Unit 1 Chemical changes and structure

Question 1

What does the word periodic describe?

Answer 1

A pattern that repeats itself at regular intervals.

The periodic table is often arranged periodically such that certain properties of elements are repeated at regular intervals.

Question 2

Why can the size of an individual atom not be measured?

Answer 2

Because the electrons in the atom are in constant motion

Question 3

What value do we use to measure the size of atoms of elements?

Answer 3

The covalent radius

Question 4

What is the covalent radius?

Answer 4

Half of the distance between two atoms joined by a covalent bond.

Question 5

What happens to the atomic size going down a group in the periodic table?

Answer 5

As you go down a group in the periodic table the number of electron shells increases, this increased number of electrons shells increases the shielding effect by which the outermost electrons are shielded from the positive charge of the nucleus. This will cause the covalent radius to increase.

Question 6

What happens to atomic size going across a period in the periodic table?

Answer 6

As you go across the periods of the periodic table the number of protons in the nucleus increases, this causes the forces of electrostatic attraction in the nucleus to increase hence the outermost electrons will experience more attraction towards the increased positive charge of the nucleus hence the covalent radius will decrease.

Question 7

What does the term Electronegativity refer to?

Answer 7

Electronegativity refers to the ability of an atom in a chemical bond to attract electrons in said chemical bond.

Highly electronegative elements will have a strong attraction for bonding electrons where elements with low electronegativity values will have a weak attraction for bonding electrons.

Question 8

What happens to values of electronegativity going across a period of the periodic table?

Answer 8

Across a period the electronegativity value of elements increases.

This is because the number of protons in the nucleus increases going across the period hence the forces of electrostatic attraction in the nucleus increase due to the increased positive charge.

Question 9

What happens to values of electronegativity going down a group in the periodic table?

Answer 9

Going down a group electronegativity decreases

the number of electron shells increases which increases the shielding effect reducing the electrostatic forces of attraction acting on the outermost electrons and reduces the electrostatic attractions acting on bonding electrons.

Question 10

What holds the electrons in an atom in place?

Answer 10

The electrostatic attractions between the positively charged nucleus and the negatively charged electrons.

Question 11

True or false certain atoms have such low electrostatic attractions to bonding electrons that they give away electrons for free?

Answer 11

False

No atom will give away electrons for free and to remove electrons from an atom energy is required.

Question 12

Define the term first ionisation energy?

Answer 12

The energy required to remove one mole of electrons from one mole of gaseous atoms.

This energy must overcome the electrostatic forces of attraction between the nucleus and electrons of the atom.

Question 13

When writing an equation for an ionisation energy what must you always include.

Answer 13

the gaseous state symbol (g)

Question 14

What is the relationship between the first and second ionisation energies?

Answer 14

The second ionisation energy of any element will always be larger than the first.

This is because after one mole of electrons have been removed from one mole of gaseous atoms the number of protons in the atom remains unchanged, for this reason the electrostatic forces acting on each individual electron increases due to there being fewer electrons in the atom. This means that the second ionisation energy will require more energy to break down this stronger electrostatic force between nucleus and electrons.

Question 15

What happens to first ionisation energy going down a group in the periodic table?

Answer 15

The first ionisation energy decreases.

This is because going down a group the number of electron shells increases, this causes the shielding effect to take place where the forces of attraction acting on the outermost electrons is reduced this means that the energy required to remove electrons from the outermost electron shell is reduced.

Question 16

What happens to the first ionisation energy going across a period in the periodic table?

Answer 16

The first ionisation energy increases

This is because as you go across a period of the periodic table the number of protons in the nucleus increases this increases the forces of attraction acting on the outermost electrons of the atom meaning that the energy required to remove an electron from the outermost shell is increased.

Question 17

What are the different types of chemical bonding in elements?

Answer 17

-Metallic lattice
-Covalent Network
-Discrete Covalent Molecular
-Monatomic Gas

Question 18

What is a London Dispersion Force?

Answer 18

An intermolecular bond that is present in all compounds, created by the electrostatic attractions between a temporary and induced dipole between molecules caused by random movement of electrons.

Question 19

What makes london dispersion forces stronger?

Answer 19

the more electrons present the more temporary dipoles form and the stronger the electrostatic attractions between atoms are.

Question 20

What happens to the melting and boiling points of the noble gases going down the group.

Answer 20

The melting and boiling points of the noble gases increase going down the group this is because as you go down a group the number of electron shells increases, hence when more electrons are present the strength of the intermolecular london dispersion forces increases increasing the melting and boiling points of the elements.

Question 21

What two categories do molecular elements fall into?

Answer 21

-Diatomic elements
-Polyatomic elements

Question 22

What are the diatomic elements?

Answer 22

-Hydrogen
-Nitrogen
-Oxygen
-Fluorine
-Chlorine
-Bromine
-Iodine

Question 23

Explain fully why group 7 elements have low melting points?

Answer 23

Because group 7 elements contain both intermolecular forces and intramolecular forces, the intramolecular forces are strong covalent bonds that are not affected by the low melting point. It is the weak london dispersion forces that are broken down and are the reason for the group 7 elements having low melting and boiling points.

Question 24

What are the polyatomic compounds?

Answer 24

-Sulfur (S8)
-Phosphorus (P4)
-fullerine(C60)

Question 25

Why do polyatomic elements have higher melting and boiling points than that of regular discrete covalent molecular compounds?

Answer 25

Because polyatomic elements have more atoms in each molecule hence more electrons are present this makes the london dispersion forces holding these molecules together stronger.

Question 26

How can covalent Networks have such high melting and boiling points?

Answer 26

As covalent networks have strong covalent bonds throughout their structure and do not have intermolecular forces as molecules are held together by these strong covalent bonds that are difficult to break down.

Question 27

Name some covalent Network elements.

Answer 27

-Carbon as diamond
-Carbon and graphite
-Silicon Dioxide
-Borron

Question 28

Describe the concept of the bonding continuum?

Answer 28

This idea places pure covalent and ionic compounds at opposite ends of a spectrum and places polar covalent compounds in the middle. Where a compound lies of the bonding continuum is dependant on the difference in the electronegativity of elements in the molecules.

Question 29

Elements with a larger electronegativity value in a compound will have a _________ Charge

Answer 29

Negative
As this element will attract bonding electrons towards it

Question 30

Elements with the lower electronegativity values in a chemical compound will have a ___________ Charge

Answer 30

Positive
As the element will weakly attract the bonding electrons and the more electronegative element will attract these bonding electrons.

Question 31

What are the different types of covalent molecular compounds?

Answer 31

• Non-Polar
• Polar

Question 32

What does the type of covalent molecular compound do to the compound?

Answer 32

It has a large influence of the strength and type of intermolecular forces that exist between molecules of the compound.

Question 33

What is a van der Waals force?

Answer 33

an intermolecular force caused by dipole interactions

Question 34

What are the two conditions that must be met for a covalent compound to be polar?

Answer 34

-It must have polar bonds between atoms in each molecule
-The three dimentional structure of the molecule must be such that the dipoles do not cancel one another out.

Question 35

what type of bonding does water have?

Answer 35

Polar, as there is a clear positive region and a clear negative region of the molecule.

Question 36

What type of bonding does Carbon Dioxide have?

Answer 36

Non-Polar as the dipoles are canceled out by the 3D structure of each individual carbon dioxide molecule.

Question 37

How can we identify if a covalent compound is polar or non-polar?

Answer 37

running the aqueous solution through a burette and placing a charged rod nearby, if the compound is polar then it will move towards the charged rod due to the electrostatic attractions between the negative dipole and the positive charge on the rod.

Question 38

What type of intermolecular forces do non-polar compounds contain?

Answer 38

non-polar compounds exclusively contain weak london dispersion forces between molecules.

Question 39

What are the predominant types of bonding in polar covalent compounds?

Answer 39

PDPD interactions (permanent dipole permanent dipole)
Hydrogen bonding

Question 40

What is meant by pdpd interactions?

Answer 40

firstly non-polar molecules rely on temporary dipoles caused by random electron movement, however in polar compounds dipoles are fixed as electrons are held in place by differences in the electronegativity of elements in the compounds. for this reason permanent dipoles have electrostatic attractions between them that are stronger than london dispersion forces

Question 41

What is meant by hydrogen bonding?

Answer 41

a special kind of pdpd interactions that occurs when a hydrogen atom is directly attached to a Nitrogen, Oxygen, or Fluorine atom. This is the strongest of the van der waals forces as the difference in electronegativity values of these elements is the greatest meaning that the strength of the electrostatic attractions between permanent dipoles is strongest.

Question 42

To ensure a fair comparison when investigating different types of van der waals forces what variable should be kept constant.

Answer 42

To ensure a fair comparison the gram formula masses of the compounds involved should be as similar as possible as all compounds contain london dispersion forces, and this ensures that the any results of melting or boiling points are not due to differences in the strength of the london dispersion forces involved.

Question 43

Compounds with large amounts of hydrocarbon character will have predominantly ______________ joining molecules together

Answer 43

london dispersion forces

This is because hydrocarbons are non-polar as the 3D structure causes dipoles to be canceled out. meaning that they contain predominantly london dispursion forces

Question 44

Define the term viscosity?

Answer 44

A measure of how a liquid resists flow

Highly viscous liquids will flow slowly where liquids with low viscosity will appear runny.

Question 45

How does viscosity relate to the intermolecular forces in a compound?

Answer 45

In general as the strength of the intermolecular forces increases the viscosity of the liquid increases.

Question 46

Define the term miscible?

Answer 46

When two liquids have the ability to mix with one another.

Question 47

Define the term immiscible?

Answer 47

When two liquids are unable to mix with one another.

Question 48

What does the term “like dissolves like” mean?

Answer 48

It means that solutes are most likely to dissolve into a solvent that shares similar types of intermolecular bonding.

For example polar or ionic substances are likely to dissolve in water whereas non-polar substances are more likely to dissolve in hexane than water.

Question 49

What makes ice float on water?

Answer 49

Due to hydrogen bonding, as when water is cooled its molecules slow down and the hydrogen bonds are able to hold the molecules together in an open lattice structure this structure means that the ice becomes less dense than the water hence it will rise to the top and float.

Question 50

What is meant by oxidation?

Answer 50

The loss of electrons, converting atoms to ions

Question 51

What is meant by reduction?

Answer 51

The net gain of electrons, in most cases converting atoms to ions.

Question 52

What is an oxidising agent?

Answer 52

A chemical that enables oxidation to take place by accepting electrons

Question 53

What is a reducing agent?

Answer 53

A chemical that enables reduction to take place by donating electrons

Question 54

Are elements with high electronegativities likely to be oxidising or reducing agents?

Answer 54

it is likely to be the oxidising agent
As high electronegativity means that it will undergo reduction easily as it will absorb electrons.

Question 55

Are elements with low electronegativity values likely to be oxidising or reducing agents?

Answer 55

Likely to be reducing agents
As they will undergo oxidation and low EN values have a weak attraction to bonding electrons hence they will more easily donate electrons to the species undergoing reduction.

Question 56

What happens to an oxidising agent in a redox reaction?

Answer 56

They will gain electrons and become less positive

Question 57

What happens to reducing agents in a redox reaction?

Answer 57

They will lose electrons and become more positive

Question 58

What are the key steps of working out a complex ion electron equation?

Answer 58

• Write out the main reactant and product and make sure that all atoms except from oxygen are balanced
  -Add water to one side of the equation to balance the number of oxygens
  -Add hydrogen ions to balance out the number of hydrogens on each side of the equation
  -Add electrons to balance the charge on either side of the equation

Question 59

What do we call the substance that is being analysed in a titration?

Answer 59

The analyte

Question 60

What should happen to the analyte in a titration?

Answer 60

It should have an accurately known volume and should be added to a conical flask using a pipette.

Question 61

What do we do with the chemical that is being used to analyse the solution?

Answer 61

The chemical should be a standard solution, meaning it has an accurately known concentration, the solution should be placed in a burette using a filter funnel. The chemical should then slowly be added to the conical flask until an end point in the reaction has been reached.

Question 62

In what circumstances would we not add an PH indicator to the reaction?

Answer 62

if the titration was self indicating, meaning that they change color due to the reaction itself.

Question 63

What are concordant values?

Answer 63

A measure to ensure that average titre volumes are accurate by only calculating the average titre volume with volumes that are within 0.2 cm3 of one another.

Question 64

What is special about potassium permanganate in titrations?

Answer 64

Potassium permanganate is a self indicator as it changes from pink to colourless or colorless to pink depending on how it is used.