Please enable JavaScript.
Coggle requires JavaScript to display documents.
CHEMISTRY CHAPTER TWO: Atoms; structure and mass (2.3: ISOTOPES (Relative…
CHEMISTRY CHAPTER TWO: Atoms; structure and mass
2.1 ATOMIC THEORY
Subatomic particles
protons
positively charged
part of the nucleus in the middle of an atom
neutrons
neutral - no charge
part of the nucleus in the middle of an atom
electrons
negatively charged
surround the nucleus of an atom in shell-like layers of different levels of energy
electrons keep bound together in their atom because of electrostatic attraction to the atom's nucleus
electrostatic attraction = attraction of positive and negative particles
2.2: DESCRIBING ATOMS
Elements
elements are made up of just one type of atom
organised in the periodic table
in the periodic table, LEFT TO RIGHT:
radius size decreases
electronegativity increases
in the periodic table TOP TO BOTTOM:
radius size increases
first ionising energy decreases
each is given a chemical symbol and some representative numbers
atomic number: the number of protons (therefore also the number of electrons because no. of p= no. of e
mass number: the number of protons and neutrons of the atom
2.3: ISOTOPES
isotopes are defined as atoms that have the same number of protons but different number of neutrons
isotopes have identical chemical properties (because neutrons are neutral) but different physical properties such as mass and density
some isotopes that have a significantly different amount of protons and neutrons are unstable and thus radioactive
these isotopes undergo radioactive decay by emitting various forms of radiation and turn into lighter, more stable nuclei
Relative Atomic Mass
relative isotopic mass(isotope 1) x (relative abundance/100)=a
relative isotopic mass(isotope 2) x (relative abundance/100)=b
a+b (plus anymore if there are any other isotopes, so the abundance adds up to 100) = relative atomic mass
given the symbol Ar
2.4: MASS SPECTROMETRY
Mass spectrometer
invented by Francis Aston in 1919
has 3 steps
1: the sample is vaporised and then ionised using high-energy electrons
2: ions are separated and accelerated according to their mass to charge ratios in an electric/magnetic field
3: ions with a particular mass to charge ratio are detected by a device that counts the number of ions that strike it
info obtained from a mass spectrometer is presented on a graph called a
mass spectrum
to find the percentage abundance of each isotope from the mass spectrum
1: measure the peak height of each isotope
2: find the total peak height by adding them all up
3: substitute the heights into this
%abundance = peak height / total peak height x 100
a technique used to measure the mass of atoms and molecules
can be used to find relative isotopic mass of elements and their isotopic abundances