bonding Flashcards
what is metallic bonding?
strong attraction between positive ions and negative sea of electrons
what are the properties of metals?
● good conductors of electricity
● good conductors of heat
● malleable
● ductile
● strong
● high melting point
why are metals a good conductor of electricity?
delocalised elections can move through structure to carry the charge
what does malleable mean?
can be beaten into shape
what does ductile mean?
can be pulled into thin wires
what does the strength of a metallic bond depend on?
● charge of ion ↑
● size of ion ↓
why do metals have high melting points?
lots of energy required to overcome strong metallic bonds
smaller ions will attract electrons…
more strongly as they are closer to nucleus
if nuclear charge is bigger…
stronger attraction
if there are more delocalised electrons…
more forces of attraction
what is ionic bonding?
● electrons are transferred
● metal and non metal
what is the ionic bonding structure?
● giant ionic lattice
● held together by strong electrostatic forces of attraction between oppositely charged ions
what are the properties of giant ionic lattices?
● electrical conductivity
● shatters easily / brittle
● high melting point
when are ions free to move in giant ionic lattices?
● when molten or aqueous ions are free to move and can conduct electricity
● when solid ions are not free to move and cannot conduct electricity
explain strength in giant ionic lattices
● shatters easily / brittle
● any disruption to structure that makes positive ions or negative ions align will cause them to repel and shatter
explain melting point in giant ionic lattices
● high
● strong electrostatic forces of attraction between oppositely charged ions
● force acts in all directions
what does the strength of an ionic bond depend on?
● the larger the charge of ion, the stronger the attraction
● the smaller the ion, the stronger the attraction
what is covalent bonding?
● shared pair of electrons
● strong
what are properties of simple covalent molecules?
● melting point and boiling points are low
what is the orbital theory?
covalent bonds are formed when orbitals, each containing 1 electron, overlap
what is the octet rule?
● tendency to prefer 8 electrons in outer shell
● we do not consider p and f electrons
● only s and d are involved
what is coordinate bonding?
● in most covalent bonds, each atom provides 1 electron
● but in some bonds, one atom provides both electrons
● shared pair of electrons but both electrons come from same atom
● have exactly same strength and length as ordinary covalent bonds once they are formed
what are coordinate bonds represented by?
● →
● points towards atom accepting bond
what is electronegativity?
the power of an atom to attract the electron density in a covalent bond towards itself it
what are the factors affecting electronegativity?
● nuclear charge - more protons, stronger attraction between nucleus and bonding pair of electrons
● atomic radius - closer to the nucleus, stronger attraction between nucleus and bonding pairs of electrons
● shielding - less shells of electrons between the nucleus and the electrons less shielding (less repulsion), stronger attraction between nucleus and bonding pair of electrons
what is the trend of electronegativity down a group?
● decreases
● nuclear charge increases, but atomic radius increases and more shielding
● therefore, less attraction between nucleus and bonding pair of electrons
what is the trend of electronegativity across a period?
● increases
● nuclear charge increases, but atomic radius decreases and shielding stays the same
● therefore, stronger attraction between nucleus and bonding pair of electrons
explain electronegativity in bonds between identical atoms
● electrons are shared equally
● no difference in electronegativity
● non polar
explain electronegativity in bonds between different atoms
● different electronegativity
● one will pull the electrons closer to its end
● it will have a slight negative charge (δ⁻)
● other will have slight positive charge (δ⁺)
● leads to a charge difference called a dipole
● dipoles can be permanent
● greater the difference in electronegativity, the greater the polarity of the bond
what are some elements with high electronegativity?
● O
● F
● N
● Cl
what is polarity?
about unequal sharing of electrons between atoms that are bonded covalently
how is bond polarity represented?
an arrow with a line at the end pointing to more electronegative atom
explain non polar molecules
● they take into account all of the dipoles across the bonds of molecule
● for molecules that are symmetrical, dipoles of any bond within the molecule can cancel out
explain polar molecules
● not all molecules containing polar bonds are polar overall
● if bond dipoles cancel each other the molecule isn’t polar
● if there is a ‘net dipole’ the molecule will be polar
is the molecule NH3 polar?
yes, shape of molecules means the dipoles do not cancel each other out
is the molecule CCl4 polar?
no, although it contains polar bonds the molecules is symmetrical so the dipoles cancel out
what do intramolecular bonds affect?
chemical bonds
what do intermolecular forces affect?
physical properties
what are the 3 types of forces between molecules?
● van der waals forces: act between all atoms and molecules
● dipole-dipole forces: act only between certain types of molecules
● hydrogen bonding: acts only between certain types of molecules
explain van der waal forces
● as electrons are constantly moving an instantaneous dipole can occur in an atom or molecule that isn’t polar
● this is where electron density shifts to one end of the molecule
● when instantaneous dipole comes close enough to another molecule it induces a new dipole in neighbouring molecule
● now also polar, the 2 are attracted to each other
what affects strength of van der waal forces?
● number of electrons
● more electrons means the stronger the instantaneous dipole will be
explain boiling point and van der waal forces
● electrons increase
● van der waal forces increase
● boiling point increases
explain dipole-dipole forces
● polar molecules have permanent dipoles
● molecule will always have a negatively and positively charged end
● forces between two molecules that have permanent dipoles are called permanent dipole - dipole forces
● δ+ end of the dipole in one molecule and the δ- end of the dipole in a neighbouring molecule are attracted towards each other
explain boiling point and dipole-dipole forces
extra attraction between dipoles means more energy must be put in to separate molecules so you get a higher boiling point than expected for a given mass
explain hydrogen bonding
● force not bond
● same characteristics as covalent bond and dipole-dipole forces
● 1/10 strength of regular covalent bond
● only occurs when hydrogen is bonded covalently to fluorine, nitrogen or oxygen
● hydrogen has large charge density (small) and F, N and O are highly electronegative
● bond is polarised so that H of one molecule forms a weak bond with F, N or O of another molecule
● often attracted to lone pairs on O and N
