Elements of life

When to know all water of crystallisation has been driven off

when mass remains unchanged (heated to a constant mass)

Mass of a proton

1

Mass of a neutron

1

Mass of an electron

0.0005

Charge of a proton

+1

Charge of a neutron

0

Charge of an electron

-1

Atomic number

the number of protons in the nucleus of an atom

How to work out number of electrons

Atoms are overall neutral in charge so the number of protons \= the number of electrons

How is the periodic table arranged?

by increasing atomic number

Mass number

the total number of protons and neutrons in the nucleus of an atom

How to work out the number of neutrons in an atom

mass number - atomic number

What is an isotope?

Atoms of the same element with a different mass number
- same number of protons and electrons but different number of neutrons

Relative atomic mass definition

the average mass of all atoms of an element relative to 1/12 the mass of an atom of carbon 12

Relative atomic mass formula

(isotope abundance x isotope mass number) + (isotope abundance x isotope mass number) / 100

Relative formula mass (ionic)/relative molecular mass (covalent) - Mr

The sum of the relative atomic masses of the elements

How to calculate percentage composition

Ar/total Mr x 100

relative isotopic mass

The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12.

Avogadro's constant

6.02 x 10^23

How to calculate percentage yield

actual yield/theoretical yield x 100

Atomic orbital

A region of space in an atom where there is a high probability of finding an electron

Shape of an s orbital

sphere

shape of p orbital

dumbbell

Covalent bonding

the sharing of electron pairs between atoms

What elements does covalent bonding involve?

non-metals

Properties of simple covalent molecules

- have a low melting and boiling point due to weak intermolecular forces/electrostatic attractions between molecules meaning they only require a small amount of energy to break
- do not conduct electricity as have no delocalised electrons or ions
- are insoluble in water as are non-polar

Properties of covalent networks

- very high melting and boiling points because of the strong covalent bonds (intramolecular electrostatic attractions) between atoms that need to be broken - require a lot of energy to break
- do not conduct electricity as have no delocalised electrons or ions
- are insoluble in water as are non-polar

What is a dative covalent bond?

A covalent bond in which a both bonding electrons come from the same atom

ionic bonding

electrons are transferred from one type of atom to another

What type of atoms are involved in ionic bonding?

metal and non-metal

Drawing an ionic lattice

- + are smaller because they have the same number of protons holding fewer electrons so attraction from the nucleus to the e-s is stronger
- always add a key stating which ions are what element
- always state that there are layers above and below (as it is a 3D structure)

properties of ionic compounds

- high melting and boiling points due to strong electrostatic attractions between opposite ions which require a vast amount of energy to break
- most are soluble in water as the charged ions can form strong attractions with water molecules
- can conduct electricity when molten or in solution as ions are then free to move and carry charge

Are any elements ionic?

no as there needs to be both a positive and negative ion

When is ionic bonding strongest?

- when ions have a greater charge because electrostatic attractions are stronger when the ions have a greater charge
- when the ions are small because the opposite ions would be closer together in the lattice

Metallic bonding

- the metal atoms lose their outer shell electrons, becoming positive ions
- the donated electrons form a sea of delocalised electrons surrounding the lattice of positive ions

Drawing a metallic diagram

Properties of metals

- high melting and boiling points due to strong electrostatic attractions between the positive ions and delocalised electrons that require a lot of energy to break
- can conduct electricity as the delocalised electrons are mobile/free and can carry charge through the structure

Why do group 2 metals have a higher m.p/b.p than the corresponding group 1 metal?

metallic bonding is stronger in group 2 because each atom has 2 outer shell electrons to donate to the sea of delocalised electrons, giving 2+ ions, and meaning there are more delocalised electrons so the electrostatic attractions are stronger

The trend of melting and boiling points across the periodic table

Melting and boiling points increase going from 1 to 4 then fall dramatically due to the type of bonding and structure of each element

Why do m.p/b.p increase from group 1 to 3

beach metallic bonding gets stronger the more outer shell electrons there are to donate to the sea hence more positively charged ions in the lattice

The trend going down group 1 and 2

Both get more reactive because it becomes easier for the atoms to lose their outer shell electrons
- more shells meaning the outer electrons are more shielded by the inner shells meaning weaker attraction
- bigger atom meaning the outer electrons are further away from the nucleus resulting in a weaker attraction

Reaction of group 2 elements with water

form a metal hydroxide and hydrogen gas
group 2 metal + water -\> metal hydroxide + hydrogen

Observations of the reaction of group 2 elements with water

- bubbles of gas
- metal dissolves
- cloudy solution

Trend of reactions with water in group 2

going down the group the reaction gets more vigorous
Mg - almost no reaction to cold water
Ca - steady bubbles
Sr - faster
Ba - even faster

Reaction of group 2 elements with oxygen

forms a metal oxide
group 2 metal + oxygen -\> metal oxide

Solubility of group 2 oxides and hydroxides down the group

solubility increases

pH of group 2 oxides and hydroxides down the group

pH increases (more alkaline)

Effect of heat on group 2 carbonates

- decompose when heated giving a solid metal oxide and carbon dioxide gas
- THERMAL DECOMPOSITION

Observations of thermal decomposition of group 2 carbonates

- end with a white solid
- when gas is bubbled through limewater it turns cloudy

Trend in thermal stability of group 2 carbonates

get more thermal stable (increases) down the group - more heat needed to decompose them
- going down the group the cations all have the same charge (2+) but they get bigger in size (more shells) so their charge density is decreasing making it harder to polarise the negative charge cloud of the carbonate ion so is therefore harder to break when heating (requires more energy)

Trend in solubility of group 2 carbonates

Decreases down the group

First ionisation enthalpy definition

the energy needed to remove one electron from every atom in one mole of separate, gaseous atoms of the element

General equation for the first ionisation enthalpy

x(g) -\> x+(g) + e-

Trend of ionisation enthalpy across a period

- generally increase
- going across a period, more protons are being added to the nucleus. The atoms also have more electrons but going into the same shell so don't shield each other from the extra positive charge in the nucleus so the outer electrons are attracted more strongly by the nucleus hence more energy is required to remove one

Why is there a dramatic decrease in first ionisation enthalpies from Ne-\>Na

There is one more proton in the nucleus but the outer electron is in the next shell out so much further from the nucleus and much more shielded so requires less energy to lose

Trend of ionisation enthalpy down a group

- decreases
- going down a group, each atom has more protons in its nucleus but there is an extra shell of electrons each time which shields the outer electrons from its nuclear charge and the outer electron is also therefore further away from the nucleus so the overall attraction from the nucleus is weaker hence less energy is needed to remove the electron

Trend in successive ionisation enthalpies

- increase each time
- once an electron has been removed from an atom the same number of protons in the nucleus are holding fewer remaining electrons so the remaining electrons are pulled in tighter and therefore the next electron required more energy to remove.

Why are there sharp jumps in successive ionisation enthalpies

The electron is being taken from the next shell in so the electron is much closer to the nucleus and is less shielded by inner shells so the attraction is stronger by the nucleus to the electron which requires more energy to break

Second ionisation enthalpy equation

x+(g) -\> x2+(g) + e-

hydrochloric acid

HCl

Nitric acid

HNO3

Sulfuric Acid

H2SO4

Reaction of group 2 oxides with water

form a metal hydroxide

Reaction of group 2 oxides with acid

salt + water

Reaction of group 2 hydroxides with acid

salt + water

Electromagnetic spectrum

- radio waves
- microwaves
- infared
- visible light
- ultraviolet
- x-rays
- gamma rays

Trend in electromagnetic spectrum

increases in frequency and decreases in wavelength going along (towards gamma rays)
- more energy going along

Absorption spectrum

black lines (where light has been absorbed) on a bright, coloured background

Explain the origin of lines in an absorption spectrum

an electron can be promoted to higher energy levels by taking in (absorbing) energy (the atom becomes excited and electrons can gain energy to then be promoted) - if white light containing all waves of energy is shone at the atom, it will absorb the light wave with the frequency given by "change in energy \= hv" and this wave will be missing when displayed as a spectrum so black lines will form at that frequency

Explaining a spectrum

- each atom/element gives a unique spectrum because they have different energy levels
- lines converge at high frequencies because energy levels get closer together at higher energies

Emission spectrum

Bright, coloured lines on a black background

Explaining emission spectrum

electrons exist in fixed energy levels. when atoms are given energy the get excited and electrons are promoted to higher energy levels. when they jump back down they emit the energy difference as light of a specific frequency according to "change in energy\=hv". each element gives a unique spectrum because they have different energy levels. the emission spectrum is bright coloured lines on a black background . there are sets of lines each representing a jump to one particular energy level. the lines converge at higher frequencies because the energy levels get closer together at higher energies.

Similarities and differences between emission and absorption spectrums

Similarities:
- both are line spectra
- lines in same position for a given element
- lines become closer (converge) at higher frequencies
- series of lines represent transitions to or from a particular energy level

differences:
- bright lines vs black lines

Flame colour of lithium

red

Flame colour of sodium

yellow

Flame colour of potassium

lilac

Flame colour of calcium

Brick red

Flame colour of barium

Apple green

Flame colour of copper

blue-green

What is a fusion reaction?

when 2 lighter nuclei join together to give a new, heavier nucleus (under conditions of high temperature and pressure)

Protons and neutrons in fusion reactions

1 1 1
1 P or 1 H 0 N

How to answer a melting point question

- type of bonding/structure
- which bonds are being broken
- strength of bonds
- energy required to break the bonds

How to answer an ionisation enthalpy/energy question
Which is higher?

- outer electron - distance from the nucleus and how many shells
- shielding - less or more
- attraction between outer electron and nucleus
- energy required to remove outer electron

Experiment to find the number of water of crystallisation molecules in a formula of hydrated salt

- weigh an empty crucible
- add known mass and weigh crucible and hydrated solid together
- heat crucible until it reaches a constant mass (all has reacted)
- weigh to find out mass of anhydrous solid left
- calculate the mass
The mass of water lost (subtract anhydrous from start mass)
- moles \= mass/mr
- find ratio

How to know when all water of crystallisation has been driven off

when mass remains unchanged (heat to a constant mass)

Empirical formula

shows the simplest ratio of atoms of each element present in a compound

Molecular formula

shows the actual number of each type of atom present in a molecule

How to prepare a solution

- weigh out solid
- dissolve in approx 50 cm^2 of distilled water in a small beaker (rinse weighing apparatus and add rinsings to ensure all the weighed solid is in the beaker
- use a funnel to transfer solution to a 250 cm^2 volumetric flask
- rinse beaker and add rinsings
- add water until bottom of meniscus is on the line at eye level
- mix solution by inverting volumetric flask several times

Experiment to compare the thermal stability of group 2 carbonates

- Magnesium carbonate is heated and the gas given off passes down a delivery tube and is bubbled through limewater. ​
This is repeated for calcium carbonate using same​
moles (NOT mass)​,
heating conditions​ and amount of limewater

OBSERVATIONS:
In both cases the limewater would go cloudy​
MgCO3 is least thermally stable so the limewater would turn cloudy more quickly than with the CaCO3. ​