The document discusses atomic structure and the development of atomic theory. It explains that: 1) All matter is made of tiny indivisible particles called atoms, as proposed by Democritus in ancient Greece. 2) Laws of conservation of mass and constant composition provided evidence supporting atomic theory by showing matter is neither created nor destroyed in chemical reactions. 3) Atoms are composed of even smaller subatomic particles - electrons orbiting a dense nucleus of protons and neutrons, held together by electrostatic attraction. The identity of an element is determined by its number of protons.

1. M4 Chemistry Matter III: Atomic Structure

2. M5 Chemistry Matter: Atomic Structure Slide of 46 Learning Objectives Concepts Microscopic, macroscopic, sub-microscopic, atom, molecule, ion, group, period Atomic structure, electron, proton, neutron, electron configuration, shell, outer shell, valence shell, valence electron, core shell, core electrons Monatomic (atomic) element, diatomic element, molecular element Law of conservation of matter, law of constant composition (proportion), atomic theory of matter, Dalton’s atomic theory Skills State that all matter is made up of atoms (atomic theory) and explain the structure of an atom. Electrical forces between oppositely charged electrons and positive nucleus (protons) hold atoms together.

3. M5 Chemistry Matter: Atomic Structure Slide of 46 Learning Objectives Explain that the enormous variety of materials in the world is the result of different combinations of a relatively small number (approximately 100) of basic ingredients (elements). State that the smallest part of an element (macroscopic) is an atom (sub-microscopic). Explain the law of constant proportions and how it relates to the submicroscopic and macroscopic views of matter. Explain that the macroscopic world is made up of sub-microscopic particles (atomic theory) and give several examples of evidence. State that the number of positive protons in the nucleus determines the identity of the atom.

4. M4 Chemistry Matter: Atomic Structure Slide of 46 Learning Objectives Be able to recall the symbol, position (atomic number), electronic structure and electronic configuration for the first 20 elements in the periodic table . Explain the significance of the noble gas electronic structures and valence electrons.

5. M5 Chemistry Matter: Atomic Structure Slide of 46 Atoms Everything, every matter is made up of small particles, sub-microscopic particles called atoms. This idea is very very very old!! As a matter of fact this idea was first proposed about 450 BC by Democritus, a Greek philosopher. He proposed that if one were to continually cut into smaller and smaller piece something like a piece of aluminum, then you ultimate reach a point when you couldn’t cut the piece into anything smaller. You can’t cut the piece of aluminum foil into infinitely smaller pieces because once you arrive at the level of aluminum atoms, you wouldn’t be able to divide then any further. Hence the term atom, meaning “not divisible.”

6. M5 Chemistry Matter: Atomic Structure Slide of 46 Atomic Theory Hardly any well known and respected philosophers of the time agreed with Democritus. They asked how it was then that, if matter is composed of such particles, they are able to keep together? Why doesn’t matter just crumble as they should if indeed they are made up of these small indivisible atoms? It wasn’t until the 1700’s that two important discoveries were made which gave support to Democritus’ assertions. The first one was the French scientist Antoine Lavoisier’s Law of Conservation of Matter and the second one the Law of Constant Composition established by another French Chemistry Joseph Louis Proust.

7. M5 Chemistry Matter: Atomic Structure Slide of 46 Law of Conservation of Mass The law of conservation of matter states that matter is neither created nor destroyed in any process. During any change (physical or chemical) matter cannot be created or destroyed. This can be easily demonstrated by conducting a reaction in a closed container placed on a top pan balance. The mass of the reactants before and after the reaction will remain constant as long as nothing escapes into the atmosphere from the reaction container. Lavoisier conducted experiments involving mass measurements of substances involved in reactions with air (and was able to demonstrate the role of oxygen in combustion and rusting).

8. M5 Chemistry Matter: Atomic Structure Slide of 46 How does this support Democritus’ contention that matter is made up of atoms? It does because if matter were made of indivisible atoms then the atoms that you start with must be the same as the atoms that you end with, but the way in which the atoms are arranged can change. Physical change: the atoms AND molecules in the starting substances are the same as the atoms AND molecules in the ending substances. The molecules may just be moving at a different speed or located different distances apart (see Chemistry Matter: State and Energy). Chemical change : the atoms are the same in the starting substances and the ending substances, BUT the molecules are different. The molecules have hit each other, broken apart, and then rearranged and bonded into new molecules. These new molecules have different properties than the starting substances.

9. M5 Chemistry Matter: Atomic Structure Slide of 46 Law of Constant Proportion Joseph Louis Proust found that a given compound always contains the same elements in the same proportion by mass. For instance mass of oxygen in water is always 88.79% oxygen and 11.21% hydrogen. Mass of carbon in carbon dioxide is always 27.29% carbon and 72.71% oxygen. How does this support Democritus’ hypothesis about what matter is made up of?

10. M5 Chemistry Matter: Atomic Structure Slide of 46 Dalton’s Atomic Theory of Matter In 1803 John Dalton, and English schoolteacher, studied these other findings and formulated the first comprehensive atomic theory of matter . His theory were based on the following postulates: Each element is composed of extremely small particles called atoms. Atoms of a given element are identical but they differ from those of any other element. atoms are neither created nor destroyed in any chemical reaction. A given compound always has the same relative number and kinds of atoms. As you learn more chemistry, you will discover that there are small but important exceptions to some of Dalton’s postulates.

11. M5 Chemistry Matter: Atomic Structure Slide of 46 Atom Nowadays, an atom is defined as the smallest particle of an element that retains the chemical identity of that element . There are 92 natural elements, which means there are 92 different naturally occurring atoms as well. The rest of the elements appearing on a modern periodic table are synthetic.

12. M5 Chemistry Matter: Atomic Structure Slide of 46

13. M5 Chemistry Matter: Atomic Structure Slide of 46 Atoms…aren’t the smallest particles Important discoveries have been made since Democritus and Dalton to warrant a revision of the way we look at atoms of course. For instance, we now know that atoms aren’t the smallest particles, contrary to what Democritus and Dalton proposed. Atoms are composed of protons, neutrons and electrons. Protons and neutrons are found in the center of the atom, called the nucleus. Electrons are found in shells orbiting around the nucleus not very much unlike planets around the sun.

14. M5 Chemistry Matter: Atomic Structure Slide of 46 Nucleus The nucleus is a tiny and extremely dense region in the centre of the atom and most of the rest of the atom is just empty. If a pea were placed in the center of a football stadium, it would represent the nucleus to the atom of the stadium!! Because they are found in the nucleus of the atom, protons and neutrons are often referred to as nucleons . Electrons move around the nucleus in orbits in much the same way as the planets orbit the sun in the solar system.

15. M5 Chemistry Matter: Atomic Structure Slide of 46 Electrostatic Attraction Do you remember which sub-atomic particles have which charge? Protons have a POSITIVE charge. Electrons have a NEGATIVE charge. Neutrons are NEUTRAL in charge. Electrons are kept in orbit by the ELECTROSTATIC ATTRACTION between the negative electrons and the positive protons. Electrons are kept in orbit by electrostatic attraction

16. M5 Chemistry Matter: Atomic Structure Slide of 46 Properties of sub-atomic Particles Outside nucleus, orbiting nucleus -1 1/1840 (negligible) Electron in nucleus 0 1 Neutron in nucleus +1 1 Proton Location in atom Relative charge Relative mass Particle

17. M5 Chemistry Matter: Atomic Structure Slide of 46 Neutrality of Atoms Atoms are electrically neutral ; they always contain the same number of positively charged protons and negatively charged electrons . For example, an atom of magnesium contains 12 positively charged protons in the nucleus and 12 negatively charged electrons orbiting the nucleus. Charge on an atom of magnesium = charge on protons + charge on electrons = 12 + (  12) = 0 Because atoms contain the same amount of positive and negative charge they are electrically neutral .

18. M5 Chemistry Matter: Atomic Structure Slide of 46 Ion If an atom gains or loses electrons then the balance is upset and the atom becomes electrically charged. Atoms which have become electrically charged by gaining or losing electrons are given a different name: they are called ions (about which we will have more to say later on in the course). Next we are going to look at the arrangement of these electrons around the nucleus of different atoms. We will look at the first ten elements in the periodic table.

19. M5 Chemistry Matter: Atomic Structure Slide of 46 Atomic Structure: Hydrogen Hydrogen is the simplest element. It has one electron and that electron in hydrogen atom is found in…

20. M5 Chemistry Matter: Atomic Structure Slide of 46 Hydrogen … the first shell . A shell is like an orbit, like the orbit of the earth around the sun where the electron is said to be going around the nucleus. The diagram above showing the electron in the first shell of hydrogen is referred to as the electronic structure of hydrogen.

21. M5 Chemistry Matter: Atomic Structure Slide of 46 Helium The next element in the periodic table is Helium and it contains 2 electrons. The second electron in Helium is found orbiting the nucleus in…

22. M5 Chemistry Matter: Atomic Structure Slide of 46 Helium … the first shell as well. The electronic structure of helium therefore contains two electrons I the outer shell. 1 H 2 He

23. M5 Chemistry Matter: Atomic Structure Slide of 46 Helium The first shell in Helium has as many electrons as it can take. That’s why helium is referred to as a noble gas , an inert (unreactive) gas. It has a full outer shell of electrons and is therefore energetically stable . 1 H 2 He

24. M5 Chemistry Matter: Atomic Structure Slide of 46 Lithium With the next element, Lithium, we move into the second period and so the third electron in this element is found orbiting in the second shell . 3 Li

25. M5 Chemistry Matter: Atomic Structure Slide of 46 Lithium A period is a row of elements on the periodic table. Remember again that the first shell can accommodate a maximum of 2 electrons. 3 Li

26. M5 Chemistry Matter: Atomic Structure Slide of 46 Beryllium As we move from one element to the next in this period, the extra electron is found in the same shell as Lithium, the second shell. 3 Li 4 Be

27. M5 Chemistry Matter: Atomic Structure Slide of 46 Boron 3 Li 4 Be 5 B

28. M5 Chemistry Matter: Atomic Structure Slide of 46 Carbon 3 Li 4 Be 5 B 6 C

29. M5 Chemistry Matter: Atomic Structure Slide of 46 Nitrogen 7 N 3 Li 4 Be 5 B 6 C

30. M5 Chemistry Matter: Atomic Structure Slide of 46 Oxygen 3 Li 4 Be 5 B 6 C 7 N 8 O

31. M5 Chemistry Matter: Atomic Structure Slide of 46 Fluorine 9 F 3 Li 4 Be 5 B 6 C 7 N 8 O

32. M5 Chemistry Matter: Atomic Structure Slide of 46 Neon And with neon we come to the last element in this period and the maximum number of electrons (8) the second shell in any element can hold. 10 Ne 9 F 3 Li 4 Be 5 B 6 C 7 N 8 O

33. M5 Chemistry Matter: Atomic Structure Slide of 46 Valence Shell & Valence Electrons The outermost shell where electrons are found for a given element is referred to as the valence shell. For example in the case of hydrogen and helium the valence shell is the first shell. For those in the second period (from lithium to neon) the valence shell is the second shell. Those in the third period the valence shell is the third shell etc. The electrons found in the valence shell are therefore referred to as valence electrons. Hydrogen has 1 valence electron (and some times it’s referred to as having a valency of 1) Helium 2, lithium 1, boron 3, nitrogen 5 etc.

34. M5 Chemistry Matter: Atomic Structure Slide of 46 Electron configuration The arrangement of electrons, the electron configuration, in shells can also be indicated by a sequence of numbers representing electrons in each shell starting with the inner most core shell. H – 1 He – 2 Li – 2, 1 Be – 2, 2 B – 2, 3 C – 2, 4 N – 2, 5 O – 2, 6 F – 2, 7 Ne – 2, 8 Na – 2, 8, 1 Mg – 2, 8, 2 etc.

35. Slide of 46 Exercise: Electronic Configuration of Group 1 Metals A column of elements are referred to as a group . Use the information shown to write down the electronic configurations of the first three group one metals and then draw the electronic configuration for lithium . 2,1 2,8,1 2,8,8,1 Lithium

36. M5 Chemistry Matter: Atomic Structure Slide of 46 Electron Configuration For the first 20 elements, the following guidelines can be used The first shell can hold a maximum of 2 electrons The second shell can hold a maximum of 8 electrons The third shell can hold a maximum of 8 electrons Any remaining electrons can be placed in the fourth shell

37. M5 Chemistry Matter: Atomic Structure Slide of 46 A Must… You MUST memorize the symbol, the position, electronic structure and configuration for the first 20 element in the periodic table. You will get a periodic table in every test but I WILL TELL YOU RIGHT NOW THAT IF YOU DON’T HAVE ALL THAT COMMITTED TO MEMORY, YOU WILL STRUGGLE TO UNDERSTAND AND MASTER THE MORE ADVANCED CONCEPTS AND SKILLS. To help you with that, prepare three sets of flash cards with the following information: Set 1. name and underneath: the question “Symbol?”. On the other side symbol and underneath the question “Name?” Set 2. Symbol and underneath, the question “Electronic structure?”. On the other side, electronic structure and the question “Symbol?”. Set 3. Atomic number and underneath “Electronic configuration?”. On the other side, electronic configuration and the question “Atomic number?”

38. M5 Chemistry Matter: Atomic Structure Slide of 46 Conclusions Notice then that the number of shells the atom of an element contains is the same as the period (row) in which the element appears in the periodic table. hydrogen (H) and helium (He) for example appear in period 1 and contain only 1 shell each Lithium (Li) and the rest of the elements in period 2 contain two shells each etc. The number of electrons in the valence shell (outermost shell) is the same as the group (column) to which the element belong. Lithium (Li), Sodium (Na) and the rest of the elements below in Group 1 contain 1 electron in their valence shell All elements in the last column (group 8) (with the exception of helium) contain 8 electrons in the valence shell etc.

39. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions 1. J05/2/5f. Astatine, At, is below iodine in Group VII of the Periodic Table. (i) How many protons does astatine have in its nucleus? [1] (iii) The most common isotope of astatine has a nucleon number (mass number) of 210. Calculate the number of neutrons in this isotope of astatine. [1]

40. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions 2. J04/2/5. Look at the list of five elements below. argon bromine chlorine iodine potassium (a) Put these five elements in order of increasing proton number. [1] (b) Put these five elements in order of increasing relative atomic mass. [1] (c) The orders of proton number and relative atomic mass for these five elements are different. Which one of the following is the most likely explanation for this? Tick one box. The number of protons must always equal the number of neutrons. The atoms easily gain or lose electrons. The presence of neutrons. The proton number of a particular element may vary.

41. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions 3. The diagram represents an atom. Choose words from the list to label the diagram. electron ion neutron nucleus

42. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions 4. This question is about the elements in the list below. aluminium astatine chlorine fluorine francium helium hydrogen iodine iron potassium Which element, from the list above : (a) is in Group 3 of the Periodic Table, ........................................... (b) is in Period 5 of the Periodic Table, ...........................................

43. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions 5. Use a periodic table to help you answer this question. This question is about elements and atoms. (a) About how many different elements are found on Earth? Draw a ring around the correct number. 40 50 60 70 80 90 [1] (b) The following are parts of an atom: [3] electron neutron nucleus proton Choose from the list the one which: (i) has no electrical charge; (ii) contains two of the other particles; (iii) has very little (negligible) mass.

44. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions: Multiple Choice 1. Which one of the following is not one of the postulates of Dalton's atomic theory? A) Each element is composed of tiny, indivisible particles called atoms. B) All atoms of a given element are identical to each other and different from those of other elements. C) During a chemical reaction, atoms are changed into atoms of different elements. D) Compounds are formed when atoms of different elements combine. E) Atoms of an element are not changed into different types of atoms by chemical reactions. 2. A molecule of water contains hydrogen and oxygen in a 1:8 ratio by mass. This is a statement of __________. A) the law of multiple proportions B) the law of constant composition C) the law of conservation of mass D) the law of conservation of energy E) none of the above

45. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions: Multiple Choice 3. Which one of the following is not one of the postulates of Dalton's atomic theory? A) Atoms are composed of protons, neutrons, and electrons. B) All atoms of a given element are identical; the atoms of different elements are different and have different properties. C) Atoms of an element are not changed into different types of atoms by chemical reactions: atoms are neither created nor destroyed in chemical reactions. D) Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. E) Each element is composed of extremely small particles called atoms.

46. M5 Chemistry Matter: Atomic Structure Slide of 46 Practice Questions: Multiple Choice 4. Of the following, the smallest and lightest subatomic particle is the __________. A) Neutron B) proton C) electron D) nucleus E) alpha particle 5. All atoms of a given element have the same __________. A) mass B) number of protons C) number of neutrons D) number of electrons and neutrons E) density 6. The atomic number indicates __________. A) the number of neutrons in a nucleus B) the total number of neutrons and protons in a nucleus C) the number of protons or electrons in a neutral atom D) the number of atoms in 1 g of an element E) the number of different isotopes of an element