4 3 Modern Atomic Theory Key Concepts What

4. 3 Modern Atomic Theory 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?

4. 3 Modern Atomic Theory The colors of fireworks are related to the behavior of electrons ________ in different atoms… Examples Compounds containing the element strontium produce red ____ light. Compounds containing barium produce ______ light. green

4. 3 Modern Atomic Theory Bohr’s Model of the Atom Bohr’s model was similar to Rutherford’s, but Bohr focused on the electrons and their ________. arrangement In Bohr’s model, electrons move with constant speed in fixed _______ orbits around the nucleus, like planets around a sun. –“planetary model” –Each electron in an atom has a ________ amount of energy specific

4. 3 Modern Atomic Theory Bohr’s Model of the Atom Energy Levels When an atom gains or loses energy, the levels energy _________ of the electron may change. between An electron cannot exist _______ energy levels, just as you cannot step in between stairs

4. 3 Modern Atomic Theory Bohr’s Model of the Atom – The landing at the bottom of the staircase is the ________ ground level or energy level ________ to the nucleus closest higher energy • Each step up represents a _______ level. • The step height represents an energy change ________ between levels. • No two elements have the same set of energy levels.

4. 3 Modern Atomic Theory Bohr’s Model of the Atom Evidence for Energy Levels Scientists can measure the energy released when the electron moves to a ________ energy level. lower light – The form of energy released is often ________ colors – Different elements will release different _______ patterns or different __________ of light

4. 3 Modern Atomic Theory Electron Cloud Model Bohr was right to place electrons into specific levels, but he was wrong about their movement ________ • Instead of moving like the planets, electrons move in a ________________ less predictable way. cloud An electron _____ is a visual model of probable the most likely or ________ locations for electrons in an atom.

4. 3 Modern Atomic Theory 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

4. 3 Modern Atomic Theory 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 _______ blur You know that the blades are located somewhere in the blur, but the exact location ______ CANNOT be pinpointed

4. 3 Modern Atomic Theory Electron Cloud Model orbital 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. An electron cloud is a good approximation of how electrons behave in their orbitals.

4. 3 Modern Atomic Theory 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 likely “orbital. ” They describe your most ______ locations. • The places you visit the most would have the highest _________ concentration of dots. • The places you visit the least would have the ___________ concentration of dots. lowest

4. 3 Modern Atomic Theory Electron Cloud Model The level in which an electron has the least lowest energy—the ________ energy level —has only ______ oneorbital. Higher energy levels have more than one orbital.

4. 3 Modern Atomic Theory Electron Configurations configuration 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 ground _________ state, which is the most _______ stable

4. 3 Modern Atomic Theory Electron Configurations A lithium atom has three electrons. • In the ground state, two of the lithium electrons are in first the orbital of the _______ energy level. • The third electron is in an orbital of the ________ energy level. second • If a lithium atom absorbs enough energy, one of its electrons can move to an orbital with a higher energy excited called an _________ state, but it will eventually move back down.

4. 3 Modern Atomic Theory Electron Configurations The ground state of a person is floor 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.

4. 3 Modern Atomic Theory Assessment Questions 1. According to Bohr’s model of the atom, which of the following can happen when an atom gains energy? a. b. c. d. 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.

4. 3 Modern Atomic Theory Assessment Questions 2. How does the modern atomic theory describe the location of electrons in an atom? a. Electrons move randomly in space around the nucleus. b. Electrons can be described as a cloud based on probable locations. c. Electrons orbit the nucleus in the same way that planets orbit the sun. d. Electrons move in a spiral pattern if increasing distance from the nucleus.

4. 3 Modern Atomic Theory Assessment Questions 3. What is meant when an atom is said to be in its ground state? a. There is no net charge on the atom. b. The number of protons equals the number of neutrons. c. The atom’s electrons all have the lowest possible energies. d. It is the isotope with the least number of neutrons.