Presentation on theme: "Chapter 5 “Electrons in Atoms”"— Presentation transcript:
1 Chapter 5 “Electrons in Atoms” Adapted from:Stephen L. CottonCharles Page High School
2 Chapter 5.2 Models of the Atom OBJECTIVES:Compare the Bohr and quantum mechanical models of the atom.Define a quantum of energy, and explain how it is related to an energy change in matter.
3 Ernest Rutherford’s Model Discovered dense positive piece at the center of the atom- “nucleus”Electrons would surround and move around it, like planets around the sunAtom is mostly empty spaceIt did not explain the chemical properties of the elements – a better description of the electron behavior was needed
4 Niels Bohr’s Model Why don’t the electrons fall into the nucleus? Move like planets around the sun.In specific circular paths, or orbits, at different levels.An amount of fixed energy separates one level from another.
5 The Bohr Model of the Atom I pictured the electrons orbiting the nucleus much like planets orbiting the sun.However, electrons are found in specific circular paths around the nucleus, and can jump from one level to another.Niels Bohr
6 Bohr’s model Energy level of an electron analogous to the rungs of a ladderThe electron cannot exist between energy levels, just like you can’t stand between rungs on a ladderA quantum of energy is the amount of energy required to move an electron from one energy level to another
7 The Quantum Mechanical Model Energy is “quantized” - It comes in chunks.A quantum is the amount of energy needed to move from one energy level to another.Since the energy of an atom is never “in between” there must be a quantum leap in energy.In 1926, Erwin Schrodinger derived an equation that described the energy and position of the electrons in an atom
8 Schrodinger’s Wave Equation Equation for the probability of a single electron being found along a single axis (x-axis)Erwin SchrodingerErwin Schrodinger
9 The Quantum Mechanical Model Things that are very small behave differently from things big enough to see.The quantum mechanical model is a mathematical solutionIt is not like anything you can see (like plum pudding!)
10 The Quantum Mechanical Model Has 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.
11 Heisenberg uncertainty principle Impossible to know where an electron is located or where it is headedScientist can not trace a path or orbit of an electronScientist can determine the probability for an electron to occupy a certain region around the nucleus.
12 Atomic OrbitalsPrincipal Quantum Number (n) = the energy level of the electron: 1, 2, 3, etc.Within each energy level, the complex math of Schrodinger’s equation describes several shapes.These are called atomic orbitals (coined by scientists in 1932) - regions where there is a high probability of finding an electron.Sublevels- like theater seats arranged in sections: letters s, p, d, and f
13 The modern model of atoms Electrons are attracted to the positively charged nucleus.Electrons are negatively charged and repel each other.To keep electrons apart and minimize repulsions and interaction energy,Electrons are found in principal energy levels (1, 2, 3…)Principal energy levels are divided into sublevels
14 The modern model of atoms Electron clouda.The sublevels are called s, p, d, and f in order of increasing energyb. Each sublevel is divided into orbitals that can contain electrons.c. Orbitals within a sublevel have equal energyd. Orbitals are regions of space. Electrons stay in their orbital 90% of the time.
15 The modern model of atoms Principal energy levelsPlacement of electrons in an atomSublevel # orbitals # electronsspdfrepelElectron cloud
16 The modern model of atoms Summary Electron cloudPrincipal energy levels (1, 2, 3…)Energy sublevels (s, p, d, f)Orbitals (up to 2 electrons)Principal energy levelscontainsrepelcontainscontainsElectron cloud
17 By Energy Level First Energy Level Has only s orbital only 2 electrons Second Energy LevelHas s and p orbitals available2 in s, 6 in p2s22p68 total electrons
18 By Energy Level Third energy level Has s, p, and d orbitals 2 in s, 6 in p, and 10 in d3s23p63d1018 total electronsFourth energy levelHas s, p, d, and f orbitals2 in s, 6 in p, 10 in d, and 14 in f4s24p64d104f1432 total electrons
19 By Energy LevelAny more than the fourth and not all the orbitals will fill up.You simply run out of electronsThe orbitals do not fill up in a neat order.The energy levels overlapLowest energy fill first.