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# Chapter 3: Electron Structure and the Periodic Law PowerPoint PPT Presentation

Chapter 3: Electron Structure and the Periodic Law. PERIODIC LAW This is a statement about the behavior of the elements when they are arranged in a specific order.

Chapter 3: Electron Structure and the Periodic Law

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## Chapter 3:Electron Structure and the Periodic Law

• PERIODIC LAW

• This is a statement about the behavior of the elements

• when they are arranged in a specific order.

• In its present form the statement is: Elements with similar chemical properties occur at regular (periodic) intervals when the elements are arranged in order of increasing atomic numbers.

• PERIODIC TABLE

• A periodic table is a tabular arrangement of the elements based on the periodic law.

• In a modern periodic table, elements with similar chemical properties are found in vertical columns called groups or families.

group/family

period

PERIODIC TABLE GROUP OR FAMILY

A vertical column of elements that have similar chemical properties.

Traditionally designated by a Roman numeral and a letter (either A or B) at the top of the column.

Designated only by a number from 1 to 18 in a modern but as yet not universally-used designation.

PERIODIC TABLE PERIOD

A horizontal row of elements arranged according to increasing atomic numbers.

Periods are numbered from top to bottom of the periodic table.

APPEARANCE OF A MODERN PERIODIC TABLE

In a modern table, elements 58-71 and 90-103 are not placed in their correct periods, but are located below the main table.

ELEMENTS AND THE PERIODIC TABLE

Each element belongs to a group and period of the periodic table.

EXAMPLES OF GROUP AND PERIOD LOCATION FOR ELEMENTS

Calcium, Ca, element # 20: group IIA, period 4

Silver, Ag, element # 47: group IB, period 5

Sulfur, S, element # 16: group VIA, period 3

THE BOHR THEORY OF ELECTRON BEHAVIOR IN HYDROGEN ATOMS

Bohr proposed that the electron in a hydrogen atom moved in any one of a series of circular orbits around the nucleus.

The electron could change orbits only by absorbing or releasing energy.

This model was replaced by a revised model of atomic structure in 1926

THE QUANTUM MECHANICAL MODEL OF ELECTRON BEHAVIOR IN ATOMS

According to the quantum mechanical model of electron behavior, the precise paths of electrons moving around the nucleus cannot be determined accurately.

Instead of circular orbits, the location and energy of electrons moving around the nucleus is specified using the three terms shell, subshell and orbital.

SHELL

The location of electrons in a shell is indicated by assigning a number n to the shell and all electrons located in the shell.

The value of n can be 1, 2, 3, 4, etc.

The higher the n value, the higher is the energy of the shell and the contained electrons.

SUBSHELL

Each shell is made up of one or more subshells that are designated by a letter from the group s, p, d, or f.

The number of the shell to which a subshell belongs is combined with the letter of the subshell to clearly identify subshells.

For example, a p subshell located in the third shell (n = 3) would be designated as a 3p subshell.

The number of subshells located in a shell is the same as the number of the shell. Thus, shell number 3 (n = 3) contains three subshells, designated 3s, 3p, and 3d.

Electrons located in a subshell are often identified by using the same designation as the subshell they occupy. Thus, electrons in a 3d subshell are called 3d electrons.

ATOMIC ORBITALS

The description of the location and energy of an electron moving around a nucleus is completed in the quantum mechanical model by specifying an atomic orbital in which the electron is located.

Each subshell consists of one or more atomic orbitals, which are specific volumes of space around the nucleus in which electrons move.

Atomic orbitals are designated by the same number and letter used to designate the subshell to which they belong. Thus, an s orbital located in a 2s subshell would be called a 2s orbital.

All s subshells consist of a single s orbital.

All p subshells consist of three p orbitals.

All d subshells consist of five d orbitals.

All f subshells consist of seven f orbitals.

According to the quantum mechanical model, all types of atomic orbitals can contain a maximum of two electrons.

Thus, a single d orbital can contain a maximum of 2 electrons, and a d subshell that contains five d orbitals can contain a maximum of 10 electrons.

ATOMIC ORBITAL SHAPES

Atomic orbitals of different types have different shapes.

THE ENERGY OF ELECTRONS IN ATOMS

Electron energy increases with increasing n value. Thus, an electron in the third shell (n = 3) has more energy than an electron in the first shell (n = 1).

For equal n values but different orbitals, the energy of electrons in orbitals increases in the order s, p, d and f. Thus, a 4p electron has more energy than a 4s electron.

RELATIONSHIPS BETWEEN SHELLS, SUBSHELLS, ORBITALS AND ELECTRONS

Members of Group IIA(2)

ELECTRONS AND CHEMICAL PROPERTIES

The valence shell of an atom is the shell that contains electrons with the highest n value.

Atoms with the same number of electrons in the valence shell have similar chemical properties.

magnesium

calcium

strontium

ELECTRON OCCUPANCY OF SHELLS

What do magnesium and calcium have in common?

2 electrons in valence shell

What predictions can be made about the number of electrons in strontium’s valence shell? Sr has similar chemical properties to Mg and Ca, so it likely has 2 electrons in its valence.

What other element on this chart has similar properties to Mg, Ca, and Sr?

Beryllium

ELECTRONIC CONFIGURATIONS

Electronic configurations give details of the arrangements of electrons in atoms.

The notation used to represent electronic configurations is 1s22s22p6…, where the occupied subshells are indicated by their identifying number and letter such as 2s and the number of electrons in the subshell is indicated by the superscript on the letter. Thus, in the example above, the 2s2 notation indicates that the 2s subshell contains two electrons.

THE ORDER OF SUBSHELL FILLING

Electrons will fill subshells in the order of increasing energy of the subshells. Thus, a 1s subshell will fill before a 2s subshell.

The order of subshell filling must obey Hund's rule and the Pauli exclusion principle.

HUND'S RULE

According to Hund's rule, electrons will not join other electrons in an orbital of a subshell if an empty orbital of the same energy is available in the subshell.

Thus, the second electron entering a p subshell will go into an empty p orbital of the subshell rather than into the orbital that already contains an electron.

THE PAULI EXCLUSION PRINCIPLE

Electrons behave as if they spin on an axis.

According to the Pauli exclusion principle, only electrons spinning in opposite directions (indicated by ↑ and ↓) can occupy the same orbital within a subshell.

FILLING ORDER FOR THE FIRST 10 ELECTRONS

When it is remembered that each orbital of a subshell can hold a maximum of two electrons, and that Hund's rule and the Pauli exclusion principle are followed, the following filling order for the first 10 electrons in atoms results.

H He Li Be B C N Ne

• Subshells are represented by small colored rectangles.

• Orbitals within the subshells are represented by circles.

FILLING ORDER FOR ALL SUBSHELLS IN ATOMS

The filling order for any number of electrons is obtained by following the arrows in the diagram.

Shells are represented by large rectangles.

AID TO REMEMBER SUBSHELL FILLING ORDER

The diagram provides a compact way to remember the subshell filling order.

The correct order is given by following the arrows from top tobottom of the diagram, going from the arrow tail to the head, and then from the next tail to the head, etc.

The maximum number of electrons each subshell can hold must also be remembered: s subshells can hold 2, p subshells can hold 6, d subshells can hold 10, and f subshells can hold 14.

SUBSHELL FILLING ORDER AND THE PERIODIC TABLE

Notice the order of subshell filling matches the order of the subshell blocks on the periodic table, if the fill occurs in the order of increasing atomic numbers.

EXAMPLES OF ELECTRON CONFIGURATIONS FOR ATOMS OF VARIOUS ELEMENTS

The following electronic configurations result from the correct use of any of the diagrams given earlier.

Magnesium, Mg, 12 electrons: 1s22s22p63s2

Silicon, Si, 14 electrons: 1s22s22p63s23p2

Iron, Fe, 26 electrons: 1s22s22p63s23p64s23d6

Galium, Ga, 31 electrons: 1s22s22p63s23p64s23d104p1

NOBLE GAS CONFIGURATIONS

With the exception of helium, all noble gases (group VIIIA) have electronic configurations that end with completely filled s and p subshells of the highest occupied shell. These configurations are called noble gas configurations.

Noble gas configurations can be used to write electronic configurations in an abbreviated form in which the noble gas symbol enclosed in brackets is used to represent all electrons found in the noble gas configuration.

EXAMPLES OF THE USE OF NOBLE GAS CONFIGURATIONS

Magnesium: [Ne]3s2. The symbol [Ne] represents the electronic configuration of neon, 1s22s22p6.

Iron: [Ar]4s23d6. The symbol [Ar] represents the electronic configuration of argon, 1s22s22p63s23p6.

Galium: [Ar]4s23d104p1. The symbol [Ar] represents the electronic configuration of argon, 1s22s22p63s23p6.

PERIODIC TABLE CLASSIFICATIONS OF THE ELEMENTS

The periodic table can be used to classify elements in numerous ways:

by Distinguishing Electron.

by status as Representative, Transition, or Inner-Transition Element.

by status as Metal, Nonmetal, or Metalloid.

CLASSIFICATION ACCORDING TO DISTINGUISHING ELECTRONS

The distinguishing electron is the last electron listed in the electronic configuration of the element.

REPRESENTATIVE, TRANSITION AND INNER-TRANSITION ELEMENTS

Elements are, again, classified according to the type of distinguishing electron they contain.

METALS, METALLOIDS AND NONMETALS

The Elements of Group VA(15)

arsenic

antimony

nitrogen

phosphorous

bismuth

PROPERTY TRENDS WITHIN THE PERIODIC TABLE

Properties of elements change in a systematic way within the periodic table.

METALLIC AND NONMETALLIC PROPERTIES

Most metals have the following properties: high thermal conductivity, high electrical conductivity, ductility, malleability and metallic luster.

Most nonmetals have properties opposite those of metals and generally occur as brittle, powdery solids or as gases.

Metalloids are elements that form a diagonal separation zone between metals and nonmetals in the periodic table. Metalloids have properties between those of metals and nonmetals, and often exhibit some characteristic properties of each type.

TRENDS IN METALLIC PROPERTIES

Elements in the same period of the periodic table become less metallic and more nonmetallic from left to right across the period.

Elements in the same group of the periodic table become more metallic and less nonmetallic from top to bottom down the group.

TRENDS IN THE SIZE OF ATOMS

For representative elements in the same period, atomic size decreases from left to right in the period.

For representative elements in the same group, atomic size increases from top to bottom down the group.

SCALE DRAWINGS OF REPRESENTATIVE ELEMENT ATOMS

TRENDS IN FIRST IONIZATION ENERGY

The first ionization energy is the energy required to remove one electron from a neutral gaseous atom of an element.

For representative elements in the same period, the general trend is an increase from left to right across the period.

For representative elements in the same group, the general trend is a decrease from top to bottom down the group.

TRENDS IN CHEMICAL REACTIVITY

Based on the photo, what is the trend for chemical reactivity with ethyl alcohol in group 1A(1)?

As the atomic number increases in group 1A(1), the chemical reaction becomes more vigorous. The rate of gas formation and the size of the bubbles indicate that reactivity increases from top to bottom in this family.

lithium

sodium

potassium