survey of chemistry i chem 1151 chapter 3 dr. augustine ofori agyeman assistant professor of...
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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