1.3 - Bonding Flashcards
How are ions formed?
Ions are formed when electrons are transferred from one atom to another
What is the charge on an Ammonium ion?
+1
What is the charge on a carbonate ion?
-2
What is the charge on a hydroxide ion?
-1
What is the charge on a nitrate ion?
-1
What is the charge on a sulphate ion?
-2
What force holds together positive and negative ions?
An electrostatic attraction which is very strong
What is a lattice?
A regular structure
Why are ionic crystals ‘giant’ lattices of ions?
They are called ‘giant’ because they have the same repeating structure over and over again
In what states do ionic compounds conduct electricity?
They conduct electricity when they are molten or dissolved, but not when they are solid. This is because when it is solid, the ions are not free to move
What are the melting points for ionic compounds?
Ionic compounds have a very high melting point. The giant ionic lattices are held together by strong electrostatic forces
Are ionic compounds soluble?
Ionic compounds tend to dissolve in water. Water molecules are polar and they pull the ions away from the lattice and cause it to dissolve
What is a molecule?
A molecule is formed when two or more atoms are bonded together
What happens to the electrons in covalent bonding?
The electrons are shared in covalent bonding
What is a simple covalent compound?
Compounds that are made up of lots of individual molecules
What is broken when simple covalent compounds are heated?
The weak intermolecular forces are broken, not the covalent bonds
What is another term for giant covalent structures?
They are sometimes called macromolecular structures
What is the structure of graphite?
The carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded to three other carbon atoms. The fourth outer electron is delocalised. The sheets of hexagons are bonded together by weak van der Waals forces
What are the properties of graphite?
The weak bonds between the layers in graphite are easily broken so the sheets can slide over each other
The delocalised electrons in graphite are free to move along the sheets so an electric current can flow
The layers are far apart compared to the length of the covalent bonds so graphite has a low density and is used to make strong, lightweight sport equipment
Because of the strong covalent bonds in the hexagon sheets, it has a very high melting point
Graphite is insoluble in any solvent; the covalent bonds in the sheets are too difficult to break
What is the structure of diamond?
Diamond is made up of carbon atoms. Each carbon atom is covalently bonded to four other carbon atoms. The atoms arrange themselves in a tetrahedral shape - its crystal lattice structure
What are the properties of diamond?
Diamond has a very high melting point
Diamond is extremely hard
Vibrations travel easily through the stiff lattice so it’s a good thermal conductor
It cannot conduct electricity because there are no delocalised electrons
Diamond is insoluble in any solvent
What is a co-ordinate (dative) bond?
One of the atoms provides both of the shared electrons
How do co-ordinate bonds form?
They form when one of the atoms in the bond has a lone pair of electrons and the other doesn’t have any electrons available to share
What affects the shape of a molecule?
The shape depends on the number of electrons in the outer shell of the central atom
What are shared electrons called?
They are called bonding pairs
What are unshared electrons called?
They are called lone pairs or non-bonding pairs
What is a charge cloud?
An area where you have a big chance of finding an electron
What is the order of repulsion (starting with the highest)?
Lone pair/lone pair, lone pair/bonding pair and bonding pair/bonding pair
What does a broken line show when drawing a molecule?
A broken line shows a bond pointing away from you
What does a wedge show when drawing a molecule?
It shows a bond pointing towards you
How is the number of electron pairs calculated?
1) Find the central atom
2) Work out how many electrons are in the outer shell of this atom
3) Add one electron for every bond on the central atom
4) Take into account the charge if looking at an ion (add one electron for each negative charge or subtract one for each positive charge)
5) Add up the electrons and divide by 2
6) Compare the number of electron pairs to the number of bonds to find the number of lone pairs and the number of bonding pairs on the central atom
What is the shape and bond angles of an atom with 2 bonding pairs?
The shape is linear and the bond angle is 180
What is the shape and bond angles of an atom with
3 bonding pairs?
The shape is trigonal planar and the bond angle is 120
What is the shape and bond angles of an atom with 4 bonding pairs?
The shape is tetrahedral and the bond angle is 109.5
What is the shape and bond angles of an atom with 3 bonding pairs and 1 lone pair?
The shape is trigonal pyramidal and has a bond angle of 107
What is the shape and bond angles of an atom with 2 bonding pairs and 2 lone pairs?
The shape is bent (or non-linear) and the bond is 104.5
What is the shape and bond angles of an atom with 5 bonding pairs?
The shape is trigonal bipyramidal and three atoms form a trigonal planar (at 120 degrees) and the other two will be at 90 degrees from them
What is the shape and bond angles of an atom with 4 bonding pairs and 1 lone pair?
The shape is seesaw and the bond angles are 86.5 and 102
What is the shape and bond angles of an atom with 3 bonding pairs and 2 lone pairs?
The shape is T-shaped with a bond angle of 87.5
What is the shape and bond angles of an atom with 6 bonding pairs?
The shape is octahedral with a bond angle of 90
What is the shape and bond angles of an atom with 5 bonding pairs and 1 lone pair?
The shape is square pyramidal with some bond angles being 90
What is the shape and bond angles of an atom with 4 bonding pairs and 2 lone pairs?
The shape is square planar with a bond angle of 90
What is electronegativity?
Electronegativity is the ability to attract the bonding electrons
What is electronegativity measured on?
The Pauling Scale
How are polar bond forms?
They are formed when a difference in electronegativity between two molecules is high enough that one side becomes slightly positive and the other slightly negative
What is a dipole?
A dipole is a difference in charge between the two atoms caused by a shift in electron density in the bond
What happens if the polar bonds are symmetrical?
It is not a polar molecule as the dipoles cancel each other out
What is an intermolecular force?
They are the forces between the molecules
What are the three types of intermolecular forces?
Van der Waals (induced dipole-dipole), permanent dipole-dipole forces and hydrogen bonding
What are van der Waals forces?
Electrons in charge clouds are moving really quickly and at some moments, the electrons are more likely to be towards one side of the molecule than the other, causing it to have a temporary dipole. This temporary dipole causes other molecules nearby to have a temporary dipole too. Even though the dipoles keep changing, the overall effect is for atoms to be attracted to each other
What factors affect the strength of van der Waals forces?
Size of the molecule - larger molecules have a larger electron cloud meaning stronger van der Waals forces
The shape of the molecule - long, straight molecules can lie closer together and this increases the strength of the van der Waals
What is the trend in boiling points of Noble Gases as you go down group 8 due to van der Waals forces?
As you go down the group, the number of electrons increases and so do the boiling points
What is the trend in boiling points of the length of the alkane chain due to van der Waals forces?
As the chain gets longer, the number of electrons in the molecule increases, allowing the van der Waals forces to increase in strength. This means that the boiling point increases
What is a permanent dipole-dipole force?
In a substance made up of molecules that have a permanent dipole, there will be weak electrostatic forces of attraction between the slightly positive and the slightly negative sides of the molecules
When do hydrogen bonds form?
They only form when hydrogen is covalently bonded to fluorine, nitrogen or oxygen. This is due to them having a high electronegativity and hydrogen atoms having a high charge density
Why is ice less dense than liquid water?
As the water cools to form ice, the molecules arrange themselves into a regular lattice structure. Since the hydrogen bonds are relatively long, the average distance between the water molecules is greater in ice than in liquid water, resulting in a lower density
Do simple covalent compounds conduct electricity?
They cannot conduct electricity because there are no free ions or electrons to carry the charge
What is the melting point of simple covalent compounds?
Simple covalent compounds have low melting points because the weak forces between the molecules are easily broken
What is the solubility of simple covalent compounds?
Some simple covalent compounds dissolve in water depending on how polarised the molecules are
What is metallic bonding?
The metals outer shell of electrons become delocalised, leaving a positive metal ion. There is an electrostatic attraction between the positive metal ion and the sea of delocalised electrons which is strong
What factors affect the strength of a metallic bond?
The number of delocalised electrons, the size of the metal ion and the lattice structure affect the melting point
Do metals have the ability to be shaped?
As there are no bonds that hold together specific ions, the metal ions can slide over each other when the structure is pulled so metals are malleable and ductile
Are metals good electrical and thermal conductors?
The delocalised electrons can pass kinetic energy to each other, making them good thermal conductors. Also, the delocalised electrons can move around to carry a charge making them good electrical conductors
Are metals soluble?
Metals are insoluble, except in liquid metals, due to the strength of the bonds
