topic 2: bonding Flashcards
what is ionic bonding?
the strong electrostatic force of attraction between 2 oppositely charged ions
what is an ionic compound?
giant lattice structure of ions, held together by electrostatic forces of attraction between oppositely charged ions
why do most ionic compounds dissolve in water?
as water molecules are polar, they attract the positive and negative ions and break up their structure
why can molten ionic compounds conduct electricity but solid ionic compounds do not?
molten ionic compounds: ions have freedom in liquids and can move to the electrodes
solid ionic compounds: ions are held strongly together and are not free to move
why do ionic compounds have very high melting points?
there are many electrostatic forces between oppositely charged ions therefore a large amount of energy is required to overcome these forces
why are ionic compounds brittle?
when struck, the layers slide over eachother and the positive ions aligned with positive and negative ions aligned with negative ones. they repel and the structure breaks apart
how does ionic charge affect the strength of the ionic bond?
the bigger the charge, the stronger the electrostatic force therefore more energy is needed to overcome these forces so they have a high melting ad boiling point
how does size of the ion affect the strength of the ionic bond?
the smaller the ion the stronger the electrostatic attraction between ions as smaller ions can pack together more closely and more energy is required to overcome the stronger forces
mp + bp are higher
what is covalent bonding?
strong electrostatic attraction between 2 positive nuclei and the shared negative electrons in the bond
what are dative covalent bonds?
covalent bond where one atom donates 2 electrons to an atom or ion to form a bond
what is bond length?
the distance between 2 positive nuclei where attractive and repulsion forces balance out eachother
how does high electron density affect bond length and bond enthalpy?
the greater the electron density between the atoms the stronger the attractive force meaning the atoms are pulled in further towards eachother
leading to a shorter bond and higher bond enthalpy
what are the characteristics of the giant covalent structure of graphite?
- each carbon is bonded 3 ties with the 4th electron
- high melting point (lots of strong covalent bonds)
- low density (layers are far apart in comparison to covalent bond length)
- layer slide easily because there are weak forces between the layers
- conducts electricity ( there are delocalised electrons between the layers of graphite)
- insoluble (covalent bonds are too strong to break)
what are the characteristics of the giant covalent structure of diamond ?
- each carbon is bonded 4 times in a tetrahedral shape
- can conduct heat well (tightly packed, rigid arrangement)
- very high mp (too many covalent bonds also is very hard)
- does not conduct electricity ( no delocalised electrons)
- insoluble ( covalent bonds are too strong to break)
what are the characteristics of the giant covalent structure of graphene ?
- one layer of graphite, one atom thick, made of hexagonal carbon rings
- lightweight n transparent
- conductor of electricity because there are delocalised free moving electrons (strengthens the covalent bonds)
what is metallic bonding?
the strong electrostatic force of attraction between the positive metal ions and negative charge of the delocalised electrons
what are the characteristics of a giant metallic lattice structure?
- positive metal ions are formed as metals donate electrons to form a sea of delocalised electrons
- good thermal conductors as the delocalised electrons can transfer kinetic energy
- high melting points due to the strong electrostatic attractions ( the more electrons an atom can donate to the delocalised electron system the higher the mp)
- solid metals = insoluble as the metallic bond is too strong to break
- good electrical conductors as the delocalised electrons are mobile and can carry an electrical current
- metals = malleable n ductile as the ion layers can slide when hit with a hammer ad still retain an attraction between ions and delocalised electrons
why does melting point increase across a group?
across a period the ions in the lattice become more highly charged and the no of delocalised electrons per ion increases
meaning there is more electrostatic attraction between cations and the delocalised electrons resulting in a higher melting point
why does melting point decrease down a group?
down the group, cation gets larger, so there is more distance between the cations nucleus and the delocalised electrons
the lager the distance the weaker the forces between them so there is weaker metallic binding
what is electronegativity?
the ability of an atom to pull a part of its electrons towards itself within a covalent bond
where do london forces occur between
atoms and molecules
how is a temporary dipole created?
when electrons in a molecule or atom can move from one end to another
how are london forces affected by the size of the molecule?
the bigger the molecule the more london forces u have, atomic radius increases down the group and there are more electrons so the outer electron becomes further from the nucleus (less nuclear attraction) and temporary dipoles are easier to introduce
enough energy is needed to overcome these forces therefore boiing point increases
how does points of contact between molecules affect the strength of london forces
straight chain alkanes can pack together closer than branched alkanes creating more points of contact and stronger london forces
where do permanent dipole dipole forces occur?
between molecules that have a permanent separation of positive and negative charges due to differences in electronegativity between atoms within the molecules
how do permanent dipole dipole forces occur
When two such polar molecules come close together, the positive end of one molecule (where the atom with lower electronegativity is located) is attracted to the negative end of the other molecule (where the atom with higher electronegativity is located).
when does hydrogen bonding occur?
when hydrogen atoms are covalently bonded to highly electronegative atoms like fluorine (F), oxygen (O), or nitrogen (N).
strongest intermolecular force
in order for substances to dissolve..
- the bonds between the substance need to break
- the intermolecular between the solvent need to break
- new bonds need to form between the substance solvent
how is salt dissolved in water?
as water is a polar molecule, the ions in NaCL are attracted to the oppositely charged ions ends on the water molecule, the ions are pulled away from their ionic lattice by the water surrounding the ions (hydration)
what is a polar solvent?
solvents made from polar molecules
what type of bonds do water from with other water molecules?
hydrogen bonds
why do alcohols dissolve in water?
the hyrogen of the OH hydroxyl group in the alcohol will form hydrogen bonds withe the oxygen of the water molecule
what type of forces do non-polar solvents form?
london forces
polar molecules dissolve in what type of solvent
non-polar molecules dissolve in what type of solvent?
- polar
- non-polar
why do polar and non-polar molecules not mix?
non-polar molecules forms london forces between the molecules, which separate easily
polar molecule forms strong hydrogen bonds which acts as a barrier to the non-polar molecule as it cannot form hydrogen bonds so they separate
