Bonding And Structure Flashcards
What are ions?
Charged particles that are formed when an atom loses or gains electrons
What is the charge of the ion when electrons are gained?
Negative
Positive when electrons are lost
What are molecular ions?
covalently bonded atoms that lose or gain electrons
Which electrons are lost when an atom becomes a positive ion?
Electrons in the highest energy levels
Do metals usually gain or lose electrons?
lose electrons
Which are the 4 elements that don’t tend to form ions and why?
-Beryllium, boron, carbon and silicon
- Requires a lot of energy to transfer outer shell electrons
What are the 3 main types of chemical bonds?
- Ionic
- Covalent
- Metallic
Define ionic bonding
The electrostatic attraction between positive and negative ions
Give an example of an ionically bonded substance
NaCl – salt
What determines the strength of an ionic bond?
- ionic radius and ionic charge
- ionic bonding is stronger and the melting points higher when the ions are smaller and/ or have higher charges
Explain the trend in ionic radius down a group
- ionic radii increases going down a group
- This is because down a group the ions have more shells of electrons
- Thus the outermost electron experience less pull from positive nucleus
Explain the trend in ionic radius for this set of isoelectronic ions [ N3-, O2-, F+, Ne, Na+, Mg2+, Al3+
-There are increasing numbers of protons from N to F and then Na to Al but the same number of electrons
- Therefore nuclear attraction between the outermost electrons and nucleus increases and ions get smaller
What are the physical properties of ionic compounds?
- high melting points
- non-conductor or electricity when solid
- Conductor of electricity when in solution or molten
- Brittle
In a solution of CuCro4 with connected electrodes which electrode will the 2 ions migrate to?
Cu2+ migrates to the negative electrode
CrO4 ^{2-} migrates to the positive electrode
Define covalent bonding
electrostatic attraction between a shared pair of electrons and the nuclei
Define metallic bonding
electrostatic attraction between the positive metal ions and the sea of delocalized electrons
Electrons in which shell are represented in a dot and cross diagram?
The outer shell
Why does giant ionic lattices conduct electricity when liquid but not when solid?
-In solid state the ions are in fixed positions and thus cannot move.
- When they are in liquid state the ions are mobile and thus can freely carry the charge
Giant ionic lattices have high or low melting and boiling points? Explain the answer
They have high melting and boiling points because a large amount of energy is required to overcome the electrostatic bonds
In what type of solvents do ionic lattices dissolve?
Polar solvents e.g. Water
Why are ionic compounds soluble in water?
Water has a polar bond. Hydrogen atoms have a +ve charge and oxygen atoms have a -ve charge. These charges are able to attract charged ions
What is it called when atoms are bonded by a single pair of shared electrons?
A single bond
How many covalent bonds does carbon form?
4
How many covalent bonds does oxygen form?
2
What is the effect of multiple covalent bonds on bond length and strength?
Double/ triple bonds exert greater electron density therefore the attraction between the nucleus and electron is greater resulting in a shorter and stronger bond
What is a lone pair?
Electrons in the outer shell that are not involved in the bonding
What is formed when atoms share two pairs of electrons?
Double bond
What is formed when atoms share three pairs of electrons?
Triple bond
What is a dative covalent bond?
A bond where both of the shared electrons are supplied by one atom
How are oxonium ions formed?
Formed when acid is added to water. H3O+
What does expansion of the octet mean?
When a bonded atom has more than 8 electrons in the outer shell
What are the types of covalent structure?
- Simple molecular lattice
- Giant covalent lattice
Describe the boding in simple molecular structures
Atoms within the same molecule are held by strong covalent bonds and different molecules are held by weak intermolecular forces
Why do simple molecular structures have low melting and boiling points?
small amount of energy is enough to overcome the intermolecular forces
Can simple molecular structures conduct electricity?
No, they are non-conductors
Why do simple molecular structures not conduct electricity?
The have no free charged particles to move around
Simple molecular structures dissolve in what type of solvent?
Non- polar solvents
Give examples of giant covalent structures
- Diamond
- Graphite
- Silicon dioxide, SiO2
List some properties of giant covalent structures? (3)
- High melting and boiling points
- Non-conductors of electricity, except graphite
- Insoluble in polar and non-polar solvents
Why does graphite conduct electricity?
Delocalized electrons present between the layers are able to move freely carrying charge
Why do giant covalent structures have high melting and boiling points?
- Strong covalent bonds within the molecules need to be broken which requires a lot of energy
Describe the structure of Diamond
3D tetrahedral structure of C atoms, with each C atom bonded to four others
what does the shape of a molecule depend on?
- Number of electron pairs in the outer shell
- Number of these electrons which are bonded and lone pairs
what is the shape, diagram and bond angle for BeCl2
Linear, 180 degrees
What is the shape, diagram and bond angle for BCl3?
Trigonal Planar, 120 degrees
What is the shape, diagram and bond angle for CH4?
Tetrahedral, 109.5 degrees
What is the shape, diagram and bond angle for PCl5?
Trigonal bipyramid, 90 degrees and 120 degrees
What is the shape, diagram and bond angle for SF6?
Octahedral, 90 degrees
What is the shape, diagram and bond angle for NH3?
Pyramidal, 107 degrees
What is the shape, diagram and bond angle for H2O?
Non-linear, 104.5 degrees
What is the shape, diagram and bond angle for NH4 {+}
Tetrahedral, 109.5 degrees
By how many degrees does each lone pair reduce the bond angle?
2.5 degrees
Define electronegativity
The ability of an atom to attract the pair of electrons (the electron density) in a covalent bond
what scale is electronegativity measured on?
Pauling scale
In which direction of the periodic table does electronegativity increase?
Top right, towards fluorine
What does it mean when the bond is non-polar?
The electrons in the bond are evenly distributed?
What is the most electronegative element?
Fluorine
How is a polar bond formed?
Bonding atoms have different electronegativities
Why is H2O polar, whereas CO2 is non-polar?
CO2 is a symmetrical molecule, so there is no overall dipole
what is meant by intermolecular force?
Attractive force between neighboring molecules
What are the 2 types of intermolecular forces?
- Hydrogen bonding
- Permanent dipoles
- London forces
Describe permanent dipole-induced dipole interactions
When a molecule with a permanent dipole is close to other non polar molecules it causes the non-polar molecule to become slightly polar leading to attraction
Describe permanent dipole- permanent dipole interactions
some molecules with polar bonds have permanent dipoles —> Forces of attraction between those dipoles and those of neighboring molecules
Describe London Forces
- London forces are caused by random movements of electrons
- This leads to instantaneous dipoles
- Instantaneous dipole induces a dipole in nearby molecules
- induced dipoles attract one another
Are London forces greater in smaller or larger molecules?
Larger due to more electrons
Does boiling point increase of decrease down the noble gas group? Why?
Boiling point increases because the number of electrons increases and hence the strength of London forces also increases
What conditions are needed for hydrogen bonding to occur?
-O-H, N-H or F-H bond, lone pair of electrons on O, F, N
- Because O, N and F are highly electronegative, H nucleus is left exposed
- Strong force of attraction between H nucleus and lone pair of electrons on O, N, F
Why is ice less dense than liquid water?
- In ice, the water molecule are arranged in an orderly patter. it has an open lattice with hydrogen bonds
- In water, the lattice is collapsed and the molecules are closer together
Why does water have a melting/ boiling point higher than expected?
hydrogen bonds are stronger than other intermolecular forces so extra strength is required to overcome the forces
What type of intermolecular forces do alkanes have? Why?
London Force => Induced dipole-dipole interaction, because the bonds are non-polar
What happens to the boiling point as alkane chain length increases? Why?
- The boiling point increases because there is more surface area and so more number of induced dipole-dipole interaction
- Therefore more energy is required to overcome the attraction
Does a branched molecule have lower or higher boiling point compared to equivalent straight chain? Why?
- The branched molecule has a lower boiling point because they have fewer surface area and hence less induced dipole-dipole interactions
Are alkanes soluble in water? Why?
Insoluble because hydrogen bonds in water are stronger than alkanes’ London forces of attraction
What kind of intermolecular forces do alcohols have? Why?
Hydrogen bonding, due to the electronegativity difference in the OH bond
How do alcohols’ melting point and boiling point compare to other hydrocarbons’ of similar C chain-lengths? Why?
Higher, because they have hydrogen bonding (strongest type of intermolecular force) => Stronger than London forces
Are alcohols soluble in water? Why does solubility depend on chain length?
- Soluble when short chain- OH hydrogen bonds to hydrogen bond in water
- Insoluble when long chain- non-polarity of C-H bond takes precedence
Explain the trend of boiling temperatures of hydrogen halides HF to HI
-There is a general increase of boiling point from HCl to HI which is caused by increasing London forces because increasing number of electrons
- There is a big drop in boiling point from HF to HCL because fluorine is very electronegative therefore the hydrogen bonding is much stronger
In what types of substances can hydrogen bonding happen?
any molecule which has a hydrogen atom directly to an oxygen or a nitrogen
