Bonding Flashcards
which substance uses metallic bonding?
the atoms in a metal are held together by metallic bonding. each metal atom is ionised and occupies fixed positions in the lattice.
what is metallic bonding?
a strong attraction between the positive ions and negative delocalised electrons
When comparing melting points of elements, what do you have to consider?
the charge
the charge density
the metallic bonding
Between lithium and sodium, which has the higher melting point and why?
They are both in the same group,so have the same charge. However, lithium has a higher charge density so it has stronger metallic bonding and has a higher melting point.
Between sodium and magnesium, which has the higher melting point and why?
They are both in the same period. However, the size of the atoms get smaller as you go across the period, so you get a higher charge density. Magnesium has a higher charge density so it has stronger metallic bonding and has a higher melting point.
What is a disadvantage of this model?
the ions are too far apart
what are the properties of metals?
they are good conductors of heat and electricity
they are strong
they are malleable and ductile
they are high melting point substances
why are metals good conductors of heat and electricity?
they have delocalised electrons
why are metals strong?
there is a high force of attraction between the positive atoms and the negative delocalised electrons
why are metals strong?
there is a high force of attraction between the positive ions and the negative delocalised electrons
why are metals malleable and ductile?
the atoms are in layers
why are metals high melting point substances?
there is a high force of attraction between the positive atoms and the negative delocalised electrons
When comparing the strength of atoms , what do you need to consider?
the charge of the ion
the size of the ion
going down group 1, what happens to the strength of the atoms?
charge stays the same
size of ion increases
charge density decreases
weaker metallic bonding/ stronger FoA
lower melting point
going across a period, what happens to the strength of the atoms?
charge increases
size of ion decreases
charge density increases
stronger metallic bonding/ stronger FoA
higher melting points
Why might aluminium(660•C) have a higher boiling point than sodium(97•C)?
higher charge
smaller ion
higher charge density
stronger force of attraction
what are the charges of these ions?:
sulfate, hydroxide, nitrate, carbonate, ammonium
sulfate SO42- hydroxide OH- nitrate NO3- carbonate CO32- ammonium NH4+
what is ionic bonding?
occurs when two or more ions combine to form an electrically neutral compound
what happens during ionic bonding?
the positive cation “loses” an electron and the negative anion “gains” the electron. the electrons are not shared between the two atoms, as the anion steals the electrons from the cation
what does GIL stand for?
giant ionic lattice
Can ionic compounds conduct electricity? why or why not?
no
they have a high melting point- there are many strong FoA between the positive ions and the negative ions, making it hard to break apart ionic compounds
conductivity- when dissolved in water or molten, ionic compounds conduct electricity. in water, the bonds dissociate(fall apart), leaving lots of ions to carry charge
Between NaF and NaCl which had the higher melting point?
NaF because it is a smaller atom, has a higher charge density and strong FoA
Between NaF and LiF, which has the higher melting point?
LiF because it is a smaller atom, has a higher charge density and strong FoA
Between NaF and Na2O, which has the higher melting point?
Na2O. The O has a -2, and F has a -1 so Na2O has a higher charge and higher density and a stronger FoA.
What is a covalent bond?
covalent bonds can be formed when a non metal reacts with a non metal
atoms share electrons to attain a full outer shell
the nuclei of each atom is attracted to the shared pairs of electrons
how many bonds do 2 shared electrons make?
1
how many bonds do 4 shared electrons make?
2
how many bonds do 6 shared electrons make?
3
How are alevel dot and cross diagrams drawn?
with lines
draw an a level dot and cross diagram of sulfuric acid
how is sulfuric acid an exception to the electron rule?
in the dot and cross diagram sulfur has 12 electrons. this shows that atoms don’t always have 8 electrons on their outer shell to be stable.
draw the covalent bond of carbon dioxide
draw the covalent bond of nitrogen
draw the covalent bond of nitrogen
what is the correlation between the number of bonds and the length of bonds ?
the more the bonds, the longer the bonds
what is the correlation between the number of bonds and the strength of the bonds?
the more the bonds, the stronger the bonds
In a covalent bond of bromine with fluorine, bromine only shares 6 electrons with flourine rather than 8(which is what is needed to get an outer shell). is this a problem?why/not?
no it’s not. boron has formed the maximum number of bonds that it can in the circumstances, and this is a perfectly valid structure.
why doesn’t boron form ionic bonds with flourine instead?
the total energy needed to remove 3 electrons and form a 3+ ion is too great.
electrons that are paired in a covalent bond are called?…
bonding pairs
electrons that are not used in bonding do what?…
they pair and form lone pairs
draw the Lewis structure for ammonia and show the lone pairs
draw the Lewis structure for ammonia and show the lone pairs
what is co-ordinate/dative covalent bonding?
A covalent bond in which both electrons come from the same atom.
Lone pairs can be donated to the other atom
It is sometimes drawn with an arrow rather than a dash
Draw a dative covalent bond with water
In a reaction between ammonia and hydrogen chloride, how are ammonium ions formed?
they are formed by the transfer of a hydrogen ion from the hydrogen chloride to the lone pair of electrons on the ammonia molecule.
when hydrogen chloride dissolved in water to make hydrochloric acid, what happens?
A hydrogen ion is transferred from the chlorine to one of the lone pairs on the oxygen atom.
what happens in the reaction between boron trifluoride and ammonia?
boron trifluoride as a compound doesn’t have a noble gas structure around the boron atom. The boron only has 3 pairs of electrons in its bonding level, whereas there would be room for 4 pairs. boron flouride is described as being electron deficient. The lone pair on the nitrogen of an ammonia molecule can be used to overcome that deficiency, and a compound is formed involving a co-ordinate bond.
To determine the shape of a compound, what pieces of information do we need to know?
Central atom
Group - this tells you the outer e
Charge - remember + means lose an e
Bonds - number of bonds
Total - add up 2+3+4
Divide by two = number of pairs ofe
Structure (not shape)
Look at 6 and 4 to work out if any lone pairs
Shape
Bond angle(s)
When drawing a shape, what do you need to remember?
all pairs of electrons are trying to repel each other as far apart as possible
what is the shape and angle of a structure with 2 bond pairs?
linear 180degrees
what is the shape and angle of a structure with 3 bond pairs?
trigonal planar 120 degrees
what is the shape and angle of a structure with 4 bond pairs?
tetrahedral 109.5degrees
what is the shape and angle of a structure with 5 bond pairs?
trigonal biprymidal 120/90 degrees
what is the shape and angle of a structure with 6 bond pairs?
octahedral 90 degrees
what is the name of the shape of methane (CH4)?
tetrahedral
what do the different bond styles tell you?
straight line=bond in the plane of the paper
triangle shape line=bond coming out of the paper
dashed line=bond going into the paper
Draw the shape of methane and explain the bonds
A diagram of a methane molecule. Two bonds are in the plane of the paper, the middle one comes out towards you and the left hand bond goes away from you.
Draw the shape of sulfur hexafluoride
Draw the shape of sulfur hexafluoride
Draw the shape of sulfur hexafluoride
What are the bond angles in sulfur trioxide molecule?
always 120 degrees
What is the electron pair repulsion theory?
Predicts the shapes of simple molecules.
Considers the repulsions between pairs of electrons (lone pair and bonding pair) within the molecule.
All electrons in bonds are trying to repel each other as far apart as possible
Lone pairs have a greater repulsive force
What is the impact of a lone pair on the bond angles?
Lone pairs will affect the angles of bonds as they push the bonding pairs away.
-2.5 degrees
Ammonia has a lone pair. What is its new bond angle and shape?
107degrees
angular
Ammonia has a lone pair. What is its new bond angle and shape?
107degrees
angular
Water has two lone pairs . What is its new bond angle and shape?
104.5degrees
angular
what are the common shapes?
4 bonding pairs-tetrahedron
3bp and 1lp-trifocals pyramid
2bp 2lp-angular
what is an uncommon shape?
1bp 3lp
what name does trigonal planar change to if it has 1lp
angular
what name does tetrahedral change to if it has 1lp
trigonal pyramid
what name does tetrahedral change to if it has 2lp
angular
what name does trigonal bipyramidal change to if it has 1lp
“see-saw”
what name does trigonal bipyramidal change to if it has 2lp
t-shaped
what name does trigonal bipyramidal change to if it has 3lp
linear
what name does octahedral change to if it has 1lp
square pyramidal
what name does octahedral change to if it has 2lp
square planar
Predict the shape of PCl4+
tetrahedral
Predict the shape of CH3+
trigonal planar
Predict the shape of IF4-
square planar
Presdict the shape of IF4-
square planar
What is a polar bond
a bond that had a delta positive and delta negative region
what is electronegativity
the ability to attract bonding electrons in a covalent bond
Explain bond polarity
In a covalent bond between two atoms of different electronegativities, the bonding electrons are pulled towards the more electronegative atoms. This makes the bond polar.
The greater the difference in electronegativity, the more polar the bond
What are the factors that affect electronegativity?
nuclear charge
distance between nucleus and shared pair of electrons
What does the difference in electronegativity cause?…
a permanent dipole
What causes a permanent dipole?
if a charge is distributed unevenly over a whole molecule, then the molecule will have a permanent dipole
does carbon dioxide have a permanent dipole
no
does hydrochloric acid have a permanent dipole
yes
does hydrochloric acid have a permanent dipole
yes
What do Van der Waals forces do?
they cause all atoms and molecules to be attracted to each other
How do VDW forces work ?
As the VDW forces increase, what happens to the boiling point?(noble gases)
increases
how are the number of electrons and size of VDW forces linked?
the more electrons, the stronger the VDW forces
How is a hydrogen bond formed?
when a lone pair of electrons from one molecule interacts with a hydrogen on another molecule
What is a hydrogen bond?
A very strong intermolecular attraction ( an only happen between hydrogen and N,O or F)
Draw the hydrogen bonding structure of water
Draw the hydrogen bonding structure of ammonia
What is the importance of hydrogen bonding
-ice is less dense than water
-water had a much higher melting and boiling point than would be expected expected
-protein folding
-DMA base pairing
-enzyme reactions
