SURVEY OF CHEMISTRY I

CHEM 1151

CHAPTER 3

DR. AUGUSTINE OFORI AGYEMANAssistant professor of chemistryDepartment of natural sciences

Clayton state university

CHAPTER 3

ELECTRONIC STRUCTURE

AND

THE PERIODIC LAW

PERIODIC TABLE OF ELEMENTS

- 117 known elements- 92 naturally occurring elements

- 25 are found in nature but made in the laboratory

Periodic Table- Elements are arranged in a tabular form (called the periodic

table) in order of increasing atomic number such that elements with similar chemical properties are positioned in vertical columns

- A tool that chemists use for organizing and remembering chemical facts

SYMBOL

Atomic number

Atomic mass

Period- The horizontal row of elements in the periodic table- Labeled with Arabic numbers from top to bottom - First row is period 1, second row is period 2, etc

Group- The vertical column of elements in the periodic table

- May be labeled with Arabic numbers (1 through 18)

Arabic numbers with letters A or B (1A, 1B, 2A, 3B, etc)Roman numerals with letters A or B (IA, IB, IIA, IIIB, etc)

PERIODIC TABLE OF ELEMENTS

Groups With Special Names

Alkali Metals- Elements in Group 1A (excluding hydrogen)

Li, Na, K, Rb, Cs, and Fr- Properties: soft, shiny, react readily with water

- Reactivity increases down the group

Alkaline Earth Metals- Elements in Group 2A Be, Mg, Ca, Sr, Ba, Ra

- Properties: soft, shiny, react moderately with water

PERIODIC TABLE OF ELEMENTS

Groups With Special Names

Chalcogens- Elements in Group 6A

O, S, Se, Te, Po- Properties: commonly found as minerals

Halogens (salt formers)- Elements in Group 7A

F, Cl, Br, I, At- Properties: reactive, colored, gas at room temperature

- Reactivity decreases down the group

PERIODIC TABLE OF ELEMENTS

Groups With Special Names

Noble Gases- Elements in Group 8AHe, Ne, Ar, Kr, Xe, Rn

- Properties: unreactive gases

PERIODIC TABLE OF ELEMENTS

ELECTROMAGNETIC RADIATION

- Also known as radiant heat or radiant energy

- One of the ways by which energy travels through space

Examplesheat energy in microwaves, light from the sun, X-ray, radio waves

The properties of light is a key concept that helps in understanding electronic structure

ELECTROMAGNETIC RADIATION

Three Characteristics of Waves

Wavelength (λ) - Distance between two consecutive peaks or troughs in a wave

Frequency (ν) - The number of waves (cycles) per second that pass

a given point in space

Speed - All waves travel at the speed of light in vacuum

(3.00 x 108 m/s)

one second

ELECTROMAGNETIC RADIATIONλ1

λ3

λ2

ν1 = 4 cycles/second

ν2 = 8 cycles/second

ν3 = 16 cycles/second

amplitude

peak

trough

Gamma rays

X rays Ultr-violet

Infrared Microwaves Radio frequency FM Shortwave AM

Vis

ible

Visible Light: VIBGYORViolet, Indigo, Blue, Green, Yellow, Orange, Red

400 – 750 nm

- White light is a blend of all visible wavelengths

- Can be separated using a prism

Wavelength (m)

Frequency (s-1)

10-11 103

1020104

ELECTROMAGNETIC RADIATION

- Inverse relationship between wavelength and frequency

λ α 1/ν

c = λ ν

λ = wavelength (m)

ν = frequency (cycles/second = 1/s = s-1 = hertz = Hz)

c = speed of light (3.00 x 108 m/s)

ELECTROMAGNETIC RADIATION

ARRANGEMENT OF ELECTRONS

The space around a nucleus in which electrons move are divided into

- Shells

- Subshells

- Orbitals

ARRANGEMENT OF ELECTRONS

Electron Shells

- Numbered from the nucleus outward using 1, 2, 3, ……n

- Electron energy increases with distance from the nucleus

- An electron in shell 2 has higher energy than an electron in shell 1

- An electron in shell 3 has higher energy than an electron in shell 2

ARRANGEMENT OF ELECTRONS

Electron Shells

- The higher the shell number, the more electrons the shell can contain

- The maximum number of electrons a shell can accommodate is given by 2n2, where n is the shell number

- The first shell (n = 1) accommodates 2 electrons maximum

- The second shell (n = 2) accommodates 8 electrons maximum

- The third shell (n = 3) accommodates 18 electrons maximum

Electron Subshells

- Each electron shell is subdivided into subshells containing electrons that have the same energy

- The shell number indicates the number of subshells

- Shell 1 contains 1 subshell - Shell 2 contains 2 subshells- Shell 3 contains 3 subshells

Subshells differ in size and energy

ARRANGEMENT OF ELECTRONS

Electron Subshells

- The higher the energy of electrons in a given subshell the larger the subshell

Subshells are designated in the order of increasing size and energy as

s, p, d, f

Subshellspdf

Maximum Number of Electrons26

1014

ARRANGEMENT OF ELECTRONS

ARRANGEMENT OF ELECTRONS

Electron Subshells

s = sharp (spherical)

p = principal (peripheral)

d = diffuse

f = fundamental

Electron Subshells

- Identified by the shell number and the subshell letter (type)

Shell 1 1 subshell 1s 2 electrons

Shell 2 2 subshell

3 subshell

4 subshell

Shell 3

Shell 4

2p2s

14 electrons10 electrons 6 electrons 2 electrons

6 electrons 2 electrons

10 electrons 6 electrons 2 electrons

3d3p3s

4f4d4p4s

ARRANGEMENT OF ELECTRONS

Electron Orbitals

- An orbital is a region of space within an electron subshell

- The electron with a specific energy has a high probability of being found

- An orbital can accommodate a maximum of 2 electrons

s subshell (2 electrons) contains 1 orbitalp subshell (6 electrons) contains 3 orbitals

d subshell (10 electrons) contains 5 orbitalsf subshell (14 electrons) contains 7 orbitals

ARRANGEMENT OF ELECTRONS

Electron Orbitals

s orbital is spherical

p orbital looks like 8 (2 lobes)

d orbital is similar to two intercrossing 8 (4 lobes)

f orbital is more complex (8 lobes or something similar)

ARRANGEMENT OF ELECTRONS

ELECTRON CONFIGURATION

- Elements in the periodic table are arranged in order of increasing atomic number (number of protons)

- Similar to protons, electrons are added one by one to the nucleus to build up elements (Aufbau Principle)

Rules for assigning electrons

- Electron subshells are filled in order of increasing energy (s, p, d, f)

- All orbitals of a subshell acquire single electrons before any orbital acquire a second electron (Hund’s rule)

- All electrons in singly occupied orbitals must have the same spin

- A maximum of 2 electrons can exist in a given orbital and must have opposite spins (Pauli’s exclusion principle)

ELECTRON CONFIGURATION

- Ordering of electron subshells is often complicated due to overlapsFor instance, the 3d subshell has higher energy than the 4s subshell

- Use of mnemonic for subshell filling is essential

1s

2s 2p

3s 3p 3d

4s

5s

4p 4d 4f

5p 5d 5f

6s

7s

6p 6d

7p

The (n+1)s orbitals alwaysfill before the nd orbitals

ELECTRON CONFIGURATION

- Subshells containing electrons are designated using the sunshell numbers and letters (types)

- The number of electrons in a given subshell is indicated by a superscript

Carbon has 6 electrons: 1s22s22p2

Nitrogen has 7 electrons: 1s22s22p3

Sodium has 11 electrons: 1s22s22p63s1

ELECTRON CONFIGURATION

ORBITAL DIAGRAMS

Hydrogen has electronic configuration written as 1s1

The orbital diagram is

H:

1s

Helium has electronic configuration written as 1s2

The orbital diagram is1s

He:

Lithium has electronic configuration written as 1s22s1

The orbital diagram is Li:1s

Boron has electronic configuration written as 1s22s22p1

The orbital diagram is1s

B:

Beryllium has electronic configuration written as 1s22s2

The orbital diagram is

2s

2s1s

2p2s

Be:

ORBITAL DIAGRAMS

Carbon has electronic configuration written as 1s22s22p2

The orbital diagram is C:

1s

Sodium has electronic configuration written as 1s22s22p63s1

The orbital diagram is1s

Na:

Nitrogen has electronic configuration written as 1s22s22p3

The orbital diagram is

2p2s

2s1s 2p

2p2s 3s

N:

ORBITAL DIAGRAMS

Neon has electronic configuration written as 1s22s22p6

The orbital diagram isNe:

1s 2p2s

The electron configuration for sodium (Na) can be abbreviated as

[Ne]3s1

Magnesium (Mg) is abbreviated as [Ne]3s2

ORBITAL DIAGRAMS

- Elements in a given group have similar chemical propertiesbecause the outer-shell electron arrangements are similar

Group 2A elementsBe: 1s22s2

Mg: 1s22s22p63s2

Ca: 1s22s22p63s23p64s2

Sr: 1s22s22p63s23p64s23d104p65s2

CLASSIFICATION OF THE ELEMENTS

- The last electron in an element’s electron configuration causes the difference in the electron configuration of the

preceding element and is referred to as the distinguishing electron

HomeworkWrite notes (one page) on the different classifications of the elements based on electronic properties. Briefly describe the

s-area, p-area, d-area, and the f-area.

CLASSIFICATION OF THE ELEMENTS

CLASSIFICATION OF THE ELEMENTS

Elements can be classified as Metals, Nonmetals, or Metalloids

- Based on physical properties

Elements can also be classified as Representative, Noble-gas,

Transition, or Inner Transition- Based on chemical properties (electron configuration)

Classification by Physical Properties

Metals - Elements on the left block of the periodic table

Characteristics: - good conductors of heat and electricity

- ductile (capable of being shaped or drawn into wire) - malleable (capable of being rolled into sheets)

- high luster (shiny)- high melting points

- high density- solids at room temperature (except mercury)

(iron, aluminum, gold, silver, copper)

PERIODIC TABLE OF ELEMENTS

Classification by Physical Properties

Nonmetals- Elements on the right block of the periodic table

Characteristics: - poor conductors of heat and electricity

- good insulators (except diamond)- no metallic luster

- nonductile- lower melting points

- lower density- solids, liquids or gases at room temperature

(oxygen, hydrogen, nitrogen, carbon, sulfur, bromine)

PERIODIC TABLE OF ELEMENTS

Classification by Physical Properties

Metals and nonmetals on the periodic table are separated by a bold steplike line running from

Group 3A through Group 6A

Metalloids - Some elements that lie along the line separating

metals from nonmetals

Characteristics:- Properties fall between those of metals and nonmetals

- Semiconductors (weak conductors of electricity) (B, Si, Ge, As, Sb, Te)

PERIODIC TABLE OF ELEMENTS

CLASSIFICATION OF THE ELEMENTS

Classification by Chemical Properties

Representative Elements

- Elements in the

s-area (Groups 1A and 2A)

first five columns of the p-area (Groups 3A, 4A, 5A, 6A, and 7A)

- Metals and nonmetals

CLASSIFICATION OF THE ELEMENTS

Classification by Chemical Properties

Noble-gas Elements

- Group 8A (18) elements on the periodic table (far right column)

- Gases at room temperature- Little tendency to form chemical compounds

- Electron configuration ends in p6

- Completes p subshell (except Helium)

- Nonmetals

CLASSIFICATION OF THE ELEMENTS

Classification by Chemical Properties

Transition Elements

- Elements in the d-area of the periodic table

- Groups 3B (3), 4B (4), 5B (5), 6B (6), 7B (7), 8B (8, 9, 10), 1B (11), and 2B (12)

- Distinguishing electron in a d subshell

- Metals

CLASSIFICATION OF THE ELEMENTS

Classification by Chemical Properties

Inner Transition Elements

- Elements in the f-area of the periodic table

- The two-row block of elements below the main table

- Distinguishing electron in an f subshell

- Metals

VALENCE ELECTRONS

- The electrons in the outer most shell of an atom

- Electrons in the inner shells

CORE ELECTRONS

VALENCE ELECTRONS

- Electrons in the outer most shell of an atom

- Apply only to representative and noble-gas elements

- These electrons are always found in the s or p subshells

VALENCE ELECTRONS

- Using electron configuration to determine the number of valence electrons

C: 1s22s22p2

O: 1s22s22p4

Na: 1s22s22p63s1

VALENCE ELECTRONS

Three important facts about valence electrons

- Representative elements in the same group of the periodic table have the same number of valence electrons

- The number of valence electrons for representative elements is the same as the group number (with A) in the periodic table

- The maximum number of valence electrons for any given element is eight

SIZES OF ATOMS

- Atomic radius tends to decrease across the periods (from left to right) in the periodic table

- Due to increase in effective nuclear charge which draws valence electrons closer to the nucleus

- Atomic radius tends to increase down the groups (from top to bottom) of the periodic table

- Due to increase in the number of shells

IONIZATION ENERGY

- The energy required to remove an electron from a gaseous atom

X(g) → X+(g) + e-

- The highest energy electron is always removed first

- First ionization energy increases across the period of the periodic table (from left to right)

- Electrons are added to the same shell and number of protons in the nucleus increase

- First ionization energy decreases down the group of the periodic table (from top to down)

- As n increases, distance from nucleus increases and electrons are easier to remove

IONIZATION ENERGY