Bonding and structure Flashcards
What is a simple covalent molecule?
2 or more non metal atoms bonded
What are examples of a giant covalent molecule?
Diamond
Graphite
Boron
Silicon
Silicon dioxide
What is a giant ionic lattice?
a metal and a non metal bonded
What is a giant metallic lattice?
the elements of the periodic table
What is a covalent bond?
The strong electrostatic force of attraction between a shared pair of electrons and the nuclei of the bonded atoms
What happens when electrons are shared?
A bond is formed (covalent)
What is a dative covalent bond?
a covalent bond where only one of the bonded atoms donates both electrons being shared
What is the shape and angle for 2 bonding pairs and no lone pairs?
Linear- 180 degrees
What is the shape and angle for 3 bonding pairs and no lone pairs?
trigonal planar- 120 degrees
What is the shape and angle for 4 bonding pairs?
tetrahedral- 109.5
What is the shape and angle for6 bonding pairs and no lone pairs?
90 degrees- octahedral
What is the shape and angle for 3 bonding pairs and 1 lone pair?
pyramidal- 107
What is the shape and angle for 2 bonding pairs and 2 lone pairs?
bent/ v shaped- 104.5
How do you explain the shape of a covalent molecule?
- State the number of bonding and lone pairs
- State electron pairs repel and try get as fair away as possible
3.If there are no lone pairs then state that the electron pairs will repel equally - If there are lone pairs of electrons then state that the lone pairs repel more that the bonding pairs
- State the actual shape and bond angle
What do molecules that have a lone pair of electrons often act as?
A base
What is a base?
A base is a proton acceptor
What is an example of a base?
When ammonia acts as a base it accepts the H+ ion to form a dative covalent bond forming the ammonium ion .
What happens as a result of lone pairs repelling more than the bonding pairs?
they reduce the bond angles (by 2.5)
What can water sometimes act as?
A base
What is a systematic way of working out the shape of a negative molecular ion?
-Use periodic table to decide how many outer shell electrons the central atom has
-Draw dot and cross diagram. Add 1 extra electron to the central atom to account for the negative charge in the ion
-Decide how many lone pairs are present and how many bonding pairs
What is the difference in repulsion for single bonds and multiple bonds?
They repel each other in the same way that singles do but less than lone pairs
Where do covalent bonds occur?
Simple covalent substances
What are induced dipole interactions?
Temporary induced dipole dipole forces and they occur between non-polar molecules
How do induce dipole dipole interactions arise?
-electrons in the molecule are constantly moving and anyone instant electron distribution may become unsymmetrical
-Produces temporary dipole in that molecule
-if another molecule approaches it with the temporary dipole and opposite dipole is induced to the adjacent molecule
Why do induced dipole dipole interactions only act for a short time?
The electrons density is constantly changing
what is the weakest intermolecular force?
induced dipole dipole- Typically, about one percent of the strength of a covalent bond
what does symmetrical molecules with no overall dipole interact through?
induced dipole dipole (non polar)
what can the increasing boiling points of the alkane homologous series? Be explained by?
increase in the number of electrons in the bigger molecules, causing an increase in the induced dipole dipole interactions between neighbouring molecules
when does the strength of induced dipole dipole interactions increase?
-as the number of electrons in the molecule or atom increases (a chance that temporary dipoles will form)
-surface contact of the molecules or atom increases for example, long chain alkanes have a larger surface contact
When do permanent dipole dipole interactions occur?
In addition to induced dipole, dipole interactions
What does it mean as permanent dipole dipole interaction are stronger than induced dipole dipole interactions?
The compounds have higher boiling points
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
What is a dipole?
The separation of charge in a bond, which occurs as a result of these differences in electronegativity
What are the most electronegative atoms?
F N O Cl
what is the difference in electronegativity in hydrogen and carbon?
Very little
why does electronegativity increase across the period?
The number of protons increase and the atomic radius decreases, because the electrons in the same shell are pulled more
Why does electronegativity decrease down the group?
because the distance between the nucleus and outer electrons increases, and the shielding of in a shell electrons increase
What do erase more differences in electronegativity do?
do not produce significant dipoles
when do polar molecules occur?
When atoms with different electronegativities bond, have permanent dipole, and the molecule is unsymmetrical
when does a polar bond occur?
When does an unequal distribution of electrons in a bond and charge separation is produced
What is a symmetrical molecule?
all the atoms are on the central atom are the same, and there are no lone pairs on the central atom- therefore dipole cancel each other out, and the molecule has no overall dipole
how do dipole act if the molecule is symmetrical?
in the opposite directions
What is the definition of hydrogen bonding?
As intermolecular bonding between molecules, contain N O or F and the h of NH OH or HF
what is the strongest intermolecular force?
Hydrogen bonding, which occurs in addition to induce dipole dipole interactions
what is the atom with the lowest electronegativity
Caesium or francium
what are the anomalously high boiling points of water, ammonia and HF caused by?
Hydrogen bonding between the molecules
What does the large difference in electronegativity between the hydrogen atom and either a nitrogen, oxygen or fluorine atom mean?
that very polar bonds are formed with the hydrogen having a strong partial charge (dipole +)
Why can water form two bonds per molecule?
Because oxygen is very electronegative, and it has two lone pairs
why does ice have low density?
The molecules are held further apart than in liquid water (The water molecules form hydrogen bonds between each other and arranged themselves into an open lattice structure)
what is the common cause for anomalous properties?
Hydrogen bonding
what is melting/boiling point in covalent substances determined by?
Type and strength of bond/intermolecular force being broken
What is electrical conductivity in covalent substances determined by?
The presence or absence of mobile charge carriers
What is water, solubility and covenant substances, determined by?
The strength of interactions with the water molecules
Why do simple materials have low melting/boiling points?
-molecules are held together by weak intermolecular forces (IDD, PDD) these require a little energy to overcome
-Atoms are held together by strong Covalent bonds, but these are not broken when boiled/melted
What is the conductivity in simple covalent molecules?
no mobile charge, carriers and so don’t conduct electricity
What is a solubility for simple, covalent materials?
Nonpolar substances can’t interact with water molecules so tend to be insoluble in water
why do giant covalent materials have high boiling and melting points?
They are held together by strong covalent bonds, which require a large amount of energy to break
Which are the two covalent materials, that conduct electricity?
graphite and graphene- they have delocalised electrons
Why are giant covalent materials insoluble in water?
They do not interact with water molecules
Why do giant metallic materials have high, melting and boiling points?
-they have strong, electrostatic attractions held together by ions and delocalised electrons
-The strong bonds require a lot of energy to break
When can giant metallic materials conduct electricity?
when molten or liquid- mobile electrons
Why are giant metallic substances soluble in water?
They do not interact with water molecules
what is the definition of a giant metallic bond?
The strong electrostatic attraction between cations and the delocalised electrons
what is an ionic bond?
electrostatic force of attraction between oppositely charged ions formed by electron transfer
why do giant ionic materials have a high melting point?
oppositely charged ions together by strong ionic bonds, which require a large amount of energy to break
when do solid ions not conduct, electricity?
When they are in a fixed regular lattice
When do ionic materials conduct electricity?
when molten or in a solution- ions are mobile so substances will conduct
why are giant ionic substances soluble in water?
They disassociate into ions, which can interact with the polar water molecules
What are two anomalous properties water in terms of h2 bonding?
Higher bp- strong hydrogen bonds
Ice less dense than water- hydrogen l bonds hold water molecules far apart in an open lattice
