The First 20 Elements

1. The First 20 Elements By Mr. Bronks

2. Mass Number - Number of protons + Neutrons. Atomic Number - Number of protons Atoms C 12 6 In a neutral atom the number of electrons and protons are the same. In Carbon it is……… 6

3. Group 1 – one electron in last shell Hydrogen The simplest atom has one negative electron orbiting one positive proton. The electron is very light compared to the proton. Electron Proton

4. Helium In this atom we see two neutrons and two protons forming the nucleus. The Neutron has no charge but is the same mass as the proton. Electron Neutron Proton

5. Atomic Particles

6. Size of Nucleus • Nucleus very small compared to atom • If the atom was a stadium the nucleus would be the size of a ball in the centre circle.

7. 7Li 3 Lithium 3 Protons 4 neutrons The first is now full so we start a new outer shell or orbit Group 1 – one electron in last shell We write it as 2,1

8. 9Be 4 Beryllium 4 Protons 5 neutrons Group 2 – Two electrons in last shell C We write it as 2,2

9. Your turn • Now you do 5-9 • Go on look them up and draw them • DON’T KEEP READING DRAW………

10. 21Ne 10 Neon Group 8 – Full last orbit 10 Protons 11 neutrons We write it as 2,8

11. 24Na 11 Sodium Group 1 – one electron in last shell 11 Protons 13 neutrons Electric configuration 2,8,1

12. Atomic number Symbol or element Mg Mass number 12 So an atom of magnesium has: • 12 protons • 12 electrons • 12 neutrons 24 – 12 = 12 24 We write it as 2,8,2

13. Electronic configuration Electronic configuration refers to the way electrons are arranged in each shell or orbit. The first shell can hold up to 2 electrons and the next shells can hold up to 8 electrons.

14. Magnesium electronic configuration As magnesium has 12 electrons, they will be arranged:  2 in the first shell  8 in the second shell  2 in the third shell or, more simply: (2, 8, 2)

15. Theeasy way to find the number of neutrons is to subtract # neutrons = Mass Number - Atomic Number = 19 - 9 = 10

17. Isotopes • Same number of protons different number of neutrons

18. Isotopes • Same Atomic number different Mass number

19. The Periodic Table • Increase in Atomic Number (more Protons) • New row as each shell fills and a new shell started. 3 4 5 10 11 14 18 19 33 89

20. Groups • All in the same group have the same properties • Group 1 – only one electron in outer shell means keen to lose it Group 1 Alkali Metals Very reactive

21. Group II • Two electrons in outer shell so less reactive Group 2 Alkali Earth Metals Less reactive

22. Group VII - Halogens • All only one space so very reactive • Chlorine and flourine Group 7 Halogens Poisonous Gases Clean Water

23. Group VIII or 0 • All in the same group have the same properties • Group 8/Noble Gases • Non-reactive/Glow with electricity Non-reactive as they have a full outer shell

24. Groups • All elements in the same group have the same properties Group 8 Noble Gases Non-reactive Glow with electricity Group 2 Alkali Earth Metals Less reactive Group 1 Alkali Metals Very reactive Group 7 Halogens Poisonous Gases Cleans Water

26. H/W • P183 • Q 11-16