Unit 1 - Chemical Changes And Structure

Question 1

How do metallic bonds form and what properties to they have

?

Answer 1

Lattice
Between two metals
Delocalised electrons
Positive charged ions
Conduct electricity
Relatively strong bonds

Question 2

What determines the strength of metallic bonds?

Answer 2

The greater the number of metallic bonds, the greater the charge on the metal ions, the greater the strength of the metallic bond and so increased mp and bp

Question 3

How do monatomic gases exist?

Answer 3

As separate or discrete atoms.
Held together when cooled by intermolecular forces
e.g. Helium, Neon, Argon - Noble gases

Question 4

What is an example of a covalent molecular gas?

Answer 4

Diatomic gases that are covalently bonded.

Question 5

What is the trend for the strength of intermolecular forces down a group?

Answer 5

Down the groups, the atoms increase in size, which increases the number of electrons. This increase in electrons increases the strength of the intermolecular forces between the molecules, as well as the strength of the covalent bonds, thus increases the mp and bp

Question 6

Give an example of a covalent molecular solid?

Answer 6

Sulphur

Phosphorous

Question 7

What structure and properties does a diamond have?

Answer 7

Covalent network
All bonds are covalent
No intermolecular forces
Very high mp and bp
Very hard substance

Question 8

Why does graphite conduct electricity but diamonds don’t?

Answer 8

Graphite has free delocalised electrons that allow electricity to pass through while all of diamonds electrons are bonded

Question 9

What is covalent radius?

Answer 9

Half the distance between two covalently bonded atoms of an element

Question 10

What is trend for covalent radius down a group?

Answer 10

Down a group, the number of filled electron shells increases, which produces a shielding effect, preventing the outer electrons from being strongly attracted to the nucleus, thus increasing the covalent radius

Question 11

What is the trend for covalent radius across a period?

Answer 11

Across a period, the number of protons increase, which increases the nuclear charge. This attracts the electrons closer to the nucleus and so decreases the covalent radius.

Question 12

Why can’t the covalent nucleus be measured for noble gases?

Answer 12

Noble gases are monatomic and so do not bond for the covalent radius to be measured

Question 13

What is electronegativity?

Answer 13

Electronegativity is a measure of an atoms nuclear attraction for the electrons in a covalent bond - can find on pg12 of data booklet

Question 14

Trend for electronegativity down a group?

Answer 14

Down a group, the number of filled electron shells increase which increases the shielding effect, preventing the outer electrons from being strongly attracted to the nucleus. This decreases the electronegativity values.

Question 15

What is the trend for electronegativity across a period?

Answer 15

Across a period, the number of protons increase, increasing the nuclear charge, attracting the outer electrons closer to the nucleus. This increases the electronegativity values.

Question 16

Why is electronegativity described as a periodic property?

Answer 16

There is a clear trend across a period and down a group

Question 17

Why aren’t there electronegativity values for the noble gases?

Answer 17

Monatomic as they have full electron shells and therefore have no bonding electrons

Question 18

What is ionisation energy?

Answer 18

The energy required to removed one electron from one mole of an atom in a gaseous state.

Question 19

Trend for ionisation energy across a period?

Answer 19

Across a period, the number of protons increase, which increases the nuclear charge that attracts the outer electrons closer to the nucleus. Therefore the ionisation energy increases as more energy is required to remove an outer electron.

Question 20

Trend for ionisation energy down a group?

Answer 20

Down a group, the number of filled electron shells increase which increases the shielding effect, preventing the outer electrons from being strongly attracted to the nucleus. This decreases the ionisation energy as less energy is required to remove an outer electron.

Question 21

When are ionic bonds formed?

Answer 21

When there is a large difference in electronegativity values between a metal and a non metal

Question 22

Properties of ionic compounds?

Answer 22

High mp and bp
Solid at room temperature
Conduct electricity when molten or in solution because ions are delocalised

Question 23

How do covalent bonds form?

Answer 23

Shared pair of electrons between non metals

Question 24

Types of intermolecular forces?

Answer 24

London Dispersion Forces (LDF’s) (Also known as temporary dipole to temporary dipole interactions)
Permanent dipole to permanent dipole interactions
Hydrogen bonding

Question 25

What intramolecular bonds make what intermolecular forces?

Answer 25

Non Polar Covalent Molecules -> London Dispersion Forces Pure Covalent Molecules -> London Dispersion Forces Polar Covalent Molecules -> Permanent Dipole to Permanent Dipole Interactions or Hydrogen Bonding

Question 26

What is defined as pure covalent bonds?

Answer 26

When there is no difference in electronegativity values - e.g. diatomic elements

Question 27

What determines the overall polarity of a molecule?

Answer 27

If there is symmetry

Question 28

When do non polar bonds form?

Answer 28

When there is a electronegativity difference between 0 and 0.4

Question 29

When do polar bonds form?

Answer 29

When the electronegativity difference is between 0.4 and 1.7

Question 30

When do hydrogen bonds form?

Answer 30

When the electronegativity value is over 1.7

Question 31

Is oxygen polar or non polar?

Answer 31

Polar

Question 32

What is the test for polarity?

Answer 32

If it deflects from a charged rod (moves towards rod) it is polar.

Question 33

How do you work out if a molecule is polar or non polar?

Answer 33

``` Draw structure Add electronegativity values Count how many polar bonds there are Count how many non polar bonds there are Symmetry? (If polar molecules are devisable by two, cancel out) Can it cancel out? If yes, non polar If no, polar ```

Question 34

What increases the strength intermolecular bonds?

Answer 34

The number electrons

Question 35

Where do hydrogen bonds form?

Answer 35

Between Hydrogen and either Nitrogen, Fluorine or Oxygen. Between molecules, not atoms

Question 36

What is responsible for the high boiling point of water?

Answer 36

Hydrogen bonds

Question 37

How would you measure visocity?

Answer 37

Choose alcohols with similar mass Apparatus -> measuring cylinder, bung, timer, ball bearing Method -> turn measuring cylinder upside down and time how long it takes for the ball bearing to reach the stopper. The longer the ball takes, the more viscous the liquid

Question 38

What does the viscosity of a liquid say about the intermolecular bonds?

Answer 38

How many hydrogen bonds there are in the liquid

Question 39

What is miscability?

Answer 39

How well a something mixes

Question 40

What is solubility?

Answer 40

How well something dissolves

Question 41

What is the best solvents for what?

Answer 41

"Like dissolves like" Non polar substances are the best solvents for other non polar substances Polar substances are the best solvents for other polar substances and ionic compounds

Question 42

How to write Redox Equations?

Answer 42

Write electron equation Scale up electrons Combine equations Score out electrons

Question 43

What is reduction?

Answer 43

A gain of electrons

Question 44

What is oxidation?

Answer 44

A loss of electrons.

Question 45

What is an oxidising agent?

Answer 45

A substance which promotes the oxidation of another substance by accepting electrons - is reduced.

Question 46

What is a reducing agent?

Answer 46

A substance which promotes the reduction of another substance by donating electrons - is oxidised.

Question 47

Uses of oxidising agents?

Answer 47

Hydrogen Peroxide and Sulphur Dioxide - bleaching | Potassium Permanganate : antiseptic

Question 48

Where do you find the best reducing agents?

Answer 48

Top right corner of page 12 of the data booklet

Question 49

Where do you find the best oxidising agents?

Answer 49

Bottom left corner of page 12 in the data booklet

Question 50

How to write full REDOX equations?

Answer 50

``` Write equation (usually given) Balance main element (e.g. Cr, N, F) Balance Oxygens by adding water Balance hydrogen by adding H+ ions Balance charge by adding electrons ```

Question 51

How to calculate titrations?

Answer 51

``` Write equation and balance Write mole ratio Work out one side Use mole ratio to transfer information to other side Scale up if required ```

Question 52

Why would a result not be included in the average volume for a titration?

Answer 52

Not concordant

Question 53

How do you make a standard solution?

Answer 53

Take a substance of known mass and dissolve it in minimal amount of water Transfer into a volumetric flask Use deionised water to rinse out beaker and to ensure all remains are transfer into flask Use deionised water to fill to known volume

Question 54

How do you perform a titration?

Question 55

What is an enzyme?

Answer 55

A biological catalyst