OCR F331 Elements of Life

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Chemistry for Life: Elements of Life
Formulae, Equations and Amount of Substance
(a) Explain and use the terms:
Atomic number The number of protons in the nucleus
Isotope Different forms of the same element, which have different mass numbers (same
number of protons but a different number of neutrons)
Avogradro Constant
6.02 x 1023 the number of particles in 1 mole of a substance
Relative Isotope Mass The mass of an atom of an isotope of an element (taking into account their
abundances) relative to carbon12
(atomic mass of isotope x abundance) = Relative Isotope Mass
100
Relative Atomic Mass (Ar)
The average mass of an atom of an element relative to carbon12
Relative Formula Mass (M r)
The average mass of a molecule or formula unit relative to carbon12 (Add up the
relative atomic mass values of all the atoms in the molecule)
Relative Molecular Mass The average mass of a molecule or formula unit relative to carbon12 (Add up the
(M r)
relative atomic mass values of all the atoms in the molecule)
(b) Use the concept of amount of substance to perform calculations involving:
Masses of Substances Number of Moles = Mass of Substance
Molar Mass
Number of Moles = Concentration x Volume in dm3
Number of Moles = Number of particles you have
23
Number of particles in a mole (6.02 x 10 )
Empirical and Molecular Empirical Formula:
Formulae 1. List all the elements in the compound
2. Underneath them, write their masses
3. Divide each mass by their molar mass to find how moles there are
4. Divide each mole by the smallest mole this is your ratio
5. Make the ratio into the simplest form this is your empirical formula
Finding the Molecular Formula from Empirical Formula:
1. Find the mass of the overall compound
2. Find the relative atomic mass of the compound using the empirical
formula
3. Calculate how many times more the mass is than the relative atomic
mass and multiply all the empirical formula elements by it
(c) Write and interpret balanced chemical equations including
state symbols
Atomic Structure
(d) Describe protons, neutrons and electrons in terms of their mass and relative charge

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Chemistry for Life: Elements of Life
Mass Charge Where?
Proton 1 +1 Nucleus
Neutron 1 0 Nucleus
Electron 0.…read more

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Chemistry for Life: Elements of Life
(h) Recall that the nuclei of some atoms are unstable and that these atoms are radioactive; recall and explain
the different properties of , , radiations; recall that the term halflife refers to the time taken for half
the radioactive nuclei in a sample to decay and that the halflife is fixed for any given isotope; carry out halflife
calculations
If an atom is unstabl e, it will break down to become stable.…read more

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Chemistry for Life: Elements of Life
4. When the hydrogen in a star's core runs out, the temperature and pressure of the core starts to rise. In a big
enough star it'll get hot enough to fuse heavier elements , starting with helium.…read more

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Chemistry for Life: Elements of Life
Bonding and Structure
(m) draw and interpret simple electron 'dotandcross' diagrams to show how atoms bond through ionic,
covalent and dative covalent bonds and be able to describe a simple model of metallic bonding; describe some
limitations of these models
What happens to electrons Atoms involved 'Dotandcross' diagram
Ionic Gains or loses electrons Between metal
Bondin Lose electron (metal) = and non metals
g positive ion
Gain electron (nonmetal)
= negative ion
Covalen Electrons are shared Between non
t…read more

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Chemistry for Life: Elements of Life
Limitations:
The dotandcross models of ionic and covalent bonding give the impression that electrons are either transferred
or shared. However most bonds aren't purely ionic or purely covalent but somewhere in between so most
compounds end up with a mixture of ionic and covalent properties.…read more

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Chemistry for Life: Elements of Life
No. of 2 3 4 3 2 5 6
Bonding
Pairs
No. of 0 0 0 1 2 0 0
Lone
Pairs
Bond
180o
120o
109.…read more

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Chemistry for Life: Elements of Life
Electrons on shells that are furthest away from
the nucleus are easier to remove because the
attraction is weaker
(q) recall that the position of an element in the Periodic Table is relative to its electron structure (main energy
levels or electron shells)
(r) describe and compare the following properties of the elements and compounds of Mg, Ca, Sr and Ba in Group
2: reactions of the elements in water, acidbase character of the oxides and hydroxides, thermal stability…read more

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Chemistry for Life: Elements of Life
M Hydroxide + Sulfuric Acid > M Sulphate + Water
e.g. Barium Hydroxide + Sulfuric Acid + Barium Sulfate + Water
M(OH)
2(aq) + H
2SO4(aq) > MSO
4(aq) + H
2O (l)
e.g. Ba(OH)2(aq) + H2
SO4(aq)
+ BaSO4(aq) +H2
O(l)
Group 2 Carbonates with Heat:
M Carbonate > M Oxide + Carbon Dioxide
e.g. Beryllium Carbonate > Beryllium Oxide + Carbon Dioxide
MCO3(s) > MO(s)
+ CO2(g)
e.g.…read more

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Chemistry for Life: Elements of Life
Mass Spectrometry can be used to calculate the relative atomic mass the height of the peaks (y axis) tells us the
abundance and the x axis (m/z) tells us the mass of each ratio.…read more

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