2. What is the atomic number?
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
What is the atomic number?
Every element has a unique atomic number. This is the number of protons in the nucleus of each atom.
What is the atomic number of this helium atom?
electron
Helium has 2 protons, so its atomic number is 2.
proton
neutron
Atoms are neutrally charged, so what links atomic number and the number of electrons?
A neutral atom must have equal numbers of protons and electrons, so the atomic number of an element also gives the number of electrons. *

3. Columns of elements What are columns of elements called? 1 2 groups 3
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
Columns of elements
What are columns of elements called? 1 2
groups 3 4 5 6 7 8 *

4. Rows of elements What are rows of elements called? periods 1 2 3 4 5 6
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
Rows of elements
What are rows of elements called?
periods 1 2 3 4 5 6 7 *

5. Patterns, atomic number and electrons
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
Patterns, atomic number and electrons
The periodic table shows that patterns in the properties of elements are linked to atomic number.
What links atomic number and the properties of elements?
Electrons!
atomic number = number of protons
number of protons = number of electrons
atomic number = number of electrons
As atomic number increases by one, the number of electrons also increases by one.
This means that the elements in the periodic table are also arranged in order of the number of electrons. *

6. Bohr Model of the Atom
Valence Shell: the outermost shell that is occupied by electrons + -
Valence electrons: electrons that occupy the valence shell.
When protons = electrons the element is neutral

7. How are electrons arranged?
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
How are electrons arranged?
Electrons are arranged in shells around an atom’s nucleus. (The shells can also be called energy levels). The outer most shell is called the Valence Shell and is full of Valence Electrons
Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first.
2nd shell holds a maximum of 8 electrons
1st shell holds a maximum of 2 electrons
3rd shell holds a maximum of 8 electrons
This electron arrangement is written as 2,8,8. *

8. H He Electrons in period 1
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
Electrons in period 1
Elements in period 1 only have electrons in the first shell.
Why are there only two elements in period 1? 1 2 3 4 5 6 7 8 H He 1 1 2
The first shell can only hold a maximum of two electrons,
so period 1 only includes the elements hydrogen and helium.
What is special about the outer shell of helium? *

9. Li Be B C N O F Ne Electrons in period 2
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
Electrons in period 2
Elements in period 2 all have a complete first shell.
What happens to electrons in the second shell in period 2? 1 2 3 4 5 6 7 8 Li Be B C N O F Ne 2
2,1
2,2
2,3
2,4
2,5
2,6
2,7
2,8
The second shell is completed one electron at a time going across the period from left to right.
What is special about the outer shell of neon? *

10. Na Mg Al Si P S Cl Ar Electrons in period 3
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
Electrons in period 3
Elements in period 3 have complete first and second shells.
What happens to electrons in the third shell in period 3? 1 2 3 4 5 6 7 8 Na Mg Al Si P S Cl Ar 3
2,8,1
2,8,2
2,8,3
2,8,4
2,8,5
2,8,6
2,8,7
2,8,8
The third shell is completed one electron at a time going across the period from left to right.
What is special about the outer shell of argon? *

11. What are the patterns of electron arrangement?
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
What are the patterns of electron arrangement?
Consider the electron arrangements of the first 20 elements in the periodic table. 1 2 3 4 5 6 7 1 1 2 2
2,1
2,2
2,3
2,4
2,5
2,6
2,7
2,8 3
2,8,1
2,8,2
2,8,3
2,8,4
2,8,5
2,8,6
2,8,7
2,8,8 4
2,8,8,1
2,8,8,2
What is the pattern of outer shell electrons in a group?
What is the pattern of outer shell electrons across a period?
What is the pattern of full electron shells in a group? *

12. Electron trends in the periodic table
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
Electron trends in the periodic table
Trends down a group:
the number of outer shell electrons is the same;
the number of complete electron shells increases by one.
The number of a group is the same as the number of electrons in the outer shell of elements in that group, except for group 8.
Trends across a period:
the number of outer shell electrons increases by one;
the number of complete electron shells stays the same.
The point at which a new period starts is the point at which electrons begin to fill a new shell. *

13. What’s the electron arrangement?
Boardworks GCSE Additional Science: Chemistry
Patterns in the Periodic Table
What’s the electron arrangement?
Teacher notes
This quiz could be used as a plenary or revision exercise to check students’ understanding of the electron configuration in the periodic table. Coloured traffic light cards could be used with this activity to increase class participation. *

14. End The Periodic Table Goal Sheet
This goal sheet will be due 10/29/14

15. What Happens if I take an electron away?

16. Cation Formation
Effective nuclear charge on remaining electrons increases.
Na atom
1 valence electron
Remaining e- are pulled in closer to the nucleus. Ionic size decreases.
11p+
Valence e- lost in ion formation
Result: a smaller sodium cation, Na+

17. Anion Formation
A chloride ion is produced. It is larger than the original atom.
Chlorine atom with 7 valence e-
17p+
One e- is added to the outer shell.
Effective nuclear charge is reduced and the e- cloud expands.