Bonding and Structure Flashcards
what type of ions will metals always form
cations
define ‘metallic bond’
the strong electrostatic attraction between metal ions and a sea of delocalised electrons
define ‘metallic radius’
half the distance between the centers of two adjacent metal ions in a metallic lattice
in terms of melting temperature, how does this change with metallic radii
the smaller the metallic radius, the greater the melting point
name 6 chemical properties of metals
- smaller first ionisation energy than non-metals in the same period
- have the lowest electronegativity levels in the periodic table
- low electronegativity and first IE means its more energetically feasible to lose electrons in bonding
- react with dilute acids to form hydrogen gas and a solution of a salt
- react with water to form an alkaline solution of a metal hydroxide and hydrogen gas
- a more reactive metal will reduce the ions of a less reactive metal
define an ionic bond
the strong electrostatic attraction between oppositely charged ions
what is the octet rule
when ions are formed they normally have a full outer shell (like that of a noble gas)
properties of ionic bonds (4)
- high melting and boiling points
- brittle and easily cleaved (split)
- soluble in water
- electrical and thermal conductors when molten or in solution
what happens when ionic bonds are hydrated
hydrogen is attracted to the negative ions and oxygen is attracted to the positive ions in the bond
why do ionic bonds have a high melting and boiling point
because of the strong electrostatic attraction between the oppositely charged ions, it requires lots of energy to overcome
what is the melting point determined by in ionic bonding
the strength of the ionic bonds
name three factors effecting the strength of ionic bonds
- the size of the ionic radius (smaller size means a greater strength)
- charge of the ions (higher charge, greater strength)
- the surface area
why does ionic radius increase down a group
the number of shells the ion contains increases
what is it called when ions have identical electron configurations
isoelectronic
why does ionic radius decrease from N3- to Al3+
the number of protons increases this increases the nuclear charge. so, the electrons face a stronger force of attraction to the nucleus, decreasing the ionic radius
define a covalent bond
the strong electrostatic attraction between the nuclei of two atoms and the shared pair of electrons between them
what is a dative covalent/coordinate bond
a bond formed where one atom donates two electrons to an atom or ion
give two examples of molecules with a dative bond
ammonium, carbon monoxide
what are dative covalent bonds represented with
an arrow
give an example of a molecule with a single covalent bond
H-F
give an example of a molecule with a double covalent bond
O=O
give an example of a molecule with a triple covalent bond
N=-N
define bond enthalpy
the energy required to break a particular covalent bond of one mole of a molecule in gaseous state (strength of a covalent bond)
shorter covalent bond. higher or lower bond enthalpy?
higher
what two forces determine bond length of a covalent bond
attraction (positive nuceli-negative electrons)
repulsion (two positive nuclei + negative electrons)
how is a high bond enthalpy created
greater electron density between atoms results in stronger forces of attraction. atoms are pulled closer to each other, shorter bond=high bond enthalpy
which has a higher bond enthalpy
H-F or N=-N
N=-N (greater electron density, shorter bonds)
Name 4 giant covalent structures
- graphite
- diamond
- graphene
- silicone dioxide
Properties of graphite
- insoluble
- good electrical conductor
- low density
- very high melting point
- lubricant
Why is graphite insoluble
Due to the strong covalent bonds between the carbon atoms
Why does graphite have a low density
Due to its layers being far apart
Why can graphite conduct electricity
Each carbon atom is bonded to three other carbon atoms. That leaves a delocalised electron as the fourth. This can carry a charge throughout the layers
Why does graphite have a very high melting point
Due to the strong covalent bonds between the carbon atoms
Properties of diamond (4)
- good thermal conductor
- poor electrical conductor
- insoluble
- high melting point
Why is diamond a good thermal conductor
It’s tightly packed, rigid arrangement allows for thermal energy to pass easily
Why is diamond a poor electrical conductor
Each carbon atom is covalently bonded to four others In a tetrahedral shape. This means there are no delocalised electrons so no charge can be carried.
Why is diamond insoluble
Due to the strong covalent bonds between carbon atoms, they are too strong to break
Why does diamond have a very high melting point
Contains strong covalent bonds between the carbon atoms
What giant covalent structure has a similar shape and properties to diamond
Silicone IV dioxide
What are the properties of graphene (3)
- lightweight and transparent
- good electrical conductor
- high strength properties
Why is graphene lightweight and transparent
It’s one layer of graphite made up of hexagonal rings but only one atom thick
Why is graphene a good electrical conductor
Contains delocalised electrons (carbon covalently bonded to only three other carbons)
Why does graphene have high strength properties
Delocalised electrons strengthen the covalent bonds between carbon atoms
What is graphene used in (3)
- aircraft shells
- super computers/high speed computers
- smart phone screens
How do covalent bonds become polar
If the atoms attached to it have a difference in electronegativity
In terms of polarity, a bigger difference in electronegativity=
A more polar bond
Give two examples of polar molecules
Hydrogen chloride
Water
Why is H-Cl polar
The chlorine atom is more electronegative, electrons shift closer to the chlorine
H—;Cl
Is Cl-Cl polar and why
No because the chlorine atoms are bonded with the same electronegativity values so the shared electrons sit in the middle
Cl-;-Cl
Why is water polar
Because it is unsymmetrical
Is CO2 polar and why
No because it is a symmetrical molecule
O;=C=;O
What makes covalent molecules non polar
If the molecule is bonded with the same/similar electronegativity values, the shared electrons will sit in the middle of the bond. Furthermore if the molecule is symmetrical.
how strong is the repulsion between two bonding pair electrons
low
how strong is the repulsion between a lone pair and a bonding pair electron
medium
how strong is the repulsion between two lone pair electrons
high
how do lone pair electrons affect the shape of the molecule
they push bonding pairs closer together, for every lone pair the bonding angle reduces by 2.5degrees
what is electronegativity
the ability of an atom to attract an electron pair
why do molecules with more electrons have larger London dispersion forces
- they will have larger fluctuations in electron density
- leads to larger temporary dipoles, and stronger dipole-dipole interactions
what type of molecules do you find permanent dipole-dipole interactions between
polar molecules
where do you find hydrogen bonds
when hydrogen atoms form a strong permanent dipole-dipole interaction between either nitrogen, oxygen or fluorine
name three examples of liquids with hydrogen bonds
water
hydrogen fluoride
ammonia
why do hydrogen bonds form
when hydrogen is bonded to an extremely electronegative element is forms a strong delta plus charge. due to its small size, hydrogen has a high charge density so it can form a strong bond with any highly delta negative atom
