Something Smaller Than An Atom?

Atomic Structure

Review of the Atom

Smallest part of matter representing an element

Once was thought to be the smallest part of matter

Later, scientists discovered atoms are made of subatomic particles

Subatomic particles

Protons - positive charge Neutrons – no charge (neutral) Electrons – negative charge

Representing a Specific Element

Mass Number

(P + + No)

Atomic Number

(P+)

A

XZ

Atomic Symbol

Nucleus: Center Stage

Ernest Rutherford discovered atoms have a nucleus (1911)

Later scientists discovered that the nucleus also contains all the neutrons

Rutherford’s Model Discovered the

nucleus Electrons moved

around in Electron cloud

Mostly empty space

Where are those electrons?

Early models of the atom showed electrons spinning around the nucleus randomly

Research showed that this is NOT true

Bohr’s Model Why don’t the electrons fall into the

nucleus? Move like planets around the sun. In circular orbits at different levels. Energy separates one level from

another.

Bohr’s Model

Nucleus

Electron

Orbit

Energy Levels

More about Bohr….. Created a model showing electrons are in

orbits of different energy around the nucleus

…… Think of the planets orbiting the sun

Bohr used the term energy levels (or shells) to describe these orbits with different amounts of energy. He also said that the energy of an

electron is quantized, meaning electrons can have one energy level or another but nothing in between.

Bohr’s ModelIn

crea

sing

ene

rgy

Nucleus

First

Second

Third

Fourth

Fifth

} Further away

from the nucleus means more energy.

There is no “in between” energy

Energy Levels

Let’s get close to the nucleus

Bohr found that the closer an electron is to the nucleus, the less energy it needs.

The farther away it is, the more energy it needs

He numbered the electron’s energy levels

Energy levels

1st level can hold up to 2 electrons 2nd level can hold up to 8 electrons 3rd level can hold up to 18 electrons And so on……..

Energy levels

E-level an electron normally occupies is called ground state

But, electrons can move to a higher –energy, less-stable level, or shell, by absorbing energy.

This higher energy, less-stable state is called the electron’s excited state.

The electron gets crunk…..

When the electron is finished being excited it goes back to its ground state by releasing some of the energy it has absorbed

Line spectrum…..what is that???

Energy released by electrons sometimes occupies part of the electromagnetic spectrum that humans detect as visible light

Problem with Bohr’s model

Unexplainable observations on complex atoms until the quantum theory was created

Quantum theory ----- matter has properties associated with waves.

It is impossible to know the exact position and momentum (speed and direction) of an electron at the same time. ------UNCERTAINTY PRINCIPLE

The Quantum Mechanical Model

Energy is quantized. It comes in chunks. Quanta - the amount of energy needed to

move from one energy level to another. Quantum leap in energy. Treated electrons as waves

Does have energy levels for electrons.

Orbits are not circular. It can only tell us the

probability of finding an electron a certain distance from the nucleus.

The Quantum Mechanical Model

The electron is found inside a blurry “electron cloud”

A area where there is a chance of finding an electron.

The Quantum Mechanical Model

Quantum mechanical model of the atom

Pay attention so you don’t get LOST !!!!!!!

Atomic Orbitals Principal Quantum Number (n) = the

energy level of the electron. Within each energy level the complex

math of Schrödinger's equation describes several shapes.

These are called atomic orbitals Regions where there is a high probability

of finding an electron.

1 s orbital for every energy level Spherical

shaped

Each s orbital can hold 2 electrons Called the 1s, 2s, 3s, etc.. orbitals.

S orbitals

P orbitals Start at the second energy level 3 different directions 3 different shapes (dumbell) Each can hold 2 electrons

D orbitals Start at the third energy level 5 different shapes Each can hold 2 electrons

F orbitals Start at the fourth energy level Have seven different shapes 2 electrons per shape

Summary

s

p

d

f

# of shapes

Max electrons

Starts at energy level

1 2 1

3 6 2

5 10 3

7 14 4

Bed check for Electrons…Electron Configurations…… Goal: Use an energy level diagram to

depict electrons for any element 1s orbital is closest to the nucleus and it

has the lowest energy At energy level 2, there are both s and p

orbitals, with the 2s having lower energy than the 2p.

Energy level diagram continued

The three 2p subshells are represented by three dashes of the same energy.

Energy levels 3, 4, and 5 are also shown Notice, that 4s has lower energy than the

3d. This is an exception to what you thought but it does occur in nature like this.

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

Electron Configurations The way electrons are arranged in

atoms. Aufbau principle- electrons enter the

lowest energy first. This causes difficulties because of the

overlap of orbitals of different energies. Pauli Exclusion Principle- at most 2

electrons per orbital - different spins

Aufbau Principle Method for remembering the order in which orbitals fill

the vacant energy levels (like a people fill up vacant rooms in a hotel)

RULE: ELECTRONS FILL THE LOWEST VACANY ENERGY LEVELS FIRST.

ANOTHER RULE: WHEN THERE’S MORE THAN ONE SUB-SHELL AT A PARTICULAR ENERGY LEVEL, SUCH AS AT THE 3P OR 4 D LEVELS, ONLY ONE ELECTRON FILLS EACH SUB-SHELL UNTIL EACH SUBSHELL HAS ONE ELECTRON.

THEN, ELECTRONS START PAIRING UP IN EACH SUBSHELL.

THIS RULE IS CALLED HUND’S RULE.

Electron Configuration

Hund’s Rule- When electrons occupy orbitals of equal energy they don’t pair up until they have to .

Let’s determine the electron configuration for Phosphorus

Need to account for 15 electrons

The first to electrons go into the 1s orbital

Notice the opposite spins

only 13 moreIncr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

The next electrons go into the 2s orbital

only 11 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 2p orbital

• only 5 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 3s orbital

• only 3 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The last three electrons go into the 3p orbitals.

• They each go into separate shapes

• 3 unpaired electrons• 1s22s22p63s23p3

The easy way to remember

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2

• 2 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2

• 4 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

• 12 electrons

Fill from the bottom up following the arrows

1s2s 2p3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

• 1s2 2s2 2p6 3s2

3p6 4s2

• 20 electrons

Draw the energy level diagram of oxygen

Find oxygen on the period table Atomic number = 8 Therefore, it has 8 protons and 8 electrons So, you put 8 electrons into your energy

level diagrams

Energy level diagram for oxygen Use arrows to represent electrons If two electrons fit in the same orbital, one

must face up and the other one down

The first electron goes into the 1s orbital, filling the lowest energy level first.

And, the second one spin pairs with the first one.

Electrons 3 and 4 spin pair in the next lowest vacant orbital – the 2 s.

Electron 5 goes into one of the 2p sub-shells

Electrons 6 and 7 go into the other two totally vacant 2p orbitals

The last electron spin pairs with one of the electrons in the 2p subshells.

Electron Configuration Oxygen 1s22s22p4

You can derive the electron configuration from the energy level diagram.

The first two electrons in oxygen fill the 1s orbital, so you it as 1s2 in the electron configuration.

The 1 is the energy level, the s represents the type of orbital, and the superscript 2 represents the number of electrons in that orbital.

The next two electrons are in the 2s orbital, so you write 2s2.

Last, you show the 4 electrons in the 2p orbital as 2p4.

That’s how you get 1s22s22p4.

Tip

The sum of the superscript numbers equals the atomic number, or the number of electrons in the atom.

Exceptions to Electron Configuration

Orbitals fill in order Lowest energy to higher energy. Adding electrons can change the energy

of the orbital. Filled and half-filled orbitals have a lower

energy. Makes them more stable. Changes the filling order of d orbitals

Copper’s electron configuration Copper has 29 electrons so we expect 1s22s22p63s23p64s23d9

But the actual configuration is 1s22s22p63s23p64s13d10

This gives one filled orbital and one half filled orbital.

Remember these exceptionss2d4 s1d5

s2d9 s1d10

Here are a couple of electron configurations you can use to check your conversions from energy level diagrams:

Chlorine (Cl)

Iron (Fe)

Answers

Answer: Cl 1s22s22p63s23p5

Answer: Fe 1s22s22p63s23p64s23d6