Topic 4 & 14 - Bonding Flashcards
What is an ionic bond?
The electrostatic attraction between oppositely charged ions
Which ions will be formed when elements in groups 1,2,3 lose electrons?
Cations
Which ions will be formed when elements in groups 5,6,7 gain electrons?
Anions
Can transition elements form more than one ion?
Yes
What kind of elements most often form ionic compounds?
Non-metals and metals together
What are common polyatomic ions formed by non-metals in periods 2 and 3?
- NO3–
- OH–
- SO42–
- CO32–
- PO43–
- NH4+
- HCO3–
What is a covalent bond?
Electrostatic attraction between a pair of electrons and positively charged nuclei
How is the covalent bond formed?
- A result of electron sharing
- Both elements partially give up their electron to mutual use
What does the Lewis structure show?
Shows all the electrons
What is a dative bond?
A bond in which both shared electrons come from one atom
What are examples of dative covalent bonds?
- H3O+
- NH4+
- CO
What is the relationship between the length of the bond and its strength?
The shorter the bond the stronger it is
What are polar bonds a result of?
Unequal sharing of electrons (electronegativity difference)
What kind of a bond is formed when there is no difference in electronegativity?
Non-polar covalent
What kind of a bond is formed when there is an electronegativity difference of about 1.8?
A polar covalent bond
What kind of a bond is formed when there is an electronegativity difference greater than 1.8?
An ionic bond
What does the VSEPR theory suggest?
Electron pairs found in the outer energy level or valence shell of atoms repel each other and thus position themselves as far apart as possible
What are the rules for applying the VSEPR theory?
- The repulsion applies to both bonding and non-bonding pairs of electrons
- Double and triple bonds behave as a signle unit known as a negative charge centre
- The total number of charge centres around the central atom determines the arrangement of the electrons
- The shape of the molecule is determined by the angles between the bonded atoms
- Non-bonding pairs of electrons have a higher charge than a bonding pair so cause more repulsion
In what order does the repulsion between electron pairs increase?
bonding pair–bonding pair < lone pair–bonding pair < lone pair–lone pair
What is the shape and bond angles of a species with two negative charge centres?
- linear
- 180°
- BeCl2, CO2, C2H2
What is the shape and bond angles of a species with three negative charge centres?
All bonded
- planar triangular
- 120°
- BF3, HCHO, NO3–
One non-bonding:
- V-shaped
- 117°
- SO2
What is the shape and bond angles of a species with four negative charge centres?
All bonding:
- tetrahedral
- 109.5° bond angles
e. g. CH4, NH4+
One non-bonding:
- trigonal pyramidal
- 107°
- NH3
Two non-bonding:
- bent or V-shaped
- 105°
- H2O
What does the polarity of a molecule depend on?
- The polar bonds that it contains
- The way in which the polar bonds are orientated with respect to each other (the shape of the molecule)
When do polar atoms form a non-polar molecule?
When the bonds are of equal polarity and are arrange symmetrically, the polarities cancel out
e.g. CO2, BF3, CCl4
When do polar atoms form a polar molecule?
When the atoms are of different polarity and the molecule is unsymmetric, the dipoles do not cancel out
e.g. CH3Cl, NH3, H2O
What are the three allotropes of carbon?
- Graphite
- Diamond
- Fullerene C60
Describe the structure and properties of graphite
- Each C is sp2 hybridised and covalently bonded to three other C atoms with 120° bond angles
- Layers are held by van der Waals’ → are able to slide over each other
- Conducts electricity due to one non-bonded electron per atom
- Used as a lubricant and in pencils
Describe the structure and properties of diamond
- Each C is sp3 hybridised and covalently bonded to four other C
- 109.5° bond angles → tetrahedral arrangement
- Does not conduct electricity because no lone pairs
- Used in tools, machinery, and cutting glass
- Also jewellery
Describe the structure and properties of fullerene C60
- Each C is sp2 hybridised and bonded to three other carbons
- Easily accepts electrons to form negative ions; a semiconductor due to some electron motility
- Soluble in benzene
- Reacts with K to make superconducting crystalline material (used to make nanotubes for electronics, catalysts, and lubricants)
Describe the structure and properties of silicon
- Each atom is covalently bonded to four others in tetrahedral arrangement
- Giant lattice structure
Describe the structure and properties of silicon dioxide
- Giant covalent structure
- Each Si is covalently bonded to four oxygen atoms and each O to two Si atoms
- Strong structure
- Insoluble in water
- High melting point
- Does not conduct electricity or heat
- Glass and sand
What are the different types of intermolecular forces?
- Van der Waals’
- Dipole-dipole
- Hydrogen bonding
What are van der Waals’ forces?
Temporary induced dipoles between non-polar molecules
How do van der Waals’ affect the boiling points of molecules?
Boiling point increases with increasing number of electrons
What is dipole-dipole attraction?
A permanent dipole resulting in opposite charges on neighbouring molecules
- Stronger than van der Waals’
What is hydrogen bonding?
- Attraction of molecules that have a covalently bonded hydrogen
- A particular case of dipole-dipole
- Only occurs between molecules which contain hydrogen bonded to fluorine, nitrogen, or oxygen
- Strongest form of intermolecular attraction
How does hydrogen bonding affect the boiling points of molecules?
- Cause the boiling points to be significantly higher than usually
What is metallic bonding?
The electrostatic attractin between a lattice of positive ions and delocalised electrons
Why are metals good conductors of electricity?
The delocalised electrons are highly mobile and can carry current
Why are metals malleable?
The delocalised electrons are not disturbed by a change in the conformation of the metal through applied pressure
Describe the melting and boiling points of ionic compounds, macromolecular compounds, and covalent compounds
- Ionic compounds have high points as the electrostatic attraction is strong and requires a lot of energy
- Macromolecular and giant covalent have high points as covalent bonds must be broken
- Covalent have lower points because only weak intermolecular forces need to be broken between the molecules
Describe the solubility of ionic compounds, polar compounds, and non-polar covalent compounds
- Ionic compounds become hydrated in water and dissolve
- Many polar compounds are soluble (sugar and ethanol form hydrogen bonds with water)
- Non-polar covalent are not readily soluble in water
- Like dissolves like
What does the electrical conductivity of a compound depend on?
Whether it contains ions that are able to move and carry a charge
- Solid ionics → no
- Molten ionics → yes
- Covalent → no
- HCl in water → yes
What is the shape and bond angles for species with five negative charge centres?
All bonded:
- triangular bipyramidal
- 90°, 120°, 180°
- e.g. PCl5
One non-bonding:
- unsymmetrical tetrahedron (seesaw)
- 90°, 117°
- SF4
Two non-bonding:
- T-shaped
- 90°, 180°
- ClF3
Three non-bonding:
- linear
- 180°
- I3–
What is the shape and bond angles for species with six negative charge centres?
All bonded:
- octahedral
- 90°
- SF6
One non-bonding:
- square pyramidal
- 90°, 180°
- BrF5
Two non-bonding:
- square planar
- 180°
- XeF4
What are the exceptions to the octet rule?
- Small atoms like Be and B form stable molecule with fewer than an octet of electrons
- Atoms of elements in the 3rd period and below may expand their octet by using d-orbitals in their valence shell
What is a sigma bond?
Bonds formed by overlapping of orbitals along the bond axis
What kind of covalent bonds are sigma bonds?
Single covalent bonds
What is a pi bond?
A bond formed when two p orbitals overlap sideways
What kind of bonds do double covalent bonds contain?
One sigma and one pi
What kind of bonds do triple covalent bonds contain?
One sigma and two pi
What is hybridisation?
The process by which atomic orbitals within an atom mix to produce hybrid orbitals of intermediate energy
(the atom is able to form stronger covalent bonds using hybrid orbitals)
What kind of properties do sp3 hybrid orbitals have?
- one s and three p
- four hybrid orbitals that are equal to each other
- their shape and energy have properties of both s and p but are more like p than s
What kind of properties do sp2 hybrid orbitals have?
- one s and two p
- three equal hybrid orbitals
- shape and energy have properties of both s and p but a tad more p than s
What kind of properties do sp hybrid orbitals have?
- One s and one p orbital
- Equal hybrid orbitals
What kind of hybridisation occurs when single bonds are formed?
sp3
What kind of hybridisation occurs when a double bond is formed?
sp2
What kind of hybridisation occurs when a triple bond is formed?
sp
What does the sp3 hybridisation say about the shape of the molecule?
It’s tetrahedral or one of its derivatives (pyramidal, v-shaped)
What does sp2 hybridisation say about the molecule’s shape?
It’s planar triangular or its derivative (v-shaped)
What does sp hybridisation say about the shape of the molecule?
It’s linear
When does resonance occur in molecules?
When more than one valid Lewis structure can be drawn for a particular molecule.
What are examples of molecules with delocalised electrons?
- NO3–
- NO2–
- CO32–
- O3
- RCOO–
- Benzene
What are properties of species with delocalised electrons?
- Intermediate bond lengths and strengths
- Greater stability
