Element Information in the Periodic Table 1s 2 2s, 2p 3 3s, 3p, 3d 4 4s, 4p, 4d, 4f Sublevels in...

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Chapter 2 - Cont.30 January 2014

The Structure of the Atom and the Periodic Table

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Element Information in the Periodic Table

20 atomic number

Ca symbol

calcium name

40.08 atomic mass

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Electron Arrangement and the Periodic Table

• The electron arrangement is the primary factor in understanding how atoms join together to form compounds

• Electron configuration - describes the arrangement of electrons in atoms

• Valence electrons - outermost electrons– The electrons involved in chemical bonding

Valence Electrons

• The number of valence electrons is the group number for the representative elements

• The period number gives the energy level (n) of the valence shell for all elements

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Valence Electrons and Energy Level

• How many valence electrons does fluorine have?

– 7 valence electrons

• What is the energy level of these electrons?

– Energy level is n = 2

Valence Electrons - Detail• What is the total number of electrons in

fluorine?

– Atomic number = 9

– 9 protons and 9 electrons

• 7 electrons in the valence shell, (n = 2 energy

level), so where are the other two electrons?

– In n = 1 energy level

– Level n=1 holds only two electrons

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Determining Electron ArrangementList the total number of electrons, total number of valence

electrons, and energy level of the valence electrons for silicon.

1. Find silicon in the periodic table• Group IVA

• Period 3

• Atomic number = 14

2. Atomic number = number of electrons in an atom• Silicon has 14 electrons

Determining Electron Arrangement #2List the total number of electrons, total number of valence electrons,

and energy level of the valence electrons for silicon.

3. As silicon is in Group IV, only 4 of its 14 electrons are valence electrons

• Group IVA = number of valence electrons

4. Energy levels:• n = 1 holds 2 electrons

• n = 2 holds 8 electrons (total of 10)

• n = 3 holds remaining 4 electrons (total = 14)

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Determining Electron ArrangementPractice

List the total number of electrons, total number of valence electrons, and energy level of the valence electrons for:

• Na

• Ar



• Na total: 11

• Ar

6



• Na total: 11, valence 1

• Ar



• Na total: 11, valence 1, energy level n=3

• Ar

7




• Ar total 18,




• Ar total 18, valence 8,

8




• Ar total 18, valence 8, energy level n=3

The Quantum Mechanical Atom

• Bohr’s model of the hydrogen atom didn’t clearly explain the electron structure of other atoms

– Electrons in very specific locations, principal energy levels

– Wave properties of electrons conflict with specific location

• Schröedinger developed equations that took into account the particle nature and the wave nature of the electrons

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Schröedinger’s equations

• Equations that determine the probability of finding an electron in specific region in space, quantum mechanics

– Principal energy levels (n = 1,2,3…)

– Each energy level has one or more sublevels or subshells (s, p, d, f)

– Each sublevel contains one or more atomic orbitals

Energy Levels and Sublevels

PRINCIPAL ENERGY LEVELS

• n = 1, 2, 3, …

• The larger the value of n, the higher the energy level and the farther away from the nucleus the electrons are

• The number of sublevels in a principal energy level is equal to n

– in n = 1, there is one sublevel

– in n = 2, there are two sublevels

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Principal Energy Levels

• The electron capacity of a principal energy level (or total electrons it can hold) is

2(n)2

– n = 1 can hold 2(1)2 = 2 electrons

– n = 2 can hold 2(2)2 = 8 electrons

• How many electrons can be in the n = 3 level?

– 2(3)2 = 18

• Compare the formula with periodic table…..

n=1, 2(1)2=2

n=2, 2(2)2=8

n=3, 2(3)2=18

n=4, 2(4)2=32

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Sublevels

• Sublevel: a set of energy-equal orbitals within a principal energy level

• Subshells increase in energy:

s < p < d < f

[sharp, principal, diffuse, and fundamental]

• Electrons in 3d subshell have more energy than electrons in the 3p subshell

• Specify both the principal energy level and a subshell when describing the location of an electron

Principal energy level (n)

Possible subshells

1 1s

2 2s, 2p

3 3s, 3p, 3d

4 4s, 4p, 4d, 4f

Sublevels in Each Energy Level

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Orbitals

• Orbital - a specific region of a sublevel containing a maximum of two electrons

• Orbitals are named by their sublevel and principal energy level

– 1s, 2s, 3s, 2p, etc.

• Each type of orbital has a characteristic shape

– s is spherically symmetrical

– p has a shape much like a dumbbell

Orbital Shapes

• s is spherically symmetrical

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Orbital Shapes

• Each p has a shape much like a dumbbell, differing in the direction extending into space

Orbital Shapes

• There are five different d shapes.• The f orbitals have seven different shapes, too

complicated and therefore seldom shown.

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Electron Spin

• Electron Configuration - the arrangement of electrons in atomic orbitals

• Aufbau Principle - or building upprinciple helps determine the electron configuration– Electrons fill the lowest-energy orbital that is

available first

– Remember s<p<d<f in energy

– When the orbital contains two electrons, the electrons are said to be paired

SubshellNumber of

orbitals

s 1

p 3

d 5

f 7

• How many electrons can be in the 4d subshell?

•10

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Rules for Writing Electron Configurations

• Obtain the total number of electrons in the atom from the atomic number

• Every electron has a place to stay• Electrons in atoms occupy the lowest energy orbitals

that are available – 1s first• Each principal energy level, n contains only n

sublevels• Each sublevel is composed of orbitals• No more than 2 electrons in any orbital• Maximum number of electrons in any principal

energy level is 2(n)2


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• Remember:– The s sublevel has one orbital and can hold two

electrons.

– The p sublevel has three orbitals. The electrons will half-fill before completely filling the orbitals for a maximum of six electrons.

– The d sublevel has five orbitals. The electrons will half-fill before completely filling the orbitals for a maximum of ten electrons.

Electron Distribution• This table lists the number of electrons in each shell for

the first 20 elements• Note that 3rd shell stops filling at 8 electrons even though if could

hold more

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Electron Distribution

Writing Electron Configurations

• H– Hydrogen has

only 1 electron– It is in the

lowest energy level & lowest orbital

– Indicate number of electrons with a superscript

– 1s1

• Li– Lithium has 3

electrons– First two have

configuration of helium – 1s2

– 3rd is in the orbital of lowest energy in n=2

– 1s2 2s1

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What noble gas configuration is this?

•Neon•Configuration is written: [Ne]3s23p1

Shorthand Electron Configurations

• Uses noble gas symbols to represent the inner shell and the outer shell or valance shell is written after

• Aluminum- full electron configuration is: 1s22s22p63s23p1

• Remember:

– How many subshells are in each principal energy level?

– There are n subshells in the n principal energy level.

– How many orbitals are in each subshell?

– s has 1, p has 3, d has 5, and f has 7

– How many electrons fit in each orbital?

– 2

– Hence: s can have 2, p 6, d 10 and f 14 electrons

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How many orbitals in 3rd principal energy level?

It contains s, p, and d

s = 1

p = 3

d = 5

Hence, the answer is 9

(and it can hold 18 electrons)

• Remember:

– How many electrons is subshells?

– There are n subshells in the n principal energy level.

s up to 2, p up to 6, d up to 10, f up to 14 electrons

Therefore:

for n=1: s subshell - up to 2 electrons

for n=2: s and p subshells - up to 8 electrons

for n=3: s, p, and d subshells - up to 18 electrons

for n=4: s, p, d and f subshell, up to 32 electrons

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Write the electron configuration for phosphorus

Phosphorus has 15 electrons

start with the sequence 1s2 2s2

1s2 2s2 2p6 3s2 3p3

Write the electron configuration for strontium

Strontium has 38 electrons

start with the sequence 1s2 2s2

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2

simplified notation: [Kr] 5s2

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Classification of Elements According to the Type of

Subshells Being Filled

The Octet Rule[eight in Latin of Greek - octo, οκτώ …ocho]

• The noble gases are extremely stable– Called inert as they don’t readily bond to other

elements

• The stability is due to a full complement of valence electrons in the outermost s and psublevels:– 2 electrons in the 1s of helium

– the s and p subshells full in the outermost shell of the other noble gases (eight electrons)

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Octet of Electrons

• Elements in families other than the noble gases are more reactive– Strive to achieve a more stable electron

configuration

– Change the number of electrons in the atom to result in full s and p sublevels

• Stable electron configuration is called the “noble gas” configuration

The Octet Rule

• Octet Rule - elements usually react in such a way as to attain the electron configuration of the noble gas closest to them in the periodic table– Elements on the right side of the table move right to the

next noble gas– Elements on the left side move “backwards” to the

noble gas of the previous row

• Atoms will gain, lose or share electrons in chemical reactions to attain this more stable energy state

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NaSodium atom

11e-, 1 valence e-

[Ne]3s1

Na+ + e-

Sodium ion10e-

[Ne]

Ion Formation and the Octet Rule

• Metallic elements tend to form positively charged ions called cations

• Metals tend to lose all their valence electrons to obtain a configuration of the noble gas

Element Information in the Periodic Table 1s 2 2s, 2p 3 3s, 3p, 3d 4 4s, 4p, 4d, 4f Sublevels in...

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