Bonding(Both) Flashcards
define a covalent bond
a pair of electrons shared between two atoms to obtain a full outer shell. both nuclei are attracted electrostatically to the shared electrons
why do simple covalent compounds have low melting and boiling points?
down to molecules within the compound having weak intermolecular forces
what is the structure of graphite?(3 points)
carbon atoms arranged in sheets of flat hexagons covalently bonded with three bonds each. the fourth outer electron of each carbon atom is delocalised. sheets are bonded together by weak van der waals forces
explain why graphite is used in pencils+dry lubricant
weak bonds between the layers are easily broken, so sheets can slide over each other making it slippery
why can graphite conduct electricity but diamond cant?
delocalised electrons are free to move along the sheets, so electric current can flow
why is graphite insoluble in any solvent and has a high melting point?
the covalent bonds in the sheets are too difficult to break
describe the structure of diamond
each carbon atom= bonded to four other carbon atoms arranging themselves in a tetrahedral stucture( crystal lattice structure)
give four properties of diamond
- very high melting point
- diamond extremely hard
- cant conduct electricity
- wont dissolve in any solvent
define an ionic bond
an electrostatic attraction between positive and negative ions
describe the electrical conductivity of ionic compounds
can conduct electricity when molten or dissolved as the ions are free to move, in a solid=fixed position
describe the melting points of ionic compounds
high melting points because of the strong electrostatic forces holding the giant ionic lattices together
describe ionic compounds solubility
tend to dissolve in water as it is polar, so the water molecules pull the ions away from the lattice so it dissolves
draw ammonia and its charge clouds
what is the 2nd biggest bond angle formed between?
lone pair/bonding pair
what forms the least biggest bond angle?
bonding pair/bonding pair
define electronegativity
the ability of an atom to attract bonding electrons in a covalent bond
why are diatomic gases non-polar?
atoms have equal electronegativities, so electrons are equally attracted to both nuclei
what is a polar bond?
a covalent bond where a difference in electronegativity has caused a shift in electron density in the bond
What are the three intermolecular forces?
-induced dipole-dipole(van der walls)
- permanent dipole-dipole forces
- hydrogen bonding
what is van der waals forces also known as?
induced dipole-dipole forces
how do van der waals forces come around?
every molecules have them as the electrons move around in the charge cloud causing a temporary dipole whereby one atom becomes delta positive the other becomes delta negative. it induces molecules nearby as the S+ on one atom will be attracted to the S- on another molecule
what is the strength of van der waals dependent on?
size of the molecule, bigger the molecule bigger the van der waals forces as larger electron clouds e.g longer the straightchain hydrocarbon
explain why branched hydrocarbons have weaker van der waals then non-branched ones
cant pack closely together therefore weakening the van der waals
explain why hydrocarbons are non polar
carbon and hydrogen have similar electronegativities
why are symmetrical molecules non polar?
electrons are pushed either side equally
what is the molecular formula of a nitrate ion?
NO3-
what is a metallic bond?
electrostatic attraction between a positive metal ion and a sea of delocalised electrons
what can the strength of a metallic bond be dependent on?
the amount of electrons an atom donates to the sea of delocalized electrons. more electrons stronger the electrostatic attraction between the positive ion and sea of delocalised electrons
give four properties of metallic bonds
-thermal conductors
- high MP
- electrical conductors
-insoluble
what is a dipole?
a difference in charge between two atoms caused by a shift in electron density in a bond
how can polar molecules be tested?
placing a charged rode near a steady stream of polar liquid like water. liquid bends towards the rod as molecules align to face oppositely charged rod
how do the hydrogen halides melting points change from HF to HI?
HF is highest-hydrogen bonding. then a significant decrease but then slightly increases as the atoms get bigger from Cl to I, increasing the strenght of van der waals
what shape of molecule has 2 electron pairs and no lone pairs and 180 degrees bond angle
linear
how many lone pair and bonding pairs does a linear shape have?
LP:0
BP:2
what bond angle does a linear shape have?
180 degrees
draw BeCl2 and what is its shape?
linear
what shape has no lone pairs and 3 bonding pairs and a bond angle of 120 degrees
trigonal planar
how many lone pairs and bonding pairs does a trigonal planar shape have?
LP: 0
BP: 3
what bond angle does a trigonal planar shape have?
120 degrees
draw BF3 and what is its shape?
trigonal planar
another type of shape is bent what does this one derive from compared to the original one?
trigonal planar
bent derived from trigonal planar, how many lone pairs does it have and bond pairs
BP:2
LP: 1
what shape has got 0 lone pairs and 4 bonding pairs with a bond angle of 109 degrees
tetrahedral
how many lone pairs and bonding pairs does tetrahedral shape have?
LP:0
BP:4
what shape has methane have? draw it
tetrahedral
what shape is trigonal pyramid derived from?
tetrahedral
how many lone pairs and bonding pairs does a trigonal pyramid shape have? what is its bond angle?
LP:1
BP:3
109 degrees
what shape does ammonia have and draw it
trigonal pyramid
what is a charge cloud?
region where around the nucleus where you have a 95% chance of finding an electron
what is the shape of the molecule dependent on?
distrubution of charge clouds around the central atom
