Chapter 8 Flashcards
How a chemical bond occurs?
When a chemical reaction occurs between two atoms, some of their electrons are reorganized, resulting in a net attractive force – a chemical bond – between the atoms.
What covalent bonding involves?
Covalent bonding involves a sharing of valence electrons between each atoms.
How an ionic bond is forming?
An ionic bond forms when one or more valence electrons is transferred from one atom to another, creating positive and negative ions
In molecules or polyatomic ions made up only of non-metal atoms, the atoms are attached by ____________ bonds
covalent bonds
Does the core electrons are involved in bonding reaction?
no, only valence electrons are involved
What are the letters of the valence electrons of the main group element (A groups) in the periodic table
For main group elements (elements of the A groups in the periodic table), the valence electrons are the s and p electrons in the outermost shell.
For main group element (A Group), the number of valence electrons is equal to ______________
the group number
For transition elements what are the letter of the valence electrons?
Valence electrons for transition elements include the electrons in the ns and (n-1)d orbitals.
What is the octet rule?
The tendency of molecules and polyatomic ions to have structures in which eight electrons surround each atom is the basis for the octet rule
What are the steps to draw Lewis dot structure?
Step 1: determine the arrangement of atoms within a molecule. The central atom is usually the one with the lowest affinity for electrons
Step 2: determine the total number of valence electrons in the molecule or ion. In a neutral molecule, this number will be the sum of the valence electrons for each atom. The number of valence electron pairs will be half to total number of valence electrons.
Step 3: place on pair of electrons between each pair of bonded atoms to form a single bond.
Step 4: use remaining pairs as lone pairs around each terminal atom (except H) so that each terminal atom is surrounded by eight electrons. If, after this is done, there are electrons left over, assign them to the central atom.
Step 5: if no valence electron pairs remain after forming single bonds and completing the octets of terminal atoms, and the central atom does not have an octet of electrons, then multiple bonds can be created by sharing one or more pairs of electrons between terminal atoms and the central atoms.
How de we choose the central atom in Lewis dot structure?
Generally the central atom is the one of lowest electronegativity.
How do we draw Lewis dot structure with a multiple bond?
Problem: draw the Lewis dot structure for CO2
Step 1: designate C as the central atom
Step 2: calculate the valence electrons
C= 1 X 4= 4
O= 2 X 6= 12
total valence electron= 16
Step 3: Two electron pairs form single bonds between C and O
Step 4: distribute three lone pairs on the terminal O atoms to complete their octets.
Step 5: none of the original 8 electron pairs remain ti be used, but the C atom does not yet have an octet of electrons. Therefore, we use lone pairs of electrons on the O atoms to form additional CO bonds, one on each side of the molecule.
to see the drawing: http://f.tqn.com/y/chemistry/1/W/N/f/1/CO2-Lewis.png
or student book p.290
How do we draw Lewis dot structure for polyatomic ions?
Problem: Draw Lewis dot structure for the ClO3^- and the NO2^+
For ClO3^-
Step 1: designate C as the central atom
Step 2: calculate the valence electrons Cl: 1 X 7= 7 O: 3 X 6= 18 negative charge (-1)= + 1
total valence electron= 26
Step 3: three lone pairs forms single bond between Cl and O
Step 4: distribute three lone pairs on each of O atoms to complete the octet of electrons around each of these atoms.
Step 5: one pair of electron remains, and it is placed on the central Cl atom to complete its octet.
* remember that you should put brackets with the charge at the drawing when its an ionic compound*
to see the drawing:
http://www.chemeddl.org/resources/models360/files/104770/clo3_.png
or student book p.291
For NO2^+
Step 1: designate N as the central atom
Step 2: calculate the valence electrons N: 1 X 5= 5 O: 2 X 6=12 positive charge (+1)= -1 5+12-1= 16
total valence electron= 16
Step 3: two electron pairs form single bonds form the N to each O
Step 4: distribute the remaining six pairs of electron on the terminal O atoms.
Step 5: the central N atom is two electron pairs short of an octet. A lone pair of electrons on each oxygen atom is converted to a bonding electron pair to give 2 N=O double bond. Each atom in the ion now has 4 electrons pairs. N has 4 bonding pairs, and each O atoms has 2 lone pairs and shared 2 bond pairs
* remember that you should put brackets with the charge at the drawing when its an ionic compound*
to see the drawing: http://reocities.com/MotorCity/highway/8497/Image8.jpg
or student book p.291
What is the definition of atom formal charge in covalent molecules and ions?
The formal charge is the electrostatic charge that would reside on an atom in a molecule or polyatomic ion if all bonding electrons are shared equally.
How the formal charge for an atom in a molecule or ion is calculated?
formal charge= NVE – (LPE + 1/2 (BE))
NVE: number of valence electrons in the uncombined atom
LPE: number of lone pair electrons on an atom
BE: number of bonding electrons around an atom
What a positive formal charge means?
A positive formal charge means that an atom in a molecule or ion “contributed” more electrons to bonding than it “got back”
Did the formal charge in a molecule must be zero?
YES, The sum of the formal charges on the atoms in a molecule must be zero
Didi the formal charge in an ion must be zero?
NO, the sum for atoms in an ion equals the charge on the ion.
What is resonance in Lewis dot structure?
Resonance structures are used to represent bonding in a molecule or ion when a single Lewis structure fails to describe accurately the actual electronic structure
Draw the resonance structure for ozone (O3)
to see it: https://i.ytimg.com/vi/Nam8Szygg-g/maxresdefault.jpg
or student book p.298
Who proposed the concept of resonance?
Linus Pauling
What is a coordinate covalent bond?
A bonding pair of electrons originates on one of the bonded atoms. like H3F→BF3. The boron atom can accommodate a fourth electron pair when that pair is provided by another atom, and molecules or ions.
Which periods in the periodic table form compounds and ions which the central element can be surrounded by more than 4 valence electron pairs?
3rd or higher periods
What is the valence shell electron-pair repulsion (VSEPR) model ?
is a method for predicting the shapes of covalent molecules and polyatomic ions. It is based on the idea that bond and lone electron pairs in the valence shell of an element repel each other and seek to be as far apart as possible
In the VSEPR model for molecules with two pairs of electrons around the central atom, what is the geometry type expected and the angle?
linear geometry is expected
with a bond angle of 180 degrees.
In the VSEPR model for molecules with three pairs of electrons around the central atom, what is the geometry type expected and the angle?
trigonal planar geometry
with 120 bond angles.
In the VSEPR model for molecules with four pairs of electrons around the central atom, what is the geometry type expected and the angle?
tetrahedral geometry
angle of 109.5 degrees
In the VSEPR model for molecules with five pairs of electrons around the central atom, what is the geometry type expected and the angle?
trigonal bipyramidal configuration
with angles of 120 degrees or 90 degrees.
In the VSEPR model for molecules with six pairs of electrons around the central atom, what is the geometry type expected and the angle?
Octahedral geometry
with 90 degrees angles
What are the effect of lone pairs on bond angles ?
Lone pairs of electrons seem to occupy a larger volume than bonding pairs, and the increased volume of lone pairs causes bond pairs to squeeze closer together.
Predicting the shapes of molecules and polyatomic ions EXERCICE
If you have the Chemistry and chemical reactivity book 9th edition, go on p 310 and try example 8.9
The answer is not on the flash cards
Answer in Chemistry and chemical reactivity book 9th edition, go on p 310 and try example 8.9
Which molecular geometries (structures) shows a central atoms with more than four valence electron pairs ?
trigonal-bipyramodal and octahedral
In a molecular geometry (structure) which have a central atom with more than four valence electron pairs, where do we draw the remaining lone pairs of electron ?
The lone pairs is often drawn in the top or bottom position to make it easier to visualize the molecular geometry, which in this case is square pyramidal.
predicting molecular shape
What is the shape of the ICl4^- ion?
Exercice 8.10: Chemistry and chemical reactivity book 9th edition p.312
The central atom is Iodine (I) with 6 valence electrons pairs.
2 of these are lone pairs
Placing the lone pairs on opposite sides leaves the 4 chlorine atoms in a square-planar geometry.
to see the shape : https://i.ytimg.com/vi/yMdbXO8M3p8/hqdefault.jpg
Do the electron pairs in double bonds and triple bonds have an effect on the overall molecular shape?
Double and triple bonds involve more electron pairs than single bonds, but this has little effect on the overall molecular shape
finding the shapes of molecules and polyatomic ions
What is the shape of the nitrate ion, NO3^- ?
Exercice 8.11: Chemistry and chemical reactivity book 9th edition p.313
The NO3^- ion is isoelectronic (having 32 electrons)
The electron-pair geometry and molecular shape of NO3^- are trigonal planar
to see it : http://image.slidesharecdn.com/vsepr-100319132250-phpapp01/95/vsepr-32-728.jpg?cb=1269005229
What is a pure covalent bonding?
atoms share an electron pair equally
In which condition a pure covalent bonding occurs?
A pure covalent bonding occurs only when two identical atoms are bonded.
What is a polar covalent bond?
A bond in which the two atoms have partial electrostatic charges
In which condition bonds are polar?
Bonds are polar because not all atoms hold onto their valence electrons with the same force or take on additional electron with equal ease
How the polarity is indicated for a polar covalent bond?
the polarity is indicated by writing the symbols δ^+ and δ^- alongside the atom symbol, where δ stands for a partial charge.
Who proposed a parameter called: atom electronegativity?
Linus Pauling
How the electronegativity of an atom is defined?
The electronegativity, χ, of an atom is defined as a measure of the ability of an atom in a molecule to attract electrons to itself.
Electronegativity values for the metalloids are ________(around, less than or greater than) __#___
around 2
Electronegativity values for the non-metals are __________(around, less than or greater than) __#___
greater than 2
estimating bond polarity
For each of the following bond pairs, decide which bond is more polar and indicate the negative and positive poles.
a) B–F and B–Cl
b) Si–O and P–P
Exercice 8.12: Chemistry and chemical reactivity book 9th edition p.316
a) B and F lie relatively far apart in the periodic table. B is a metalloid, and F is a nonmetal.
Here, X for B=2.0, and X for F= 4.0. Similarly, B and Cl are relatively far apart in the periodic table, but Cl is below F in the periodic table (X for Cl= 3.2) and is therefore less electronegative than F.
The difference in electronegativity for B–F is 2.0, and for B–Cl is 1.2.
Both B–F and B–Cl bonds are expected to be polar, with B positive and the halide atom negative, but a B–F bond is more polar than a B–Cl bond.
b) The P–P bond is nonpolar because the bond is between two atoms of the same kind.
In the case of Si–O, the O atom has a greater electronegativity (3.5) than Si (1.9), and the bond is highly polar (deltaX=1.6), with O the more negative atom.
What is the geometry of an H3O atom ?
tetrahedral
to see the shape: http://chemistry.elmhurst.edu/vchembook/images/205hydronium.gif
How is called the way electrons are distributed in a molecule or ion?
is called its charge distribution.
What is electroneutrality?
electrons will be distributed in such a way that the charges on all atoms are as close to zero as possible
In the concept of electroneutrality, if a negative charge is present where the negative charge should reside?
it should reside on the most electronegative atoms.
