Modern Atomic Modern Atomic TheoryTheory

4.34.3

Bohr’s modelBohr’s model

A.A. Concentrated on placement of Concentrated on placement of electrons around the nucleuselectrons around the nucleus

B.B. Looks like planets revolving around Looks like planets revolving around the sunthe sun

C.C. Electrons move at constant speed Electrons move at constant speed in fixed orbits around nucleusin fixed orbits around nucleus

D.D. Electrons can gain or lose energy by Electrons can gain or lose energy by moving to different energy levels moving to different energy levels (also called shells)(also called shells)

E.E. When electrons move to a lower When electrons move to a lower energy level, they emit light or give energy level, they emit light or give off heatoff heat

Electron Cloud ModelElectron Cloud Model

A.A. Electrons don’t really move in a Electrons don’t really move in a predictable way, like the planets in predictable way, like the planets in the solar systemthe solar system

B.B. Electron cloud model shows the Electron cloud model shows the most likely location of electronsmost likely location of electrons

1. Hard to predict exactly where they are1. Hard to predict exactly where they are

Atomic OrbitalsAtomic Orbitals

A.A. Orbital – space around the nucleus Orbital – space around the nucleus where an electron is likely to be where an electron is likely to be foundfound

1. electron cloud represents all the 1. electron cloud represents all the orbitals in an atomorbitals in an atom

B.B. Each energy level has different Each energy level has different number of orbitalsnumber of orbitals

Energy Level

Number of Number of OrbitalsOrbitals

Max. # of Electrons

1 (K)1 (K) 11 22

2 (L)2 (L) 44 88

3 (M)3 (M) 99 1818

Electron ConfigurationElectron Configuration

A.A. Electron configuration – the Electron configuration – the arrangement of electrons in the arrangement of electrons in the orbitals of an atomorbitals of an atom

B.B. The most stable electron The most stable electron configuration is one in which the configuration is one in which the electrons are in the lowest possible electrons are in the lowest possible orbital – this is the ground stateorbital – this is the ground state

C.C. When electrons move away from When electrons move away from the ground state to a higher orbit, the ground state to a higher orbit, they become “excited” and the they become “excited” and the atom is less stableatom is less stable

D.D. When the electrons move back to When the electrons move back to the ground state, they give off lightthe ground state, they give off light

Example: neon, argon, xenonExample: neon, argon, xenon