Bonding

Question 1

How should you draw a dot and cross diagram?

Answer 1

• Draw the electrons being transferred to the other atom with crosses and do the other atom in dots
• State which noble gases the ions formed have the same electron configuration as
• Draw square brackets around each ion with a plus or a negative charge on each one, e,g + , 2+ or 3+

Question 2

Describe the properties of ionic compounds

Answer 2

-They have very high melting and boiling points because it takes a great deal of energy to overcome the strong forces of electrostatic attraction, this can only be achieved at high temperatures
-Soluble in polar substances such as water as when they dissolve in the water the water molecules surround the ions and can overcome the forces of electrostatic attraction
-If charge on each ion increases solubility often decreases
-Only dissolve when dissolved in water because when they are solid the ions are locked in place by electrostatic forces of attraction and cannot move through the structure and carry a charge

Question 3

What is a covalent bond

Answer 3

A bond that forms between a pair of non metals, they share some of their outer electrons so they can have noble gas arrangements. A covalent bond is a shared pair of electrons
The pair of electrons is attracted to the nuclei of the atoms forming the bond. Atomic orbitals overlap from each of the the two atoms and share a new electron density

Question 4

How do you draw a dot and cross diagram that represents a covalent bond?

Answer 4

Draw the two ions with overlapping circles with the element symbol in the middle of each. Draw the covalent bond in the circle that is formed in the overlap. If there is more than one covalent bond forming keep them on the lines of the circles.

Question 5

What is a dative bond?

Answer 5

-When one atom provides both of the electrons to form a covalent bond
-The atom that accepts the electron pair is an atom that does not have a filled main outer shell of electrons, the atom is electron deficient
-The atom that donates the electrons has a pair of electrons that is not being used in a bond called a lone pair
-They are exactly the same as a normal covalent bond
_ Both of he shared electrons come from one bonding pair

Question 6

How do we represent a dative covalent bond and how is this different to how a normal covalent bond is displayed?

Answer 6

An arrow that points towards the atom that accepts the electron pair is a dative bond however a normal covalent bond is displayed using an

Question 7

What is electron pair repulsion theory?

Answer 7

The shape of a molecule is determined by the electron pairs that surround the central atom, only referring to the outer level. This is based on the fact that electron pairs will repel other electron pairs, and they will move as far apart as possible to minimise this repulsion

Question 8

Describe the shape of a molecule when there is 2 pairs of electrons around the central atom?

Answer 8

The shape will be linear as the furthest apart that the two electrons can be is 180 degrees

Question 9

Describe the shape of a molecule when there is 3 pairs of electrons around the central atom

Answer 9

They will be 120 degrees apart, the molecule is planar and is called a trigonal planar e.g boron triflouride

Question 10

Describe the shape of a molecule when there are 4 pairs of electrons around the central atom

Answer 10

They form a tetrahedron shape , for example methane and ammonia. They are 109.5 degrees away from each other.

Question 11

Describe the shape of a molecule when there are 5 pairs of electrons around the central atom

Answer 11

Trigonal bipyramid for example phosphorous pentachloride with 120 degree angles and 90 degres

Question 12

Describe the shape of a molecule when there are 6 pairs of electrons around the central atom

Answer 12

Adopts a octahedral shape with bond angles of 90 degrees

Question 13

What effect does lone pairs of electrons have on the shape of a molecule?

Answer 13

They repel more strongly than bonding pairs which decreases each bond angle by 2.5 degrees

Question 14

What is the bond angle and shape of a molecule with 3 bonding pairs and one lone pair? GIve examples

Answer 14

107 degrees because 109.5 has taken away 2.5 degrees
Ammonia
These have a trigonal pyramidal shape

Question 15

What is the bond angle and shape for a molecule with 2 bonding pairs and 2 lone pairs? Give an example

Answer 15

It has 4 charge clouds with two lone pairs so this decreases the angle by 2.5 degrees for each pair so it is 104.5 degrees. V shaped
Example is water

Question 16

Describe why magnesium chloride has a high melting point

Answer 16

Giant ionic lattice structure with strong electrostatic forces of attraction between oppositley charged ions

Question 17

Describe the bonding in magnesium

Answer 17

Attraction between MG 2 plus ions and delocalised electrons

Question 18

3 bonds and 2 lone pairs?

Answer 18

T shape

Question 19

2 lone pairs and 2 bonds

Answer 19

Bent o

Question 20

How does the sharing of electrons in an atom hold the atom together?

Answer 20

The negative electron pairs in the outermost orbitals are electrostatically attracted to the positive nuclei of each atom pulling the atoms together

Question 21

Describe how ammonia acting as a base is an example of dative covalent bonding

Answer 21

The forming of an ammonium ion, NH4 ,from ammonia and a hydrogen ion is an example of this because ammonia has a lone pair of electrons which occupy a full orbital in the central N atom. The hydrogen ion is formed when an electron is removed from a hydrogen atom, meaning this ion is just a singular proton with the remaining empty orbital. When the full orbital from the N atom and the empty orbital from the H ion come close enough these orbitals overlap, creating a new bonding orbital where electrons are shared, creating a co ordinate bond

Question 22

Why do ionic bonds between atoms form a lattice

Answer 22

Electrostatic forces of attraction between oppositley charged ions occur in all directions in the molecule
There are also forces of replusion between the like charges of the ipns so they arrange themselves in order to be as far apart as possible to minimise replusion

Question 23

How are instantaneous dipoles formed?

Answer 23

Electrons move very quickly and randomly across a whole molecule , meaning at any one time electrons may not be equally shared between the two atoms. These electrons have a negative charge so when there are more electrons on one certain side it will have a partial negative charge, and the other side will have a partial positive charge. This causes a dipole as electrons are unevenly distributed.

Question 24

How can a molecule be induced to have a dipole?

Answer 24

• An instantaneous dipole in a molecule can cause another molecule next to it to have an induced dipole
• One side of the molecule with the instantaneous dipole has a slight negative charge, which repels the electrons in the neighbouring molecule causing the electrons to move to the other side of the atom, giving it a slight negative charge in this area and a positive charge in the next area
• The forces between the instantaneous dipole and the induced dipoles are van deer waals

Question 25

What is the force called when a molecule is induced to have dipole

Answer 25

Van deer walls

Question 26

How does the strength of van deer walls change with increased size of an atom?

Answer 26

Larger the molecule the stronger the van deer walls meaning larger molecules have higher melting and boiling points

Question 27

What is a permanent dipole dipole interaction caused by?

Answer 27

When there is an uneven distribution of electrons in a molecule leading to partially positive and partially negative regions of charge which can interact with neighbouring molecules. In this molecule the atoms might have a relatively large difference in electro negativity and the electrons will attract to the atom with the higher electronegativity meaning electron distribution is uneven. This means there is a polar bond within this molecule so the charges of the polar bond align themselves with opposite charges on other molecules next to it, this is an electrostatic attraction which forms a permanent dipole dipole interaction

Question 28

How is a hydrogen bond formed?

Answer 28

When a very electronegative element such as F, Br, or N bonds with a hydrogen atom that is not electronegative and it forms a very polar molecule This then gives rise to permanent dipole dipole interactions between lone pairs of electrons on the electronegative atom with a slight negative charge, and the partially positive charge on the hydrogen atom from a neighbouring molecule forming hydrogen bonds

Question 29

Define electronegativity

Answer 29

The ability of an atom to be able to pull an electron pair in a covalent bond towards itself

Question 30

How do polar bonds form?

Answer 30

When two atoms with different electronegativity bond together but the atom with the higher electronegativity will pull the electrons closer to itself with more force than the other atom can, meaning it has a greater share of a negative charge giving it a partial negative charge and the other side a partial positive charge

Question 31

Define ionic bonding

Answer 31

Electrostatic force of attraction between oppositely charged ions formed by electron transfer

Question 32

Define covalent bond

Answer 32

Shared pair of electrons

Question 33

Define metalic bond

Answer 33

Electrostatic force of attraction between the positive metal ions and the delocalised electrons

Question 34

Describe mp and bp of ionic compounds

Answer 34

- High BP and MP, giant lattice of ions with strong electrostatic forces between oppositely charged ions acting in all directions - Large amount of energy is needed to break these bonds

Question 35

Describe solubility in water of ionic compounds

Answer 35

- Soluble because both ionic compounds and water are polar - Partial charges of water break apart the ionic lattice pulling oppositley charged ions apart so compounds dissolve

Question 36

Describe the conductivity of ionic compounds

Answer 36

- Can only conduct when molten or dissolved in solution as ions of the compound are able to freely move and carry a charge - Cannot conduct when solid as ions are not free to move and carry a charge

Question 37

Describe mp and bp of simple molecules

Answer 37

-Low mp and bp because of weak intermolecular forces between molecules - not much energy is required to overcome them

Question 38

Describe solubility of simple molecules in water

Answer 38

- Insoluble in water

Question 39

Describe conductivity of simple molecules

Answer 39

- Cannot conduct, no ions to conduct and electrons are localised

Question 40

Describe mp and bp of giant covalent structures

Answer 40

- HIgh MP and BP due to many strong covalent in macromolecular which takes alot of energy to overcome the bonds

Question 41

Describe solubility of giant covalent structures in water

Answer 41

Insoluble in water

Question 42

Describe conductivity of giant covalent molecules

Answer 42

Diamond and sand- poor because electrons are localised, cannot move and carry a charge Graphite-good as free delocalised electrons can move and carry a charge between layers Neither can conduct when solid

Question 43

Describe the mp and bp of metallic structures

Answer 43

High MP and BP because there are strong electrostatic forces between positive ions and sea of delocalised electrons

Question 44

Describe solubility of metallic structures

Answer 44

Insoluble in water

Question 45

Describe conductivity of metallic structures

Answer 45

Good molten and solid as delocalised elecrrons can move throughout the structure and carry a charge

Question 46

Describe a property of symetrica

Question 47

What is needed in order for a hydrogen bond to form

Answer 47

- A hydrogen bonded to a strongly electronegative element F,Cl or N - The strongly electronegative element must have at least one lone pair of electrons

Question 48

Which type of intermolecular force can be used to describe why the solid form of water is less dense than the liquid form?

Answer 48

- Hydrogen bonding - Water in its liquid state has hydrogen bonds which break and reform as the molecules are always moving about - When water freezes, the water molecules are no longer allowed to move around and the hydrogen bonds hold the molecules in fixed positions - In order to fit into this structure molecules are slightly less closley packed that in water - This is why ice forms on water, with the purpose of insulating ponds below it enabling living organisms under it to survive

Question 49

Describe and explain the trend in boiling points of the hydrocarbons

Answer 49

Increases as the chain length increases As bigger molecules have more electrons, larger instantaneous dipoles are formed Larger induced dipoles are formed by these instantaneous dipoles, causing more, STRONGER van der waals

Question 50

Describe and explain the trend in boiling points of the noble gases

Answer 50

BP increases down the group, as atomic number increases Due to more electrons,larger instantaneous dipoles are formed Larger induced dipoles are then formed by these instantaneous dipoles, causing more stronger van der waals

Question 51

Explain why some molecules with polar bonds may not have a permanent dipole

Answer 51

- Charges may cancel out on some of these molecules with more than one polar bond, leaving a molecule with no dipole moment - Molecule has identical bonds with no lone pairs, even if there are individual polar bonds dipole cancel out - E.g carbon dioxide is a linear molecule so dipoles cancel out - E.g Tetrachloromethane has a tetrahedral shape so dipoles cancel - E.g dichloromethane has an unsymmterical shape so dipoles do not cancel out so it has a permanent dipole