2. bonding and structure Flashcards
what is an ion
a positively or negatively charged atom
how are ions formed
when electrons are transferred from one atom to another
what is a positively charged ion called
cation
what is a negatively charged ion called
anion
what is an ionic bond
the strong electrostatic forces of attraction between positive and negative ions
how does ionic charge affect bonding
the greater the charge of an ion the stronger the bond. therefore higher melting and boiling points
how does ionic radii affect bonding
smaller ions can pack closer together so have stronger ionic bonds as electrostatic attraction weakens with distance
what does the size of an ion depend on
electron shells and atomic number
- ionic radii increases down the group because the atomic number increases and electron shells are added
what is an isoelectronic ion
ions with the same number of electrons
what happens to ionic radii of isoelectronic ions
it decreases as the atomic number increases as the number of protons increases so the attraction to the nucleus is greater
physical properties of ionic compounds
- high melting points
- soluble in water but not non-polar solvents
- dont conduct when solid but do when molten or dissolves
-cant be shaped
how does migration of ions prove charged particles (experiment)
when you electrolyse copper chromate solution on wet filter paper the paper turns blue at the cathode and yellow at the anode. when a current is passed through a solution it causes positive ions to move to the cathode and negative ions to move to the anode
what is a covalent bond
the strong electrostatic force of attraction between the two positive nuclei and the shared electrons in the bond
how is bond enthalpy related to bond length
higher the electron density = stronger the attraction
higher the bond enthalpy = shorter the bond
what is bond length
the distance between two nuclei where attractive and repulsive forces balance
what is a dative covalent bond
both electrons come from one atom
what is a bonding pair
pairs of electrons are shared with another atom in a covalent bond
what is a lone pair
pairs of electrons that are not shared
what repels more lone pairs or bonding pairs
lone pairs
how to predict the shape of a molecule
- find the central atom
- work out the number of electrons in outer shell
- work out how they are bonded and shared
- find the number of electron pairs
- compare electron pairs to bonds
- compare electron pairs, lone pairs, bonding pairs and centres to predict the shape
properties of giant covalent structures
- high melting points
- hard
- good thermal conductors
- insoluble
- cant conduct electricity
what is graphite
carbon atoms form sheets. each carbon connected to 3 leaving outer electron to move freely and conduct electricity
what is graphene
a single layer of graphite. joined in hexagons. 1 atom thick, can conduct, strong, transparent, light
properties of giant metallic latices
- high melting point
-malleable
-ductile
-good thermal conductor - insoluble
- good electrical conductor
what is electronegativity
the ability of an atom to attract the electrons in a covalent bond
why does electronegativity increase across periods and up groups
the elements have higher nuclear charge and smaller atomic radii
what is polarisation
when the two bonding atoms have different electronegativities so the bonding electrons are pulled to the more electronegative atom creating a charge
what is a dipole
a difference in charge between two atoms caused by a shift in electron density in the bond
using the pauling scale to work out ionic character
the higher the difference in electronegativity the higher the ionic character
1. work out the difference in ionic character
2. compare to ionic character scale
what makes a polar molecule
an overall dipole caused by the presence of a permanent charge
what are the three types of intermolecular forces
london forces
permanent dipole
hydrogen bonding
what do london forces do
cause all atoms and molecules to be attracted to each other
how do london forces work
- electrons move quickly and are likely to be on one side that the other so a temporary dipole is created
- this induces another opposite dipole on the neighboring atom. the two dipoles then attract and the process repeats
- as electrons constantly move and dipoles are created and destroyed the overall affect is that the atoms are attracted
what structure do london forces make
simple molecular structures
more electrons and bigger electron cloud =
more london forces so stronger molecule therefore higher melting and boiling points
what is a permanent dipole - permanent dipole bond
delta + and delta - charges on polar molecules cause weak electrostatic forces of attraction between molecules.
these occur alongside london forces so generally have higher melting and boiling points than molecules that cant form these
what is a hydrogen bond
