Unit 2 Flashcards
What is a chemical bond
It’s an INTRAmolecular bond that holds various constituents (atoms, ions, etc.) together
Chemical bonds have an effect on
The chemical and physical property of the chemical
List the three types of chemical bonds
- ionic bond( metal and a non metal)
- metallic bond ( metal and metal)
- covalent bond( non metal and a non metal)
The octet rule states that
Atoms tend to gain or lose electrons until they have achieved an outer shell that contains an octet of electrons (eight electrons)
What is an ionic (electrovalent bond)
Is formed by the electrostatic attraction between positive and negative ions
When large number of ions gather together they form
Ionic solid which has a regular, crystalline structure that allows for maximum attraction of ions, given thier particular size
Who invented the Lewis symbol
Gilbert N. Lewis
Ionic substances exist because
Of the enormous release of energy when they form a solid
What is the lattice energy? List it’s characteristics
- is the enthlapy change that occurs when 1 mol of ionic solid separates into a gaseous ion ➡️this is endothermic
- is the enthlapy change that occurs when the gaseous ions coalesce into a crystalline solid➡️this is exothermic
- Is the measure of the coulombic attractive forces between the combing ions
- it indicates the strength of ionic interactions, influence melting point, hardness, solubility and other properties
Finding the lattice energy by experiment is hard how do we find it
By using the born haber cycle
The reasoning is based on Hess’s law which states that an overall reactions enthlapy change is the sum of the enthlapy changes for the individual reactions that make it up
There is a greater ease of formation of an ionic bond when there is ?
- low ionization energy
- high electron affinity
- larger lattice energy
Why does larger lattice energy cause an ease for the formation of an ionic bond
Because the more the energy( lattice energy) the more stronger the coulombic attraction forces which means a more stable or a stronger ionic bond is formed
Lattice energy is directly and inversely proportional with
Directly : the product of the ionic charges
Inversely: the distance between them
Do smaller ions have larger or smaller lattice energy
Larger lattice energy
True or false : ionic solids exist only because the lattice energy exceeds the energy required for the electron transfer
True
Give some examples of less than octet elements
H , li , be , b
What happens to compounds less than an octet
They may be stable but they will attempt to form a fourth bond to get eight electrons
Some post transition and transition elements don’t obey the octet rule and obey the 18 electron rule because of
The involvement of d orbitals of these atoms
Give some examples of elements that obey the octet rule
Transition elements: iron and zinc
Post transition elements: gallium and Tin
The electron configurations of elements than obey the 18 electron rule can generally be represented as
Ns2 np6 nd10
List some physical ( I think ) properties of ionic compounds
- are generally soluble in polar solvents and insoluble in non polar solvents
- have high melting point and can decompose upon heating
- don’t conduct electricity in solid form
- conduct electricity in molten or aqueous solution
A covalent bond is formed when
A pair of electrons are shared between two atoms
Substances that contain covalent bonds are called
Molecules
The optimum distance between nuclei is called
The bond length
The bond length of H2 molecule is
74pm
Some characteristics of a molecule in bond length are
- attractive forces are maximized
- the most stable arrangement
- the minimum energy
The representation of covalent bonding through Lewis symbols and shared electron pairs is called
Lewis structure
The shared pairs of electrons in a molecule are called
bonding pairs
The other electron pairs that stay with on atom and are not shared are called
non-bonding pairs or lone pairs
A bond consisting of two covalent bond is known as
Double bond
What is a coordinate covalent bond or dative bond
Covalent bonds that form when one atom donates both electrons ( a lone pair) to another atom that has a vacant valance orbital
Some examples of coordinate-covalent bond include
NH3
BCl3,
H3O+and AlCl4 −
Our need for more than one Lewis structure is( resonance structure)
-to show the ozone molecule is the result of electron-pair delocalization( to show that the electrons aren’t just in one place but are spread out)
-to explain the known bond length
Electron Deficent compounds are
Compounds in which an element has an incomplete octet
The three exceptions to the octet rule in covalent bonding are
1 less than octet
2 more than octet
3 molecules containing an odd number of electrons
List some characteristics of less than octet( in covalent bonding)
- the central atom have fewer than eight electrons
- the molecules central atoms are from group 2 and group 3
Some examples of less than octet ( in covalent bonding)
BeCl2, BF3 and AlCl3,
List some characteristics of more than octet ( in covalent bonding)
- elements with an expanded valance has more than 8 electrons( often 10 and 12 )
- elements in the third period or below have an expanded valance because of thier larger radii and the availability of empty d orbitals
Some examples of more than octet( in covalent bonding)
XeF4 ,PF5 and SF6
What is a characteristic of a Molecules containing an odd number of electrons
- stable molecules of free radicals don’t obey the octet rule
Give an example of a molecule containing an odd number of electrons
ClO2, NO and NO2
What is a non polar covalent bond
In a covalent bond If the electronegativity is equal and the bonding electrons are shared equally it’s called a non polar covalent bond
What is a polar covalent bond
In a covalent bond if there is a difference between the electronegativity then the electrons spend more of their time around the more electronegative atom such a bond is called a polar convalent bond
When representing polar covalent bond the partial charge implies
That it’s less than a full charge of an ion but it’s partially there
What is the bond moment
It’s the measure of polarity of a diatomic ( between two atoms ) covalent bond
What is the dipole moment
- it measures the overall polarity of a molecule
- it’s the vector sum of the bond moments in a molecule
What is the si unit of a dipole moment ? And what is often expressed in ?
Si unit is coulomb metre
It’s often expressed in the non si unit Debye
The formula for the dipole moment is
δ× d
δ is the magnitude of the charge
D is the distance that separates the charge
A very polar molecule will have a large or small dipole moment
Large dipole moment
A non polar molecule will have a dipole moment of
Zero dipole moment
The dipole of a polyatomic molecule depends on
The geometry of the molecule
Give an example of covalent molecule that is solid at room temperature
Iodine
Some liquid covalent molecules are
Br2
Some gas covalent molecule are
H2
Cl2
Nh3
Some properties of covalent compound are
- have low melting and boiling point as a result they’re volatile
- most are soluble in non polar solvents
- insoluble in water ( polar solvent)
- liquid covalent compounds don’t conduct electricity
- non polar covalent compounds don’t conduct electricity ( non electrolytes)
- are liquid or gas at room temperature ( because of low intermolecular forces)
- exist as separate molecules ( bc electricity neutral atoms form them and the forces of attraction between these molecules are relatively weak)
What is molecular geometry
Is the three dimensional arrangement of atoms
We can predict molecular geometry by using
Valance shell electron pair repulsion ( VSEPR) model
The basic principle of VSEPR theory is that
is that the pair of valence-shell electron pairs around the central atom arrange as far away from one another as possible to minimize electron- pair repulsions
What is the difference between electron pair arrangement and molecular shape
The electron pair arrangement is concerned by the distribution of pairs of electrons both bonding and non bonding
While molecular shape is defined by the position of the terminals
Atoms can have the same electron pair arrangement and molecular shape of there are no lone pairs
In VSEPR we count double or triple bonds as
One
2 electron pair
Linear
3 electron pair
Trigonal planar
4 electron pair
Tetrahedral
5 electron pair
Trigonal bipyramid
6 electron pair
Octahedral
The three types of repulsive forces in a molecule are? Arrange them in strength
Lone pair vs lone pair > lone pair vs bonding pair > bonding pair vs bonding pair
Does the Lone pair on Sulphur tetraflouride have an axial or equatorial position
Equatorial position
Molecular shape affects _____________ which affects ____________
-Molecular polarity
-Melting point , boiling point,solubility and reactivity
What are the two factors that determine if there is a dipole moment
- the polarity of the bonds
- molecular geometry
What is the difference between intermolecular and intramolecular bonds
- intermolecular are found between particles while intramolecular are found within
-Intermolecular affects the physical property while intramolecular affects chemical property - intermolecular is weaker that intramolecular
What do we mean by intermolecular force affects physical properties
- it affects boiling and melting point
-it’s affects a substances ability to be solid , liquid and gas ( idk abt this )
What are the three intermolecular forces that exist between neutral molecules
- dipole- dipole molecules
- dispersion or London forces
- hydrogen bond
What are some characteristics of dipole dipole forces
-Act between molecules possessing permanent dipole
- occurs when polar molecules are brought near each other
- the attractive forces decreases with increased distance
- is weaker than ion- ion interactions because it’s only partial charge
List some characteristics of dispersion or London forces
- weak attraction forces that occur because of temporary change of position of electrons
- they make it possible for polar molecules to form liquids and solids
- temporary dipole
- shapes that allow more points of contact have more attraction
List some characteristics of hydrogen bonds
- polar molecule containing hydrogen bonded with nitrogen, oxygen and fluorine
- are the strongest type of forces between covalent molecules
Arrange intermolecular forces in strength
Hydrogen bonding > dipole - dipole > London forces
