A LEVEL CHEMISTRY - 2.1 - ATOMS AND REACTIONS

explain the current model of the atom

• small, dense central nucleus

• electrons orbit in shells

• discovered in the Rutherford scattering experiment

what does the nucleus contain?

protons and neutrons

relative masses of p / n / e

1 / 1 / 1/2000

relative charges of p / n / e

+1 / 0 / -1

what is the atomic number?

the number of protons in an atom

another name for atomic number

proton number

what letter is the atomic number represented by?

Z

what is the mass number?

the sum of protons and neutrons in an atom

what letter is the mass number represented by?

A

what is an ion?

• formed when an atom loses or gains electrons

• have an overall charge

calculate number of electrons in an ion

(number of protons) - (ionic charge)

what is an isotope?

• atoms of the same atomic number but a different mass number

• same number of protons, different number of neutrons

• different physical properties due to different mass number

why do different isotopes of the same element react in the same way

they have the same number of electrons and same electron structure

relative atomic mass (Ar)

the weighted mean mass of an atom of an element, relative to one twelfth of the mean mass of an atom of the carbon-12 isotope

Ar takes the relative _ of the different isotopes of an element into account

abundances

Ar equation

mean mass of an atom of an element / (1/2 x mean mass of C-12 isotope)

relative isotopic mass

the mass of an isotope relative to one twelfth of the mean mass of an atom of the carbon-12 isotope

relative molecular mass (Mr)

the weighted mean mass of a molecule of a compound relative to one twelfth of the mean mass of an atom of the carbon-12 isotope

calculating Mr

add the Ar values of the elements together

relative formula mass

similar to Mr but used for compounds with giant structures

mass spectrometry

used to identify different isotopes and find the relative atomic mass of an element

what type of technique is mass spectrometry?

analytical

Time of flight (TOF) mass spectrometry

• records the time it takes for ions of each isotope to reach a detector

• spectra can be produced showing each isotope present

• the signals reflect the abundances of the isotope present

calculate Ar from a spectra

sum of (m/z x abundance) / total abundance

Ionic bonding occurs between…

A metal and non metal

Nitrate ion

NO3-

Sulfate ion

SO4 2-

Carbonate ion

CO3 2-

Hydroxide ion

OH-

Ammonium ion

NH4+

Calculate number of particles

Moles x avogadro constant

Molar mass

Mass per mole

Molar mass unit

gmol-1

Molar gas volume

Gas volume per mole

Molar gas volume unit

dm3mol-1

Empirical formula

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

Molecular formula

The number and type of atoms of each element in a molecule - the number of each atom in the molecule

Water of crystallisation

• Water that is part of the crystalline structure

• The molecules are stoichiometrically chemically bonded into the crystal structure

An anhydrous substance …

Contains no water of crystallisation

A hydrated substance …

Contains water of crystallisation

Standard solution

A solution of known concentration

Limiting reagent

• The reactant that is not in excess

• Used up first and causes the reaction to stop

Trends of gases and volatile liquids under standard conditions

• pressure is proportional to temperature

• Volume is proportional to temperature

• Pressure and volume are inversely proportional

Ideal gas equation

pV = nRT = mRT/Mr

What does R represent

The ideal gas constant

Percentage yield equation

(Experimental mass/theoretical mass) x 100

Atom economy equation

(Mr desired product/Mr reactants) x 100

Acid

Releases H+ ions in aqueous solution

Alkali

• water soluble base

• Releases OH- ions in aqueous solution

Strong acid

Fully disassociates in aqueous solution

Weak acid

Partially dissociates in aqueous solution

Neutralisation

The reaction of an acid with a base

Neutralisation ionic equation

H+ (aq) + OH- (aq) → H2O (l)

Acid + carbonate →

Salt + water + carbon dioxide

Acid + metal oxide →

Salt + water

Oxidation number

Gives the oxidation state of an element of ionic substance

Oxidation number of an element

0

Oxidation numbers of a neutral compound

Add up to 0

Oxidation numbers in a charged compound

Add up to the total charge

Hydrogen oxidation number

+1

Oxygen oxidation number

-2

Halogens oxidation number

-1

Group 1 metals oxidation number

+1

In metal hydrides, oxidation number of hydrogen is

-1

In peroxides, the oxidation number of oxygen is

-1

Oxidation

• loss of electrons

• Oxidation number becomes more positive

Reduction

• gain of electrons

• Oxidation number becomes more negative

Redox reactions

Oxidation and reduction happen simultaneously in a reaction

Oxidising agent

• accepts electrons from the species that is being oxidised

• Gains electrons

• Reduced

• Oxidation number gets less positive

Reducing agent

• donates electrons to the species being reduced

• Loses electrons

• Oxidised

• Oxidation number gets more positive

Disproportionate reaction

• In a disproportionate reaction, a species is both oxidised and reduced

Metal + acid →

Salt + hydrogen