Chem Essay

4323 Words Nov 16th, 2015 18 Pages
1.1 Atomic structure

The Structure of the Atom
Mass Spectrometry
Electronic Structure
Ionisation Energies

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THE STRUCTURE OF THE ATOM

a) Protons, neutrons and electrons

Atoms are made up of three fundamental particles: protons, neutrons and electrons.

Protons and neutrons are found in the nucleus and are collectively called nucleons. Electrons orbit the nucleus in a similar way to that in which planets orbit a sun. In between the electrons and nucleus there is nothing (empty space).
The nucleus is very small; if an atom were the size of a football pitch, the nucleus would be the size of a drawing pin.

The basic properties of these three particles can be summarized in
…show more content…
Everything else is measured relative to this quantity.

b) Atomic numbers, mass numbers and isotopes

An atom is named after the number of protons in its nucleus. If the nucleus of an atom has 1 proton, it is hydrogen; if it has two protons, it is helium; if it has 3, it is lithium etc. The number of protons in the nucleus of an atom is called the atomic number. It has the symbol Z.

|The atomic number is the number of protons in the nucleus of an atom |

Not all atoms of the same element have equal numbers of neutrons; this may vary slightly. The sum of the number of protons and neutrons in the nucleus of an atom is called its mass number. It is represented by the symbol A.

|The mass number is the sum of the number of protons and neutrons in the nucleus of an atom |

The nucleus of an atom can thus be completely described by its mass number and its atomic number. It is generally represented as follows:

AZE

Eg. 94Be, 126C, 2412Mg

Atoms with the same atomic number but with different mass numbers (ie different numbers of neutrons) are called isotopes.

|Isotopes are atoms with the same atomic number but with different mass numbers |

Eg magnesium (atomic number 12) has 3 naturally occurring isotopes:

2412Mg: 12 protons, 12 neutrons
2512Mg: 12 protons, 13 neutrons
2612Mg: 12 protons, 14

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