1 Chapter 3 Electronic Structure and the Periodic Law 3.2 Electronic Arrangements in Atoms Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 Bohr Model or the Solar System Model Niels Bohr in 1913 introduced his model of the hydrogen atom. Electrons circle the nucleus in orbits, which are also called energy levels. An electron can “jump” from a lower energy level to a higher one upon absorbing energy, creating an excited state. The concept of energy levels accounts for the emission of distinct wavelengths of electromagnetic radiation during flame tests. Niels Bohr ( )

3 Bohr’s Orbit Model Definitions Quantum is the smallest increment of energy, for example, in an atom emitting or absorbing radiation. Ground state is the condition of an atom in which all electrons are in their normal, lowest energy levels. Excited state is an unstable, higher energy state of an atom.

4 The Atomic Orbital Model Orbits are replaced with atomic orbitals, volumes of space where the electrons can be found. The arrangement of electrons in the orbitals is the electronic configuration of an atom, which determines the chemistry of an atom. Bohr’s Orbit Model (continued)

5 Definitions Electrons in the highest occupied energy level are the greatest stable distance from the nucleus. These outermost electrons are known as valence electrons to be discussed in section 3.3. Shell is a principal energy level defined by a given value of n, where n can be 1,2,3,4 etc… and is capable of holding 2n 2 electrons. An orbital is a region of three-dimensional space around an atom within which there is a significant probability (usually shown as 90%) that a given electron will be found. Subshells have different energy levels (orbitals) within a given shell that is designed by a letter from the group s,p,d,& f

6 Energy Levels Energy levels are assigned numbers n = 1, 2, 3, 4 and so on. increase in energy as the value of n increases. are like the rungs of a ladder with the lower energy levels nearer the ground. n = 4 n = 3 n = 2 n = 1

7 Energy levels are spaced differently, like ladder rungs Credit: Foto-Search.com

8 Atomic energy levels are like floors of a house

9 State transitions for hydrogen

10 Energy Levels Energy levels have a maximum number of electrons equal to 2n 2. Energy levelMaximum number of electrons n = 12(1) 2 = 2(1) = 2 n = 22(2) 2 = 2(4) = 8 n = 32(3) 2 = 2(9) = 18

11 Orbitals An orbital is a three-dimensional space around a nucleus where an electron is most likely to be found. has a shape that represents electron density (not a path the electron follows). can hold up to 2 electrons.

12 s Orbitals An s orbital has a spherical shape around the nucleus. is found in each energy level. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings n = 1 n = 2 n = 3

13 p Orbitals A p orbital has a two-lobed shape. is one of three p orbitals in each energy level from n = 2. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

14 Atomic Orbitals.

15 Electrons in Energy Levels n = 1- 4 Energy Orbitals Maximum Total Level No. of Electrons Electrons 1 1s s 28 2p 6 3 3s 218 3p 6 3d10 4 4s 232 4p 6 4d10 4f14

16 The number of A. electrons that can occupy a p orbital is 1) 1.2) 2.3) 3. B. p orbitals in the 2p sublevel is 1) 1.2) 2.3) 3. C. electrons in the n =3 level 1) 3.2) 6.3) 18. Learning Check

17 The number of A. electrons that can occupy a p orbital is 2) 2. B. p orbitals in the 2p sublevel is 3) 3. C. electrons in the n =3 level 3) 18. Solution