Bonding Flashcards
what is ionic bonding?
Metals lose outer electrons to non-metals to form positive and negative ions
how are ions attracted to each other + other oppositely charged ions?
electrostatic forces
what do ionic compounds always exist as?
lattices
what are the properties of ionic lattices?
- always solids at room temperature
- giant structures so high melting points (lots of energy required to break up lattice of ions
- conduct electricity when motel or aqueous solution due to ions being free to move to carry a current
- brittle and shatter easily due to being a lattice of alternating positive and negative ions which if distorted, can cause contact between ions with like charges
what does the strength of an ionic bond depend on?
- charge on the ions, ions with higher charges will have a greater electrostatic attraction
- distance between the ions, smaller ions have smaller internuclear distance so electrostatic attraction is greater
what is covalent bonding?
between non-metals which share outer electrons to create a stable noble gas arrangement
what are covalent bonds held by?
held together by electrostatic attraction between nuclei and shared electrons which takes place in the molecule - these forces balance when the nuclei are a certain distance apart
what is a double covalent bond?
4 electrons are shared
what are the properties of substances with molecular structures?
- low melting points because strong covalent bonds are only between atoms within the molecules but there is a weak attraction between the molecules so they do not need a lot of energy to move apart
- poor conductors as no charged particles to carry the current
what is a dative covalent bond?
one atom provides both electrons in the covalent bond (represented by an arrow to atom accepting pair of electrons)
- the atom that accepts the electron pair is an atom that does not have a filled outer main level of electrons (electron deficient)
- atom that is donating the electrons has a pair not being used in a bond (lone pair) e.g NH3 ammonia, in its ion (NH4+) Nitrogen uses lone pair to form a dative covalent bond with H+ ion
what is metallic bonding?
metals consist of a lattice of positive ions within a sea of electrons which are delocalised
what are the properties of metallic bonds?
- giant structures
- good conductors of electricity and heat due to delocalised electrons/sea of electrons
- strength depends on charge and size of ion (greater the charge, greater number of delocalised electrons and stronger electrostatic attraction between positive ions and electrons) + (the smaller the ion the closer the electrons are to the positive nucleus and the stronger the bond)
- metals are strong as delocalised electrons extend through the solid so there are no individual bonds to break
- high melting points as are giant structures
- malleable and ductile due to ions being able to slide/move past each other
what is electronegativity?
The power of an atom to attract the electron density in a covalent bond towards itself
what is electron density?
How negative charge is distributed in the molecule
what is the pauling scale?
Pauling scale measures electronegativity from 0-4, the greater the number the more electronegative
what does electronegativity depend on?
Electronegativity depends on:
- nuclear charge
- distance between the nucleus and the outer shell electrons
- the shield of the nuclear charge by the the electrons in inner shells
therefore the _____ the atom, the _____ the nucleus is to the outer main level electrons and _____ its electronegativity
- smaller 2. closer 3. greater
What happens to electronegativity as you go up a group?
Going up a group, electronegativity increases (atoms get smaller) and there is less shielding by electrons in inner shells
What happens to electronegativity as you go across a period?
Going across a period, electronegativity increases. the nuclear charge increases but the number of inner levels stay the same and atoms become smaller.
Where are the more electronegative atoms found?
More electronegative atoms found in top right corner of periodic table e.g fluorine, oxygen, nitrogen and chlorine
What is polarity?
Polarity - unequal sharing of electrons between atoms that a bonded covalently (represented by partial negatives and partial positives)
How are electrons shared in a covalent bond with two of the same atoms? + what is the polarity of the bond
electrons in the bond are shared equally, so both have same electronegativity and bond is non-polar
How are electrons shared in a covalent bond with two different atoms? + what is the polarity of the bond
electrons will not be shared equally, e.g one might be slightly positive and one might be slightly negative (HF) as a result it is polar. the greater the difference in electronegativity, the more polar the covalent bond
What are the 3 types of intermolecular forces?
- van der waals : act between all atoms and molecules
- dipole-dipole : only between some
- hydrogen : only between some
What are the properties of van der waals forces?
van der waals → produce weak electrostatic attractions between all atoms and molecules
→ distribution of charge is constantly changing
What are the properties of dipole-dipole forces?
dipole-dipole → slightly positive on one side and slightly negative on the other (+ of one molecule will attract - of another) they are only found in polar molecules
What are the properties of hydrogen bonds?
hydrogen bonds → very strong permanent dipole-dipole, formed when H bonds to O, N or F e.g water of ammonia
→ develops a strong delta+ charge
What is the electron pair repulsion theory?
pairs of electrons around atoms will repel other electron pairs therefore the pairs of electrons will take up positions as far as possible to minimise repulsion
what are the names of the different shapes of molecules from 1-6 pairs of electrons + bond angles?
two pairs of electrons - linear (180 degrees)
three pairs of electrons - trigonal planar (120 degrees)
four pairs - tetrahedral (109.5 degrees)
five pairs - trigonal bipyrimidal
six pairs - octahedral (90 degrees)
what do electron pairs do in the outer shell to minimise repulsion?
arrange themselves as far apart as possible
what is the difference between bonding pairs and lone pairs in terms of repulsion?
Bonding pairs repel each other equally. While lone pairs repel other pairs more because they are more electron dense.
