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Chapter 10Chapter 10

Modern Atomic Theory Modern Atomic Theory and the Periodic Tableand the Periodic Table

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10.1 A brief history10.1 A brief historyatoms proposed by Greek philosopherDalton’s model of atomThomson’s modelRutherford’s modelthere remain questions can not be answered:․ how atomic structure relates to the periodic

table (arrangement of electrons)․ how to explain line spectrum of atom

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10.2 Electromagnetic radiation10.2 Electromagnetic radiationenergy and light – energy travels through space is by electromagnetic radiation, all radiations travel at the same speed –

v = λ • υ = 3 × 10-8 m/sλ : wavelength υ : frequency

electromagnetic spectrum

wavelike nature -- radiationbehaves like particle -- photonexplain the properties of electromagnetic radiation by both wave and particle properties

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10.3 The Bohr atom10.3 The Bohr atomat high temperature or when subjected to high voltage, elements in the gaseous state give off colored lighta set of brightly colored lines – line spectrum

ex. line spectrum of hydrogen

line spectrum indicates that light is being emitted only at certain wavelength (or frequency)1912 Bohr model of hydrogen• electrons exit in specific regions at various

distance from the nucleus• the electrons as revolving in orbits around the

nucleus like planets rotating around the Sun

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Max Planck energy quantathe energy is never emitted in a continuous stream but only in small discrete packets called quantaelectrons are only in several energy levelshydrogen atom absorbs one or more quanta of energy, the electron will jump to a higher energy level

ground state– the lowest energy level

excited states– the higher energy levels

when an electron falls from a high-energy level to a lower one, a quantum of energy is emitted as light at a specific frequency

Bohr model 1) suggesting quantized energy levels for electrons2) showing that spectral lines result from the

radiation of small increments of energy when electrons shift from one energy level to anotherhowever, Bohr model only succeeded in H atom, did not succeed for heavier atoms

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1924 de Broglie all objects have wave propertiesfor small objects such as an electron, the wave properties become significant

1926 Schrödinger Schrödinger equationa mathematical model that described electrons as wavesthe probability of finding an electron in a certain region around the atom can be determined

wave mechanics or quantum mechanicsforming the basis for our modern understanding of atomic structure we cannot locate an electron precisely within an atomelectrons are not revolving around nucleus in orbits as Bohr postulatedorbital a region where a high probability of

finding a given electron

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10.4 Energy levels of electron10.4 Energy levels of electronBohr the energy of the electron is quantized

the electron is restricted to only certain allowed energies

wave-mechanics also predicts discrete principal energy levels within the atom

these energy levels are designated by the letter nn: positive integer

as n increases, the energy of the electron increases, and the electron is found on average farther from the nucleuseach principal energy level is divided into sublevels

n = 1 1 subleveln = 2 2 sublevelsn = 3 3 sublevels

each of these sublevels contains space for electrons called orbitals

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n = 1 1s orbital spherical shapethe electron does not move around on the surface of sphere, the surface encloses a space where there is a 90% probability that the electron may be found

how many electrons can fit into a 1s orbital?spin a property of electroneach electron can only spin in two directions representation of the spin ↑ or ↓two electrons with the same spin cannot occupy the same orbitalPauli exclusion principle – an atomic orbital can hold a maximum of two electrons which must have opposite spins

n = 1 energy level contains one type of orbital (1s) that hold a maximum of 2 electrons

n = 2 2s spherical shape hold a maximum of two electrons2p – 2px, 2py, 2pz

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each p orbital has two lobes and can hold a maximum of two electronsthe total number of electrons that can reside in all three p orbitals is 6

n = 2 energy level contains two types of orbitals (a 2s and three 2p) that hold a maximum of 8 electrons

n = 3 3s3p – 3px, 3py, 3pz3d – 3dxz, 3dxy, 3dyz, 3dz2, 3dx2 – y2

n = 3 energy level contains three types of orbitals (a 3s, three 3p, five 3d) that hold a maximum of 18 electrons

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n = 4 energy level contains four types of orbitals (a 4s, three 4p, five 4d , seven 4f) that hold a maximum of 328 electrons

hydrogen atom consists of a nucleus (one proton) and one electron occupying a region outside of the nucleus

10-13 cm

10-8 cm

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10.5 Atomic structures of the first 18 10.5 Atomic structures of the first 18 elementselements

all atoms contain orbitals similar to those found in hydrogen systematically placing electrons in these hydrogen like orbitals, following the guidelines:

1. no more than two electrons can occupy one orbital

2. electrons occupy the lowest energy orbitalsavailable s < p < d < f for a given n value

3. each orbital on a sublevel is occupied by a single electron before a second electron enters

ex. atomic structure diagrams of F, Na and Mg

there are two ways to show the arrangement of the electrons in the orbitals:i) electron configuration

number of electrons in sublevel orbitals2p6

principal energy level type of orbital

ii) orbital diagramorbital □ spin ↑ ↓

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valence electrons – the electrons un the outmost (highest) energy level of an atom

ex. O 1s2 2s2 2p4 6 valence electronsMg 1s2 2s2 2p6 3s2 2 valence electrons

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10.6 Electron structures and the periodic 10.6 Electron structures and the periodic tabletable1869 Mendeleev & Meyer

periodic arrangements of the elements based on increasing atomic masses

periodic table

period – horizontal rowthe outmost energy level

group or family – vertical columnelements behave in a similar mannerIA ~ VIIA, IB ~ VIIB, VIII, noble gases1 ~ 18

representative elements – A group elementstransition elements – B group elementsIA – alkali metals IIA – alkaline earth metalsVIIA – halogens

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the valence electron configurations for H ~ Ar

• the valence electron configuration for the element in each column is the same, but the number for the energy level is different

• the chemical behavior and properties of elements in a particular family are similar and must be associated with the electron configuration

abbreviated electron configurationB 1s2 2s2 2p1 [He] 2s2 2p1

Cl 1s2 2s2 2p6 3s2 3p5 [Ne] 3s2 3p5

Na 1s2 2s2 2p6 3s1 [Ne] 3s1

n = 4 K 1s2 2s2 2p6 3s2 3p6 4s1 [Ar] 4s1

Ca 1s2 2s2 2p6 3s2 3p6 4s2 [Ar] 4s2

element 21 ~ 30 transition elementselectrons are placed in the 3d orbitals

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arrangement of elements according to the sublevel being filled

inner transition elementslanthanide series – 4f actinide series – 5f

ex. 10.1 write the electron configuration forP and Sn

P 1s22s22p63s23p3 [Ne]3s23p3

Sn 1s22s22p63s23p64s23d104p65s24d105p2

[Kr] 5s24d105p2

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groups of elements show similar chemical properties because of the similarity of these outmost electron configurations

the periodic table illustrates several important points:1. the number of the period corresponds with

the highest energy level occupied by electrons

2. the group numbers for the representative elements are equal to the total number of outmost electrons in the atom

3. the elements of a family have the same outmost electron configuration, but in different energy level

4. the elements within each of the s, p, d, fblocks are filling the s, p, d, f orbitals

5. within the transition elements some discrepancies in the order of filling occur