Bonding And Structure Flashcards
Covalent bond definition
A covalent bond is the electrostatic attraction between two nuclei and a shared pair of electrons.
Ionic bond definition
An ionic bond is the electrostatic attraction between two ions of opposite charges
Metallic bond definition
A metallic bond is the electrostatic attraction between positively charged metal ions and delocalised electrons.
Intermolecular forces definition
Intermolecular forces are the weak forces of attraction that exist between molecules
Electrostatic definition meaning
Electrostatic attraction is the attraction between positively-charged and negatively-charged particles (eg. protons &
electrons, + and – ions or + ions and electrons)
Crystal structure definition
The crystal structure of a substance is the type of structure it has: giant covalent lattice, simple molecular covalent,
giant ionic lattice, or giant metallic lattice.
Metallic lattice definition
A metallic lattice is a giant, regular, repeating structure of positive metal ions existing in a ‘sea’ of delocalised
electrons.
Ionic lattice definition
An ionic lattice is the arrangement of ions into a large structure, consisting of alternating positive ions and negative
ions.
What 2 things affect the strength of an ionic bond?
- Ionic charge; the greater the charge of an ion, the stronger the ionic bond; and therefore the greater the melting/ boiling point
- Ionic radii; smaller ions can pack more closely, the closer the ions, the greater the electrostatic attraction and ionic bond. So smaller ionic compounds have higher melting/ boiling points than larger ions
How do you know if there’s a single, double or triple covalent bond?
- 1 pair of shared electrons is single
- 2 pairs of shared electrons is double
- 3 pairs of shared electrons is triple
What is dative covalent bonding?
It’s when both electrons come from 1 atom
What is so special about covalent bonds in AlCl3?
- the Aluminium in the molecule doesn’t have a full outer shell (it only has 6), this means that 1 molecule can bond to another AlCl3 molecule to form Al2Cl6
What is the difference between a lone pair of electrons and a bonding pair of electrons?
A bonding pair means they were used in the covalent bond and are shared between 2 atoms, a lone pair is ones that are leftover and not shared.
Do lone pairs or bonding pairs give a larger angle?
Lone pair/ lone pair angles are the biggest, lone pair/ bonding pair are the second biggest and bonding pair/ bonding pair are the smallest
What are the different shapes of molecules with 2 electron pairs around the central atom?
linear;
- angle of 180
- e.g. CO2, BeCl2
What are the different shapes of molecules with 3 electron pairs around the central atom?
Trigonal planar;
- 120 degrees
- e.g. BF3, BCl3, SO3, NO3-
What are the different shapes of molecules with 4 electron pairs around the central atom?
Tetrahedral;
- no lone pairs
- 109.5 degrees
- e.g. CH4, SO4 2-, SiCl4, NH4
Bent;
- 2 lone pairs
- 104.5 degrees
- e.g. H20
Trigonal Pyramidal;
- 1 lone pair
- 107 degrees
- e.g. SO3 2-, NH3
What are the different shapes of molecules with 5 electron pairs around the central atom?
Trigonal bipyramidal;
- 90 degrees, 120 degrees
- e.g. PCl5
What are the different shapes of molecules with 6 electron pairs around the central atom?
Octahedral;
- 90 degrees
- SF6
What are some properties of giant covalent structures?
~ very high melting points-you need to break a lot of bonds to melt/ boil the substance, and this requires lots of energy
~ extremely hard-because of the strong bonds through ought the lattice
~ good thermal conducts-because vibrations travel easily through the stiff lattice
~ insoluble-covalent bonds means atoms are more attracted to their neighbouring atoms, than the solvent molecules
~ can’t conduct electricity because ther is no free ions or delocalised electrons that can move freely and carry charge
Electronegativity definition
The ability of an atom to attract bonding electrons in a covalent bond. Electronegativity can be measured by the Pauling scale, higher nuclear charges and smaller atomic radii increases the Electronegativity of an element ( Fluorine is the most electronegative element in the periodic table).
How can bonding electrons be affected by Electronegativity?
If both atoms in a covalent bond have similar or identical electronegativities, the bonding electrons are approximately halfway between the atoms, and the bond will be non-polar. Examples include homonuclear, diatomic nuclear gases such as H2, Cl2.
If two atoms have different electronegativities, the bonding electrons will be attracted to the more electronegative atom, causing each atom to be slightly charged, this means the bond is polar.
In a polar bond, the difference in electronegativities of the atoms causes a dipole. A dipole is a difference in charge between 2 atoms caused a shift in electron density in the bond.
So the greater the difference in electronegativities, the greater the shift in electron density and the more polar the bond.
How can bonding electrons be affected by Electronegativity?
If both atoms in a covalent bond have similar or identical electronegativities, the bonding electrons are approximately halfway between the atoms, and the bond will be non-polar. Examples include homonuclear, diatomic nuclear gases such as H2, Cl2.
If two atoms have different electronegativities, the bonding electrons will be attracted to the more electronegative atom, causing each atom to be slightly charged, this means the bond is polar.
In a polar bond, the difference in electronegativities of the atoms causes a dipole. A dipole is a difference in charge between 2 atoms caused a shift in electron density in the bond.
So the greater the difference in electronegativities, the greater the shift in electron density and the more polar the bond.
What type of intermolecular forces are there?
~ London forces (instantaneous dipole induced dipole bonds)
~ permanent dipole-permanent dipole bonds
~ hydrogen bonds (strongest type of intermolecular forces)
What are London forces?
- cause all atoms and molecules to be attracted to each other
- electrons in charge clouds move really quickly, at any particular moment, electrons in an atom are likely to be more on one side than the other. At this moment, atom would have a temporary dipole
- this dipole can induce another temporary dipole in the opposite direction on a neighbouring atom. The two dipoles are then attracted to each other. This can become a domino effect.
- electrons are constantly moving, the dipoles are being created and destroyed all the time. Overall, the atoms are attracted to each other
- larger molecules have larger electron clouds, meaning stronger London forces
- molecules with a larger surface area have a higher exposed electron cloud, so have stronger London forces
What are permanent dipole permanent dipole forces?
- The δ- and δ+ charges on molecules can cause weak electrostatic forces of attractions between molecules, e.g. hydrogen chloride gas.
- Permanent dipole permanent dipole bonds happen as well as London forces not instead.
- So molecules that have both London forces and permanent dipole permanent dipole forces generally have higher boiling and melting points than those with similar London forces but no permanent dipole permanent dipole forces.
What is hydrogen bonding?
- Covalent bonding only happens when hydrogen is covalently bonded to nitrogen, oxygen or fluorine.
- nitrogen, oxygen and fluorine are very electronegative, so draw the bondong electrons away from the hydrogen atom.
- the bond is so polarised, and hydrogen has such a high charge density because its so small, that hydrogen forms weak bonds with lone pairs of electrons from nitrogen, fluorine or oxygen atoms of other molecules.
- examples include: water, ammonia and hydrogen fluoride
- organic molecules that often form hydrogen bonds include alcohols and amine groups (-OH, -NH)
- substances that form hydrogen bonds are also soluble in water, because they can form hydrogen bonds with the water
How do hydrogen bonding explain why ice floats on water?
- ice is an example of a simple molecular structure
- in ice, the water molecules are arranged so that there is the maximum number of hydrogen bonds - the lattice structure formed this way wastes lots of space
- as the ice melts , some of the hydrogen bonds are broken and the lattice breaks down, allowing molecules to fill the spaces
- this effect means ice is much less dense than water - which is why ice floats
How is solubility affected by bonding?
- Bonds in the substance have to break
- Bonds in the solvent have to break
- New bonds have to form between the substance and the solvent
What are polar solvents?
- made of polar molecules, such as water. Water molecules bond to each other with hydrogen bonds. Not all polar solvents form hydrogen bonds. E.g. propanone only forms London forces and permanent dipole permanent dipole forces
What are non-polar molecules?
Are made of molecules that are not polar. E.g. hexane, bond to each other through London forces
How do ionic substances dissolve in polar solvents?
- When an ionic substances mix in water, the ions in the ionic substance are attracted to the oppositely charged ends of the water molecules, the ions are pulled away from the ionic lattice and the water molecules surround the ions, this is called hydration. Some ionic substances don’t dissolve because their ionic bonds are too strong
Do halogenoalkenes dissolve in water and why?
- they contain polar bonds but their dipoles aren’t strong enough to form hydrogen bonds with water
- the hydrogen bonding between water molecules is stronger than the bonds that would be formed with halogenoalkanes, so halogenoalkanes don’t dissolve
- but halogenoalkanes can form permanent dipole permanent dipole bonds, and can dissolve in polar solvents tha form permanent dipole permanent dipole bonds
