ELECTRONIC STRUCTURE: DRAWING ELECTRON DOT DIAGRAMS: November 1st, 2010

Drawing electron dot diagrams:

• The nucleus is represented by the atomic symbol
• For individual elements determine the number of valence electrons (electrons in the outermost energy level of an atom; for most atoms, it is available to be gained, lost, or shared in the formation of chemical bonds)
• Electrons are represented by dots around the symbol
• Four orbitals (one of each side of the nucleus) each holding a max of 2 electrons
• Each orbital gets 1 electron before they pair up to make a lone pair (a pair of electrons- 2 of them)

An atom of Neon can be represented by the diagram on the left. But in this case, we are drawing electronic dot diagrams. For neon, we must determine a) number of valence electrions b) place dots around the element to represent the valence electrons. Since there are 10 electrons, 2 go in the first shell but the rest (8 electrons) are in the second shell, therefore, these electrons are considered to be in the valence shell, and we label them.

Lewis Diagrams for compounds and Ions:

-In covalent compounds electrons are shared

1. Determine the number of valence electrons for each atom in the molecule

2. Place atoms so that valence electrons are shared to fill each orbital.

Compound:

We have just learned how to draw a Lewis dot diagram for a single element and a compound. An Ionic Compound presented as an electronic dot diagram has the follow:

-An ionic compounds electrons transfer from one element to another

-Determine the number of valence electrons on the cation (+) and move these to the anion (-).

-Draw [ ] around the metal and non-metal (write the charges on the outside bracket)



An example of an ionic compound: Lewis Dot Diagram



 Next we have a more complicated diagram, because it consists of a "DOUBLE BOND".

DOUBLE & TRIPLE BONDS:

Sometimes the only way covalent compounds can fill all their valence levels is if they share more than one electron.

This periodic table can also help you when drawing Electronic Dot Diagrams. Notice a trend in each group (group 1 has 1 valence electron, group 15 has 5 valence electrons and so on)

Yay, you've mastered the art of drawing Electronic dot Diagrams!

Post by Ren Flores

TRENDS ON THE PERIODIC TABLE: October 28, 2010

Elements close to eachother on the periodic table display similar characteristics

There are 7 important periodic trends:

1) Reactivity

2) Ion Charge

3) Melting Point

4) Atomic Radius

5) Ionization Energy

6) Electronegativity

7) Density

(There are more than just these 7, but these are the most important ones for us to learn at this time...)

1) REACTIVITY

- metals and non-metals shoe different trends

- the most reactive metal is Francium; the most reactive non-metal is Fluorine

-reactivity increases as you go down for metals and up for non-metals

-Noble gases are very unreactive

2) ION CHARGES

- elements ion charges depend on their group (column)

3) MELTING POINT

- elements in the centre of the table have the highest melting point

- noble gases have the lowest melting points

- starting from the left and moving right, melting point increases (until the middle of the table, it then starts to decrease)

-an exception to this rule is Carbon. Carbon has a high melting point!

4) ATOMIC RADIUS

- radius decrease to the up and the right

- Helium has the smallest atomic radius

- Francium has the largest atomic radius

5) IONIZATION ENERGY
- ionization energy is the energy needed to completely remove an electron from an atom

- it increases going up and to the right

- all noble gases have high ionization energy

- Helium has the highest I.E.

- Francium has the lowest I.E.

- opposite trend from atomic radius
-Quick note: think about why Ionization energy has the opposite trend of the Atomic radius. Since the atomic radius gets smaller when ionization energy increases, it tells us that when the shells are smaller, the energy needed to completely remove an electron is easier, therefore, electrons can leave their small atomic radius which is an increase in ionization energy.

6) ELECTRONEGATIVITY

- refers to how much atoms want to gain electrons
- same trend as I.E.

7) DENSITY

...yet to be learned!

and our own pictures!

Post by: Adrienne Ross (with pictures from Ren Flores)

ISOTOPES AND ATOMS: October 26, 2010

Today we learned about Isotopes! We have already learned that ions are atoms that are either missing or have extra electrons. Let's say an atom is missing a neutron or has an extra neutron. That type of atom is called an isotope. An atom is still the same element if it is missing an electron. The same goes for isotopes. They are still the same element. They are just a little different from every other atom of the same element.

*Note: the most common ion charge is listed on top (if theres 2 or more charges)

* Atomic mass - Atomic number = # of neutrons

*If you are given the atomic number and number of neutrons, add them to get the mass number

A decimal found in the atomic mass is an average of the isotopes

Going good so far? Great.

Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of charged particles.^[1] It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and other chemical compounds. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass-to-charge ratios.^[1] In a typical MS procedure:

1. A sample is loaded onto the MS instrument, and undergoes vaporization
2. The components of the sample are ionized by one of a variety of methods (e.g., by impacting them with an electron beam), which results in the formation of charged particles (ions)
3. The ions are separated according to their mass-to-charge ratio in an analyzer by electromagnetic fields
4. The ions are detected, usually by a quantitative method
5. The ion signal is processed into mass spectra

-Source: Wikipedia

Now its your turn! Fill out the chart on isotopes!

Answers: Row 1: 28 neutrons. Row 2: Mn(Manganese) Protons:25 Netruons: 31 Row 3: Mass # 12, Atomic #:6, # of protons: 6, # of neutrons 6

Post by Ren Flores

BOHR'S MODEL: October 15, 2010

Now that you know the history of atomic theory, let's move on to the more modern stuff, such as Bohr's atomic model!

BOHR (1920S)

• Rutherford's model was inherently usable (protons and electrons should attract to eachother, no?)
• Matter emits light when it is heated (black body radiation)
• Light travels as photons
• The engerdy photons carry depend on their wave length
• Bohr based his model on the engery (light) emitted by different atoms
• - Each atom has a specific spectra of light
• To explain this emission spectra, Bohr suggested that electrons occupy shells or orbitals

Summerizing Bohr's Theory

• Electrons exist in orbitals
• When they absorb energy, they move to a higher orbital
• As they fall from a higher orbital to a lower one, they release energy as a photon of light

Hmm...

When electrons move from level to level (depending on the energy), they don't travel there, they actually just appear there, you could call it "transporting".

This led to us learning (by questioning Mr.Doktor) that scientists have tried harnessing this power to transport more than just an electron. Too bad the most they've ever managed to transport was about 5 atoms...

Still, we never know what lies in the future! Maybe one day we will all quit walking and physical activity and just transport everywhere we go!

Borh-d? (Get it?...Haha.)

Check out

http://phet.colorado.edu/en/simulation/hydrogen-atom

to play around with a hydrogen atom and see many of the different atomic models!

Post by Adrienne Ross