A Whirlwind Introduction to Bohr Model and Quantum

Mechanical Model

We’ve got a lot to do, so let’s get going!!

Remember Niels Bohr?

• What was Bohr’s main contribution?– Planetary model of the atom– Electrons orbit the nucleus.

• Each orbit (also called shells) has a specific amount of energy.

• Each orbit also has a maximum number of electrons it can hold.

– Electrons must be in an orbit; they cannot be in between.

How About Those Energy Levels?

• Orbits labeled with whole numbers, n=1, n=2, n=3, etc.

• Closer to the Nucleus = Less Energy.

How Much Can an Orbit Hold?

Must fill up the lower-energy shells before moving outward.

How to Draw Bohr Models

1. Find number of electrons.• For a neutral (no charge) atom,

atomic # = # protons = # electrons

2. Draw a nucleus in the middle.

3. Draw circles for electron shells.

4. Place dots on shells to represent electrons.

What Would be the Bohr Model for Al?1. Atomic # = ?

• # protons = ?• # electrons = ?

2. Maximum numbers to fill up shells• Maximum # electrons in 1st shell?

– Do you have that many to put in there?– If you fill up that shell, how may e- are left?

• Maximum # electrons in 2nd shell?– Do you have that many to put in there?– If you fill up that shell, how may e- are left?

• Maximum # electrons in 3rd shell?– Do you have that many to put in there?– Can you leave the very outer one partly empty?– So how many total will you put in the 3rd level?

3. Then draw it!

13

1313

2yes

13-2=11

8yes

11-8 = 318

noyes

3

Isn’t It Pretty?

Notice e- are in pairs except for n=1. Not necessary, but would be good to start practicing.

You Do One!

• You knew that was coming, didn’t you?

• Do Chlorine, Cl!

Check It!• Cl: atomic number = 17 = 17p+ = 17e-

• 1st shell holds 2 (17-2 = 15 left)• 2nd shell holds 8 (15-8 = 7 left)• 3rd shell holds 18 (rest will fit in there)

Groupwork, Everybody’s Favorite!

1. Without leaving your seat, find a group of 3.

2. Slide your desks together gently.

3. ONE person from each group needs to come get 1 piece of paper and 1 marker.

4. Hold it portrait style.

5. Draw lines to make three even sections.

6. Lay your heads down when you’re done.

In each section…

Element Name, Symbol

1st shell = ___ electrons Bohr

2nd shell = ___ electrons model

3rd shell = ___ electrons

Now Homework…Yay!

• More practice with Bohr models!!– Hydrogen, H– Oxygen, O– Helium, He– Magnesium, Mg

• Don’t get excited; we’re not done!

Electron Movements

• Ground state: energy level an electron usually occupies

• But it can move to a higher-energy, less stable level, called an excited state.

• After it’s done being excited, the electron can release the energy and move back down to ground state.

See?

I’ve Had Enough of Bohr…

• Bohr’s model worked great for H, but not so great for the rest of the elements.

• Quantum Mechanical Model was established and in use today!

Quantum Mechanical Model

• Like Bohr’s model, electrons exist in energy levels (and not in between).

• Like Bohr, the levels are labeled as whole numbers, from the inside to the outside.

• Like Bohr, the lower n, the lower energy.

• Unlike Bohr, this model has electron clouds (also called orbitals) instead of orbits which show where an electron is likely to be.

Sounds Fascinating, Right?!

• It is!!

• The different electron clouds have different shapes, and there is a letter associated with each!

• Get excited!!

s orbital

• Spherical shape• Can hold up to 2 e-

• Lowest energy

Color in s-blockHelium belongs with the s-block!

p orbital• Dumb-bell shaped• Can hold up to 6 e-

• More energy than s orbital

Color in p-blockHelium belongs with the s-block!

d orbital

• Different shapes.• Can hold up to 10 e-

• More energy than p orbital.

Color in d-block

f orbital• Very odd shapes• Can hold up to 14 e-

• Highest energy

Color in f-block:

Make them the same color…

Now let’s go practice with the shapes.

• Partners.

• Lab tables.

• Aprons, no goggles.

• 1 group per bowl.

• Put your hands on your head when you get there and are ready to go.

Instructions:

• In your bowl, add:– 1/4 cup of flour (1 scoop)– 2 tablespoons of salt (2 scoops)– 29 mL of water

• Mix well, with a spatula or your hands.

• You may make school-appropriate shapes until everyone catches up.