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Order of Orbitals

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

Aufbau Principle

*govern filling of orbitals by electrons
The Aufbau principle is an expression of how electrons generally get added to an atom or a molecular system. It states that orbitals with lower energy are filled before those with higher energy.
*Electrons enter orbitals of lowest energy first

Hund's rule

*govern filling of orbitals by electrons
when elements occupy orbitals of equal energy one electron enters each orbital until all the orbitals contain one electron with spins parallel.

Pauli exclusion principle

*govern filling of orbitals by electrons
An atomic orbital contains a maximum of two electrons
No more than two electrons can occupy an orbital, and this they can only do if they have opposite spin.
(orbital filling diagram- only two per box)

Highest occupied energy level

It is the highest energy level (from the nucleus) that an electron occupies in an atom
-where valence electrons are located

Inner shell electrons

These are the electrons that are not the valence electrons and are also known as core electrons.
*electrons that are the closest to the nucleus

Octet of electrons

Elements like Helium, Neon, or Group 8a on periodic table, all have 8 valence electrons and are stable.
-filled outer shell and stable atom.

Atom electron configuration

arrangement of electrons in an atom

Three methods used to represent arrangement of electrons

electron configuration (noble gas shortcut), orbital filling diagram, Lewis dot structure

Group Number and number of electrons in outer energy level

Group number in periodic table equals the number of valence electrons

S sub level

have spherical orbitals

p sub level

have dumbbell orbitals

d sub level

have clover leaf orbitals

As orbitals occupy higher energy levels...

the orbital size gets bigger (so that its area is further from the nucleus)
the farther away it is the higher the energy


Each orbital is assigned to a level and sublevel
1s= 1 orbital
2s= 1 orbital
2p= 3 orbitals
3s= 1 orbital
3p= 3 orbitals
3d= 5 orbitals
4s= 1 orbital
4p= 3 orbitals
4d= 5 orbitals
4f= 7 orbitals

Number of electrons in sublevel

n=1 2 electrons
n=2 8 electrons
n=3 18 electrons
n=4 32 electrons
n-7 98 electrons



octet rule

atoms gain or lose electrons to achieve a filled outer energy level of electrons

Valence electons

Outermost principal energy levels
Only s and p in highest energy levels
Since total number of electrons possible in s and p sub levels is 8, there can be no more than 8 valence electrons.


Atoms with 3 or fewer valence electrons lose those electrons forming a positive ion, or cation

Atoms with 5 or more valence electrons gain electrons forming a negative ion, or anion.

Sub energy levels in Energy levels

1= s
2= s p
3= s p d
4= s p d f

why are outermost electrons only ones included in orbital filling diagram?

they are the only ones involved in chemical reactions and bonding.
make it easier to decide what it could be bonded to and its characteristics, also its placement on periodic table.

What do the arrows on orbital filling diagram indicate?

The arrows represent the spin the electrons have. The pair of electrons spin in opposite directions, one clockwise and the other counterclockwise, and they repel each other.

Electron will spend about ___% of its time in ______

Describe orbitals using quantum numbers

Bohr model

How does a 2s orbital differ from a 1s orbital? how does a 2px orbital differ from a 2py orbital?

2s orbital is farther from the nucleus meaning it has more energy. (different level) 2px differs because they are on different axis and different places in space.
(px, py pz)
x axis, y axis, z axis, )

Periods in Period Table

Even though they skip some squares in between, all of the rows go left to right. When you look at a periodic table, each of the rows is considered to be a different period (Get it? Like PERIODic table.). In the periodic table, elements have something in common if they are in the same row. All of the elements in a period have the same number of atomic orbitals. Every element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbitals for their electrons. It goes down the periodic table like that. At this time, the maximum number of electron orbitals or electron shells for any element is seven.

Groups in Periodic Table

..and Your Groups
Periodic Table showing Groups Now you know about periods. The periodic table has a special name for its columns, too. When a column goes from top to bottom, it's called a group. The elements in a group have the same number of electrons in their outer orbital. Every element in the first column (group one) has one electron in its outer shell. Every element on the second column (group two) has two electrons in the outer shell. As you keep counting the columns, you'll know how many electrons are in the outer shell. There are some exceptions to the order when you look at the transition elements, but you get the general idea.

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