2 - Atoms, Ions and compounds Flashcards
Define isotope
atoms of the same element with different numbers of neutrons and different masses.
// most elements are mixtures of isotopes
Mass of subatomic particles
Relative mass is used since subatomic particles have tiny masses.
Proton mass ~~ neutron mass
electrons have negligible mass
Proton = 1
Neutron = 1
Electron = 1/1836th mass of a proton
Charge of subatomic particles
Proton = +ve || +1
Neutron = neutral, no charge || 0
electron = -ve || -1
charge of proton is equal but opposite to charge of electron, so charges are balanced. Relative charges used.
proton actual charge = 1.6 x 10^-19C
electron actual charge = -1.6 x 10^-19C
Define atomic number
Number of protons in the nucleus of an atom.
Define mass number
The sum of the number of protons and neutrons in the nucleus - also known as nucleon number
Describe the atomic structure of atoms
Most of the atoms mass is in the nucleus. Nucleus contains neutrons and protons.
Atoms have the same number of protons and electrons, so total positive charge is cancelled by total negative charge of electrons. Overall atom is neutral.
Electrons are in shells around the nucleus.
Role of neutrons?
Neutrons can be thought of as providing the glue that holds the nucleus together despite electrostatic repulsion between the positively charged protons.
Most atoms contain same/ more neutrons than protons.
As the nucleus gets larger more neutrons are needed.
Define ion // atomic structure of ions
A charged atom or covalently bonded group of atoms where number of electrons is not equal to the number of protons.
Positive ions = CATIONS . Fewer electrons
Negative ions = ANIONS. More electrons
Chemical and physical properties of isotopes
Chemical properties depend on electrons -> number of neutrons = no effect on reactions of an element -> different isotopes of an element react similarly.
Isotopes may differ in physical properties - high MP, BP, density.
Define relative atomic mass
Weighted mean mass of an atom compared with 1/12th the mass of an atom of carbon-12
Define relative isotopic mass
Mass compared with 1/12th the mass of a carbon-12 atom
When is mass spectrometry used
- For determination of relative isotopic masses and relative abundances of the isotope
- for calculation of relative atomic mass of an element from relative abundance’s of its isotopes
Relative molecular mass vs relative formula mass
For simple molecules, relative molecular mass used
For compounds with giant structures, relative formula mass used
Nitrate ion
NO3 -
Carbonate ion
CO3 2-
Sulfate ion
SO4 2-
Hydroxide ion
OH-
Ammonium ion
NH4 +
Zinc ion
Zn 2+
Silver ion
Ag +
Nitrite ion
NO2 -
Hydrogencarbonate ion
HCO3 -
manganate (VII) (permanganate) ion
MnO4 -
Sulfite ion
SO3 2-
dichromate (VI) ion
Cr2O7 2-
phosphate ion
PO4 3-
Binary compound
Contains 2 elements only
Are nitrates soluble
Yes
Are chlorides soluble
Yes, except AgCl and PbCl2
Are Sulfates soluble
Yes, except BaSO4, PbSO4, SrSO4
Are carbonates soluble?
No, except Group1 x NH4 +
Metal + acid = ?
Metal + acid = salt + hydrogen
Metal hydroxide + acid = ?
Metal hydroxide + acid -> salt + water
Metal oxide + acid = ?
Metal oxide + acid -> salt + water
Metal carbonate + acid = ?
Metal carbonate + acid -> salt + water + carbon dioxide
How to determine relative atomic mass?
% of isotopes in sample of element can be found experimentally using mass spectrometer
- Sample placed in mass spectrometer
- Sample is vaporised
- Sample is ionised to form positive ions
- Ions are accelerated. Heavier ions move more slowly & more difficult to deflect than lighter ions, so ions if each isotope are separated.
- Ions detected on mass spectrum as mass-to-charge ratio (m/z). Each ion reaching detector adds to the signal. Greater abundance = larger signal.
mass-to-charge ratio (m/z) = relative mass of ion / relative charge on ion
