Unit 1.4 - Bonding Flashcards
What are the two types that chemical bonding can be divided into?
Intramolecular bonding
Intermolular bonding
Intramolecular bonding
Bonds that form within the molecule - they hold atoms in place
What are the bonds that form within a molecule?
Intramolecular bonding
What are the bonds that hold atoms in place?
Intramolecular bonding
Intermolecular bonding
Bonds formed between molecules
What are the bonds formed between molecules?
Intermolecular bonding
Give an example of intermolecular bonding
Hydrogen bonding
What is hydrogen bonding an example of?
Intermolecular bonding
Which type of bonding is stronger - Intramolecular or intermolecular?
Intramolecular
Energy per mole of bonds for Intramolecular bonds
100 - 1000kJ per mole of bonds
What are Intramolecular bonds responsible for within the molecule?
The chemical reactivity of the molecule
What are the intermolecular bonds responsible for in a molecule?
The physical properties of the molecule
What type of bonds are responsible for the chemical reactivity of a molecule?
Intramolecular bonds
What type of bonds are responsible for the physical properties of a molecule?
Intermolecular bonds
How can the chemical reactivity of a molecule be observed?
In a chemical reaction
What can be observed of a molecule during a chemical reaction?
Its chemical reactivity
What are physical properties?
Properties that can be observed or measured without changing the identity of the substance
Name some physical properties
Melting point
Boiling point
Solubility
Under which type of bonds do ionic, covalent and coordinate bonds fall?
Intramolecular bonds
Name 3 Intramolecular bonds
Ionic bonds
Covalent bonds
Coordinate bonds
Ionic bonds
A bond formed by the electrical attraction between positive and negative ions (cations and anions)
A bond formed by the electrical attraction between positive and negative ions (cations and anions)
Ionic bond
Covalent bonds
Has a pair of electrons with opposed spin shared between 2 atoms with each one giving 1 electron
Has a pair of electrons with opposed spin shared between 2 atoms with each one giving 1 electron
Covalent bonds
Coordinate bond
A covalent bond in which both of the shared pair of electrons come from 1 of the atoms
A covalent bond in which both electrons come from 1 of the atoms
Coordinate bond
When do ions form?
When atoms gain or lose electrons by electron transfer
When does the process of forming ions stop?
When the atom which loses and the one which gains an electron have stable electronic structures
Describe the charges on two ions formed during electron transfer
Opposite charges
What forms when atoms gain or lose electrons?
Ions
What usually loses an electron to what during ionic bonding?
Metals to non-metals
What do metals form during ionic bonding?
Positive ions (cations)
What form positive ions (cations) during ionic bonding?
Metals
What do non-metals form during ionic bonding?
Negative ions (anions)
What form negative ions (anions) during ionic bonding?
Non-metals
Cations
Positive ions
Positive ions
Cations
Negative ions
Anions
Anions
Negative ions
What IS the ionic bond during ionic bonding?
The electrostatic force of attraction between 2 ions of opposite charge
Which rule do we follow for ionic bonding and what does this mean?
The octet rule - 8 electrons in the outer shell
What do we use to show ionic bonding?
Dot-cross notation
What is the charge on an in equal to?
The amount of electrons gained or lost by the atom
What do many elements form ions which have the same electronic configuration as?
Noble gases
What do atoms do during covalent bonding?
Share electrons
What type of bonding involves atoms sharing electrons?
Covalent bonding
What does a single covalent bond contain?
Two electrons, one from each atom, shared between them with opposite spins
What do the electrons in a covalent bond have?
Opposite spins
How many electrons are shared in a double covalent bond?
4
How many electrons are shared in a triple covalent bond?
6
What type of bonding involves two electrons shared?
Single covalent bond
What type of bonding involves 4 electrons shared?
Double covalent bond
What type of bonding involves 6 electrons shared?
Triple covalent bonding
What type of elements usually for covalent bonds?
Non-metals
What do non-metals usually form?
Covalent bonds
When does covalent bonding come to an end?
When both atoms have stable electronic configurations (the same as a noble gas)
What IS a covalent bond?
An electrostatic force of attraction between the 2 nuclei and the shared electrons
What’s stronger - a covalent or an ionic bond?
Covalent
How is a single covalent bond demonstrated?
—
What does — represent?
A single covalent bond
How is a double covalent bond shown?
==
What does == demonstrate?
A double covalent bond
What’s the name for the electrons not used in bonding?
Lone electrons
Lone electrons
Electrons not used in bonding
Describe triple covalent bonds - which elements has these?
Nitrogen - they’re strong bonds
Why is nitrogen an unreactive gas?
It has strong triple covalent bonds
What do triple covalent bonds in nitrogen cause it to be? Why?
Unreactive, as this is a strong bond
What is added to crisp packets and why?
Nitrogen, as it’s an Unreactive gas due to its strong triple covalent bond
Give a use for nitrogen and explain why
In crisp packets, as it’s an Unreactive gas so it keeps them crisp
What’s another word for coordinate bonds?
Dative bonds
What are dative bonds?
Coordinate bonds (old word for it)
What are coordinate bonds a type of?
Covalent bond
Where do the electrons come from for coordinate bonds?
Both electrons are supplied by 1 atom
Where does a coordinate bond form between 2 atoms?
Between an atom which has a lone pair or electrons and another atom which is electron deficient (i.e - has an empty orbital)
Electron deficient
Has an empty orbital
What is an atom which has an empty orbital?
Electron deficient
What forms between an atom with a lone pair of electrons and another which is electron deficient?
A coordinate bond
Give 3 examples of coordinate bonds forming
-between ammonia + boron trifluoride
-hydrated proton (H30+)
-ammonia ion (NH4+)
What do the following all form?
-ammonia and boron trifluoride
-hydrated proton (H30+)
-ammonia ion (NH4+)
Coordinate bonds
Which element can expand its octet rule during ionic bonding and what to?
P, to 10 electrons in the outer shell
What type of compound is sodium chloride?
Ionic
What shape ions do sodium and chlorine have?
Nearly spherical
Name 2 ions which have a nearly spherical shape?
Sodium and chlorine
What’s special about a spherical ion?
Uniform electric field around it - can attract ions of opposite charge in all directions
What type of ions have a uniform electrical field around them and can attract ions of opposite charge in all directions?
Spherical ions
What can an ionic bond be classed as and why?
Non-directional as it can attract ions of opposite charge in all directions
What type of bond is non-directional and why?
Ionic as it can attract ions of opposite charge in all directions
Even though ionic bonds are non-directional bonds, what do we have to consider? Why?
Due to the number of ions being very large, we have to consider repulsion between ions of the same charge and attraction forces
What occurs between ions of the same charge?
Repulsion
What do repulsion and attraction forces do?
Restrict the number of ions of opposite charge which can pack around an ion and the positions which the ions can occupy
Restrict the number of ions of opposite charge which can pack around an ion and the positions which the ions can occupy
Repulsion and attraction forces
When are there many repulsion and attraction forces to consider?
When the number of ions is very large
How do ions pack and what does this mean?
A lattice arrangement - there’s an equilibrium between the attractive and the repulsive forces
Lattice arrangement
Equilibrium between the attractive forces and repulsive forces (ions)
What does ions lattice arrangement depend on?
The charges on the two ions and their relative sizes
What do the charges on two ions and their relative sizes affect?
The lattice arrangement
Why are chlorine ions larger on the sodium chloride lattice?
Due to a larger atomic radius (extra shell of 8 electrons)
What’s strongest - ionic or covalent bonds?
Covalent
What’s an example of covalent bonds being the strongest?
Carbon has a giant covalent structure, and has the highest melting point of all
Which element has the highest melting point and why?
Carbon due to its giant covalent structure
What does Carbon’s giant covalent structure give it?
The highest melting point
Where is most of electron density centred?
Around nuclei
What is mostly centred in the nuclei?
Electron density
What IS a covalent bond?
Attractive force between the positive nuclei and the negative charge cloud of the shared electron pair
Attractive force between the positive nuclei and the negative charge cloud of the shared electron pair
Covalent bond
Where are the shared electrons in a covalent bond?
Between the nuclei
What’s the net affect of the shared electrons being between the 2 nuclei in a covalent molecule?
The net effect of the attractive forces between the electrons and the nuclei is to hold the 2 nuclei together
What holds two nuclei together in a covalent molecule?
The net effect of the attractive forces between the electrons and the nuclei is to hold the 2 nuclei together
Repulsive forces between ions
Forces between inner shells of electrons on each atom
Forces between the positive charges on nuclei
Forces between inner shells of electrons and charge cloud of the bond
What determine a bond’s length?
The balance between the attractive and repulsive forces
What do the balance between the attractive and repulsive forces determine?
The bond length
Under which conditions do metals easily lose up to 3 outer electrons?
As long as there’s a non-metal available to form an ionic bond
What 2 types of elements for ionic bonds?
Metal with a non-metal
What does a metal with up to 3 outer electrons do if there’s no non-metal present?
Merge the outer main levels of all of its atoms so that electrons are no longer associated with any 1 atom, but are shared between all of them
What type of bond occurs when atoms merge their outer main levels so that electrons are associated with all atoms?
Metallic bonding
What does 2 atoms merging their outer main levels together form?
A sea of electrons, or a pool of delocalised/valence electrons
When does a pool of delocalised/valence electrons form?
When metals merge the outer main levels of their atoms when there’s no non-metal available for ionic bonding
A pool of..what type of electrons? (Metals merging their outer main levels of atoms)
Delocalised/valence
How are the “sea” of electrons and the metal atoms charged?
Sea = negative
Metal atoms = positice
What IS a metallic bond?
The attraction between the negatively charged “sea” of electrons and the positive metal atoms
The attraction between the negatively charged “sea” of electrons and the positive metal atoms
Metallic bond
What can metals do well and why?
Conduct electricity and heat (delocalised electrons can carry a current)
What type of materials can conduct electricity and heat well and why?
Metals due to the delocalised electrons being able to carry a current
What does more delocalised electrons mean for a metal?
Higher melting point and a better conductor of electricity
What makes a metal a better conductor of electricity and gives it a higher melting point?
Having more valence electrons
What decides how many delocalised electrons a metal has?
How many electrons the atom can lose
What does how many electrons a metal atom can lose affect?
The amount of delocalised electrons
What happens to melting and boiling points across the period and why?
Increase
Ionic charge increases
Ionic size decreases
Number of outer shell electrons increases
Attraction increases
Electronegativity
The ability of an atom to attract a pair of electrons to itself in a covalent bond
The ability of an atom to attract a pair of electrons to itself in a covalent bond
Electronegativity
What are the most electronegative elemtents?
N, O and F (F is most)
What’s the electronegativity of all noble gases and why?
0
Cannot accept electrons de to a full outer shell
Which elements have an electronegativity value of 0 and why?
Noble gases as they cannot accept electrons due to a full outer shell
Electronegativity trend across a period + explanation
Increases (increased nuclear charge)
Electronegativity trend down a group + explanation
Decreases (increased screening)
What type of elements have low Electronegativity values?
Metals
What type of elements have high electronegativity values?
Non-metals
Describe the electronegativity values of the elements in the middle of the periodic table
Intermediate
What is electronegativity measured on?
A Pauling scale
What ca electronegativity determine?
The type of bond that will be formed
What determines the type of bond that will be formed?
Electronegativity
The greater the difference in electronegativity…
…the more ionic the character of the bond
What makes the character of a bond more ionic?
Greater difference in electronegativity
Which two elements have the biggest difference in electronegativity and what does this mean?
Potassium and fluorine - they form the most ionic bond
What do many ionic bonds have?
Covalent character
What type of bond is an ionic bond if it has covalent character?
Polar covalent
Polar covalent bond
Ionic bond with covalent character
What type of bond is between 2 identical species? Why?
Non-polar covalent - there’s no difference in electonegativity
What do non-polar covalent bonds occur in and why?
Two identical species as there’s no difference in electronegativity
What type of bond ones no difference in electronegativity lead to?
Non-polar covalent
Where is the electron pair in a polar covalent bond?
Isn’t always situated exactly between the 2 atoms - it’s pulled towards the more electronegative one in a covalent bond
In what type of bond is the electron pair not situated exactly equally between 2 atoms?
Polar covalent bond - pulled towards the more electronegative one in a polar bond
What’s caused in a polar bond?
Difference in electronegativity causes a permanent dipole
What causes a permanent dipole?
The difference in electronegativity in a polar bond
What does a greater difference in electronegativity mean for a bond?
More polar bond
What makes a bond more polar?
Greater difference in electronegativity
Describe the atoms in a non-polar covalent bond?
The two atoms are the same, so they have equal electronegativity
Where is the electron pair in a non-polar covalent bond? Why?
Shared equally between the two atoms as they’re the same and have equal electronegatives
What type of bond has the electron pair shared equally and why?
Non-polar due to the atoms being the same, so they have equal electronegativity
What moves towards the more electronegative element?
Electron densiy
Where does electron density move?
Towards the more electronegative element
What do we have if ALL of the electron density is by one element?
Exclusive + and - charges (ionic bond)
In what type of bond do we have exclusive + and - charges?
Ionic bond
Where is the electron density in an ionic bond?
All next to the more electronegative element
Where is electron density in a polar covalent bond?
Towards the more electronegative element
What type of bond is formed when the electron density is towards the more electronegative element?
Polar covalent bond
Draw an electron density diagram presenting a non-polar covalent bond
(Check notes)
Draw an electron density diagram presenting a polar covalent bond
(Check notes)
Draw an electron density diagram presenting an ionic bond
(Check notes)
In the electron density diagram for what type of bond would it be distorted towards the electronegative end?
Polar covalent bond
In what type of electron density diagram are the electronegatives equal?
Non-polar covalent bond
In what type of electron density diagram do we have exclude + and -?
Ionic bond
What does a very large difference in electronegativity mean?
Fully ionic bond (higher % ionic character)
Do ionic bonds show some covalent character?
Yes
What character do ionic bonds still show?
Some covalent character
Polarisation of ions
When small positive ions (cations) pull electron density off neighbouring ions due to some covalent character
When small positive ions (cations) pull electron density off neighbouring ions due to some covalent character
Polarisation of ions
When is polarisation of ions easier?
If the anion is large and has a high negative charge
Which process is easier is an anion is large and has a high negative charge?
Polarisation of ions
What pull electron density off of neighbouring ions during the polarisation of ions?
Small positive ions (cations)
What happens eventually during polarisation of ions?
Electrons become shared and the bond increased in covalent character
In which process do bonds increase in covalent character?
Polarisation of ions
What do cations pull away and from what during polarisation of ions?
Electron density off neighbouring ions
Draw an ionic bond with some covalent character
(Check notes)
Draw an ionic bond with substantial covalent character
(Check notes)
In general, what value of electronegativity difference forms non-polar covalent bonds?
Less than 0.4
What does an electronegativity difference of less than 0.4 generally show?
A non-polar covalent bond
Generally, what do electronegativity differences between 0.4 and 18 show?
Polar covalent bond
What value for the difference in electronegativity generally represents a polar covalent bond?
0.4 - 1.8
What does an electronegativity of more than 1.9 generally represent?
Ionic bond
What difference in electronegativity implies an ionic bond?
1.9+
Which forces explain physical properties of covalent molecules?
Intermolecular forces
What properties do intermolecular forces explain and in what?
Physical properties of covalent molecules
Name 2 Van der Waal forces
Induced dipole-induced dipole forces
Dipole-dipole forces
What are induced-dipole induced-dipole and dipole-dipole forces examples of?
Van der Waal forces
What’s the weakest Van der Waal force?
Induced dipole-induced dipole force
What creates a higher boiling point?
Larger molecule
More electrons
Stronger intermolecular forces
How do the quantity of electrons reflect on the strength of the intermolecular forces in a compound?
More electrons = stronger intermolecular forces
Can each halogen be liquified? Why is this strange?
Yes, even though the covalent bond between the molecules is non-polar
What does a stronger attraction between electrons lead to?
Higher melting points
Why do larger molecules lead to higher boiling points?
More electrons
Greater fluctuation in the electron cloud
Larger dipoles
Stronger attraction
What forms a stronger attraction in terms of dipoles?
Larger dipoles = stronger attractions
What causes a larger dipole?
A greater fluctuation in the electron cloud due to more electrons
What is a greater fluctuation in the electron cloud caused by and what does this lead do?
More electrons
Larger dipoles
How can non-polar covalent bonds form temporary dipoles?
At any instant, the distribution is not equal with the electrons being more under the influence of 1 atom due to constant movements of electrons in the atom
Why is the distribution of electrons in a non-polar covalent bond not always equal?
Constant movements of the electrons in an atom
What does the constant movements of electrons in an atom lead to?
Non-polar covalently bonded molecules forming temporary dipoles
Draw the temporary dipole between iodine molecules with a non-polar covalent bond
(Check notes)
When can a halogen (with a non-polar covalent bond) be liquified?
When forming temporary dipoles through induced dipole-induced dipole forces
What can a temporary dipole do to another temporary dipole in a nearby molecule?
Induce it to cause a force of attraction between them
Induced dipole - induced dipole force
When a temporary dipole induces another temporary dipole in a nearby molecule, causing a force of attraction between them
When a temporary dipole induces another temporary dipole in a nearby molecule, causing a force of attraction between them
Induced dipole - induced dipole force
What type of molecules do induced dipole - induced dipole forces occur in?
ALL molecules
Which Van der Waal force occurs in ALL molecules?
Induced dipole - induces dipole forces
What do dipole-dipole forces occur in?
Molecules containing a dipole (polar covalent bond)
Which Van der Waal force occurs in molecules containing a dipole?
Dipole-dipole forces
What does a dipole include?
One end with a slightly positive charge
Once end with a slightly negative charge
(Due to differences in electronegativities)
What’s the name for a molecule with one end that has a slightly positive charge and the other with a slightly negative charge?
Dipole
Why do dipoles exist?
Due to differences in electronegativity
Which Van der Waal forces are temporary and which are permanent?
Temporary - induced dipole - induced dipole forces
Permanent - dipole dipole forces
Dipole-dipole forces
When dipoles arrange themselves so that the negative region of one molecule is close to the positive region of another molecule
When dipoles arrange themselves so that the negative region of one molecule is close to the positive region of another molecule
Dipole-dipole forces
Which type of force is generally referred to with “Van der Waal force”?
Induced dipole -induced dipole force
Which Van der Waal force strengthens intermolecular forces doing between molecules the most?
Dipole-dipole force
What do dipole-dipole forces do more than induced dipole - induced dipole forces?
Strengthen intermolecular forces
Compounds with which type of forces have the highest boiling points with similar molar mass - dipole dipole or induced dipole-induced dipole?
Dipole-dipole forces
How does having stronger intermolecular forces affect molecules with dipole-dipole forces? (Physical property)
Higher boiling point
What are two molecules with identical molar mass that have completely different boiling points and why?
Propanone and butane
Much higher in propanone - dipole dipole forces
Induced dipole - induced dipole in butane
What’s propanone also known as?
Acetone
What’s acetone?
Propanone
What’s the issue with dipole-dipole forces?
Dipoles aren’t always aligned to produce an attraction between them due to the random movements of molecules
Very weak
Which type of force has an issue with the alignment of dipoles?
Dipole dipole forces
How do dipole dipole forces get stronger?
Strength of the force increases with the number of electrons in the molecule (i.e - its size)
What does a larger molecule mean for the dipole-dipole force?
More electrons in the molecule - strength of the force increases
What’s hydrogen bonding a special case of?
The dipole-dipole force
Name a special case of a dipole-dipole force?
Hydrogen bonding
Describe the trend in terms of boiling points for the period II hydrides compares to period III and explain why this is unexpected
Boiling points of period II hydrides are greater than period III
You’d expect the intermolecular forces to be stronger in period III
What’s proof for the existence of hydrogen bonding?
The fact that the boiling points of period II hydrides are reader than period III (which is unexpected as you’d expect the intermolecular forces to be stronger in period III) - must be a stronger intermolecular force
Hydrogen bond
An electrostatic force of attraction which forms between a hydrogen atom bonded to a highly electronegative atom in one molecule and a highly electronegative atom such as N, O or F in another molecule
An electrostatic force of attraction which forms between a hydrogen atom bonded to a highly electronegative atom in one molecule and a highly electronegative atom such as N, O or F in another molecule
Hydrogen bond
Highly electronegative elements
N, O or F
Draw and label hydrogen bonding in water
(Check notes)
Describe the covalent bonds in water
Very polar
What’s longest - hydrogen bonds or covalent bonds?
Hydrogen bonds
What does hydrogen bonding occur between?
2 electrostatic atoms
Why does hydrogen bonding exist?
Hydrogen atoms are very small, and the atom in another molecule is highly electronegative
Describe the hydrogen atom that attracts a lone pair of electrons for hydrogen bonding
Highly polarising 𝛿+ small hydrogen atoms
What does the 𝛿+ hydrogen atom attract in a hydrogen bond?
A lone pair of electrons form a highly electron ache you’ve atom in another molecule
Which bonds are we breaking when boiling water or melting ice?
Hydrogen bonds
How do we break hydrogen bonds in water
Boil water
Melt ice
What, apart from water, does hydrogen bonding occur in?
Alcohol, ethanol and ammonia
What type of bonding occurs in alcohol, ethanol and ammonia?
Hydrogen bonding
Draw and label hydrogen bonding in ammonia
(Check notes)
Which physical properties of compounds does hydrogen bonding affect ?
-higher boiling points than compounds with similar molar mass and no hydrogen bonding
-more soluble in water
What do compounds have higher boiling points than with hydrogen bonding?
Compounds with similar molar mass and no hydrogen bonding
What type of bonding makes a substance more soluble and gives it a higher boiling point?
Hydrogen bonding
Compare ice’s density to water
Less dense than water (only substance where the solid is less dense than the liquid)
Describe the structure of ice
Open stucture
Held by hydrogen bonds
Tetrahedral
Angles of 109.5 degrees
Why is ice less dense than liquid water?
When it melts, hydrogen bonds are broken and water molecules are able to move closer together
What properties does hydrogen bonding give liquid water?
Unusually high boiling point
High surface tension value
What gives water an unusually high boiling point and a high surface tension value?
Hydrogen bonding
Name 3 types of compounds that are soluble in water
Alcohols, carboxylic acids, amines
Why are alcohols, carboxylic acids and amines all soluble in water?
They form hydrogen bonds with it
Is ammonia soluble in water? Why?
Yes, because it can for hydrogen bonds with it
What type of compounds are soluble in water?
Ones that can form hydrogen bond with it
What does a compound’s ability to form hydrogen bonds with water do to it?
Makes it soluble in water
Is methane soluble in water? Why?
No, as it only has Van der Waal forces between molecules and cannot form hydrogen bonds with water
Give an example of an Intramolecular force
Covalent bond
What type of force is a covalent bond?
Intramoleular
Intramolecular forces
Within molecules
Forces within molecules
Intramolecular forces
What do Intramolecular forces influence?
Chemical properties of molecules
What affect ehe chemical properties of molecules?
Intramolecular forces
Give examples of intermolecular forces
Van der Waal’s forces, Hydrogen bonding
What type of forces are Van der Waal’s forces and hydrogen bonding types of?
Intermolecular forces
Where do intermolecular forces exist?
Between molecules
What type of forces exist between molecules?
Intermolecular forces
What do intermolecular forces affect (give examples)?
The physical properties of molecules (melting and boiling points, solubility)
What affects the physical properties of molecules (melting and boiling points, solubility)?
Intermolecular forces
How do boiling points change down the group and why?
Increase down the group due to larger molecules having stronger Van der Waal forces
When a compound boils, which bonds are broken and which are not?
Covalent bonds are NOT broken
Intermolecular forces ARE broken
What’s an example of intermolecular forces being broken when a compound boils, not covalent bonds?
When water boils into steam, it doesn’t turn into hydrogen and oxygen. Steam is gaseous water.
List the three main forces in order of strength, starting from the strongest
Covalent bonds
Hydrogen bonds
Van der Waal’s forces
Which force us the strongest?
Covalent bonds
Which force is the weakest?
Van der Waal’s forces
Why are covalent bonds stronger than hydrogen and Van der Waal’s forces?
Distance between atoms is shorter due to increased attraction
Draw ethanol (C2H2OH) forming hydrogen bonds with water
(Check notes)
What would make something more insoluble in water? Why?
More non-polar groups, due a decreased effect of hydrogen bonds
What would more non-polar groups do to a compound in water?
Make it more insoluble due to a decreased effect of hydrogen bonds
What would decrease the effect of hydrogen bonds? What would this lead to?
More non-polar groups - become more insoluble in water
What do we use to determine shapes of molecules and ions?
Valence shell electron pair repulsion theory (VSEPR)
VSEPR
Valence shell electron pair repulsion theory
What is the general rule of VSEPR?
The shape adopted by a simple molecule or ion is that which keeps repulsive forces to a minimum
What’s VSEPR used for?
Determining the shapes of molecules or ions
How is VSEPR used to determine the shapes of molecules or ions?
By defending the number of electron pairs in the outer shell (valence shell) of a central atom
Outer shell
Valence shell
Valence shell
Outer shell
The outer shell of which atom do we use for VSEPR?
A CENTRAL atom
What do we determine for a central atom in VSEPR?
The number of electron pairs in the outer shell
What does the shape of a simple molecule or ion do?
Keep repulsive forces to a minimum
What type of bonds do molecules have?
Covalent bonds
What do covalent bonds consist of and what’s significant about these?
A pair of electrons
Electrons are negatively charged
Each bond repels other bonds
Why do bonds repel other bonds?
Electrons are negatively charged (a covalent bond consists of a pair of electrons)- each bond repels other bonds
What type of bond consists of a pair of electrons?
Covalent bond
What do bonds duo due to them being repulsive of each other?
Push each other as far apart as possible to reduce repulsive forces
Why do bonds push each other as far apart as possible?
To reduce repulsive forces
What would equal repulsions of bonds cause?
Equally spaced bonds
What causes equal spaces between bonds?
Equal repulsions
What would bonds be with less repulsive forces?
Further
When would bonds be further away from each other?
With less repulsive forces
How would bonds be with greater repulsive forces?
Closer
When would bonds be closer?
With greater repulsive forces
What’s a simple molecule?
One with a central atom and other’s bonded to it
Molecule with a central atom and others bonded to it
Simple molecule
What do most simple molecules have?
Standard shapes
Equal bond angles
Why do most simple molecules have standard shapes and equal bond angles?
Equal repulsions between bond pairs
What do equal repulsion’s between bond pairs in simple molecules do?
Give them standard shapes and equal bond angles
What affects the angles between bonds and therefore the shapes of molecules?
Lone pairs on the central atom
Where do lone pairs cause an effect?
On the central atom of a molecule
What do lone pairs on the central atom of a molecule affect?
-angles between bonds
-shapes
Bond pairs
These electrons are spread out so that they spend time around both atoms in the bond
These electrons are spread out so that they spend time around both atoms in the bond
Bond pairs
Lone pairs
They’re attached to 1 atom only and are not involved in bonding
They’re attached to 1 atom only and are not involved in bonding
Lone pairs
Do bond pairs or lone pairs have a greater power of repulsion? Why?
Lone pairs as they occupy a smaller volume of space
Which type of pairs of electrons occupy the smallest volume of space and what does this mean?
Lone pairs, so they have a greater power of repulsion
How are electrons found in the outer shell around central atoms?
In pairs
Where are electrons found in pairs?
Around central atoms
What do electron pairs do to each other?
Repel one another as far away as possible until they’re at their most stable spatial arrangement
What leads to a stable spartial arrangement in a molecule?
Electron shells repelling one another as far away as possible
What repel each other as far away as possible for a stable spartial arrangement in a molecule?
Electron pairs
Sequence of repulsion
Least repulsive: bond pair-bond pair
Lone pair-bond pair
Most repulsive: Lone pair-lone pair
Which pairs of electrons are most repulsive of each other?
Lone pair-lone pair
Which pairs of electrons are least repulsive of each other?
Bond pair-bond pair
When do we confide the affects of lone pairs?
After the arrangement of electron pairs has been worked out
2 electron pairs…
Shape?
Bond angle?
Example?
Linear
180°
BeCl2
How many electron pairs does a linear shaped molecule have?
2
2 WHAT does a linear arrangement of a molecule have?
Electron pairs
3 electron pairs…
Shape?
Bond angle?
Example?
Trigonal planar
120 °
BF3
4 electron pairs…
Shape?
Bond angle?
Example?
Tetrahedral
109.5 °
CH4
5 electron pairs…
Shape?
Bond angle?
Example?
Trigonal bipyramid
90/120 °
PCl5
6 electron pairs…
Shape?
Bond angle?
Example?
Octahedral
90 °
SF6
Bond angle 180 ° shape and electron pairs
Linear, 2
Bond angle 120 ° shape and electron pairs
Trigonal planar, 3
Bond angle 109.5 ° shape and electron pairs
Tetrahedral
Bond angle 90 °/120 ° shape and electron pairs
Trigonal bipyramid, 5
Bond angle 90 ° shape and electron pairs
Octahedral, 6
What do bond angles represent in molecules?
The furthest distance bonding pairs can get
Around which pair do lone pairs start causing effects to the shape and bond angle of a molecule?
Around the central atom
What around the central atom causes effects for the bond angle and shape of molecules?
Lone pairs
What would we expect to form with BeCl2 and why is this not the case?
Ionic bonds, but Be is small with a high charge, and so has a high polarising power to form covalent compounds
Why does BeCl2 not form ionic bonds?
Be is small with a high charge, so it has a high polarising power to form covalent compounds
Beryllium dichloride shape + explanation
(See notes)
Boron trifluoride shape and explanation
(See notes)
What type of diagram do we have to draw to represent the 3D shape of molecules?
Wedge diagrams
Methane shape + explanation
(See notes)
Phosphorus (V) chloride shape + explanation
(See notes)
What can phosphorus do?
Make use of its d orbitals to expand its octet
Name 2 elements that can make use of their d orbitals to expand their octets
Phosphorus, sulphur
How do phosphorus and sulphur expand their octets?
Make use of their d orbitals
What do potassium and sodium make use of their d-orbitals for?
Expanding their octets
Sulphur (VII) shape + explanation
(See notes)
Sketch a linear shape molecule
(Check notes)
Sketch a Trigonal planar shaped molecule
(See notes)
Sketch a tetrahedral shaped molecule
(See notes)
Sketch a Trigonal bipyramid molecule
(See notes)
Sketch an octahedral molecule
(See notes)
How do we work out the shapes of molecules and ions?
1.number of electrons in the outer shell of the central atom
2.number of electrons provided by the other atoms (1 per atom)
3. (For ions) - what is the contribution of charge?
Add 1 electron for every negative charge
Remove 1 electron for every positive charge
4.number of electron pairs (divide total by 2)
5.number of bond pairs (formula shows) and lone pairs (whatever’s left over) - what effect does this have on the shape?
How many electrons does each attached atom provide?
1
What are irregular shapes caused by?
Extra repulsion caused by lone electrons
What does extra repulsion from lone electrons cause?
Irregular shapes
Name 2 molecules with irregular shapes - why?
Ammonia and water due to the greater repulsive effect of the lone pair reducing the bond angle
Is the bond angle larger or smaller than expected with lone pairs causing their repulsive effects?
Smaller
Draw (approx.) ammonias shape + explain
(See notes)
Draw waters (approx.) shape and explain
(See notes)
What shape does ammonia have?
Based on a tetrahedron, but as one of the pairs is a lone pair, it has a more pyramidal shape
Molecule with a pyramidal shape
Ammonia
Molecule with an angular shape
Water
What shape is a water molecule?
Based on a tetrahedron, but has an angular shape due to lone pairs
Sketch CO2s molecule + explain
(See notes)
How do we calculate the shape of a molecule itch double bonds and why?
It’s calculated in the same way, as the double bond repels other bonds as if it were single, causing the same shape
Difference between the shape of molecules with double bonds and regular ones
No difference - the bond repels other bonds as if it were single
What’s important to remember when sketching CO2’s molecule?
It has double bonds
What do we need to remember to include when drawing hydrogen bonds?
-polarisation (little charges) of everything involved
-lone electrons
-correctly placed hydrogen bonds
What makes a bond polar?
The elements involved having a difference in electronegativity
What does a difference in electronegativity mean in a bond?
That it’s polar
Give 2 examples of species containing a coordinate bond
Ammonium ion (NH4+)
Hydrated proton (H30+)
What do we do when asked to show any permanent dipoles?
Draw the little charges
How is ammonia able to act as a base?
Has a lone pair of electrons on the nitrogen atom, so it can form a coordinate bond
So, it accepts a proton H+
What’s the strongest from the following?
dipole-dipole
induced dipole-induced dipole
dipole-dipole
What are induced dipole-induced dipole forces usually found in?
diatomics
What does increased electronegativity mean in terms of the time taken for a reaction to take place?
More electronegative = faster reaction
Shape of molecule with 3 bond pairs and 1 lone pair
Trigonal pyramidal
Shape of molecule with 2 bonding pairs and 2 lone pairs
Bent
Do noble gases have high or low boiling temperatures? Why?
Low
Does not form molecules and exists as separate atoms
Atoms are held together by weak induced dipole- induced dipole forces
What do I need to remember to put down in all VSEPR questions?
That the shape is laid out in this way in order to keep repulsive forces to a minimum
Name of shape of molecule with 3 bond pairs and 1 lone pair
Pyramidal
