Bellwork How many electrons can any orbital hold? How many orientations of an s orbital are there? How many orientations of a p orbital are there? What orbitals are in the 2 nd energy level? How many electrons can this level hold?

Chapter 4 Section 3 Modern Atomic Theory

Bellwork 2/17 1.What is the relationship between electrons, orbitals and energy levels. 2.Compare the positions of electrons in Bohr’s model with their positions according to modern atomic theory. 3.What is the maximum number of electrons that each energy level can hold. 4.Compare the four types of orbitals.

Things we get to learn about! 1. Bohr's model of the atom and the wave- particle model. 2. Electron orbitals (not orbits), electron energy levels, and valence electrons. 3. What a photon is and what photon absorption and emission mean.

Where a ping-pong ball plays the part of an electron... A volunteer, please! We get to see the difference between potential energy and kinetic energy...

Dalton's theory had to be modified... The model of the atom has been revised many times to explain new discoveries. When we left our model, Chadwick had put the finishing touches on the nucleus. Everything there is all sorted out. The question remained, however, what are those pesky electrons doing?

Niels Bohr to the rescue! One way to visualize Bohr's model is to compare an atom to a stairless building.

Niels Bohr suggested that the energy of each electron was related to the electron's path around the nucleus. He figured that electrons can be in only certain energy levels. They must gain energy to move to a higher energy level or must lose energy to move to a lower energy level. What do you notice about the height of each floor?

The energy difference between energy levels decreases as the energy level increases. Bohr's description of energy levels is still used by scientists today.

Imagined that the nucleus is in a deep basement. The energy levels begin on the 1st floor. Electrons can be on any floor, but they cannot be between floors. The electrons gain energy by riding up the elevator and lose energy by riding down.

But by already obsolete. By 1925, Bohr's model no longer explained everything known about electron behavior. Bohr's model had electrons orbiting the nucleus, like planets around the sun. It turns out, that's not what they do! Electrons behave more like waves on a vibrating string than like particles.

The exact location of an electron cannot be determined.

Electron orbitals Determining the speed and direction of an electron and determining the exact location of an electron at the same time is impossible. The best that scientists can do is to calculate the chance of finding an electron in a certain place within an atom.

One way to show the likelihood of finding an electron in a given location is by shading. The darker the shading, the better the chance of finding an electron in that location. The shaded region is called an orbital.

Definition of an orbital This is the region in an atom where there is a high probability of finding electrons.

Electron energy levels This is an important concept: Electrons don't stay in rings around the nucleus. Energy levels aren't ring shaped. They consist of orbital shapes.

Each energy level can hold a certain number of electrons.

The number of energy levels that are filled in an atom depends on the number of electrons. Look at lithium. How many electrons does it have?

It has 3 electrons. It can have 2 electrons in the first energy level and one in the 2nd.

Valence electrons The electrons in the outer energy level of an atom are called valence electrons. Valence electrons determine the chemical properties of an atom. Lithium has 3 total electrons, but 1 electron in its outer most energy level. It has 1 valence electron.

Valence electron practice The group number (of main group elements) tells you how many valence electrons each element has. Group 1: Group 2: Groups 13 – 18 We’ll talk about transition metals later, but these metals don’t follow the same general patterns of main-group elements.

There are 4 types of orbitals... based on their shape. Within each energy level, electrons occupy orbitals. There are 4 kinds of orbitals: s, p, d and f.

The s orbital is the simplest. An s orbital is shaped like a sphere. It only has one orientation in space. It has the lowest energy. It can only ever hold 2 electrons.

A p orbital is shaped like a peanut... Or a dumbbell. It can be oriented in one of three ways. Each p orbital can hold 2 electrons, so the three p orbitals can hold a total of 6 electrons.

The d and f orbitals are much more complex. There are five possible d orbitals and seven possible f orbitals. They have different shapes, but still only hold a maximum of 2 electrons in each orbital.

Ask your partner: For each energy level, how many electrons is it possible for a d orbital to hold? How many electrons is it possible for an f orbital to hold? Is there an s orbital at each energy level? Is there a p orbital at each energy level?

Let’s figure out how many electrons are in those energy levels… The number of orbitals determines the total number of electrons in that energy level. We can make a table to sort this out.

Electrons fill the lowest energy orbitals first. When electrons build up in an atom, they always start at energy level 1 with the s orbital. The Aufbau principle shows the order in which electrons occupy orbitals. According to this principle, an electron will fill the lowest energy orbitals first then they’ll move up to higher levels. But only after the lower ones are full.

Aufbau: low to high…

Hund’s Rule: Think “one at a time”

Electrons prefer to be unpaired whenever possible. They like to go it alone until they’re forced to buddy-up.

Electron transitions The modern model of the atom limits the location of electrons to specific energy levels. An electron is never found between these levels. Instead, it “jumps” from one level to another.

What makes an electron move from one level to another? Electrons move between energy levels when an atom gains or loses energy. The lowest state of energy of an electron is called its ground state. When it gains energy, it moves to an excited state in a higher energy level.

Photons Electrons gain energy by absorbing photons. A photon is the smallest unit of light energy. It’s kind of like an atom of light. When an electron falls to a lower energy level, it releases one photon. Photons have different energies. That energy affects which energy level an electron can move to. The higher the energy, the higher the energy level the electron can jump to.

With a partner, identify the ground state and excited state electron.

Atoms and light The energy of a photon is related to the wavelength of the light. The energy that an element gains or loses corresponds to light of different wavelengths, or colors.

The colors of light that are emitted or absorbed by an element… These colors can identify the element.

Fireworks are a good example! The wavelength of visible light determine the color of the light.

Section review Handout…

Target Qs 1.What the state of an electron at low energy? At high energy? 2.What does an electron emit/absorb when it moves to different energy levels? 3.What do photons relate to (that we measure and see)? 4.The color of the light spectrum can ________ an element.