The Atom

The Atom The atom has three parts: Protons Neutrons Electrons

1 PROTON = 1 POSITIVE Charge Protons Protons: Found in the nucleus Mass: one (1) Atomic Mass Unit have a (+) positive charge, 1 PROTON = 1 POSITIVE Charge

Protons (Cont’d) On the periodic table, each element is numbered. This number equals the number of Protons in the nucleus.

Neutrons Also found in the nucleus. Mass: one (1) Atomic Mass Unit. They have NO charge. Neutron = Neutral

Electrons Found around the nucleus (like planets around the Sun) An Electron’s mass is almost nothing…almost Have a negative (-) charge ELECTRONS = NEGATIVE

Standard Atomic Notation Mass Number = mass of all the protons and neutrons in the nucleus 9 Be Element Symbol – eg. Beryllium 4 Atomic Number = number of protons in the nucleus and the number of electrons orbiting the nucleus To find the number of neutrons in the nucleus, subtract atomic number from mass number. There would be 9 – 4 or 5 neutrons in a Beryllium atom

Remember The periodic table is organized by atomic number (the number of protons the element has in its nucleus) Protons are + and electrons are - The number of protons = the number of electrons (positives = negatives)

Let’s try some! Have your periodic table ready How many protons, neutrons and electrons in one atom of: Hydrogen? Carbon? Beryllium? Calcium? Fluorine? 1 p+, 1 e-, 0 n 6 p+, 6 e-, 6 n 4 p+, 4 e-, 5 n 20 p+, 20 e-, 20 n 9 p+, 9 e-, 10 n

Bohr Rutherford Diagrams

Bohr-Rutherford Diagrams Named after the work done by Neils Bohr and Ernest Rutherford (nobody before them gets any respect!) Flattened model of the inside of an atom Unique for each atom

Electron Shells First Shell, maximum 2 electrons

Why only 2 in the first shell? 2 elements in first row (period)

Electron Shells Second Shell, Maximum 8 electrons

Why 8 in the second shell? 8 elements in second period

Electron Shells Third shell, max # 8 electrons Note: Magnesium only needs 2 electrons in this shell because it has 12 total

Bohr-Rutherford Diagrams Eg. Magnesium

Guess this element 82 protons = element 82 which is LEAD

The Noble Gases Column to the far right of the periodic table, He, Ne, Ar, Kr, Xe, & Rn

So, how would Magnesium look like Neon?

So, if Mg lost two Electrons, but still had the same number of Protons, what is its Charge? +2

Charges The outer electrons on an atom are called: Valence electrons. Atoms want a Bohr-Rutherford Diagram that look like the Noble Gases because… have the most stable structure Won’t react when mixed Usually, this means the atom ends up with a Charge.

Fluorine - 1 What does F need to look like a Noble gas? If we add one Electron, what will the Charge of the atom be? - 1

Ions Ion= a Charged atom in which the number of ELECTRONS (-) is different from the number of PROTONS (+). Ionic Charge= is the number of positive (+) or negative (-) Charges on an atom. Ex: Mg+2

Groups Mg Be (Berylium)

So… Even though each element has a different # of PROTONS and ELECTRONS, each element in a group has a similar Bohr-Rutherford Diagram This means they want to gain or lose the same number of Electrons. It also means elements in a Group will react similarly in Chemical Reactions