Atoms – the building blocks

1. All substances are made from very tiny particles called atoms. John Dalton had ideas about the existence of atoms about 200 years ago but only recently have special microscopes been invented that can “see” them. Atoms – the building blocks Water

2. Elements are the simplest substances. There are about 100 different elements. Two of John Daltons ideas were: Elements contain different types of atom. Each element has only one type of atom. Elements – different types of atom O S N Fe K C

3. Atoms are about 1/100,000,000 cm across. They are small. To make an atom the size of a football we would have to magnify it to around 3,000,000,000 times its normal size If we magnified the size of a football by the same amount it would stretch from the UK to the USA! N X 3,000,000,000 Atoms – How Small?

4. For some time people thought atoms were the smallest particles and that they could not be broken into anything smaller. We now know that atoms are themselves made from even smaller and simpler particles. These particles are Protons Neutrons Electrons Even Smaller Particles!

5. Protons, neutrons and electrons are NOT evenly distributed in atoms. The protons and neutrons exist in a dense core called the nucleus. Around the outside are very thinly spread electrons. These electrons exist in layers called shells. The Nucleus a dense core of protons and neutrons containing nearly all the mass of the atom ‘Shells’ of electrons electrons are really very very tiny so the atom is mostly empty space. How Are the Particles Arranged?

6. There are two properties of sub-atomic particles that are especially important: Mass Electrical charge Properties of Sub-atomic Particles Element atoms contain equal numbers of protons and electrons and so have no overall charge

7. The atom of any particular element always contains the same number of protons. E.g. Hydrogen atoms always contain 1 proton Carbon atoms always contain 6 protons Magnesium atoms always contain 12 protons The number of protons in an atom is known as its atomic number. It is the smaller of two numbers shown in most periodic tables Atomic Number 12 C 6

8. Note that any element has a definite and fixed number of protons. If we change the number of protons in an atom then this changes that atom into a different element. Changes in the number of particles in the nucleus (protons or neutrons) is very rare. It only takes place in nuclear processes such as radioactive decay, nuclear bombs or nuclear reactors. How Many Protons?

9. The mass of each atom results almost entirely from the number of protons and neutrons that are present. (Remember that electrons have a relatively tiny mass). The sum of the number of protons and neutrons in an atom is the mass number. Mass Number

10. It is not strictly true to say that elements consist of one type of atom. Whilst atoms of a given element always have the same number of protons, they may have different numbers of neutrons. Atoms that differ in this way are called isotopes. How Many Neutrons 2 Remember: The number of protons defines the element

11. Isotopes are virtually identical in their chemical reactions. (There may be slight differences in speeds of reaction). This is because they have the same number of protons and the same number of electrons. The uncharged neutrons make no difference to chemical properties but do affect physical properties such as melting point and density. How Many Neutrons 3

12. Natural samples of elements are often a mixture of isotopes. About 1% of natural carbon is carbon-13. 13 12 C C 99% 1% 6 6 Protons Electrons Neutrons Isotopes: Carbon 6 6 6 6 6 7

13. Hydrogen exists as 3 isotopes although Hydrogen-1 makes up the vast majority of the naturally occurring element. 1 2 H H 3 H 1 1 1 Protons Electrons Neutrons Protons Electrons Neutrons Protons Electrons Neutrons Hydrogen (Deuterium) (Tritium) Isotopes: Hydrogen

14. About 75% of natural chlorine is 35Cl the rest is 37Cl. Cl 37 Cl 35 17 17 75% 25% 17 Protons Electrons Neutrons Protons Electrons Neutrons 17 17 18 17 20 Isotopes: Chlorine

15. Almost all of natural oxygen is 16O but about 0.2% is 18O. Produce a Table showing the particles in each isotope. Activity Protons Electrons Neutrons Protons Electrons Neutrons Isotopes of Oxygen 16 O 8 Oxygen-16 Oxygen-18 8 8 8 8 8 10

16. Many natural elements are a mixture of isotopes. This means that when we react atoms of an element we are using a mixture of atoms with different mass numbers. The relative atomic mass given in the periodic table takes account of this. Isotopes and Relative Atomic Mass • E.g.. For 100 atoms of chlorine: • Mass of 75 atoms of Chlorine 35: 75 x 35 =2625 • Mass of 25 atoms of Chlorine 37: 25 x 37 =925 • Total = 3550 • Average (divide by 100) = 35.5

17. Activity Drag the statements at the top onto the correct side of the table

18. Activity Drag the statements at the top onto the correct side of the table

19. The nucleus. Dense: contains nearly all the mass of the atom in a tiny space. Made up of protons and neutrons. Has a positive charge because of the protons. The electrons. Exist thinly spread around the outside of the atom. Very small and light. Negatively charged. Exist in layers called shells. Can be lost or gained in chemical reactions. Summary: The atom so far!

20. Electrons are not evenly spread. The exist in layers known as shells. The arrangement of electrons in these shells is often called the electron configuration. 2nd Shell 3rd Shell 4th Shell How Are Electrons Arranged? 1st Shell

21. Each shell has a maximum number of electrons that it can hold. 1st Shell: 2 electrons 2nd Shell: 8 electrons 3rd Shell: 8 electrons How Many Electrons per Shell? The maximum

22. Opposites attract. Protons are + and electrons are – charged. Electrons will occupy the shells nearest the nucleus unless these shells are already full. 1st Shell: Fills this first 2nd Shell: Fill this next 3rd Shell: And so on Which Shells Do Electrons go into?

23. How many electrons do the element atoms have? (This will equal the atomic number). Keeping track of the total used, feed them into the shells working outwards until you have used them all up. 1st Shell: Fills this first 2nd Shell: Fill this next Working Out Electron Arrangements Drawing neat diagrams helps you keep track!

24. The Electrons in Carbon

25. The Electrons in Neon

26. The Electrons in Silicon

27. Electrons in Phosphorus

28. The Electrons in Argon

29. The Electrons in Sodium

30. The Electrons in Fluorine

31. The Electrons in Aluminium

32. The Electrons in Nitrogen

33. The Electrons in Sulfur

34. The Electrons in Oxygen

35. The Electrons in Chlorine

36. The Electrons in Magnesium

37. Ions are atoms that have either extra electrons added or electrons removed. e.g. Protons Electrons Atoms Lose 1 electron Gain 1 electron Protons Electrons 1+ ion Protons Electrons 1- ion Ions and Electron Structures So in ions the number of electrons no longer equals the number of protons

38. These are ions formed by the atom losing one or more electrons. They are called cations. This is because during electrolysis they move towards the cathode. (Or because they are “pussytive”!). The charge on the ions is equal to the number of electrons that the atom has lost. In equations the charge is usually shown above and to the right of the symbol. (E.g. Mg2+ ). Lost 1 e- Lost 2 e- Lost 3 e- Positive Ions + It is nearly always metal atoms that lose electrons Ions usually have OUTER electron shells that are either completely full or else empty 2+ 3+

39. In the sodium atom Atomic number = number of protons = 11 Number of electrons = 11 Na+ Na Electron lost The Electrons in a Sodium Ion 23 Na 11 Bye! Electron arrangement: 2.8.1 (Incomplete Shell) Electron arrangement: 2.8 (Full Shells)

40. In the magnesium atom Atomic number = number of protons = 12 Number of electrons = 12 Bye! Mg2+ Mg Bye! 2 electrons lost The Electrons in a Magnesium Ion 24 Mg 12 Electron arrangement = 2.8.2 (Incomplete shell) Electron arrangement 2.8 (Full Shells)

41. Activity • How many electrons? • How many electrons in the first shell? • How many electrons in the second shell? What electron arrangement? 1st Shell = 2: full Li+ Li 2nd Shell = 1: not full How many electrons to lose? New electron arrangement? Include a diagram The Lithium Ion 3 7 Li 3 2 1 2.1 1 Bye! 2.(0)

42. Activity • How many electrons? • How many electrons in the first shell? • How many electrons in the second shell? What electron arrangement? 1st Shell = 2: full B3+ B 2nd Shell = 3: not full Bye! Bye! How many electrons to lose? Bye! New electron arrangement? The Boron Ion 5 11 B 5 2 3 2.3 3 2.(0)

43. These are ions formed by the atom gaining one or more electrons. They are called anions. This is because during electrolysis they move towards the anode. The charge on the ions is equal to the number of electrons that the atom has gained. In equations the charge is usually shown above and to the right of the symbol. (E.g.. O2- ). Gain 1 e- Gain 2 e- Gain 3 e- Negative Ions. - It is nearly always non-metal atoms that gain electrons Ions usually have OUTER electron shells that are either completely full or else empty 2- 3-

44. In the sulphur atom Atomic number = number of protons = 16 Number of electrons = 16 S S2- 2 electrons gained The Electrons in a Sulphide Ion. 32 S 16 Electron arrangement: 2.8.6 (incomplete shell) Electron arrangement 2.8.8 (Full shells)

45. In the fluorine atom Atomic number = number of protons = 9 Number of electrons = 9 F F2- 1 electron gained The Electrons in a Fluoride Ion. 19 F 9 Electron arrangement: 2.8.7 (incomplete shell) Electron arrangement 2.8.8 (Full shells)

46. Activity • How many electrons? • How many electrons in the first shell? • How many electrons in the second shell? What electron arrangement? 1st Shell = 2: full O O2- 2nd Shell = 6: not full How many electrons to gain? New electron arrangement? The Oxide Ion 8 16 O 8 2 6 2.6 2 2.8

47. Drag the words at the top to their correct places in the sentences.

49. Word check

50. Which of the following is not a sub-atomic particle? Proton. Isotope. Neutron. Electron.