Electrons and the Periodic Table

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The Bohr Model of the Atom

Neils Bohr developed a model of the atom to explain the structure of the atom changes when it undergoes transitions

the energy of an atoms is quantized; amount of energy in the atom is related to the electron’s position in the atom

In the Bohr model, electrons travel in orbits around the nucleus

each orbit has a specific amount of energy

when the atom gains energy, the electron moves from lower energy orbit to one that is further from the nucleus

when the electron moves to the next energy orbit or shell, it gives off energy in a photon of light called a quantum of energy

since the distance between the orbits in atoms are not all the same, no two leaps in an atom will have the same energy

This makes the emission spectrum unique to the element

The Quantum-Mechanical Model of the Atom

Erwin Schrodiner came up with an equation to predict the probability of finding an electron with a particular amount of energy at a particular location in the atom.

The resulted in the mapping or orbitals.

Orbitals: a region where there is a high probability of finding the electron

In his equation, there are 3 quantum numbers; n represents the principal quantum number

Each shell has one or more subshell

the quantum number the designates the subshell is given a letter such as s, p, d, or f.

Each of the orbitals has a specific shape

Electron Configuration

Each subshell contains one or more orbitals

S subshells have 1 orbital

p subshells have 3 orbitals

d subshells have 5 orbitals

f subshells have 7 orbitals

each shell & subshell has a max number of electrons it can hold

s=2

p=6

d=10

f=14

Filling an Orbital with electrons

Aufbau principle: place electrons in the energy shells and subshells in order of energy from low to high

Pauli Exclusion Principle: each orbital may have max of 2 electrons

electrons spin on an axis which generates their own magnetic field

electrons in the same orbital must have opposite spinning directions so they cancel each other magnetic fields

Starting from s shell fill it from lowest energy to the highest

Hund’s Rule: when filling orbitals that have the same energy, place one electron in each before completing pairs

Electron Configurations of Atoms in Ground State

electron configuration is listing of the subshells in order of filling with the number of electrons

a short hand way of writing out the configuration is using the symbol of the previous element in [ ] to represent the inner electrons and then writing the las set.

Valence Electrons

Valence Electrons: the electrons in all the subshells with the highest principal energy shells

Core electrons: electrons in lower energy shells

Kr has 36 electrons = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

The highest electron shell is the 4th has 8 valence electrons with 28 core electrons

Ions: Losing and Gaining Electrons

Ions: atoms that lose/gain electrons to form charge particles

Cations: positive

Anions: negative

the charge is shown in the upper right corner

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