M2.2 + M2.3

M2.2 Atoms, ions and compounds M2.3 Amount of substance

define Isotopes

Atoms of an element with the same atomic number (protons) but with a different number of neutrons, resulting in a different mass number.

chemical properties/ chemical reactions of isotopes

• number of neutrons has no effect on reactions of an element

• different isotopes of an element react in the same way

• chemical reactions involve the electrons surrounding the nucleus

how are physical properties of isotopes affected?

• may be small differences in physical properties

• higher-mass isotopes have higher

  • m.p

  • b.p

  • density

why do neutral atoms of isotopes of an element have identical chemical properties?

isotopes of an element have the same number of protons and electron configuration is the same.

why do neutral atoms of isotopes of an element have different physical properties?

due to their different mass numbers

how can u calculate the maximum number of orbiting electrons that can be held by a single shell

depends on the number of the shell (the period)

(n is number of shell)

calculate using: 2n²

Define relative isotopic mass

The mean mass of 1 mole of atoms of an isotope compared to 1/12th the mass of 1 mole of carbon-12 atoms.

Define relative atomic mass

The weighted mean mass of an atom of an element compared to 1/12th the mass of one mole of carbon-12 atoms.

Define Relative molecular mass

The weighted mean mass per mole of molecules compared to 1/12th the mass of 1 mole of carbon-12 atoms.

Define Relative formula mass

The weighted mean mass per mole of one formula unit compared to 1/12th the mass of 1 mole of carbon-12 atoms.

how to calculate Mr

the sum of all of the atomic masses of each element present in the formula

what is relative atomic mass used for?

for an atom e.g (Na) and ion (Na+)

what is Relative molecular mass used for?

For simple molecules

what is Relative formula mass used for?

for compounds with giant structures

Define Mass number

The number of protons and neutrons in the nucleus.

Define Atomic number

The number of protons in the nucleus (also equal to the number of electrons in an atom)

Define m/z

mass-to-charge ratio

mass of each ion divided by charge

what is mass spectrometry

Analytical technique used to measure the m/z ratio of molecules present in a sample

what can mass spectrometry be used for?

• used to calculate the exact molecular mass of sample content

• find the overall relative

  • isotopic mass of the isotope

  • relative abundance of the isotope

what does a mass spectrum show?

Each peak shows a component of unique m/z in the sample,

and Heights of the peaks connote the relative abundance of the various components in the sample.

y axis- perecntage abundance

x axis- m/z ratio

how to calculate RAM (relative atomic mass)

∑ (mass x abundance) / 100

define ion

• charged particle/ group of particles

• number of electrons is different to the number of protons

• due to loss or gain (transfer) of electrons

define cation

• positively charged ion

• fewer electrons than protons

define anion

• negatively charged ion

• more electrons than protons

define binary compound

contains two elements only

define polyatomic ion

• an ion containing

• atoms of more than one element bonded together

formula of the small molecule of phosphorus which it naturally exists as

P₄

formula of the small molecule Sulfur which it naturally exists as

S8

how to write ionic equation

1. write the balanced formula, with state symbols

2. re-write any aqueous, ionic species as separate ions

3. cancel out spectator ions

4. this is the ionic equation

define solubility

measure of the maximum mass that will dissolve in a given volume of solvent at a particular temperature.

define precipitate

an insoluble solid product that forms when two solutions are mixed and react together.

common ionic salts- soluble

• group 1

• ammonium NH₄⁺

• nitrate NO3-

• group 7 (w/ exceptions)

• sulfate SO₄²- (w/ exceptions)

• ONLY hydroxides of: NH₄⁺, Li⁺, Na+, K+

is hydroxide soluble?

no

exceptions of soluble compounds with OH-

NH₄⁺, Li⁺, Na+, K+

are group 1 metals soluble

yes

are group 7 elements soluble

yes

exceptions of insoluble group 7 salts

insoluble

Ag+, Pb²⁺, (Hg2)²⁺

exceptions of insoluble sulfates

insoluble

Ba²⁺, Ca²⁺, Pb²⁺, Ag+, Sr²⁺

define Amount of substance (n)

the number of particles in a substance

define mole

• (mol) unit the amount of substance is measured in

• 1 mole contains exactly 6.022×10²³ particles

• number of particles in exactly 12.00g of C-12

how to calculate moles and mass

n = m/M

define Avogadro’s constant, N_A

• the number of particles that make up 1 mole of a substance =6.022×10²³ mol^-1

define Molar mass, M

Mass per mole of a substance in (g mol^-1)

how to calculate M

sum of atomic masses

define Molar gas volume

Volume per mole of gas molecules in (dm³ mol^-1 ) at RTP

define empirical formula

simplest whole number ratio of atoms of each element in a compound

determined by mass or % composition

define molecular formula

the number and type of atoms of each element in a molecule

molecular formula Sulfur

S8

molecular formula Phosphorus

P4

define anhydrous

containing no water molecules

define hydrated

a crystalline compound containing water molecules

water of crystallisation

• water molecules that are bonded into a crystalline structure of a compound

• represented with a large dot

assumptions of experimental formula in hydrated salts

1. all of the water has been lost

2. no further decomposition

how to deal with assumption 1. and ensure all water is lost

heat to constant mass, repeatedly reheat crystals until mass of residue is unchanged » suggests all water removed

define concentration

• the amount of particles in a fixed volume

• measured in

  • mol dm^-3

  • g dm^-3

concentration equation (moles)

c = n/V (dm³)

concentration equation (mass)

c = m/V (dm³)

define standard solution

solution of known concentration

how to prepare standard solution

dissolving an exact mass of solute in a solvent

then making up the solution to an exact volume

define molar gas volume (V_m)

the volume per moles of gas molecules at a stated temperature and pressure.

values of RTP

20°C and 101 kPa

V_m at RTP

24 dm³

why is V_m 24dm³ at RTP

at RTP 1 mole of gas has a volume of approx 24dm³

moles of gas equation @ RTP

n= V (dm³)/ V_{m (dm³)}

when is the ideal gas equation used?

when gases are not at RTP

the ideal gas equation

pV= nRT

worded ideal gas euqation

pressure x volume = No.moles x gas constant x temperature

(Pa) x (m³) = (mol) x 8.31 (J mol^-1 K^-1 ) x k

assumptions made for molecules making up an ideal gas

• random motion

• elastic collisions

• negligible size

• no intermolecular forces

universal/ perfect gas constant value

8.31 J mol^-1 K^-1

8.31446261815324 J mol^-1 K^-1

value of absolute zero

-273°C

convert from °C to K

+273

define stoichiometry

the ratio of amount, in moles, of each substance in a chemical equation

percentage yield equation

% yield = Actual yield/ theoretical yield

using moles to calculate (% yield)

• must convert mass to moles

• much more precise

• as cannot directly compare masses of different substances

define theoretical yield

maximum possible amount of product if all reactants are converted to products

why is theoretical yield difficult to achieve

• losses during the practical (transfer to apparatus/ during purification)

• unwanted by-products forming (side reaction)

• reversible reaction may take place

• incomplete reactions

how to improve yield of a reaction

• change the way you make a product

• change the apparatus

• optimise reaction conditions

define limiting reagent

• the reactant which is not in excess

• will be completely used up first and stop the reaction

atom economy equation

A.E = Mr of desired product/ Mr of all reactants x 100

Why is high atom economy important?

• industrial processes are more efficient, sustainable, economically viable

• preserves raw materials

• reduces waste and pollution

other than A.E and %yield what else should be considered for sustainable industrial reactions

• costs for obtaining starting materials

• energy used for obtaining reactants

• if reaction has both a high A.E and also a high %yield

moles equation

amount in moles (n) = mass/ Molar mass

concentration equation

C = moles/ volume

(mol dm^-3)

define molar gas volume

volume occupied by 1 mole of any gas at RTP

molar gas volume value

24dm³

24 L

24000 cm³

worded equation linking moles of gas with molar gas volume

n, moles (mol) = volume (dm³) / 24 dm³

equation linking moles of gas with molar gas volume

n = V x 24

formula: nitrate

NO3-

formula sulfate

SO₄²-

formula: carbonate

CO₃²⁻

formula: hydroxide

OH¯

formula: ammonium

NH4⁺

formula: zinc

Zn²⁺

formula: silver

Ag⁺

determining formula of hydrated salt

1. calculate moles of anhydrous salt

2. calculate mass and moles of water

3. find smallest whole number molar ratio to find value of X

define standard solution

solution of known concentration

how can you prepare a standard solution?

dissolving a known mass of solid in a solvent and making it up to a known volume.

how to convert from g/dm³ to mol/dm³

÷Mr

how to convert from mol/dm³ to g/dm³

xMr

ml to cm³

1ml = 1cm³

dm³ to l

1l = 1dm³