Atoms Flashcards
Isotopes
- Atom of the same element with a different number of neutrons.
- therefore it has a different mass number ~ different physical properties
- has the same number of protons (atomic number) and electrons ~ react chemically in the same way.
Relative atomic mass ( Ar)
The weighted mean mass of an atom of an element, relative to one twelfth of the weight of an atom of carbon-12.
Ar = (mass of each isotope x % abundance of each isotope) / 100
Relative isotopic mass
The isotopic mass of an isotope, relative to one twelfth of the mass of carbon-12.
Relative molecular mas (Mr)
The weighted mean mass of a molecule of a compound, relative to one twelfth of the mass of an atom of carbon-12.
Relative formula mass
The weighted mean mass of a formula unit compared with one twelfth of the mass of an atom of carbon-12.
Daltons theory- 1800s
- atoms are tiny particles that make up elements
- atoms cannot be divided
- all atoms of a given element are the same.
- atoms of one element are different from those of a different element.
Thompson- 1897
Discovered that cathode rays were a stream of particles and is now known as electrons.
electron properties:
- they have a negative charge
- deflected by a magnet and electric field
- very very small mass
Plum pudding model:
Atoms are made up of negative electrons moving around in a sea of positive charge.
Rutherford-1909
Fired alpha particles at a thin sheet of gold foil.
Results:
- most did not deflect at all
- small % were deflected at various angles
- very few deflected back to the source
Conclusions:
- The positive charge and most of the atoms mass is located in the centre in the nucleus.
- negative electrons orbit the nucleus
-most of the atoms volume is located in the space between the nucleus and the orbiting electrons.
- The overall positive and negative charge must balance.
Modern Day atom
- protons and neutrons are found in the nucleus
- electrons orbit the nucleus in shells
- most of the atom is empty space.
positive ions with 1+ charge
Hydrogen ~ H+
lithium ~ Li+
sodium ~ Na+
potassium ~ k+
silver ~ Ag+
ammonium ~ NH4+
copper(I) ~ cu+
positive ions with 2+ charge
Magnesium ~ mg 2+
Calcium ~ ca 2+
Barium ~ Ba 2+
Zinc ~ Zn 2+
Lead (II) ~ Pb 2+
Copper (II) ~ Cu 2+
Iron (II) ~ Fe 2+
positive ions with 3+ charge
Iron(III) ~ Fe 3+
Aluminium ~ Al 3+
Negative ions with 1- charge
Fluoride ~ f-
chloride ~ Cl-
Bromide ~ Br -
Iodide ~ I-
Hydroxide ~ OH-
Nitrate ~ NO3 -
Nitrite ~ NO2 -
Hydrogen carbonate ~HCO3 -
Manganate ~ MnO4 -
Negative ions with 2- charge
oxide ~ O2-
sulfide ~ S2-
sulfate ~ SO4 2-
Sulfite ~ SO3 2-
Carbonate ~ CO3 2-
Dichromate ~ Cr2O7 2-
Chromate ~CrO4 2-
Negative ions with 3- charge
Phosphate ~ PO3 3-
Nitride ~ N 3-
Writing formulae for compounds
- in an ionic compound the charges of the metal and non metal have to balance.
Examples:
Calcium Oxide ~ CaO
( The positive 2 charge and negative 2 charge cancel out)
Sodium Carbonate ~ Na2CO3
(Na has a +1 charge and carbonate has a 2- charge therefore 2 sodium are needed to balance the charges)
Chromium (III) oxide ~ Cr2O3
(Cr has a 3+ charge and oxide has a 2- charge, so the charges are switched)
Formation of ions in the periodic table
- metals lose electrons to form cations
- non metals gain electrons to form anions.
- Be ,B,C and Si do not form ions as the loss of their outer electrons requires too much energy.
- Transition metals except zinc and silver can form ions of different charges.
Representing elements in equations
- elements are shown as their symbol because they exist as giant structures.
- some exist as small molecules so are shown as follows:
Hydrogen ~ H2
nitrogen ~ N2
oxygen ~ O2
fluorine ~ F2
Chlorine ~ Cl2
Bromine ~ Br2
Iodine ~ I2
Phosphorus ~ P4
Mass spectrometry
- used to identify the abundance of isotopes of elements and the structure of unknown compounds.
Uses:
- monitoring the breath of anaesthetised patients during surgery
- detecting banned substances in athletes
- analysing compounds in space
How it works:
- inject the sample
- the sample is ionised as a gas
- electrons are fired at the sample to turn the atoms into positively charged ions.
- the sample is accelerated into magnetic field using positively charge plates
- the magnetic field deflects and separates ions based on their m/z value(all the relative isotopic masses of the element)
- the lighter the isotope, the more it is deflected
interpreting a mass spectrum
x axis ~m/z ratio
(the ratio of the mass of each ion to its charge)
y axis ~ relative abundance (%)
why is the term RELATIVE used?
We want to know how much HEAVIER one subatomic particle is COMPARED with another .
OR
What the CHARGE of one subatomic particle is COMPARED to another.
We are not concerned with ACTUAL masses or charges.
The atom : 1913-1932
1913 ~ Neils Bohr
- Electrons orbit the nucleus in shells.
- Helped to explain the energy of electrons at different distances from the nucleus
1918 ~ Rutherford
Discovered the proton
1932 ~ James Chadwick
Discovered the neutron.
Subatomic particle masses and charges
Proton:
charge ~ 1+
mass~ 1
Electron :
charge ~ 1-
mass ~ 1/2000
Neutron :
Charge ~ 0
Mass ~ 1
