This document provides an overview of chemical bonding concepts including ionic bonds, covalent bonds, electronegativity, and molecular shapes. Key points covered include: 1) Ionic bonds form between cations and anions via electrostatic attraction while covalent bonds form through the sharing of electron pairs. 2) Electronegativity determines the polarity of covalent bonds, with more electronegative atoms attracting bonding electrons. 3) VSEPR theory predicts molecular geometry based on electron pair-atom repulsion.
The chemical Bond: Electronic concept of valency. Different types of chemical bond e.g. ionic, covalent, coordinate covalent metallic, dipole, hydrogen bond etc. Theories of covalent bonding and hybridization.
The chemical Bond: Electronic concept of valency. Different types of chemical bond e.g. ionic, covalent, coordinate covalent metallic, dipole, hydrogen bond etc. Theories of covalent bonding and hybridization.
chemical bonding and molecular structure class 11sarunkumar31
hybridisation, bonding and antiboding, dipole moment, VSPER theory, Molecular orbital diagram, Phosphorous pentachloride, ionic bond, bond order, bond enthalpy, bond dissociation, sp and sp2hybridisation, hydrogen bonding,electron pair,lone pair repulsion, resonance structure of ozone, how to find electron pair and lone pair, sp3 hybridization of methane.
chemical bonding and molecular structure class 11sarunkumar31
hybridisation, bonding and antiboding, dipole moment, VSPER theory, Molecular orbital diagram, Phosphorous pentachloride, ionic bond, bond order, bond enthalpy, bond dissociation, sp and sp2hybridisation, hydrogen bonding,electron pair,lone pair repulsion, resonance structure of ozone, how to find electron pair and lone pair, sp3 hybridization of methane.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
This pdf is about the Schizophrenia.
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Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
2. 2
Chapter 12 5
• An ionic bond is formed by the attraction between
positively charged kations and negatively charged
anions.
• This “electrostatic attraction” is similar to the
attraction between opposite poles on two magnets.
Ionic Bonds
Chapter 12 6
• The ionic bonds formed
from the combination
of anions and cations
are very strong and
result in the formation
of a rigid, crystalline
structure. The structure
for NaCl, ordinary table
salt, is shown here.
Ionic Bonds
Chapter 12 7
• Cations are formed when an atom loses valence
electrons to become positively charged.
• Most main group metals achieve a noble gas
electron configuration by losing their valence
electrons and are isoelectronic with a noble gas.
• Magnesium (Group IIA/2) loses its two valence
electrons to become Mg2+.
• A magnesium ion has 10 electrons (12 – 2 = 10 e-)
and is isoelectronic with neon.
Formation of Cations
Chapter 12 8
• We can use electron dot
formulas to look at the
formation of cations.
• Each of the metals in
Period 3 form cations by
losing 1, 2, or 3 electrons,
respectively. Each metal
atom becomes
isoelectronic with the
preceding noble gas,
neon.
Formation of Cations
3. 3
Chapter 12 9
• Anions are formed when an atom gains electrons
and becomes negatively charged.
• Most non-metals achieve a noble gas electron
configuration by gaining electrons to become
isoelectronic with a noble gas.
• Chlorine (Group VIIA/17) gains one valence
electron and becomes Cl–.
• A chloride ion has 18 electrons (17 + 1 = 18 e-)
and is isoelectronic with argon.
Formation of Anions
Chapter 12 10
• We can also use electron
dot formulas to look at the
formation of anions.
• The non-metals in Period
3 gain 1, 2, or 3 electrons,
respectively, to form
anions. Each non-metal
ion is isoelectronic with
the following noble gas,
argon.
Formation of Anions
Chapter 12 11
• The radius of a cation is smaller than the radius
of its starting atom.
• The radius of an anion is larger than the radius
of its starting atom.
Ionic Radii
Chapter 12 12
• Covalent bonds are formed when two non-metal atoms
share electrons and the shared electrons in the covalent
bond belong to both atoms.
• When hydrogen chloride (HCl) is formed, the hydrogen
atom shares its one valence electron with the chlorine,
This gives the chlorine atom eight electrons in its valence
shell, making it isoelectronic with argon.
• The chlorine atom shares one of its valence electrons
with the hydrogen, giving it two electrons in its valence
shell and making it isoelectronic with helium.
Covalent Bonds
4. 4
Chapter 12 13
Chapter 12 14
• When a covalent bond is formed, the valence shells of the
two atoms overlap with each other.
• In HCl, the hydrogen 1s energy sublevel overlaps with
the chlorine 3p energy sublevel. The mixing of sublevels
draws the atoms closer together.
• The distance between the two atoms is smaller than the
sum of their atomic radii and is the bond length.
Bond Length
Chapter 12 15
• Energy is released when two atoms form a covalent bond:
H(g) + Cl(g) HCl(g) + heat
• Conversely, energy is needed to break a covalent bond.
• The energy required to break a covalent bond is referred
to as the bond energy.
• The amount of energy required to break a covalent bond
is the same as the amount of energy released when the
bond is formed:
HCl(g) + heat H(g) + Cl(g)
Bond Energy
Kekuatan Ikatan Kovalen
• Kekuatan ikatan diindikasikan dengan besarnya
energi yang diperlukan untuk memutuskan ikatan
tersebut.
• Entalpi ikatan: energi yang diperlukan untuk
memutuskan 1 mol ikatan.
• Makin panjang ikatan kovalen, makin kecil energi
ikatannya.
5. 5
Chapter 12 19
• In Section 6.8 we drew electron dot formulas for
atoms.
• The number of dots around each atom is equal to
the number of valence electrons the atom has.
• We will now draw electron dot formulas for
molecules (also called Lewis structures).
• A Lewis structure shows the bonds between atoms
and helps us to visualize the arrangement of atoms
in a molecule.
Electron Dot Formulas of Molecules
Chapter 12 20
1. Calculate the total number of valence electrons
by adding all of the valence electrons for each
atom in the molecule.
2. Divide the total valence electrons by 2 to find the
number of electron pairs in the molecule.
3. Surround the central atom with 4 electron pairs.
Use the remaining electron pairs to complete the
octet around the other atoms. The only
exception is hydrogen, which only needs two
electrons.
Guidelines for Electron Dot Formulas
6. 6
Chapter 12 21
4. Electron pairs that are shared by atoms are called
bonding electrons. The other electrons complete
octets and are called nonbonding electrons, or
lone pairs.
5. If there are not enough electron pairs to provide
each atom with an octet, move a nonbonding
electron pair between two atoms that already
share an electron pair.
Guidelines for Electron Dot Formulas
Chapter 12 22
1. First, count the total number of valence electrons: oxygen has 6
and each hydrogen has 1 for a total of 8 electrons [6 + 2(1) = 8 e-].
The number of electron pairs is 4 [8/2 = 4].
2. Place 8 electrons around the central
oxygen atom.
3. We can then place the two hydrogen atoms
in any of the four electron pair positions.
Notice there are 2 bonding and 2
nonbonding electron pairs.
Electron Dot Formula for H2O
Chapter 12 23
• To simplify, we represent bonding electron
pairs with a single dash line called a single
bond.
• The resulting structure is referred to as the
structural formula of the molecule.
Electron Dot Formula for H2O
Chapter 12 24
1. First, count the total number of valence electrons: each oxygen
has 6 and sulfur has 6 for a total of 24 electrons [3(6) + 6 = 24 e-].
This gives us 12 electron pairs.
2. Place 4 electron pairs around the central
sulfur atom and attach the three oxygens.
We started with 12 electron pairs and have
8 left.
3. Place the remaining electron pairs around
the oxygen atoms to complete each octet.
4. One of the oxygens does not have an octet,
so move a nonbonding pair from the sulfur
to provide 2 pairs between the sulfur and
the oxygen.
Electron Dot Formula for SO3
7. 7
Chapter 12 25
• The two shared electron pairs
constitute a double bond.
• The double bond can be placed
between the sulfur and any of the 3 oxygen
atoms and the structural formula can be shown
as any of the structures below. This
phenomenon is called resonance.
Resonance
Chapter 12 26
1. The total number of valence electrons is 5 – 4(1) – 1 =
8 e-. We must subtract one electron for the positive
charge. We have 4 pairs of electrons.
2. Place 4 electron pairs around the
central nitrogen atom and attach
the four hydrogens.
3. Enclose the polyatomic ion in
brackets and indicate the charge
outside the brackets.
Electron Dot Formula for NH4
+
Chapter 12 27
1. The total number of valence electrons is 4 + 3(6) + 2 =
24 e-. We must add one electron for the negative charge.
We have 12 pairs of electrons.
2. Place 4 electron pairs around the
central carbon atom and attach the
three oxygens. Use the remaining
electron pairs to give the oxygen
atoms their octets.
3. One oxygen does not have an
octet. Make a double bond and
enclose the ion in brackets.
Electron Dot Formula for CO3
2-
Chapter 12 28
• Covalent bonds result from the sharing of valence
electrons.
• Often, the two atoms do not share the electrons
equally. One of the atoms holds onto the electrons
more tightly than the other.
• When one of the atoms holds the shared electrons
more tightly, the bond is polarized.
• A polar covalent bond is one in which the
electrons are not shared equally.
Polar Covalent Bonds
8. 8
Chapter 12 29
• Each element has an innate ability to attract
valence electrons.
• Electronegativity is the ability of an atom to
attract electrons in a chemical bond.
• Linus Pauling devised a method for measuring the
electronegativity of each of the elements.
• Fluorine is the most electronegative element.
Electronegativity
Chapter 12 30
• Electronegativity increases as you go left to right
across a period.
• Electronegativity increases as you
go from bottom to top
in a family.
Electronegativity
Chapter 12 31
• The electronegativity of H is 2.1; Cl is 3.0.
• Since there is a difference in electronegativity
between the two elements (3.0 – 2.1 = 0.9), the
bond in H–Cl is polar.
• Since Cl is more electronegative, the bonding
electrons are attracted toward the Cl atom and
away from the H atom. This will give the Cl atom
a slightly negative charge and the H atom a
slightly positive charge.
Electronegativity Differences
Chapter 12 32
• We use the Greek letter delta, d, to indicate a
polar bond.
• The negatively charged atom is indicated by the
symbol d–, and the positively charged atom is
indicated by the symbol d+. This is referred to as
delta notation for polar bonds.
d+ H–Cl d–
Delta (δ) Notation for Polar Bonds
9. 9
Chapter 12 33
• The hydrogen halides HF, HCl,
HBr, and HI all have polar
covalent bonds.
• The halides are all more
electronegative than hydrogen and
are designated with a d–.
Delta Notation for Polar Bonds
Chapter 12 34
• What if the two atoms in a
covalent bond have the same or
similar electronegativities?
• The bond is not polarized and it
is a nonpolar covalent bond. If
the electronegativity difference is
less than 0.5, it is usually
considered a nonpolar bond.
• The diatomic halogen molecules
have nonpolar covalent bonds.
Nonpolar Covalent Bonds
Chapter 12 35
• A covalent bond resulting from one atom donating
a lone pair of electrons to another atom is called a
coordinate covalent bond.
• A good example of a molecule with a coordinate
covalent bond is ozone, O3.
Coordinate Covalent Bonds
Chapter 12 36
Hydrogen Bonds
• The bond between H and O in water is very polar.
• Therefore, the oxygen is partially negative, and the
hydrogens are partially positive.
• As a result, the hydrogen
atom on one molecule is
attracted to the oxygen
atom on another.
• This intermolecular interaction
is referred to as a
hydrogen bond.
10. 10
Chapter 12 37
• Electron pairs surrounding an atom repel each
other. This is referred to as Valence Shell
Electron Pair Repulsion (VSEPR) theory.
• The electron pair geometry indicates the
arrangement of bonding and nonbonding electron
pairs around the central atom.
• The molecular shape gives the arrangement of
atoms around the central atom as a result of
electron repulsion.
Shapes of Molecules
Chapter 12 38
• Methane, CH4, has four pairs of bonding electrons
around the central carbon atom.
• The four bonding pairs (and, therefore, atoms) are
repelled to the four corners of a tetrahedron. The
electron pair geometry is tetrahedral.
• The molecular
shape is also
tetrahedral.
Tetrahedral Molecules
Chapter 12 39
• In ammonia, NH3, the central nitrogen atom is
surrounded by three bonding pairs and one
nonbonding pair.
• The electron pair geometry is tetrahedral and the
molecular shape is trigonal pyramidal.
Trigonal Pyramidal Molecules
Chapter 12 40
• In water, H2O, the central O atom is surrounded
by two nonbonding pairs and two bonding pairs.
• The electron pair geometry is tetrahedral and the
molecular shape is bent.
Bent Molecules
11. 11
Chapter 12 41
• In carbon dioxide, CO2, the central C atom is
bonded to each oxygen by two electron pairs (a
double bond).
• According to VSEPR, the electron pairs will repel
each other, and they will be at opposite sides of
the C atom.
• The electron pair geometry and the molecular
shape are both linear.
Linear Molecules
Chapter 12 42
Summary of VSEPR Theory
Chapter 12 43
Nonpolar Molecules with Polar Bonds
• CCl4 has polar bonds, but the overall molecule is
nonpolar
• Using VSEPR theory, the four chlorine atoms are
at the four corners of a tetrahedron
• The chlorines are each δ–, while the carbon is δ+.
• The net effect of the
polar bonds is zero, so
the molecule is
nonpolar.
Chapter 12 44
Diamond vs. Graphite
• Why is diamond colorless and hard, while graphite
is black and soft if both are pure carbon?
• Diamond has a 3-dimensional structure, while
graphite has a 2-dimensional structure.
• The layers in graphite are able to slide past each
other easily.
graphite
diamond
12. 12
Chapter 12 45
• Chemical bonds hold atoms together in molecules.
• Atoms bond in such a way as to have eight
electrons in their valence shell: the octet rule.
• There are 2 types of bonds: ionic and covalent.
• Ionic bonds are formed between a cation and an
anion.
• Covalent bonds are formed from the sharing of
electrons.
Chapter Summary
Chapter 12 46
• Electron dot formulas help us to visualize the
arrangements of atoms in a molecule.
• Electrons are shared unequally in polar covalent
bonds.
• Electronegativity is a measure of the ability of an
atom to attract electrons in a chemical bond.
• Electronegativity increases from left to right and
from bottom to top on the periodic table.
Chapter Summary, continued
Chapter 12 47
• VSEPR theory can be used to predict the shapes
of molecules.
• The electron pair geometry gives the arrangement
of bonding and nonbonding pairs around a central
atom.
• The molecular shape gives the arrangement of
atoms in a molecule.
Chapter Summary, continued