’) = 140 pm, while other sources prefer to list "effective" ionic radii based on rion(O2âˆ’) = 126 pm. The latter values are thought to be a more accurate approximation to the "true" relative sizes of anions and cations in ionic crystals.
The ionic radius is not a fixed property of a given ion, but varies with coordination number, spin state and other parameters. Nevertheless, ionic radius values are sufficiently transferable to allow periodic trends to be recognized. As with other types of atomic radius, ionic radii increase on descending a group. Ionic size (for the same ion) also increases with increasing coordination number, and an ion in a high-spin state will be larger than the same ion in a low-spin state. Anions (negatively charged) are almost invariably larger than cations (positively charged), although the fluorides of some alkali metals are rare exceptions. In general, ionic radius decreases with increasing positive charge and increases with increasing negative charge.
An "anomalous" ionic radius in a crystal is often a sign of significant covalent character in the bonding. No bond is completely ionic, and some supposedly "ionic" compounds, especially of the transition metals, are particularly covalent in character. This is illustrated by the unit cell parameters for sodium and silverhalides in the table. On the basis of the fluorides, one would say that Ag+ is larger than Na+, but on the basis of the chlorides and bromides the opposite appears to be true. This is because the greater covalent character of the bonds in AgCl and AgBr reduces the bond length and hence the apparent ionic radius of Ag+, an effect which is not present in the halides of the more electropositive sodium, nor in silver fluoride in which the fluoride ion is relatively unpolarizable.
The concept of ionic radii is based on the assumption of a spherical ion shape. However, from a group-theoretical point of view the assumption is only justified for ions that reside on high-symmetry crystal lattice sites like Na and Cl in halite or Zn and S in sphalerite. A clear distinction can be made, when the point symmetry group of the respective lattice site is considered, which are the cubic groups O6 and Td in NaCl and ZnS. For ions on lower-symmetry sites significant deviations of their electron density from a spherical shape may occur. This holds in particular for ions on lattice sites of polar symmetry, which are the crystallographic point groups C1, C1h, Cn or Cnv, n = 2, 3, 4 or 6. A thorough analysis of the bonding geometry was recently carried out for pyrite-type disulfides, where monovalent markup languagesSGML, HTML, XHTML and XML, a character entity reference is a reference to a particular kind of named entity that has been predefined or explicitly declared in a Document Type Definition (DTD). The "replacement text" of the entity consists of a single character from the Universal Character Set/Unicode. The purpose of a character entity reference is to provide a way to refer to a character that is not universally encodable.
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From Yahoo Answers
Question:What is the relationship between electro-negativity and the ionic character of a chemical bond?
Answers:The greater the electronegativity difference, the greater the percent ionic character in a bond.
Percent ionic character = 100(1-e^-DEN^2/4))
Question:The property useful in the prediction of percentage of ionic character in a covalent molecule is
1. electron gain enthalpy
3. ionisation potential
4. ionic radii
The greater the electronegativity difference between two bonded atoms, the greater the percentage ionic character.
Question:What is the percent ionic character of al2o3 and what type of bonding is expected from al? al2o3?
Answers:Percent ionic character is determined by finding the difference in electronegativity values (can be found in data tables) and then relating this to percentage ionic character data in another table.
This http://www2.ucdsb.on.ca/tiss/stretton/database/electronegativity.htm gives you both.
Al: el. neg 1.5 and O: el.neg 3.5 so difference is 2 which gives 63% ionic character.
(if you want to see how these numbers are calculated see http://www.chemistry.mcmaster.ca/esam/Chapter_7/problems.html)
Given the percent ionic character I would describe the Al-O bond as highly polar covalent.
Question:Everyone has a personality of a cartoon character. Have you ever asked yourself what cartoon character do you most resemble?
A group of investigators got together and analyzed the personalities of well known and modern cartoon characters. The information that was gathered was made into this test.
Answer all the questions (only 10) with what describes you best, add up all your Points (which are next to the answer that you choose) at the end and look for your results.
Do not cheat by looking at the end of the e-mail before you are done.
Then forward this to all your friends ( including the person who sent it to you ) and change the subject of this message to what character is you.
1. Which one of the following describes the perfect date?
.a) Candlelight dinner (4 pts .)
.b) Fun/Theme Park (2 pts .)
.c) Painting in the park (5 pts )
.d) Rock concert (1 pt ..)
.e) Going to the movies (3 pts .)
2. What is your favorite type of music?
.a) Rock and Roll (2 pts .)
.b) Alternative (1 pt .)
.c) Soft Rock (4 pts .)
.d) Country (5 pts .)
.e) Pop (3 pts .)
3. What type of movies do you prefer?
.a) Comedy (2 pts .)
.b) Horror (1 pt .)
.c) Musical (3 pts ..)
.d) Romance (4 pts .)
.e) Documentary (5 pts .)
4. Which one of these occupations would you choose if you only could choose one of these?
.a) Waiter (4 pts .)
.b) Professional Sports Player (5 pts .)
.c) Teacher (3 pts .)
d) Police (2 pts .)
.e) Cashier (1 pt )
5. What do you do with your spare time?
.a) Exercise (5 pts .)
.b) Read (4 pts .)
.c) Watch television (2 pts .)
.d) Listen to music (1 pt .)
.e) Sleep (3 pts .)
6. Which one of the following colors do you like best?
.a) Yellow (1 pt .)
.b) White (5 pts .)
.c) Sky Blue (3 pts .)
.d) Dark Blue (2 pts .)
.e) Red (4 pts .)
7. What do you prefer to eat?
.a) Snow (3 pts .)
.b) Pizza (2 pts .)
.c) Sushi (1 pt .)
.d) Pasta (4 pts .)
.e) Salad (5 pts .)
8 What is your favorite holiday?
.a) Halloween (1 pt .)
.b) Christmas (3 pts .)
.c) New Year (2 pts .)
.d) Valentine's Day (4 pts .)
.e) Thanksgiving (5 pts .)
9. If you could go to one of these places which one would it be?
.a) Paris (4 pts )
.b) Spain (5 pts )
.c) Las Vegas (1 pt )
.d) Hawaii (4 pts )
.e) Hollywood (3 pts )
10. With which of the following would you prefer to spend time with?
.a) Someone Smart (5 pts .)
.b) Someone attractive (2 pts .)
.c) Someone who likes to Party (1 pt .)
.d) Someone who always has fun (3 pts .)
.e) Someone very sentimental (4 pts .)
Now add up your points and find out the answer you have been waiting for!
Put your character in the subject line and forward to your friends and back to the person that sent this to you.
It is very interesting to see "who" your friends are!
(10-16 points) You are Garfield :
You are very comfortable, easy going, and you definitely know how to have fun but sometimes you take it to an extreme. You always know what you are doing and you are always in control of your life. Others may not see things as you do, but that doesn't mean that you always have to do what is right. Try to remember, your happy spirit may hurt you or others.
(17-23 points) You are Snoopy:
You are fun, you are very cool and popular. You always know what's in and you are never are out of style You are good at knowing how to satisfy everyone else. You have probably disappeared for a few days more than once but you always come home with the family values that you learned Being married and having children are important to you, but only after you have had your share of fun times
(24-28 points) You are Elmo :
You have lots of friends and you are also popular, always willing to give advice and help out a person in need. You are very optimistic and you always see the bright side of things. Some good advice: try not to be too much of a dreamer. Dreaming too big could cause many conflicts in your life.
(29-35 points) You are Sponge Bob Square Pants:
You are the classic person that everyone loves. You are the best friend that anyone could ever have and never wants to lose. You never cause harm to anyone and they would never not understand your feelings. Life is a journey, it's funny and calm for the most part. Stay away from traitors and jealous people, and you will be stress free.
(36-43 points) You are Charlie Brown:
You are tender, you fall in love quickly but you are also very serious about all relationships. You are a family person. You call your Mom every Sunday. You have many friends and may occasionally forget a few Birthdays. Don't let your passion confuse you with reality.
(44-50 points) You are Dexter :
You are smart and definitely a thinker... Every situation is fronted with a plan. You have a brilliant mind. You demonstrate very strong family principles. You maintain a stable routine but never ignore a bad situation when it comes. Try to do less over thinking every once in a while to spice things up a bit with spontaneity! I'm Sponge Bob Square Pants
Answers:Sponge Bob YAY!
Transformers: War for Cybertron Multiplayer Character Trailer :GameSpot presents us the Multiplayer details of Transformers: War For Cybertron, which features 4 Character Classes: Soldier, Scout, Scientist and Leader. Also, we are treated with a brief look at the Character Customization Screen, showing-off the Cybertronian Weapon Systems, which the player must equip. To top it all up, a sneak peek at the Character Special Abilities and Repaints. Watch and Download High Definition versions here : www.gamespot.com
Children Books That Teach Good Character Traits :"Books should definitely teach us good character traits," says Sherri Carden, author of the children's series "Mocha Latte With a Dash of Chili." "In fact, Mocha Latte is extremely helpful, has an optimistic approach to things, and is a leader." The problem is that it's hard to find characters that your kids will love and learn from that don't bore you, the parent, to tears. Sherri created her kids series to provide fun, creativity, flights of fancy and hands on learning. Meet Mocha Latte, Dash, and Chili. Three animal friends learning life lessons and having a blast together in Hawaii. She's also taken the mystery out of finding great books for young readers. Here are a few tips that are sure to help your kids find and enjoy stories that will stretch their imaginations: 1. The Main Character/s Look for characters that are respectful, thoughtful and helpful. You won't be sorry when you kids learn that's a great way to act and have fun. 2. The Setting Help your child find stories that will allow them experiences they don't get everyday. 3. What Values does it teach? Entertainment only books, while popular, tend to teach things like competition, irresponsibility, and violence. ********** About the Author: Dr. Proactive, Randy Gilbert producer of Inside Success Radio, enjoyed learning from Sherri Carden (www.MochaLatteWithADashOfChili.com) when she was interviewed on The Inside Success Show. Get many more tips by enjoying the entire interview for free. Go to http