Bonding and Structure Flashcards
what is metallic bonding
The attraction between positively charged ions in a sea of delocalised electrons
why can metals conduct electricity
The delocalised electrons are free to move in the solid lattice. These mobile electrons can act as charge carriers in the conduction of electricity or in the conduction of heat.
what happens to the strength of metallic bonding as you go across a period
bond strength increases
what happens to the strength of metallic bonding as you go down a group
bond strength decreases
why does metallic bond strength increase going across a period
The number of electrons in the outer shell increases, so the atoms are smaller, meaning of electrons are closer to the core
why does metallic bond strength decrease going down a group
The number of electron shells is increasing so atoms are larger mean in the electrons are further away
what does the increasing bond strength going across a period explain
the increasing melting and boiling points in metals going across a period
what does the decreasing bond strength going down a group explain
the decreasing melting and boiling pints in metals going down a group
what are the noble gases
single atoms (monatomic)
why is no value given for the atomic radii of the noble gases
because noble gases are unreactive, so don’t form bonds
what are intramolecular bonds
bonds within the molecule (covalent, ionic)
what are intermolecular bonds
bonds between the molecules (van der waals)
what types of intermolecular forces of attraction do non metals and monatomic gases contain
London Dispersion Forces (LDF’s)
what is a temporary dipole
when electrons in an atom become unevenly distributed
what happens to the strength of LDFs as the size of the atom increases
their strength increases
what happens to the boiling point of the noble gases as you go down the group
The boiling point increases as the size of the atom increases. This happens because the LDFs increase with increasing numbers of electrons. More electrons means bigger the dipole, so the stronger LDFs
what is the molecular formula of carbon
C60
what is the molecular formula of sulfur
S8
what is the molecular formula of phosphorous
P4
what is the boiling point of covalent molecular substances described to be
low
what bonding exists within covalent molecular substances
strong covalent
what bonding exists between the molecules of covalent molecular substances
intermolecular forces
why is the melting/boiling point of covalent molecular substances so low
because only very weak LDFs/intermolecular forces exist between the particles and these require little energy to break. resulting in low, melting and boiling points.
what bonds do the halogens contain
strong intramolecular forces (covalent bonds) but weak intermolecular forces
why do the halogens have low melting and boiling points
the weak intermolecular forces are easily overcome
what happens to the boiling point of the halogens as you go down the group
the boiling point increases
why does the boiling point of the halogens increase as you go down the group
As a size of the halogen atom increases, there is a greater number of electrons this means a greater number of LDFs between the molecules. The more LDFs present the more energy required to break them.
what are fullerenes
a form of Carbon exist as covalent molecules, are a large family of carbon cage molecules, each made up of rings of carbon atoms.
elements that exist as covalent networks
Carbon (diamond, graphite)
Boron
Silicon
what is a polymorph
Different forms of the same element, for example, carbon in the form of diamond and graphite
why does diamond not conduct
Because all of the four of the electrons on the carbon atoms are used in the bonding, so there are no delocalised electrons
why does graphite conduct
because only three outer electrons in the carbon atom are used in bonding so each carbon atom has one outer electron not used in bonding. These electrons are delocalised so graphite can conduct
why is diamond so difficult to break
The bonds around each carbon atom are in a tetrahedral shape (3D) this makes diamond strong. To cut a break, diamond means breaking laws of covalent bonds (intramolecular) This requires a lot of energy so it is difficult to break
why is graphite brittle
The bonds within graphite are arranged in layers between the layers are very weak LDFs. To cut our break time and means breaking the weak LDFs so it is easier to cut or break.
what elements exits as solid covalent molecular
sulphur and phosphorus
what elements exists as covalent networks
Carbon in the forms of diamond and graphite, boron and silicon
what is ionic bonding
The attraction between positive and negative ions
what is covalent bonding
The attraction of the shared electrons for the nuclei of both the bonded atoms
why do ionic compounds have high melting and boiling points
because separating the ions in the lattice, involves the breaking of strong ionic bonds (intramolecular) which means high melting points
why do covalent molecular solids have low melting points
Because separating molecules involved little energy as they’re only weak intermolecular forces between the molecules
why do covalent network compounds have high melting points
Because melting them involves breaking the network of strong covalent bonds (intramolecular), which means lots of energy is required
what is electronegativity
A measure of the attraction an atom involved in a bond has for the electrons in a bond
what happens to electronegativity as you move along a period
it increases
what happens to electronegativity as you go down group
It decreases
why does electronegativity increase going across the period
going across the period, the nuclear charge increases this pulls the electron shell closer to the nucleus as a result, the electronegativity increases
why does the electronegativity decrease as you go down group
because going to the group, the nuclear charge increases the number of electron shells also increases as a result of shielding and an increase in distance between the outer shell of electrons and the nucleus, electronegativity decreases
what is a non polar covalent bond
where within a bond the electrons are equally shared due to the same electronegativity values.
what is a polar covalent bond
A bond between two different atoms where the electrons are not shared equally, the electrons in the bond will be closer to the more electronegative atom, due to the difference in electronegativity. This produces a permanent dipole between molecules in an atom.
what does a greater difference in electronegativity mean
The greater the difference in electronegativity, the more polar the bond will be
why is CCl4 non polar
within this molecule there is polar bonding, but it is not a polar molecule. This is because they have a negative charges at both ends of the nucleus, so it is a nonpolar molecule as the charges are symmetrical.
how do molecules with a permanent dipole attract each other?
through dipole-dipole interactions, these are stronger than LDFs
why are the boiling points of NH3, H20 and H2F higher then expected
Because they contain hydrogen bonding
what is hydrogen bonding
It’s a special type of dipole-dipole interaction that occurs in compounds, which of hydrogen atoms bonded to very electronegative elements such as N, O, and F. Hydrogen bonds are stronger than LDFs and permanent dipoles but weaker than covalent and ionic bonds
what does hydrogen bonding cause
It causes melting and boiling points and viscosity of a chemical to be higher than expected
what is viscosity
Viscosity is a measure of a thickness
what does high viscosity mean
High viscosity means strong, intermolecular forces are present
what does ‘Like Dissolves Like’ mean
it means that polar an ionic substances tend to dissolve in polar solvents, so a nonpolar substance will not dissolve in a polar solvent only in a non polar solvent. For example, water is able to dissolve sodium chloride as they are both polar molecules.
