bonding Flashcards
what is structure of ions
A regular lattice of alternating positive and negative ions
lattice held by electrostatic forces
Crystal structure
properties of lattice and why (5)
very high melting point due to strong electrostatic attraction between oppositely charged ions therefore requires a lot of energyy to break
Generally soluble in H2O- as water is very polar so it can disrupt the electroctatic attractions between the ions and break them up
insulator when solid- ions are fixed in position so cannot carry a charge
Electrical conductors when molten/ dissolved- as ions are free to move so able to carry a charge
Brittle - when moved. Ions no longer have an alternating arrangement which means they repel each other and the lattice breaks
what is a covalent bond
shared pair of elctrons with opposite spins, and one electron is donated by each atom
(multiple eg double bond when 2 pairs of e- shared etc)
what does a covalent bind form between
forms between elements that have high electronegativty values (non-metals)
what forces are involved in a covalent bond
highly negative/ high e- density where elctrons shared
And the very strong attraction between the electrons and positive nuclei
types of covalent structures
molecular:
simple covalent i.e CH4, H2O
macromolecular:
giant covalent i.e. diamond and graphite
what is a coordinate bond (dative)
a covalent bond formed when both electrons are donated by the same atom
once formed, acts in the same way as a covalent bond
how is ice formed
H2O is a covalent bonded molecule therefore hydrogen bonding exists between molecules
between 0ºC - 100ºC, bonds hold molecules close to each other but allow free movement
Below 0ºC, molecules have less energy so hydrogen bonding fix molecules in position
what structure does ice have
Ice has 3d hexagonal crystal structure
how are properties of ice affected by structure (2)
ice floats: spaces creates b/c of 3D hexagonal crystal structure
spaces created between spaces
spaces are caused to expand and become less dense
relatively high mp: strong hydrogen bonding between the molecules
what is bonds between iodine
is a covalently bonded molecule (covalent bond is very strong)
weak induced dipole/ van der waal’s forces between molecules which gives crystal structure
iodine properties (5)
shiny grey at room temperature
Low melting point- weak vane dear wall’s forces are very easily broken but I2 molecules stay intact
Sublime(s=>g) when heated the grey solid turns into purple gas
Slightly soluble in H2O- b/c I2 is non-polar
Only in potassium iodide solution and iodide ions allows it to dissolve
structure of diamond
Each C atom form 4 single covalent bonds with 4 other C atoms
Tetrahedral arrangement (109.5)
Forms a 3d lattice of solid carbon
properties of diamond
Very hard: Due to the structure of double carbon covalent bonds
Very high melting point: Due to strong double carbon bonds, require a a lot of energy to break
Electrical insulation: All electrons involved on bonding/ no delocalised e-
Insoluble: Due to strong double carbon bonds
structure of graphite
Each carbon forms 3 single covalent nods with 3 other carbons
4th is delocalised
Trigonometry planar shape (120)
Forms a 2d hexagonal structure with delocalise delctrons
Weak van dear ewaals forces between the layers
properties of graphite
soft: due to weak van dear wall’s forces therefore layers can slide over each other
Very high melting point- strong double carbon covalent blonds therefore requires a lot of energy to break
Electrical conductor- delocalised elctrons are able to carry a current
Insoluble due to strong strong double cc bonds
what is a metallic bond
occurs between pure metals and alloys
A regular lattice of cations surrounded by a sea of delocalised electrons
Has non-directional electrostatic attractions between these
forms a metallic crystal structure
properties of metallic crystal structure
High melting points: due to strong electrotatics attractions
Conducts electricty: delocalised delctrons free to carry a charge
Conducts heat: delocalised elcetrons quickly transfer energy
Malleable/ductile: delocalised elctrons able to move with the ions when moved so don’t remove non-directional electrostatic attractions hence able to change shape.
what are trends in mp in metallic crystal structure
variations:
increases across a period due to increasing charge on ions
Decreases down a group due to increased shielding
what is VESPR
Valence shell electron pair repulsion
Used to determine the shapes of covalent molecules with 3 or more atoms
Molecules can contain both:
bonding pairs (covalent, coordinate, double, triple) and Lone pairs (unbounded electron pairs on the central atom)
repulsion: electron pairs repel each other and settle in a position to minimise repulsion i.e maximisawe bond angle
list of most repulsive to least
lone pair-lone pair
lone pair- bonding pair
bonding pair-bonding pair
3D structure notation:
methane
what shape does these electron pairs make:
2 bonding pairs and no lone pairs
linear
what shape does these electron pairs make:
2 bonding pairs and 2 lone pairs
bent
what shape does these electron pairs make:
3 bonding pairs and no lone pairs
trigonal planar
what shape does these electron pairs make:
3 bonding pairs and 1 lone pairs
trigonal planar
what shape does these electron pairs make:
4 bonding pairs and no lone pairs
tetrahedral
what shape does these electron pairs make:
5 bonding pairs and no lone pairs
trigonal bipyramidal
what shape does these electron pairs make:
6 bonding pairs and no lone pairs
octrahedral
what shape does these electron pairs make:
4 bonding pairs and 2 lone pairs
square planar
how to find shape of unknowns
1) Decide central atom
2) Count valence e-
3) Count e- used by outer atoms to make bonds with central
4) Sum of 2) and 3) and divide by 2 = 2 VSEP
5) Use no. of BP and LP to predict geometry
how to find bond angles of unknowns in larger molecules
eg ethanol
eg hydrazine
eg glucose
split molecule into smaller version as the overall shape is going to be combined
find bonding angles of :
ethanol (C2H5OH)
1) Find the h-c-h bond angle where 4 BP(+0LP) around central c atom
Tetrahedral therefore 109.5
2) Find the c-o-h bond angle where 2 BP +2 LP around the central o atom
Bent therefore 104.5
find bond angles of:
hydrazine (N2H4)
1) Find the h-n-h bond angle wher 3 BP + 1LP around the central n atom
Trigonal pyramidal therefore 107
(happens twice)
find bond angles in:
glucose (C6H12O6)
1) C-c-c bond angle is 109.5
3 BP around c atom trigonal planar
2) C-o-c bond angle =104.5
what is electronegativity
the power of an atom to attract a bonding pair of electrons
trends on periodic table with electronegativity
- Where the least negativity is low effective charge = on nucleus and high shielding
- where the most electronegativity is high effective charge= on nucleus and low shielding
Group 8 is discounted b/c full outer shell therefore not reactive
how does elctronegativity affect bonding in
what: Electrons are shared equally
why: electronegativity is the same
properties: Non-polar, No di-pole, 2 of the same element
eg. H2, N2, F2
how does electronegativity affect
a) covalent
b) ionic
bonding
Covalent- a difference in electronegativity causes pairs of electrons in a bond to be shared unequally
Ionic- difference in elctronegativity so big so elctrons are transferred
how does electronegativty affect bonding in
what: Electrons shared unequally
why: Y has a greater electronegativity so BP of e- drawn towards it
properties: Polar, Dipole, 2 elements that are different
how does electronegativity affect in
what: electrons shared unequally in favour of X
why: Large difference in electronegativity
Specifically: h-f, h-o, h-n
properties: Polar, Dipole, Hydrogen bonding
what are induced dipole forces
Occur between all molecules
Weakest intermolecular forces
Strength varies- increased with increasing Mr (more electrons involved)
examples of induced dipole forces (3)
eg. monatomic elements, cannot be polar because no elctronegativity
eg. Diatomic elements, have no permanent dipole because atoms have same elctronegativity
Eg larger non-polar molecules, moloceules are symmetrical therefore. No obvious poles (f+ f-)
All these examples show increasing strength of imf with increased mr
Therefore show increased mp/gp as more energy needed to break imf
what are permanent dipole forces
occur between polar molecules
Stronger that induced dipole forces but weaker than h bonding
Causes these compounds to have a higher than expected mp/bp
example of permanent dipole forces
what is hydrogen bonding?
occurs between molecules taht contain a H atom directly bonded to N, O or f
strongest IMF
(basically just a really strong dipole)
hydrogen bonding in simple molecules
eg. hydrogen fluoride
eg water
eg ammonia
causes compounds to havre a much greater mp/ bp than expected
trends of compounds with hydrogen bonding
increases due to increased mr
anomalies due to hydrogen bonding
hydrogen bonding in organic molecules
eg. alcohols
eg carboxylic acids
eg. amines
example 1 of comparing mp/bp
which has higher mp/bp
example 2 of comparing mp/bp
which has higher mp/bp
example 3 of comparing mp/bp
which has higher mp/bp
example 4 of comparing mp/bp
which has higher mp/bp
