atoms, molecules and ions chapter 2. properties of the electron, proton & neutron amu = atomic...
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Properties of the Electron, Proton & NeutronProperties of the Electron, Proton & Neutron
amu = atomic mass units
1 amu = 1.66x10-24 g
Mass of carbon-12 = 12 amu
The Modern View of Atomic Structure
The nucleus of an atom has a structure– It is composed of protons and neutrons
The proton a nuclear particle positive charge equal to that of the
electron mass more that 1800 times that of the
electron.
The neutron a nuclear particle having a mass almost identical to that
of the proton but no electric charge.
Atomic number (Z) = number of protons in the nucleus of an atom.
Isotopes, Atomic Numbersand Mass Numbers
Mass number (A) = the total number of protons and neutrons in a nucleus.
An element is a substance whose atoms all have the same atomic number.
Nuclide symbols
You write the nuclide symbol for the naturally occurring sodium nuclide as follows:
Na23
11
Mass number
Atomic number
A nuclide is an atom characterised by a definite atomic and mass number.
Periodic table of the elements
A tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements.
Mendelev
Molecules and Molecular Compounds
A molecule is a definite group of atoms that are chemically bonded together - that is tightly connected by attractive forces.
Molecular compounds compounds that consist of molecules
The chemical formula of a substance is a notation that uses atomic symbols with numeric subscripts to convey the relative proportions of atoms of the different elements in the substance.
eg. Alumina = Al2O3
Salt = NaCl
Ethanol = C2H6O
A molecular formula gives the exact number of different atoms of an element in a molecule
eg. Ethanol = C2H6O
Polymers are very large molecules that are made up of a number of smaller molecules repeatedly linked together.
Monomers are the small molecules that are linked together to form the polymer
... ...
H3C CH2 CH2 CH3( )n
e.g. ethylene to polyethylene
Ions and Ionic Compounds Not all substances are molecular, some are made up of ions.
An ion is an electrically charged particle obtained from an atom or chemically bonded group of atoms by adding or removing electrons.
Anion - a negatively charged ion
Cation - a positively charged ion
An ionic compound is a compound composed of cations and anions, eg NaCl
The empirical formula of a substance is the relative number of atoms or ions symbolized in the formula.
Use the smallest set of integers to express the correct ratios of atoms present.
Eg. Consider hydrogen peroxide:
Molecular formula = H2O2
Empirical formula =