Summary
Summary Chemistry Unit 1 Definitions
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Topic 1.5 Atomic structure and the periodic tableDefinitions
Nucleus
A dense region at the core of the atom which contains most of the mass of the atom
Proton
A positively charged fundamental particle (relative mass = 1, relative charge = +1) found in the nuclei of atoms
Neutron
An uncharged fundamental particle (relative mass = 1, relative charge = 0) found in the nuclei of atoms
Electron
A negatively charged fundamental particle (relative mass = 1/1840, relative charge = -1) found outside the nuclei of atoms
Atomic number
The number of protons in the nucleus of an atom
Mass number
The total number of protons and neutrons in the nucleus of an atom
Isotope
Isotopes are atoms of the same element which have the same number of protons but different numbers of neutrons
Isotopes of an element have the same atomic number but a different mass number
Nuclide
A nucleus with a specified number of protons and neutrons
Relative isotopic mass
The relative isotopic mass is the mass of one atom of that isotope divided by one twelfth of the mass of one atom of
carbon-12 ( 126 C )
Relative atomic mass (Ar)
The relative atomic mass of an element is the weighted average mass of atoms of that element divided by one twelfth of the
mass of one atom of carbon-12
Relative formula mass (Mr)
The sum of the relative atomic masses of all the atoms in the formula of a substance
Relative molecular mass (Mr)
The sum of the relative atomic masses of all the atoms in one molecule of a substance
First ionisation energy (enthalpy) (∆HIE1)
The enthalpy change (endothermic) when one mole of electrons is removed from one mole of atoms in the gas phase to
form one mole of singly charged positive ions
M(g) → M+(g) + e-
Second ionisation energy (enthalpy) (∆HIE2)
The enthalpy change (endothermic) when one mole of electrons is removed from one mole of singly charged positive ions in
the gas phase to form one mole of doubly charged positive ions
M+ (g) → M2+(g) + e-
Atomic orbital
A region of space within an atom which may be occupied by up to two electrons
s-block
The section of the periodic table in which atoms of the elements have their highest energy electron(s) in an s-subshell
p-block
The section of the periodic table in which atoms of the elements have their highest energy electron(s) in a p-subshell
i.e. Groups III to VIII (or 0)
d-block
The section of the periodic table in which atoms of the elements have their highest energy electron(s) in a d-subshell
02/06/2009
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