Unit 1-4 Flashcards
What happens to atomic radius across a row?
Decreases because there’s a greater nuclear attraction as proton number increases, pulling the shell slightly inwards
What happens to atomic radius down a group?
Increases since successive elements have an extra shell
Why are cations smaller than the parent atom
Has lost electrons and has less shells
Why are anions larger than the parent atom?
Less effective nuclear charge as there are more electrons for the same number of protons
Where are repulsive forces present in an ionic bond?
Ions of the same charge
Inner shells of electrons in the ions
Positive nuclei (to a lesser extent)
What are isoelectronic ions?
Different ions with the same electronic configuration and number of electrons
Note: Different atomic radii
Example: O2−, F−, Na+, Mg2+and Al3+ all have 10 electrons
What is an ionic bond?
Electrostatic force of attraction between two oppositely charged ions
Formed by transfer of one or more electrons from a metal to nonmetal
Note: Individual molecules don’t exist
Why do ionic lattices have a high melting temperature?
Large amount of energy needed to break strong electrostatic attraction
Why are ionic lattices soluble in water?
Polar solvents stabilise the separated ions
All group 1, nitrate and most halide compounds are soluble in water
Note: Insoluble in non-polar solvents
Why are ionic lattices electrolytes when molten or dissolved in water?
Because the ions are free to move and carry the charge
Why are ionic lattices very brittle?
Repulsion of similarly charged ions splits the crystal after dislocation
What is a normal covalent bond?
Electrons are shared
Attractive forces exist between positively charged nuclei and the negative charge cloud of the shared electron pair
What is a coordinate covalent bond?
All electrons are donated by a single atom with a lone pair
Bonds are delocalised
The charge of the ions involved is distributed across the molecule
Note: Impossible to distinguish between bonds of the same atom
Where are repulsive forces present in a covalent bond?
Inner shells of electrons on each atom
Each of the positively charged nuclei
The electron shells and charge cloud
Why are covalent molecules liquids and gases at room temperature?
Low melting point as bonds are easy to break
Where is electron density in a covalent bond?
Bulk of electron density will surround the nuclei
Some will occur in the inter-nuclear region
Why are covalent molecules non-conductive?
No free ions or electrons
What does electron deficient mean?
Didn’t gain enough electrons after bonding and still don’t have a full outer shell
What is a lone pair of electrons?
Unbonded electrons in the outer shell
Can be donated with electron deficient atoms to form coordinate bonds
What is electronegativity?
The ability of an atom to pull electron density towards itself within a covalent bond
Note: Shown by the Pauling scale
Why does electronegativity increase across a row?
Nuclear charge increases for only a slight or no increase in shielding
Why does electronegativity decrease down a group?
Less effective nuclear charge due to increased shielding and distance from the nucleus
How is polarity determined?
By the difference in electronegativity in atoms
What is a pure covalent bond?
0 difference in electronegativity
Electrons are shared equally
Only occurs between identical atoms
What is a pure ionic bond?
Too much difference in electronegativity
The least electronegative gives its electrons
What makes a covalent bond polar?
The most electronegative atom pulls electron density towards itself
A dipole is formed
An atom with a small (𝛅) positive (𝛅+) and negative pole (𝛅-)
Note: Greater difference results in stronger polarity
What makes a covalent bond non-polar?
Similar electronegativity so electrons are shared equally on average
Temporary dipoles will form at any given instant
What do Fajan’s rules represent?
The likely conditions for ionic bonding
What is Fajan’s first rule?
The charges on the ions are low
Example: Na+ favours ionic character
C4+ favours covalent character
What is Fajan’s second rule?
The ionic radius of the cation is large
Example: Na+ has a radius of 0.095nm (favours ionic character)
C4+ has a radius of 0.015nm (favours covalent character)
What is Fajan’s third rule?
The ionic radius of the anion is small
Example: F- has a radius of 0.136nm (favours ionic character)
I- has a radius of 0.216nm (favours covalent character)
What are intermolecular forces
Attraction between neighbouring molecules
Influences the physical properties of a compound
How do intermolecular forces influence the physical properties of a compound?
Volatility is much higher than expected based on Mr
More energy is required to break the extra H or VDW bonds
What is volatility?
Boiling point
What are intramolecular bonds?
Attraction between neighbouring atoms within molecules
Ionic and covalent bonds
Influences chemical properties
What are hydrogen bonds?
Bonding between hydrogen atoms bonded to nitrogen, oxygen or fluorine in one molecule to nitrogen, oxygen or fluorine in another molecule
Occurs towards the lone pair
Why are nitrogen, oxygen or fluorine needed for a hydrogen bond to form?
Hydrogen has to be in a very polar molecule
N, O and F are the most electronegative atoms
N, O and F have a lone pair after bonding
What are Van-Der-Waals bonds?
Dipole - dipole attraction
Between the positive and negative dipoles of polar molecules
Temporary dipole - temporary dipole attraction
Between neighbouring temporary dipoles of non polar molecules
What are temporary dipoles?
Temporary dipoles will form at any given instant
Electron density will be greater at one side of the nucleus
Instantly replaced by another in a different orientation
What happens to temporary dipoles across a period?
Strengthens since the number of electrons increases
How does the size of molecules affect temporary dipoles
Stronger in long molecules as electrons are more easily displaced
What is the the valence shell electron pair repulsion theory?
The shape of a molecule or ion depends on the number of electron pairs in the valence shell of the central atom, since these electron pairs tend to keep as far apart as possible in order to minimise repulsion
What are bonding pairs of electrons?
Electrons from each atom bond to form a pair
Note: Coordinate bonds act exactly the same
What are non-bonding pairs?
Lone pair which has not bonded
What is the order of repulsion?
BP-BP (strongest)
LP-BP
LP-LP (weakest)
What is an ionic crystal?
A large structure held together by strong electrostatic forces between oppositely charged ions
Note: No overall charge
What does it mean for a structure to preserve electrical neutrality?
No overall charge
What is the coordination number?
The number of oppositely charged ions which surround an ion
What is the structure of sodium chloride?
Giant ionic lattice of Na+ cations and Cl- anions
Coordination number of 6:6
Each ion is surrounded by 6 of the oppositely charged ion
Na+ ions cant fit many Cl- ions around it due to small ionic radius
What is the structure of caesium chloride?
Giant ionic lattice made of Cs+ cations and Cl- anions
Coordination number of 8:8
Each ion is surrounded by 8 of the oppositely charged ion
Cs+ ions can fit many Cl- ions around it due to a large ionic radius
What is metallic bonding?
The attraction between positive cations and a sea of negative delocalised electrons
What is a delocalised electron?
An electron which moves around both the ion they belong to and nearby ions
Why does the strength of metallic bonding increase with the number of electrons in the valence shell?
Cations increase in positivity
The number of delocalised electrons increases
Why do metals have a high melting point?
Strong attraction between the positive cations and sea of delocalised electrons
Why are metals electrolytes?
Electrons are free to move and carry electrical energy when potential difference is applied
Why are metals malleable and ductile?
Layers of metal ions can slide past each other since the sea of delocalised electrons move to maintain metallic bonding
Why are metals hard and strong?
Strong metallic bonds require large amounts of energy to separate the cations and sea of delocalised electrons
Unit 1.5
What is a macromolecular structure?
Covalent bonding extending indefinitely in three dimension
Bonds per atom and direction of bonds are the same as the molecule
Describe the linear shape of BeCl2 and CO2
2 bonding pairs
0 lone pairs
180° bond angle
Describe the non-linear/angular/bent/V-shape of SO2
2 bonding pairs
1 lone pairs
120° bond angle
The LP-BP repulsion creates a maximum bond angle of 120°
Describe the non-linear/angular/bent/V-shape of H2O
2 bonding pairs
2 lone pairs
105° bond angle
LP-LP repulsion is > than LP-BP repulsion, therefore the BP are pushed closer, creating a smaller bond angle on a 3D plane
Describe the trigonal planar shape of BCl3, SO3 and C2H4
3 bonding pairs
0 lone pairs
120° bond angle
3 BP of electrons repel each other equally
Describe the trigonal pyramidal shape of NH3
3 bonding pairs
1 lone pairs
107° bond angle
The LP-BP repulsion is > than BP-BP repulsion so the 3 BP are pushed closer together
Describe the tetrahedral shape of CH4 and SO4^2-
4 bonding pairs
0 lone pairs
109.5° bond angle
To minimize repulsion the bonds adopt a 3D spacial arrangement that maximizes bond angle
How can a molecule have more than 4 bonding pairs if the valence shell can only hold 8 electrons?
The extra electrons are accommodated by the next energy level
Unit 1.4
Describe the trigonal bipyramidal shape of PCl5
5 bonding pairs
0 lone pairs
90° and 120° bond angle
3 Cl are 120° to eachother on one plane, while on the opposite plane 1 Cl is found above and below the triangle of Cl, creating 2 pyramids with P in the middle
https://shorturl.at/buzGK
Unit 1.4
Describe the octohedral shape of SF6 and (Al(H2O)6)^3+
6 bonding pairs
0 lone pairs
90° bond angle
4 F/H2O are 90° to eachother on one plane, while on the opposite plane F/H2O is found above and below the square of F/H2O, creating 2 pyramids with S/Al in the middle
https://t.ly/WJDv7
