2.1 atoms and reactions

define an isotope

• isotopes are atoms of the same element with the same number of protons AND electrons but different number of neutrons

describe basic atomic structure (sub atomic particles, their relative charge and mass)

• atoms are made of sub- atomic particles- protons, neutrons and electrons

• electrons orbit the nucleus in orbitals (regiosn around the nucleus which take up most of the volume of the atom)- relative mass is 1/2000 or 1/1836. relative charge is -1

• protons and neutrons are located in the nucleus. Nucleus makes up most of the mass. protons relative charge- +1, relative mass- 1. neutrons relative charge- 0, relative mass- 1.

what is the ‘A’ symbol

mass number- number of protons and neutrons in the nucleus

what is the ‘Z’ symbol 

atomic number - the number of protons in the nucleus 

• also the number of electrons but ONLY in neutral atoms 

different isotopes of an element have the same ‘what’ number but a differet ‘what’ number

different mass number, but the same atomic number 

define an ion 

an ion is a charged atom - one that has lost or gained electrons.

• negative ions have more electrons than protons

• positive ions have more protons than electrons 

define relative atomic mass 

relative atomic mass, Ar, is the weighted mean mass of an atom of an element compared with 1/12 mass of carbon-12

• RAM takes into account the isotopes present in a sample of an element and the relative abundance of the isotopes 

  • relative atmic mass is an average- so usually not a whole number 

how can relative atomic mass be calculated 

using mass spectrometry- a mass spectrum is obtained- showing the isotopes present in a sample and their abundances. The positive ions of isotopes are shown as a mass/charge ratio, m/z. Provided that the ionic charge is +1, m/z is the same as the mass of the ion.the relative abundances show the different proportions of each isotope in the sample.

how can the relative atomic mass be calculated as a weighted mean mass

(mass no x abundance)+ (mass no x abundance) all /100

define relative isotopic mass

the mass of an atom of an isotope of an element compared with 1/12 of the mass of an atom of carbon-12

define relative formula mass 

the average mass of a formula unit, compared to 1/12 of the mass of an atom of carbon-12. 

• it’s used for giant ionic/ covalent compounds

• to find the relative formula mass just add up the Ar of all the ions in the formula unit

define relative molecular mass

the average mass of a molecule compared to 1/12 of the mass of an atom of carbon-12

• used for ismple molecular compounds eg ethene

• to find the relative molecular mass, just add up the Ar values of all the atoms in the molecule

• USES THE SYMBOL Mr

recall the formula for nitrate and carbonate

NO(3-) and CO*3(2-)

recall the formula for sulfate, hydroxide and ammonium ions

SO*4(2-) and OH(-) and NH*4(+)

recall the formula for zinc and silver ions

Zn (2+) and Ag(+)

describe the steps of writing an ionic equation

• write the formula of the reactants and the products in an unbalenced reaction  and WRITE STATE SYMBOLS 

• balence the equation 

• write out all of the ions present, only split up (aq)

• remember to take in account stoichiometry

• cancel out spectator ions 

• leaving you with your ionic equation 

define dissacociation

the process of splitting ionic compounds into their respective ions

why do we use carbon-12 as a standard for measuring relatie atomic masses (off spec- only for understanding)

Carbon-12 is chosen as the standard for atomic mass due to its stability, abundance, and the fact that its atomic mass is defined as exactly 12 atomic mass units (amu), making it a reliable reference point for measuring other elements.

one mole of a substance contains the same number of particles as there are atoms in exactly ‘-’g of ‘-’

12g of carbon-12

name avodagros constant 

6.022 × 10²³ mol^-1 - the number of particles per mol of particles 

define molar mass or Mr and units

Molar mass is the mass in grams of 1 mole of a substance and is given the unit of g mol-1

define ammount of a substance 

• Amount of substance refers to the quantity used to count particles in a substance

  • It is represented by the symbol n in equations

  • The unit of amount of substance is the mole (mol)

give the formula for an ammount of a substance/ aka mol equation

ammount,n,= mass,m/molar mass,M   or mol= mass/RAM

what is the molar mass the same as (ie what other labels)

same as relative atomic mass, relative formular mass, relative molecular mass

how to calculate the number of particles

by multiplying the ammount in moles by the avogadros constant

• ie number of particles = n(mol) x 6.02 × 10²³

• Np = n x A

define molar gas volume

This is the volume of 1 mole of a gas at a given temperature and pressure.

• All gases have this same volume. At room pressure (1atm) and room temperature 25oC

• the molar gas volume is 24 dm3 mol–

how many mg in one gram

1000 mg =1g

how many g in 1kg

1000 g =1kg 

how many kg in one tonne 

1000kg = 1 tonne

equation for molar gas volume

• vol= mol x 24 v= n x Vm

• n = number of moles of gas (mol)

• V = volume of gas (dm³)

• V_m = molar volume (dm³ mol^-1) - 24dm³ mol^-1

define empirical formula

the SIMPLEST whole number ratio of atoms of each element present in the compound- eg molecular formula of butane is C4H10 however this can be simplified to C2H5

define molecular formula

the number and TYPE of atoms in each element in a molecule eg empirical formula of butane is C2H5, molecular formula is C4H10

steps to calulate empirical formula

can be calculated from the percentage composition, by mass or mass of the elements in the compound

• find the mass and RAM then CALCULATE MOLES 

• using the moles, find the smallest value and divide all other values by this 

• you should have near whole numbers, if not then must scale up to simplest whole number ratio

what is the Mr symbol 

relative molecular mass

what are amu/u  units for

atomic masses

what is the Ar symbol

relative atomic mass

define atomic number and mass number

number of protons/electrons (only neutral atoms) ATOMIC NUMBER 

number of protons and neutrons- MASS NUMBER 

ammonia and ammonium

NH3 and NH4^+

how to calculate molecular formulae

• only found if the empirical formula and the relative molecular mass are known

• find the relative molecular mass (Mr)

• find the empirical formula mass

• Molecular mass/empirical formula mass to find a scale factor

• then multiply the empirical formula values by the scale factor to find the molecular formula

define a hydrated salt

a hydrated compound is crystalline and contains water molecules 

define anhydrous salt

an anhydrous salt has no water molcules from crystallisation 

define water of crystallisation

refers to the water molecules that are bonded into the crystalline structure of a hydrated compound

• in the formul, the ammount of water is shown after a dot

A compound has an empirical formula of CH and a molar mass of 78.0 g mol^-1.

Determine its molecular formula.

Step 1: Calculate empirical formula mass

C: 12.0 g mol^-1

H: 1.0 g mol^-1

Empirical formula mass = 12.0 + 1.0 = 13.0 g mol^-1

Step 2: Divide molecular mass by empirical formula mass

Step 3: Determine the number of empirical units per molecule

The compound contains 6 empirical units per molecule.

Step 4: Write the molecular formula

The molecular formula is C₆H₆.

name the following: CuSO4(s) and CuSO4 . 5H2O (s)

anhydrous copper (II) sulfate and hydrated copper (II) sulfate

• hydrated copper (II) sulfate contains 5 moles of water of crystallisation per mole of the hydrated salt.

The formula of a hydrated ionic compound can be experimentally determined from the mass loss on heating using the following steps:

1. Heat the hydrated salt to remove water, leaving anhydrous salt.

2. Calculate moles of water lost and anhydrous salt remaining. - via mass measure
   + Mr

3. Find the mole ratio of salt to water.

4. Express this ratio in the formula as a whole number.

describe steps for heating to a constant mass

use this to check that the water of crystallisation has been fully removed

• the hydrated salt is heated and weighed

• the salt is heated again and reweighed

• continue until the mass no longer changes

you can then assume all of the water of crystallisation has been removed

Calculate the formula of a hydrated magnesium sulfate, MgSO₄•xH₂O, given that heating 24.6 g of the hydrated salt leaves 12.0 g of anhydrous MgSO₄.

Step 1: Calculate mass of water lost

Mass of water lost = Initial mass Final mass = 24.6 - 12.0 = 12.6 g

Step 2: Calculate moles of anhydrous MgSO₄

mass/Mr 12/120.3 = 0.100 mol

Step 3: Calculate moles of water lost

mass/Mr 12.6/18 -=0.700 mol

Step 4: Determine the simplest H₂O : MgSO₄ mole ratio

H₂O : MgSO₄ = 0.700 : 0.100 = 7 : 1

x = 7

Step 5: Write the molecular formula

The molecular formula is MgSO₄•7H₂O.

describe why different isotopes of the same element react in the same way (2)

• neutrons have no impact on the chemical reactivity

• reactions only involve electrons, yet isotopes have the same number of electrons in the same arangement

how to calculate numer of neutrons

mass number - atomic number

what charge do ionic compounds have overall 

neutral 

what does (aq) mean

aqueous/ dissolved in water

under what circumstances does a percipitation reaction occur (understanding only)

two solutions containing ions are mixed to form as percipitate

what units does relative atomic mass use

none

the relative isotopic mass is the same as which number

mass number

what two assumptions are made when calculating mass number 

• contribution of the electron is neglected 

• mass of both proton and neutron is taken as 1.0 u 

uses of mass spectrometry

• identify unknown compounds

• find relative abundance of each isotope of an element

• determine structural infomation

simple explanation of how a mass spectrometer works

• the sample is made into positive ions

• pass through the apparatus and are seperated according to mass to charge ratio 

• a computer will analyse the data and produces the mass spectrum 

how is the group number related to the number of electrons 

group number = number of electrons in the outer shell 

what are molecular ions

covalently bonded atoms that lose or gain electrons

what is the equation for concentation and define the two ways of measuring concentration 

conc =   mol / vol

  volume is in dm³ 

1000cm³ = 1 dm³

• concentration is the ammount in mol of dissolved substance in 1.00 dm³ of solution 

• units is mol dm^-3 

• alternative way is the mass of dissolved substance in grams of 1 dm³ of solution. This ‘mass concentration has the units of g dm^-3

define molar gas volume and what happens to this value when temp increases or decreases

molar gas volume is the volume per mole of as gas at a stated temp and pressure

• molar gas vol increases as temp increases

• molar gas volume decreases as temp decreases 

at room temp and pressure (RTP), 1.00 mol of any gas occupies a vol of ‘-’ and has a molar gas vol of ‘-’

24 dm ³ and 24dm³ mol^-1

• the gas doesnt matter- 1 mol of any mass occupies 24 dm ³ at RTP - although the number of moles and volume are the same, the masses are different and the gases have different densities

what is the ideal gas equation and give all the units 

pV= nRT

• p = pressure in Pa

• V= volume in m³

• n = ammount (in mol)

• R = gas constant (given)= 8.314 J mol^-1 K^-1

• T = temperature (in K)

convert the units: 1kPa to Pa

1000Pa

convert C to kelvin

to convert to Kelvin, add 273

convert cm³ to metres cubed

1cm³ = 10^-6 m³ or 0.000001

convert cm³ to dm³

1cm³ = 0.001 dm ³

convert dm³ to metres³

1 dm³= 0.001m³ or 1 × 10^-3

1dm³ is the same as how many cm³ and how many litres

1000cm³ and 1 litre

what do balencing numbers show 

the ratio of the moles invloved in the chemical reaction. This ratio is called stoichiometry 

how to calculate atom economy

the percentage proportion of reactants that are converted into useful products - indicating efficiency

• atom economy = sum of molar masses desired product / sum of molar masses of all products x 100

• or RFM desired/ RFM total x100

• ALWAYS BALENCE EQUATION

Calculate the atom economy for the production of ethanol (C₂H₅OH) from the fermentation of glucose (C₆H₁₂O₆). The balanced chemical equation is:

C₆H₁₂O₆ ➔ 2C₂H₅OH + 2CO₂

Step 1: Calculate M_r of desired product

M_r of C₂H₅OH = 2(12.0) + 6(1.0) + 16.0 = 46.0

Step 2: Multiply by reaction stoichiometry

Since the equation produces 2 moles of C₂H₅OH the total M_r for C₂H₅OH = 2 × 46.0 = 92.0

Step 2: Calculate ΣM_r of all reactants

M_r of C₆H₁₂O₆ = 6(12.0) + 12(1.0) + 6(16.0) = 180.0

Step 4: Equation

% atom economy = Mr desired products/ Mr of all reactants x100

Step 5: Substitution and correct evaluation

92/ 180 ×100 = 51.1

This calculation shows that 51.1% of the reactant atoms are incorporated into the desired product, indicating a moderate atom economy for this reaction

why is the atom economy of additon reactions always 100%

because there is a single product

why is the atom economy of substitution reactions always less than 100 
%

In a substitution reaction, some atoms are substituted between reactants, generating at least two products - the desired product and an unavoidable by-product. For example, chloromethane reacts with potassium hydroxide in a substitution reaction:

CH₃Cl + KOH ➔ CH₃OH + KCl

Here the desired product is methanol, but potassium chloride is also produced as waste. The atom economy will be less than 100%.

name 3 reasons regarding the enviro importance of a high atom economy

Reactions with higher atom economies are more sustainable and better for the environment because:

• Less waste is generated, reducing disposal impacts.

• Raw materials are used more efficiently, preserving limited resources.

• Less energy intensive conditions are often required.

name 3 reasons regarding the econ importance of a high atom economy

Economic: High atom economy also has financial advantages:

• Reduced costs for separating products from waste.

• Lower raw material demands decrease expenses.

• Energy costs for heating and pressurising reactions are minimised.

give the equation for percentage yield and definition

The theoretical yield of a chemical reaction is the maximum mass of product that could be produced, assuming the reaction goes to completion with no loss of product.

• % yield = actual yield / predicted yield  x100

how to calculate theoretical yield

To calculate the theoretical yield, follow these steps:

1. Use a balanced chemical equation to find the mole ratio between reactants and products.

2. Calculate the moles of the limiting reagent present.

3. Determine the mass of product that these moles of limiting reagent could produce, using the mole ratio.

For example, in the reaction:

C₂H₅OH + [O] ➔ CH₃CHO + H₂O

The C₂H₅OH : CH₃CHO mole ratio is 1 : 1.

So if 0.300 mol (13.8 g) of C₂H₅OH is present and [O] is in excess, the theoretical yield of CH₃CHO is 0.300 mol (13.2 g).

5 reasons why the actual yield is always less than the predicted

The actual yield is always lower than the theoretical yield because of several factors:

• reaction may be at equilibrium

• reactants may be impure

• side reactions could occur

• reactants or products may be left on apparatus/ when transferring

• loss of products during separation and purification

state avogadros law

under the same temp and pressure, one mole of any gas would occupy the same volume

name the ideal ways in which gases behave (5)

• they are in continuous motion 

• no intermolecular forces experienced

• exert pressure when they collide with another or the container 

• no kinetic energy is lost in collisions 

• when temp increases, kinetic energy of the gases also increases

(not sure if need to know) 1 atmos pressure is equal to how many pascal

1 atm= 101325 Pa

does 100% yield mean 100% atom economy 

no because even if all the reactants are converted into products, not all the products of the reaction will be the required products

define element

a group of atoms which have the same number of protons