For students doing A Level Chemistry under the OCR A specification.
This module is for AS Level too.
The main themes in this summary guide include:
Atoms, compounds, molecules and equations;
Amount of substance;
Acid–base and redox reactions;
Electrons, bonding and structure.
The chapt...
Atomic Structure and
Isoptopes
Nearly all the other an atom’s mass is in the nucleus
Protons have a positive charge.
Neutrons can be thought of as providing the glue that holds
the nucleus together despite the electrostatic repulsion
between its positively charged protons.
Electrons have a negative charge.
the electron shell is a group of atomic orbitals with the same
principal quantum number n. Also known as the main energy
level.
Relative masses:
- A proton has virtually the same mass as a neutron.
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- An electron has negligible mass, about the mass of a
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proton.
Atomic number Z is the number of protons in the nucleus of
an atom; also known as proton number.
Isotopes are atoms of the same element with different
numbers of neutrons and different masses.
Mass number A is this some of the number of protons and
neutrons in the nucleus; also known as nucleon number.
An ion is a positively or negatively charged atom or group of
atoms (polyatomic ion), where the number of electrons is
different from the number of protons.
A cation is a positively charged ions with fewer electrons than
protons.
An anion is a negatively charged ion with more electrons than
protons.
, Relative Mass
Carbon-12 is the international standard for the measurement
of atomic masses. The unit used for the atomic mass is called
the atomic mass unit, u. The standard mouse fur atomic mass
is 1 u, the mass of 1/12th of an atom of carbon-12; on this
scale 1 u is approximately the mass of the proton or a
neutron.
Relative atomic mass Ar is the weighted mean mass of an
atom of an element compared with 1/12 of the mass of an
atom of carbon-12.
Relative isotopic mass is the mass of an isotope compared
with 1/12 of the mass of an atom of carbon-12.
, Formulae and Equations
State Symbols:
(g) – gas
(l) – liquid
(s) – solid
(aq) – aqueous (dissolved in water)
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