Atomic Structure

Atoms are made up of 3 subatomic particles

Protons Neutrons and…

Electrons !

are located in the nucleus of an atom. Protons and Neutrons are located in the nucleus of an atom.

Electrons Whiz around the outside of the nucleus in energy levels, also known as orbitals, electron clouds, or shells

Each particle has a mass...

measured in a.m.u.'s (atomic mass units)

Protons have a mass of 1 amu

Neutrons also have a mass of 1 amu

Electrons barely weigh anything at all! (1/1836 amu)

Each particle is assigned a charge...

Protons have a positive (+) electrical charge

Neutrons have no charge (0)

Electrons have a negative ( - ) electrical charge

Let's build an atom!

We’ll use the element sodium as an example… Sodium Na

Sodium has the atomic number 11, and an atomic mass number of 23.

Step 1: Find the # of protons!

11 23 Step 1: Sodium Na There are 11 protons + in one atom of sodium The smaller number is the atomic number. It tells the number of protons in the atom ( the atom's identity) Sodium 11 Na 23 There are 11 protons + in one atom of sodium

Na atomic # 11 23 p+ p+ p+ p+ p+ p+ p+ p+ p+ p+ p+ There are 11 protons + in the nucleus of a sodium atom

Step 2: Find the # of neutrons!

Sodium Step 2: 11 Na Subtract the number of protons + (11) from the number of particles in the nucleus (23) 23 minus 11 = 12 neutrons 23 The larger number is the atomic mass number. It tells the number of protons and neutrons together. There are 23 particles, or atomic mass units. 11 protons + 12 neutrons = 23 amu’s total

23 Protons and neutrons 11 Protons - - = 12 neutrons

Na atomic # 11 23 mass # p+ no p+ no no no p+ p+ no no p+ no p+ p+ p+ 11 protons + 12 neutrons o 11 protons + 12 neutrons = 23 amu

Step 3: Find the # of electrons!

Therefore, the number of Step 3: Most atoms are electrically neutral. Therefore, the number of electrons can also be determined by the atomic number. There are usually the same number of electrons as there are protons. Sodium 11 Na 23 11 electrons - 11 protons usually means 11 electrons, too

Na e- atomic # 11 e- e- no no p+ p+ no no p+ no p+ p+ e- p+ e- no no L K e- e- 11 electrons - total

atomic # 11 Na 11 electrons - orbit in energy levels, or shells, around the densely packed nucleus of the sodium atom.

atomic # 11 Na But there are specific numbers of electrons that can fit in each energy level of the atom.

Na Only 2 electrons - can fit in the first, or “K” shell atomic # 11 no no p+ p+ no no p+ no p+ p+ p+ no no p+ no e- e- p+ p+ no no p+ p+ no no K 2 electrons - so far…. (9 more to go)

Na 8 electrons - can fit in the second, or “L” shell atomic # 11 e- e- no no p+ p+ no no p+ no p+ p+ e- p+ e- no no p+ no e- e- p+ p+ e- no no p+ p+ e- no no M L K e- e- 10 electrons - so far……. ( 2 + 8 added)… one more to go!

Electrons also fit in the valence, or outside shell, which in this case is the “M” shell. atomic # 11 Na e- e- no no p+ p+ no no p+ no p+ p+ e- p+ e- no no p+ no e- e- p+ p+ e- no no p+ p+ e- no no M L K We only need to add one more electron for sodium, which fits easily in the “M” shell. e- e- 11 electrons – total (2 + 8 + 1)

All together now....

Sodium atom Na e- atomic # atomic # 11 e- e- 23 mass # 23 -11 = 12 no p+ p+ no p+ p+ no e- no no e- p+ p+ no no e- e- p+ p+ no no p+ p+ e- e- no p+ no no M L K 11 protons + 12 neutrons e- e- 11 electrons -

Review

Protons have a mass of 1 amu

Protons have a positive (+) electrical charge

Neutrons have a mass of 1 amu

Neutrons have no charge (0)

Electrons weigh only 1/1836 amu

An electron's charge is negative ( - )

Sodium 11 Na 23

Sodium atom Na e- atomic # 11 e- e- 23 mass # no no p+ p+ no no p+ no L K 11 protons + 12 neutrons o 11 electrons - e- e-

Congratulations! You are an atom builder!