chemistry LVI - atoms and equations

atomic/proton number

the number of protons in the nucleus of an atom

mass number

the sum of the number of protons and neutrons in the nucleus

isotopes

atoms of the same element with different number of neutrons and different masses

relative atomic mass

the weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon 12

relative isotopic mass

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

amu

atomic mass unit

relative molecular mass

the weighted mean mass of a molecule compared with 1/12th of the mass of an atom of carbon 12

Br has 2 isotopes (79, 81) what are the 3 forms of a bromine molecule

Br 160 = most probable, Br 158, Br 162

relative formula mass

the weighted mean mass of a formula unit compared with 1/12th of the mass of an atom of carbon 12

how does a mass spectrometer work

• ionisation- atom is ionised by knocking electrons off (creating positive ions)

• acceleration- ions are accelerated so that they all have the same KE

• deflection - ions are deflected by a magnetic field according to their masses (the lighter the more deflected, the more the ion is charged the more it is deflected)

• detection- ions are detected electrically as Mass: charge ratio

mass to charge ration

relative mass of ion (usually just Mr)/relative charge of ion (usually just 1)

why is a mass spectrometer maintained under a high vacuum

so that the reactant cant collide with other molecules + react

oxidation

loss of electrons/gain of oxygen

reduction

gain of electrons/ loss of oxygen

oxidising agent

species that oxidises another species by removing one or more electrons. When OA reacts it is reduced

reducing agent

species that reduces another species by giving it one or more electrons. when RA reacts it is oxidised

oxidation number for uncombined element eg F₂

0

oxidation number of a simple ion (1 element) eg Na⁺

equal to its charge (+1)

group 1 elements oxidation number (when reacted)

always 1+

group 2 elements oxidation number (when reacted)

always +2

hydrogen oxidation number

+1 except when in metal hydrides eg NaH where it becomes -1

oxygen oxidation number

-2 except in peroxides (H₂O₂) when it is -1

florine oxidation number

always -1

chlorine oxidation number

usually -1 → not when it reacts with non metals eg ClF₃

in a compound the sum of oxidation numbers =

the charge

sum of oxidation numbers in combined elements

0

other elements eg N oxidation numbers

variable

MnO₄^- oxidation numbers + explain

0 = -2, Mn = +7 therefore given manganate(VII) numerals= oxidation number of variable one

CuO + H₂ → Cu + H₂O what has been oxidised/ reduced

H has been oxidised, Cu has been reduced

disproportionation

when an element is both oxidised and reduced in a Redox reaction (must occur from the same species)

Cl₂ + 2OH^- → Cl^- + ClO^- + H₂O

Cl has been reduced and oxidised (disproportionation)

use oxidation numbers to balance this equation Mn²⁺ + BiO₃^- + H⁺ → MnO₄^- + Bi³⁺+H₂O

2Mn²⁺ + 5BiO₃^- + 14H⁺ → 2MnO₄^- + 5Bi³⁺+7H₂O