Energy LevelsEnergy Levels

Each electron in an atom has a specific Each electron in an atom has a specific

amount of energy. If an atom gains or loses amount of energy. If an atom gains or loses

energy, the energy of an electron can changeenergy, the energy of an electron can change

..

Energy LevelsEnergy Levels

Energy Levels: the possible energies that Energy Levels: the possible energies that electrons in an atom can have electrons in an atom can have

Example: A person walking up and down Example: A person walking up and down steps on a stair casesteps on a stair case

An electron in an atom can move from one An electron in an atom can move from one energy level to another when the atom energy level to another when the atom gains or loses energygains or loses energy

Evidence for Energy LevelsEvidence for Energy Levels What evidence is there that electrons can move What evidence is there that electrons can move

from one energy level to another?from one energy level to another?

Scientists can measure the energy Scientists can measure the energy gained when the electrons move to a higher gained when the electrons move to a higher energy level. They can measure the energy energy level. They can measure the energy released when the electron returns to the lower released when the electron returns to the lower energy levelenergy level

Example: The movement of electrons between Example: The movement of electrons between energy levels explains the light you see when energy levels explains the light you see when fireworks explodefireworks explode

Electron Cloud ModelElectron Cloud Model

Bohr’s model was improved as scientists Bohr’s model was improved as scientists made further discoveries.made further discoveries.

Bohr was correct when he said that Bohr was correct when he said that electrons are located in certain energy electrons are located in certain energy levels. However he was incorrect in levels. However he was incorrect in assuming that electrons moved like assuming that electrons moved like planets in a solar system. Today scientists planets in a solar system. Today scientists know that electrons move in a less know that electrons move in a less predictable way.predictable way.

Electron Cloud ModelElectron Cloud Model

Electron Cloud: a visual model of the most Electron Cloud: a visual model of the most likely locations for electrons in an atom. likely locations for electrons in an atom.

The cloud is denser at those locations where The cloud is denser at those locations where the probability of finding an electron is high. the probability of finding an electron is high. Scientists use the electron cloud model to Scientists use the electron cloud model to describe the possible locations of electrons describe the possible locations of electrons around the nucleus. around the nucleus.

Example: Plane propellerExample: Plane propeller

Atomic OrbitalsAtomic Orbitals

Orbital: a region of space around the Orbital: a region of space around the nucleus where an electron is likely to be nucleus where an electron is likely to be found.found.

The electron cloud represents all the The electron cloud represents all the orbital in an atom. It is a good orbital in an atom. It is a good approximation of how electrons behave in approximation of how electrons behave in their orbitaltheir orbital

Atomic OrbitalsAtomic Orbitals

The level in which an electron has the least The level in which an electron has the least energy- the lowest energy level- has only one energy- the lowest energy level- has only one orbital. Higher energy levels have more that one orbital. Higher energy levels have more that one orbital.orbital.

Example: See figure 15 in the book on Example: See figure 15 in the book on page 117page 117

**Notice the maximum number of electrons in an **Notice the maximum number of electrons in an energy level is twice the number of orbital. Each energy level is twice the number of orbital. Each orbital can contain two electrons at most.orbital can contain two electrons at most.

Electron ConfigurationsElectron Configurations

A configuration is an arrangement of A configuration is an arrangement of objects in a given space. Some objects in a given space. Some configurations are more stable than configurations are more stable than others, meaning that they are less likely to others, meaning that they are less likely to change.change.

Electron configuration: the arrangement of Electron configuration: the arrangement of electrons in the orbital of an atom.electrons in the orbital of an atom.

Electron ConfigurationsElectron Configurations

The most stable electron configuration is the one The most stable electron configuration is the one in which the electrons are in orbital with the in which the electrons are in orbital with the lowest possible energies.lowest possible energies.

When all the electrons in an atom have the When all the electrons in an atom have the lowest possible energies, the atom is said to be lowest possible energies, the atom is said to be in its ground state.in its ground state.

When an electron moves to an orbital with When an electron moves to an orbital with higher energy this is referred to as the excited higher energy this is referred to as the excited state.state.