CHM-3 Bonding Flashcards
….. bonds form between two metals.
Metallic bonds
….. bonds form between two nonmetal atoms or a nonmetal and a metal atom.
Covalent Bonds
….. bonds form between atoms with similar negativity.
Non-polar covalent bonds
….. bonds form between atoms of some-what difference in electronegativity
Polar covalent bonds
….. bonds form between atoms of significant electronegativity difference
Ionic bonds
What is the Octet Rule?
An atom tends to form bonds with other atoms until a stable electron configuration of 8 (Oct) valence electrons are achieved.
How do Ionic bonds form?
When there is a complete transfer of one or more electrons between a metal and a nonmetal atom.
Which element has the highest electronegativity value, and what is the value?
Fluorine (4.0)
What are the three properties of ionicly bonded compounds?
High melting and boiling points
High electrical conductivity.
Electronegativity values on the periodic table are … in the bottom left and ….. on the top right.
Low, High
How do covalant bonds occur?
By sharing two valence electrons between two atoms.
In covalent bonding, as the number of shared electron pairs increases… (3 points)
The atoms are pulled closer together
Decreased bond length
Increased bond strength
What is non-polar covalent bonding?
Where covalent bonding forms between atoms of similar or equal electronegativities.
What is polar covalent bonding? (3 points)
When there is a small difference in electronegativity between atoms (0.4 - 2.0).
Greater than this, it is an ionic bond.
The more electronegative atom requires a partial negative charge and vice versa.
What is coordinate covalent bonding? (2 points)
Occurs when the shared electron pair comes from the lone pair of electrons from one of the atoms.
Typically form between Lewics acids (electron acceptors) and Lewis bases (electron donors).
What is a ‘Lewis Structure’?
A representation of covalent bonding where shared electrons are shown as lines or a pair of dots.
What are lone pairs?
Electrons which do not participate in covalent bonding, e.g 4 electrons on Oxygen in H2O
What are resonance structures?
A representation to express a molecule with more than one bonding structure, expressed by a two-headded arrow between each lewis structure.
What is a resonance hybrid?
A merge of a number of resonance structures with bonding expressed as a line and a dotted line.
What is a formal charge?
A calculated charge assigned to each atom in a lewis structure.
What is the formula for the value of formal charge?
Formal Charge = V - (N + B)
V - Total number of VALENCE electrons in a free atom
N - Total number of NONBONDING electrons
B - HALF total number of BONDING electrons.
The sum of the formal charges of an ion must…
Equal the ion’s overall charge.
3 Rules for selecting the best lewis structure
The structure in which the formal charges equal zero is the best.
Strucures with smaller formal charges are better than larger
Where negative charges are found on the most electronegative atoms and vice versa.
When does Sulphur not fulfill the octet rule?
When it is the central atom of a molecule/ polyatomic ion.
What is partial ionic character?
Where a covalent bond has partial charges caused by electronegativity difference.
As ionic character increases, bond strength…
Decreases
What is a Lewis acid?
Any substance that ACCEPTS an electron pair to form a covalent bond.
What is the VSEPR model?
The Valence-Shell Electronic Pair Repulsion model is used to predict molecular geometries.
Formula to Calculate VSEPR number of electron pairs around an atom (A)
((No. Valence Electrons involving A + No. Single bonds involving A) - No. Double bonds Involving A) / 2
In VSEPR, the following bonds count for:
- Single Bond
- Double Bond
- Triple Bond
- 1 sigma bond
- 1 sigma bond and 1 pi bond
- 1 sigma bond and 2 pi bonds
Which atom is always assigned a double bond, unless it’s a central atom and isn’t attachedto any other atom?
Oxygen
What is always assigned a single bond?
A halogen
When using VSEPR and dealing with cations…
Subtract the charge of the ion from the total number of electrons
When using VSEPR and dealing with anions…
Add the charge of the ion to the total number of electrons
Angle for a trigonal planar arrangment of 3 electron pairs
120 Degrees
Angle for a tetrahederal arrangement
109.5 Degrees
Angle for a Trigonal bipyramidal arrangement
90 on top and bottom and 120 degrees on the sides
Angle for an octohederal arrangement
90 Degrees
