Bonding Flashcards
The 3 types of strong chemical bond
- Ionic
- Covalent
- Metallic
What do ionic bonds form between?
a metal and a non-metal
What do covalent bonds form between?
non-metal elements
What do metallic bonds form between?
metallic elements
Metallic bonding
Metallic bonding is the strong electrostatic attraction of positive metal ions surrounded by a sea of delocalised electrons.
Conductivity of metals
All metals are good electrical and thermal conductors. They are good conductors of heat because the delocalised electrons help transfer energy through the metal very efficiently. The delocalised electrons can also flow and hence metals can also conduct electricity very well.
Strength of metals
The majority of metals are very strong as there is a strong electrostatic attraction between the positive metal ions and delocalised electrons. The strength of the metallic bonding depends on the balance between the charge on the metal ions, the size of the metal ions and the number of electrons in the sea of delocalised electrons. The strongest metals have ions which are small, have a large positive charge, and many delocalised electrons.
Malleable and Ductile Metals
Metals can be hammered into shape (are malleable) and can be pulled into wires (are ductile) because rows of metal ions can slide past one another. If the ion lattice changes shape the delocalised electrons will still move with the ions to continue holding them together.
Melting and Boiling Points of Metals
This is directly linked to the strength of the metallic bonds. The stronger they are, the higher the melting point and boiling point will be.
Ionic Bond
An ionic bond is the strong electrostatic attraction between oppositely charged ions.
Covalent Bond
A covalent bond is a shared pair of electrons between two atoms.
Coordinate Bond
A coordinate bond is a shared electron pair which have both come from the same atom
How many bond pairs and/or lone pairs are in a molecule with a square planar shape?
2 lone pairs and 4 bond pairs
What is something that is always true of inorganic ionic compounds?
they form giant structures
What is the bonding of silicon dioxide?
- Each silicon atom bonds with four oxygen atoms so each silicon atom forms four single covalent bonds
- It is an example of a giant covalent structure
How to tell if a molecule will have permanent dipole forces?
it has high difference in electronegativity between its atoms but if it is spread evenly then the dipole cancels out
Does graphite contain delocalised electrons?
Yes
What molecules form hydrogen bonds?
any molecule that has a hydrogen atom directly attached to an oxygen or nitrogen
Does ammonium chloride contain a coordinate bond?
Yes
What drawing the shape of an ion, what must you remember to add?
Square brackets around the shape and the charge of the ion
What is the bond angle of a molecule with a tetrahedral shape?
109.5
Explain why tetrahedral molecules have that bond angle?
electron pairs repel equally/electron pairs repel to be as far apart as possible
What are intramolecular forces?
forces within a molecule and are usually covalent bonds
Give examples of types intramolecular forces
single, double, triple covalent bonds and coordinate bonds
What are intermolecular forces?
weaker (than intramolecular) forces between the molecules
What are the three types of intermolecular forces?
- induced dipole-dipole forces
- permanent dipole-dipole forces
- hydrogen bonding (special type of permanent dipole-dipole forces)
What are induced dipole-dipole forces also known as?
van der Waals or London dispersion forces
Which force is stronger: covalent bonding or hydrogen bonding?
covalent bonding
Which force is stronger: permanent dipole-dipole forces or hydrogen bonding?
hydrogen bonding
Which force is stronger: instantaneous dipole-induced dipole forces or permanent dipole-dipole forces?
permanent dipole-dipole forces
Which force is stronger: covalent bonding or instantaneous dipole-induced dipole forces?
covalent bonding
Which force is stronger: hydrogen bonding or instantaneous dipole-induced dipole forces?
hydrogen bonding
When is a covalent bond non-polar?
when two atoms in a covalent bond have the same electronegativity
When is covalent bond polar?
when the two atoms in a covalent bond have different electronegativities
Where are electrons drawn to in a polar covalent bond?
the more electronegative atom
What word is used to describe the electron distribution in a polar covalent bond?
asymmetric
What makes a covalent bond more polar?
a greater difference in electronegativity
What type of molecules have permanent dipoles?
polar molecules
What is meant by a permanent dipole?
the molecule will always have a negatively charged end and a positively charged end
What are the forces between two molecules that have permanent dipoles called?
permanent dipole-dipole forces
How do permanent dipole-dipole forces occur?
the slightly positive end of the dipole in one polar molecule and the slightly negative end of the dipole in a neighbouring polar molecule are attracted towards each other
What molecules do induced dipole-dipole forces exist between?
between all atoms or molecules
How do instantaneous dipole-induced dipole forces occur?
1, in a non-polar molecule, the electron cloud moves creating a (temporary) instantaneous dipole
2, as the instantaneous dipole approaches another non-polar molecule, it induces a dipole in the neighbouring non-polar molecule
3, the slightly positive end of the dipole in one molecule and the slightly negative end of the dipole in a neighbouring molecule are attracted towards each other
How are temporary dipoles created in non-polar molecules/atoms?
- the electron charge cloud in non-polar molecules or atoms are constantly moving
- during this movement, the electron charge cloud can be more on one side of the atom or molecule than the other
- this causes a temporary dipole to arise
For small molecules with the same number of electrons which is stronger permanent dipoles or induced dipoles?
permanent dipoles
What is the strongest form of intermolecular bonding?
hydrogen bonding
Hydrogen bonding is a type of what type of bonding?
permanent dipole-permanent dipole bonding
What is needed for hydrogen bonding to take place?
a species which has an O, N or F (very electronegative) atom bonded to a hydrogen
How do hydrogen bonds occur?
- when hydrogen is covalently bonded to an O, N or F the bond becomes highly polarised
- the H becomes so ‘delta’ positively charged that is can form a bond with the lone pair of an O, N or F atom in another molecule
What is the shape of the molecule with 4 bond pairs and 2 lone pairs?
square planar
Which repel more: lone pairs or bond pairs?
lone pairs
If two molecules both only have vdW forces, which one will have stronger/more vdW forces?
the molecule with:
- larger Mr/more electrons/larger molecules
What is the bond angle in a molecule with a trigonal planar shape?
120 degrees
What is the bond angle in a molecule with a linear shape?
180 degrees
What is the bond angle in a molecule with a tetrahedral shape?
109.5 degrees
What is the bond angle in a molecule with a pyramidal shape?
107 degrees
What is the bond angle in a molecule with a non-linear shape?
104.5 degrees
What is the bond angle in a molecule with an octahedral shape?
90 degrees
What is the bond angle in a molecule with a trigonal bipyramidal shape?
120 degrees and 90 degrees
What is the shape of molecule with 3 bond pairs and 1 lone pair?
trigonal pyramidal
Ethanethiol (C2H5SH) and ethanol molecules have similar shapes. Explain why ethanol has the higher boiling point. (2 marks)
- ethanol contains hydrogen bonding
- which is stronger than van der Waal’s forces in ethanethiol
Explain why the boiling point of a spherical molecule is lower than that of its straight-chain isomer. (2 marks)
- the straight-chain molecule has a larger surface area
- so molecules are able to get closer to one another to more strongly feel the van der Waal’s forces
