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Chem - Atoms, Molecules & Ions

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Atoms, molecules & Ions

Protons: +1

Electrons: -1

Neutrons: no charge

Generally, there is the same number of protons as electrons in an atom (to balance it).

The mass number is equal to the number of protons and the number of neutrons. They sit in the center of the atom, and electrons sit further away (on orbits). The atomic number is the number of protons.

Atomic number: Z

Mass number: A

[pic 1]

Isotopes have a different number of neutrons, but the same number of protons. Z is the same, A changes. Atomic mass/weight is an average of all the isotopes of that element.

Periodic Table:

[pic 2]

Most elements are metals (conductivity, malleability, ductility, lustrous). They lose electrons. Nonmetals lack these properties & generally gain electrons.

Groups: vertical columns. Elements in the same group have the same number of valence electrons.

Periods: horizontal columns. Elements in the same period have the same number of electron shells.

Quantum Numbers

They describe properties of the orbital.

N- the principal quantum number. It has integral values of 1,2,3… It is related to the size and energy of the orbital. As n increases, the electrons spends time father from the nucleus and it means higher energy.

L- the angular momentum quantum number. It has value from 0 to N-1. It is related to the shape of the atomic orbitals.

L=0 is s

L=1 is p

L=2 is d

L=3 is f

L=4 is g

ML- the magnetic quantum number. It has integral value from L to –L, including 0.  It is related to the orientation of the orbital in space relative to other orbitals in the atom.

[pic 3]

These orbital have nodes that increase as N increases.

4th quantum number: Ms- electron spin number. It it either -½ or ½. Two electrons in the same orbital must spin in opposite directions since in a given atom no 2 electrons can have the same set of 4 quantum numbers. This is the Pauli exclusion principle.



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