Chemical Bonding and Forces NOTES

What is the difference between a bond and a force?

Bond: just molecules

Force: molecules interacting with each other

What is an intermolecular bond?

a bond which occurs between atoms within molecules

What are the three types of intermoloecular forces?

1. covalent bonding

2. ionic bonding

3. metallic bonding

What is a covalent bond?

sharing of at least one pair of electrons by two non-metal atoms

What is non-polar covalent (pure covalent) ?

an equal sharing of electrons

What is a polar covalent bond?

is unequal sharing of electrons leading to a dipole forming (as a result of electronegativity difference)

What are the two types of covalent bonds and the differences between them?

1. Non-polar covalent/pure covalent bonds

equal sharing of electrons (electronegativity difference is 0)

2. Polar covalent bonds

unequal sharing of electrons leading to a dipole forming (electronegativity difference is from 0 to 1.9)

What is electronegativity?

a measure of the tendency of an atom to attract a bonding (shared) pair of electrons

The greater the electronegativity difference

the more polar the bond

What an ionic bond?

transfer of electrons and subsequent electrostatic attraction - metal and non-metal

What happens during an ionic bond?

the metal donates its electron to form a cation, and the non-metal accepts the electron to form an anion, leading to strong electrostatic forces of attraction that cause the atoms to form giant ionic lattices

When is a bond pure covalent?

△EN = 0

When is a bond polar covalent?

0 < △EN =< 1.9

When is a bond ionic?

△EN > 2

What is metallic bonding?

bond between positive atomic kernels and a sea of delocalised electrons

Which atoms can make more than four covalent bonds?

Atoms like sulphur and phosphorous can make more than four covalent bonds as they have empty d-orbitals, which electrons can move if energy is available.

What is a dative covalent bond?

the overlapping of a filled orbital contains an ion pair with the empty orbital of another atom or ion and one is formed It is no different from a covalent bond

Examples:

H⁺ + H₂O → H₃O⁺

H⁺ + NH₃ → NH₄⁺

When is a molecule symmetrical?

the electron distribution around the molecule will be symmetrical ( one side is positive, the other side is also positive, and vice versa)

What are the 5 molecular shapes?

1. Linear

2. Angular

3. Trigonal planar

4. Pyramidal

5. tetrahedral

What molecular shape(s) can two atoms have ?

linear only

What molecular shape(s) can three atoms have *subscript will be 1/2 ?

linear and angular

How can you tell whether a three-atomed molecule is angular or linear?

linear: no lone pairs

angular: the central atom has lone pairs (the electrons push the other atoms down to make angular shape)

Name the two linear, three-atomed molecules you need to know and describe their symmetry and polarity

HCl is asymmetrical and therefore polar

CO2 is symmetrical and therefore non-polar

Describe the symmetry and polarity of linear molecules

symmetrical and asymmetrical, polar and non-polar

Name the two angular, three-atomed molecules you need to know and describe their symmetry and polarity

H₂O: asymmetrical and therefore polar

H₂S: asymmetrical and therefore polar

Describe the symmetry and polarity of angular molecules

asymmetrical and therefore polar

What molecular shape(s) can four atoms have *subscript will be 3?

Trigonal planar and pyramidal

Name the two trigonal planar, four-atomed molecules you need to know and describe their symmetry and polarity

BH₃: symmetrical and non-polar

BF₃: symmetrical and non-polar

Describe the symmetry and polarity of trigonal planar molecules

symmetrical and therefore non-polar

Name the two pyramidal, four-atomed molecules you need to know and describe their symmetry and polarity

NH₃: asymmetrical and therefore polar

PH₃: asymmetrical and therefore polar

Describe the symmetry and polarity of pyramidal molecules

asymmetrical and therefore polar

What molecular shape(s) can five atoms have *subscript will be 4?

Tetrahedral

Name the two tetrahedral, five-atomed molecules you need to know and describe their symmetry and polarity

CH₄: symmetrical and therefore non-polar

CCl₄: symmetrical and therefore non-polar

Describe the symmetry and polarity of tetrahedral molecules

symmetrical and therefore non-polar

How does one determine whether a molecules is polar ?

They have covalent bonds and are asymmetrcial

How does one determine whether a molecule is non-polar ?

They do/do not have covalent bonds , but are symmetrical

How does one determine whether a molecule is dipole?

1. bonds are polar

2. asymmetrical

What are intermolecular forces?

weak force of attraction between molecules or between atoms of noble gases.

What is the difference between intramolecular forces and intermolecular forces?

intra: forces between atoms of a compound vs

inter: force between molecules

What is an intramolecular bond?

a bond occurs between atoms within molecules.

What are Van der Waals forces?

intermolecular forces of attraction

What are the 3 types of Van der Waals forces?

1. London forces (induced dipole/dispersion forces)

2. dipole-dipole forces

3. hydrogen bonding

Name the weakest to strongest Van der Waals forces?

London System Forces

Dipole-dipole

Hydrogen-bonding

What are London System Forces?

IMF between non-polar molecules when a temporary dipole is formed between the molecules (all interaction between parts creates some sort of London forces)

How is a temporary dipole (molecule with London forces) formed?

When the electron cloud in one molecules is temporarily dispersed to one side, this causes electron clouds in adjacent molecules to also become dispersed.

What phase are London molecules usually in?

gas, as they are the weakest IMF

What elements have London forces?

noble gases and diatomic molecules

As the size of the molecule increases, so does the strength of the IMF. Explain why

The large molecules have more electrons, which results in a greater electron density and greater interactive surfaces. a larger temporary dipole, which lasts longer in the case of noble force molecules

The strength of a molecule is dependent on its:

molecule size

What are dipole-dipole forces?

attraction between polar molecules, where the positive end of one polar molecule and the negative end of another polar molecule are attracted to each other like HCl

What is a hydrogen bonding?

a special type of dipole-dipole forces/polar molecules , (but are much stronger than them) between molecules which contain hydrogen eg. HF or H₂O

How do you identify a hydrogen bond?

Hydrogen and one molecule of N/O/F (first elements of group 5,6,7)

What are the 3 characteristics of hydrogen bonding?

1. Atoms within molecules are small

2. A large electronegativity difference between atom and molecules

3. The atom bonding with the hydrogen atom has at least one lone pair

What are the 4 types of solids and their private properties ?

1. Ionic Solids

2. Metallic solids

3. Networks Solids (giant structures)

4. Molecular solids

What are the properties ionic solids ?

- made out of ions

- good conductors of electricity in molten or liquid phase as the ions are free to move, but not in solid phase as the ions cannot move not allowing them to conduct electricity

- high melting and boiling point

- hard and brittle

What are the melting and boiling points of ionic solids determined by?

the electrostatic forces of attraction (ionic bonds) between the cations and anions in the lattice structure

How do you know a question in a paper is referring to ionic solids ?

states ions

What are ionic solids made up of?

cations and anions held together by strong electrostatic forces of attraction in a fixed position that forms a ionic lattice

What are metallic solids made up of?

the valence orbitals of neighbouring atoms that overlap where the valence electrons are free to move from one atom to the next as they are delocalised electrons and do not belong to a specific atom but rather to the entire metal lattice

How do you know a question in a paper is referring to metallic solids ?

states the metals

What are the properties metallic solids ?

good conductors of electricity in slid and liquid phase due to the free (mobile) electrons

What are network solids made up of?

atoms which are covalent bonded to one another in a continuous network like diamond , silicon dioxide and graphite

How do you know a question in a paper is referring to network solids ?

states atoms or diamond , carbon or graphite is mentioned

What are the properties network solids?

does not conduct electricity (as all the valence electrons are bonded )

What does diamond and graphite consist of?

carbon atoms covalently bonded to each other:

in diamonds: all four valence electrons are covalently bonded to each other

in graphite: each carbon atom is covalently bonded to only three other carbon atoms so that all carbon atoms lie in the same plan forming sheets which held together by weak Van De Waals forces

What are the characteristics of graphite ?

good conductor (due to fourth valence electron being delocalised ) high melting point due to the strong covalent bonds but is soft due to the weak Van de Waals forces holding the layers together

What types of forces occur between molecular solids ?

London forces or hydrogen bonds

How do you know a question in a paper is referring to molecules solids ?

states molecules

What are the melting and boiling points of molecular solids determined by?

the strength of intermolecular forces as the stronger the intermolecular forces the more energy required to overcome the intermolecular forces between the molecules

How to compare the melting and boiling points of substances that involve hydrogen bonding?

look at the number of hydrogen bonds that occur as the more hydrogen bonds a molecule can form the greater the strength of the intermolecular force and the greater the melting and boiling point of the substance

How to compare the melting and boiling points of substances that are within the group?

compare their molecular mass as the greater the mass the higher the melting and boiling points of the substance

How to compare the melting and boiling points of substances that have the same homologous series group?

compare their chain length ( more sites for London forces and greater contact surface area) and branching (the less branching the least amount "bulges" therefore more London contact sites )

How to compare the melting and boiling points of substances that have different groups?

the strength if the bonds: ascending order

alkanes, alkenes, alyknes - London forces

*esters and haloalkanes - dipole dipole

alcohols - London/hydrogen bonding

carboxylic acid - London/hydrogen bonding

How to discuss whether a non-metal/molecule/metal will be HIGHER THAN, LOWER THAN or EQUAL TO?

1. state the branching (very/more branched or not very branched )

2. amount of sites for London forces / contact surface area therefore have strongest/weakest IMF

3. amount of energy (least/most) to overcome the IMF / separate the molecules

therefore have the highest/lowest melting/boiling point