2.1.2 The simple Atomic Structure of the First Twenty Elements in the Periodic Table

List the elements or their symbols Give their atomic number Let us revise the atomic structure of these elements by drawing a table [In the back of your practical books - see next slide] List the elements or their symbols Give their atomic number Then their atomic mass Then their number of protons Then their number of neutrons Then the numbers of electrons The finally their electron patterns

Atomic Number Element 1 Hydrogen 2 Helium 3 Lithium 4 Beryllium 5 Boron 6 Carbon 7 Nitrogen 8 Oxygen 9 Fluorine 10 Neon 11 Sodium 12 Magnesium 13 Aluminium 14 Silicon 15 Phosphorus 16 Sulphur 17 Chlorine 18 Argon 19 Potassium 20 Calcium

Next comes the atomic mass Compare the atomic mass number to the atomic number Is there a pattern? In many tables there are decimal points – ignore these

Atomic Number Atomic Mass Element 1 1 Hydrogen 2 4 Helium 3 7 Lithium 4 9 Beryllium 5 11 Boron 6 12 Carbon 7 14 Nitrogen 8 16 Oxygen 9 19 Fluorine 10 20 Neon 11 23 Sodium 12 24 Magnesium 13 27 Aluminium 14 28 Silicon 15 31 Phosphorus 16 32 Sulphur 17 35 Chlorine 18 40 Argon 19 39 Potassium 20 40 Calcium

What did you notice? Atomic mass gets bigger as the atomic number increases – as a general rule But K lighter than Argon The atomic mass is roughly twice the atomic number

Proton Number Atomic Number Atomic Mass Element 1 1 1 Hydrogen 2 4 2 Helium 3 7 3 Lithium 4 9 4 Beryllium 5 11 5 Boron 6 12 6 Carbon 7 14 7 Nitrogen 8 16 8 Oxygen 9 19 9 Fluorine 10 20 10 Neon 11 23 11 Sodium 12 24 12 Magnesium 13 27 13 Aluminium 14 28 14 Silicon 15 31 15 Phosphorus 16 32 16 Sulphur 17 35 17 Chlorine 18 40 18 Argon 19 39 19 Potassium 20 40 20 Calcium

What did you notice? The number of protons equals the atomic number It is the atomic number that determines what the element is. If the atomic number changes then the element becomes a different element

Proton Number Neutron Number Atomic Number Atomic Mass Element 1 1 1 Hydrogen 2 4 2 2 Helium 3 7 3 4 Lithium 4 9 4 5 Beryllium 5 11 5 6 Boron 6 12 6 6 Carbon 7 14 7 7 Nitrogen 8 16 8 8 Oxygen 9 19 9 10 Fluorine 10 20 10 10 Neon 11 23 11 12 Sodium 12 24 12 12 Magnesium 13 27 13 14 Aluminium 14 28 14 14 Silicon 15 31 15 16 Phosphorous 16 32 16 16 Sulphur 17 35 17 18 Chlorine 18 40 18 22 Argon 19 39 19 20 Potassium 20 40 20 20 Calcium

What did you notice? The number of neutrons is the atomic mass minus the atomic number The number of neutrons is roughly the same as the number of protons

Proton Number Neutron Number Electron Number Atomic Number Atomic Mass Element 1 1 1 1 Hydrogen 2 4 2 2 2 Helium 3 7 3 4 3 Lithium 4 9 4 5 4 Beryllium 5 11 5 6 5 Boron 6 12 6 6 6 Carbon 7 14 7 7 7 Nitrogen 8 16 8 8 8 Oxygen 9 19 9 10 9 Fluorine 10 20 10 10 10 Neon 11 23 11 12 11 Sodium 12 24 12 12 12 Magnesium 13 27 13 14 13 Aluminium 14 28 14 14 14 Silicon 15 31 15 16 15 Phosphorus 16 32 16 16 16 Sulphur 17 35 17 18 17 Chlorine 18 40 18 22 18 Argon 19 39 19 20 19 Potassium 20 40 20 20 20 Calcium

What did you notice? Number of electrons is equal to the number of protons This is why atoms are neutral [positive protons and negative electrons cancel out] The number of electrons is also equal to the atomic number

Proton Number Neutron Number Electron Number Atomic Number Atomic Mass Electron Pattern Element k l m n 1 1 1 1 1 Hydrogen 2 4 2 2 2 2 Helium 3 7 3 4 3 2 1 Lithium 4 9 4 5 4 2 2 Beryllium 5 11 5 6 5 2 3 Boron 6 12 6 6 6 2 4 Carbon 7 14 7 7 7 2 5 Nitrogen 8 16 8 8 8 2 6 Oxygen 9 19 9 10 9 2 7 Fluorine 10 20 10 10 10 2 8 Neon 11 23 11 12 11 2 8 1 Sodium 12 24 12 12 12 2 8 2 Magnesium 13 27 13 14 13 2 8 3 Aluminium 14 28 14 14 14 2 8 4 Silicon 15 31 15 16 15 2 8 5 Phosphorus 16 32 16 16 16 2 8 6 Sulphur 17 35 17 18 17 2 8 7 Chlorine 18 40 18 22 18 2 8 8 Argon 19 39 19 20 19 2 8 8 1 Potassium 20 40 20 20 20 2 8 8 2 Calcium

What did you notice? Shells fill from inside outwards When outer shell becomes full something different happens - shown by shading Atoms become very stable Octet rule because usually when there are eight electrons in outer shell Helium is an exception

Summary

Atomic number is a series Atomic number tells number of protons Number of protons determines what the element is. Atomic Mass is about twice atomic number Number of neutrons calculated by atomic mass – atomic number

Number of electrons = number of protons = atomic number Electrons fill shells from inside out 2,8,8,(2) is maximum – brackets because not full If an outer shell is full the atom is very stable Usually 8 electrons fill the outer shell – Octet rule Helium is one exception