section 3 ; bonding Flashcards
what is an ion
formed when electrons are transferred from one atom to another. Simplest ions are single atoms that have lost or gained 1,2,3 electrons to have a full outer shell
what is ionic bonding
electrostatic attraction holds positive and negative ions together (very strong). When atoms are held together in a lattice it is called ionic bonding. When oppositely charged ions come together and form ionic bonds you get an ionic compound
what substances ionically bond
metal with non metal
what is the structure of ionic bonding
giant lattice structure of pos and neg ions - ions held together by ionic bonds (ES attraction between pos and neg ions)
what are the melting points and boiling points of ionic bonds
HIGH strong electrostatic forces of attraction (ionic bonds) need to be broken higher b and m points happen depending on size and charge of ions
are ionic compounds conductive
YES when molten or dissolved ions are free to move and carry charge
are ionic compounds soluble
tend to dissolve in water water molecules are polar - part of the molecule has a small negative charge and the other bits have a small positive charge, water molecules pull the ions away from lattice causing it to dissolve
what is a giant lattice
a regular structure = lattice basic same unit (lattice) repeated over and over again = giant lattice
how does covalent bonding occur
two atoms share electrons so both got full outer shells of electrons. A single covalent bond contains a shared pair of electrons, both the pos nuclei are attracted electrostatically to the shared electrons
what is a simple molecular (simple covalent) compound
elements are diatomic atoms eg. N2 O2 compounds are non metals with non metals
what bonding is involved with simple molecular
covalent
are B and M points low or high with simple molecular
generally low - weak intermolecular forces between molecules , easy to break (NOT breaking strong covalent bonds between atoms) M and B increase depending on size of molecule/ Mr and the type of intermolecular
are simple molecular compounds good conductors
generally no - no delocalised e to carry the charge
are simple molecular compounds soluble
no
what is a giant covalent structure
lattice structure in which all atoms are joined to others by covalent bonds eg. graphite graphene diamond silicon dioxide - type of crystal structure - sometimes called macromolecular structures
what bonding holds together giant covalent structures
covalent
what are the B and M points of giant covalent structures like
VERY HIGH - breaking strong covalent bonds between atoms depends on number and strength of covalent bonds
are giant covalent good conductors
no EXECPT graphite and graphene
what is a metallic giant lattice
lattice structure of metal ions with outer shell electrons free to move through the structure. Strong electrostatic force of attraction between positive ions and negative delocalised electrons. closely packed positive ions in a sea of delocalised electrons (metallic bonding) - between metals
what are the M and B points like for metallic bonding
HIGH strong electrostatic force of attraction between positive ions and sea of delocalised electrons increases/depends on n of delocalised electrons
can giant metallic lattices conducted electricity
YES because of sea of delocalised electrons able to carry the charge
are giant metallic lattices soluble
no
what is the strength of ionic bonds like
the smaller the ions and the greater the charge on the ions the stronger the attraction between pos and neg ions (usually)
what is the strength of covalent bonds like
the shorter the bond the stronger the bond (usually) triple bonds are stronger than double which are stronger than single
what is the strength of metallic bonds like
the smaller the metal ions, the greater charge of the ions and the more delocalised outer shell electrons there are the stronger the attraction between ions and electrons (usually) and therefore higher melting and boiling points
explain charge density in reference to ionic bonding
how spread out the charge is over large area (atom size) the charge is more ‘dilute’ eg. if two different atoms have same charge but one is larger, the smaller one has stronger bonds and therefore higher melting and boiling points.
explain how single, double and triple bonds are formed with reference to covalent bonds
- two shared e-s = single bond - four shared e-s = double bond - six shared e-s = triple bond
what is hybridisation
when atoms merge energy levels to allow room for more electrons
explain how to draw covalent molecule diagrams
show free electrons as ‘X’
remember to highlight double or single bonds
what are co-ordinate (dative covalent) bonds
where BOTH the electrons come from the same species
- often drawn with a “->” rather than a “-“ showing the direction in which the electrons are donated
- however once formed they are identical to covalent bonds
how to draw allotropes of carbon in exam
why do graphite and graphene conduct electricity
4th delocalised e- in between layers , free to move and pass current
define toughness in terms of chemistry
ability of a material to absorb energy without fracturing
why is graphite a soft metal
layers can slide
- weak vander waals forced between layers
why is ice less dense than water
ice is in a regular lattice rather than a random arragement like water
- in ice there are hydrogen intermolecular forces which hold the molecules in the lattice far apart (more than in water)
- this means ice is less dense
why would an ionic compound be soluble
depending on how polarised the molecules are (water attracks them)
what are van der waals forces
an intermolecular force present in all molecular substances
- also known as induced dipole-dipole forces or london dispersion forces
why do van der waals forces exist
because electrons are constantly moving around and uneven electron distribution at any given time
- causes a temporary dipole within an molecule which induces a temporary dipole in an neighbouring molecule
- attraction between these molecules , temporary induced dipole-dipole attraction
- the more electrons there are, the larger the dipole
how does van der waals forces increase
the bigger the molecule
-straight chain have more than branched due to increased surface contact area for bonds to form
what is a permanent dipole-dipole attraction
permanent dipole-dipole attraction between polar molecules
what is a hydrogen bond
- special case of permanent dipole-dipole attraction where a hydrogen atom is attracted to a very electronegative atom (eg. F, O, N)
- simply a strong intermolecular force NOT a bond
show and explain how to draw hydrogen bonds between molecules
- always show all lone pairs of electrons , all partial positive and negative charges and dotted line representing hydrogen bond
describe the different strengths of intermolecular forces
H- bonding > permanent DD > wav der waals
what determines the shape of a molecule
- bonding pairs (the two shared electrons in a covalent bond)
- lone pairs (two electrons in a pair not involved in bonding)
These electron pairs will repel each other as far as possible
The shape of any molecule or ion is a consequence of the number of electron pairs which repel each other as far as possible
explain the five basic shapes
explain how to work out the shape for molecules and ions (single bonds only)
1) work out how many outer shell electrons are on the central atom (accounting for any charge on the species)
2) work out how many atoms are bonded to the central atom (= the number of bonding pairs)
3) work out how many lone pairs there (half difference between 1 and 2)
how do lone pairs of electrons affect the angles between bonded atoms to the main atom
reduces the angle by 2.5 degrees
show the other shapes you must remember for 6 electron pairs
state the meaning of electronegativity
the power of an atom to attract the two electrons in an covalent bond
name the factors that affect electronegativity
1) proton number (nuclear charge) - the more protons the stronger the attraction between the protons and es - greater electro neg
2) sheilding - the more shells the harder it is for the protons to attract the electrons , lower EN
3) size - smaller the atom the stronger the ESFOA
explain the trend of electronegativity down a group
decreases as more shells so more sheilding
- larger atoms too, less attraction
explain the trend in electronegativity across a period
increases
- atoms are smaller (smaller atomic radius) and higher number of protons
explain what non-polar covalent bonds are
when two atoms in a covalent bond have the same electronegativity
- the two electrons are shared equally
eg. Cl-Cl
what are polar covalent bonds
when two atoms in a covalent bond have a different electronegativity
- the more electronegative atom has a greater share of the two electrons while the less electronegative has a lower share
eg. H-Cl
are C-H bonds counted as being polar in organic molecules
no
explain bond dipole moment
measure of strength and direction of the polarity in the bond , the bigger the difference in EN the bigger the bond dipole moment
show shapes for 5 electron pair molecules
show the shapes for 4 electron pair molecules
show the shapes of 3 electron pair molecules
show the shapes of 2 electron pair molecules
