Key Concepts What can happen to electrons when atoms gain or lose energy? What models do scientists use to describe how electrons behave in atoms? What is the most stable configuration of electrons in an atom?

The colors of fireworks are related to the behavior of ________________ in different atoms… Examples Compounds containing the element strontium produce ________ light. Compounds containing barium produce ____________ light. electrons red green

Bohr’s Model of the Atom Bohr’s model was similar to Rutherford’s, but Bohr focused on the electrons and their ________________. In Bohr’s model, electrons move with constant speed in fixed _____________ around the nucleus, like planets around a sun. “planetary model” Each electron in an atom has a ________________ amount of energy arrangement orbits specific

Bohr’s Model of the Atom Energy Levels When an atom gains or loses energy, the energy _________________ of the electron may change. An electron cannot exist _____________ energy levels, just as you cannot step in between stairs levels between

Bohr’s Model of the Atom The landing at the bottom of the staircase is the _______________ level or energy level ________________ to the nucleus Each step up represents a _____________ energy level. The step height represents an energy ________________ between levels. No two elements have the same set of energy levels. ground closest higher change

Bohr’s Model of the Atom Evidence for Energy Levels Scientists can measure the energy released when the electron moves to a _______________ energy level. The form of energy released is often _______________ Different elements will release different _____________ or different ___________________ of light lower light colors patterns

Electron Cloud Model Bohr was right to place electrons into specific levels, but he was wrong about their _______________ Instead of moving like the planets, electrons move in a ___________ ________________ way. An electron __________ is a visual model of the most likely or ________________ locations for electrons in an atom. movement less predictable cloud probable

Electron Cloud Model The electron cloud model replaced Bohr's vision of electrons moving in predictable paths. The electron cloud is a visual model of the probable locations of electrons in an atom. The probability of finding an electron is higher in the denser regions of the cloud. The nucleus contains protons and neutrons Electron Cloud Model

Electron Cloud Model This photograph provides an analogy for an electron cloud. When the blades are moving, they spin so fast that you see only a ______________ You know that the blades are located somewhere in the blur, but the exact location ___________ be pinpointed blur CANNOT

Electron Cloud Model An __________________ is a region of space around the nucleus where an electron is likely to be found. The electron cloud represents all the orbitals in an atom. orbital An electron cloud is a good approximation of how electrons behave in their orbitals.

Electron Cloud Model For an analogy to the concept of an orbital, imagine marking your location on a map of your school every 10 minutes… The dots on your map are a model of your “orbital.” They describe your most ____________ locations. The places you visit the most would have the _________________ concentration of dots. The places you visit the least would have the _____________________ concentration of dots. likely highest lowest

Electron Cloud Model The level in which an electron has the least energy—the _______________ energy level—has only ___________ orbital. Higher energy levels have more than one orbital. lowest one

Electron Configurations An electron ________________________ is the arrangement of electrons in the orbitals of an atom. When all the electrons in an atom have the lowest possible energies, the atom is said to be in its _________________ state, which is the most _____________ configuration ground stable

Electron Configurations A lithium atom has three electrons. In the ground state, two of the lithium electrons are in the orbital of the ______________ energy level. The third electron is in an orbital of the _______________ energy level. If a lithium atom absorbs enough energy, one of its electrons can move to an orbital with a higher energy called an _________________ state, but it will eventually move back down. first second excited

Electron Configurations The ground state of a person is on the ______________. A gymnast on a balance beam is like an atom in an excited state—not very stable. When she dismounts, the gymnast will return to a lower, more stable energy level. floor

Assessment Questions According to Bohr’s model of the atom, which of the following can happen when an atom gains energy? An atom returns to its ground state. A neutron can be changed into a proton. A proton can move to a higher energy level. An electron can move to a higher energy level.

Assessment Questions How does the modern atomic theory describe the location of electrons in an atom? Electrons move randomly in space around the nucleus. Electrons can be described as a cloud based on probable locations. Electrons orbit the nucleus in the same way that planets orbit the sun. Electrons move in a spiral pattern if increasing distance from the nucleus.

What is meant when an atom is said to be in its ground state? Assessment Questions What is meant when an atom is said to be in its ground state? There is no net charge on the atom. The number of protons equals the number of neutrons. The atom’s electrons all have the lowest possible energies. It is the isotope with the least number of neutrons.