bonding Flashcards
what is an ionic bond
an ionic bond is the electrostatic forces of attraction between oppositely charged ions
what is a covalent bond
a covalent bond is the electrostatic forces of attraction between a shared pair of electrons and both the nuclei of the two atoms
what is a metallic bond
a metallic bond is the electrostatic force of attraction between the positive metal ions and the sea of delocalised electrons
what is electronegativity
electronegativity is the ability of an atom to attract a pair of electrons in a covalent bond
what kind of electronegativities in an ionic bond
when there is a big difference of electronegativity the electrons are transferred from the element of low electronegativity and the bonding is ionic
what kind of electronegativity in a covalent bond
when both atoms have a medium to high electronegativity and there is a small difference the electron pair is shared evenly between the two elements and the bonding is covalent
what kind of electronegativity in metallic bonds
when both atoms have low electronegativity and there is only a small difference they tend to form metallic bonds
what are polarised ions
electron clouds in ions become distorted and lop sided resulting in partial sharing of electrons
what are polar molecules
one end of the molecule is slightly more negative than the other
generally metals have … electronegativity values and so only hold on … to their outer shell electrons
low
weakly
generally non metals have … electronegativity and so hold on … to their outer shell electrons
high
strongly
metal atoms … electrons to form … ions
non metal atoms … electrons to form … ions
lose
positive
gain
negative
explain ionic compounds mpt and bpt
ionic bonds are very strong and it takes a lot of energy to overcome them. this means that ionic compounds are solids at room temp and have high mpt and bpt
the strength of ionic bonds increases as
the charge on ions …
the size of ions …
increases
decreases
explain whether ionic compounds conduct electricity
ionic compounds don’t conduct electricity when they are in the solid state however they do when molten or dissolved in water because ions are free to move
explain solubility of ionic compounds
ionic compounds are generally soluble in polar solvents like water and insoluble in non polar solvents like cyclohexene
explain hardness in ionic compounds
Ionic compounds are relatively hard due to the strength of the bonds between oppositely charges ions therefore a lot of force is required to overcome these bonds
explain brittleness in ionic compounds
ionic compounds are brittle and break when a large enough force is applied in a specific direction. this is caused by laters of ions slipping over each other and the ions of same charge come into contact repelling and break the structure
electron pairs that form bonds are called … pairs. electron pairs that are not involved in bonding are called … pairs
bonding
lone
which bond is stronger a C-H or a Si-H bond and why
C-H because C is smaller atom than Is and so the shared electrons are closer to the nucleus of carbon and so are attracted more strongly than Si
what is the general rule about atom size and bond strength
the smaller the atom the shorter the bond length and the stronger the bond
what is a dative or coordinate bond
both bonding electrons come from the same atom in the molecule
once it has formed it behaves the same way as an ordinary covalent bond
a coordinate bond is shown with an arrow
the basic shape of a molecule or compound ion is determined by the number of … electrons around the central atom. these pairs of electrons … each other as far away as possible and this mutual … determines molecular shape
pair
repulse
repulsion
basic shape of molecule may be distorted by the presence of ….
why are they distorted
lone pairs
closer to the nucleus than bonding pairs so they repel more strongly
basic shapes of two pairs of electrons
linear
180°
basic shape of three pairs of electrons
trigonal planar
120°
basic shape of four pairs of electrons
tetrahedral
109.5°
basic shape of five pairs of electrons
trigonal bipyramidal
90° axial position
120° equatorial position
basic shape of six pairs of electrons
octahedral
90°
how much does a lone pair reduce a bond angle
by 2.5°
basic shape 2 bonding 1 lone pair
117.5°
bent or v shaped
basic shape 3 bonding 1 lone pair
107°
pyramidal
basic shape 2 bonding 2 lone pair
104.5°
bent or v shaped
basic shape 4 bonding 1 lone pair
see saw shaped
87.5° - axial
117.5° - equatorial
basic shape 3 bonding 2 lone pair
t shaped
85°
basic shape 2 bonding 3 lone pair
linear
180°
basic shape 5 bonding 1 lone pair
square based pyramid
basic shape 4 bonding 2 lone pair
square planar
not affecting bond angles because they re in opposite positions and so their effects cancel each other out
explain why SiH4 is tetrahedral
outer shell of silicon there are four bonding pairs of electrons only. these electron pairs repel each other equally and the molecule adopts the shape hat minimises the repulsive forces
the further… and … you go in the periodic table the more electronegative the element is
up
right
what is the most electronegative element
fluorine
what can help quantify electronegativity of element
pauling scale
covalent bonds can become polar if the atoms attached to it have a …
difference in electronegativity
… of charge leads to polar molecules
uneven distribution
what are van der waals
induced dipole dipole forces that exist between atoms and molecules
rank the intermolecular forces by strength
hydrogen bonding
permanent dipole
van der waals- weakest
how does a dipole form
when electrons in a molecule or atom move from one end to another
how does size of particle affect van Der waals
the bigger the molecule or atom, the more van der waals forces as you have larger electron clouds
branched vs non branched hydrocarbon bpt
longer straight chain hydrocarbons have more van der waals and so more energy needed so higher bpt, branched hydrocarbons means that they can’t pack together as close weakening van der waals and lowering bpt
what are dipole dipole forces
weak electrostatic forces that exist between molecules with a polarity
what is hydrogen bonding
strongest intermolecular force and occurs when you have very electronegative elements
when does hydrogen bonding occur
hydrogen bonding occurs when hydrogen on one molecule forms a bond with the lone pair of nitrogen oxygen or fluorine
why is ice less dense than liquid water
in water hydrogen bonds constantly break and reform as molecules move about
in ice hydrogen bonds hold the molecules in fixed positions, this makes them slightly further apart than in liquid water
how is metal thermal conductivity
very good as delocalised electrons can transfer kinetic energy
