Pre-IB/Pre-AP CHEMISTRY

1. Pre-IB/Pre-AP CHEMISTRY Chapter 3 – Atoms: The Building Blocks of Matter

3. Section 1 Objectives • Be able to define and explain: law of conservation of mass, law of definite proportions, law of multiple proportions. • Be able to summarize the five essential points of Dalton’s atomic theory. • Be able to explain the relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and the law of multiple proportions

4. Review • Matter is anything that occupies space and has mass. It’s simply what everything around us is made of.

5. Review • Mass is the amount of matter contained in an object. SI unit = kilogram

6. Review • All matter is either a pure substance or a mixture of substances. • A pure substance is made of only one type of matter. It is the same throughout.

7. Review • A mixtureis made of two or more pure substances that can be separated very easily. • Substances in a mixture do not lose their identities (Ex. salt in water).

8. Pure Substances • Pure substances can be divided into two categories: elements and compounds.

9. Ag Ag Ag Review • Elements are the simplest subtances of matter. Everything in the universe is made of one or more elements. There are over 100 known elements. (Letters of the alphabet)

10. Review • The smallest particle of an element that still has all the properties of that element is called an atom.

11. Review • Transformation of a substance or substances into one or more new substances – CHEMICAL reaction.

12. Story of the Atom • The ancient Greek philosophers described an atom as the smallest particle of matter which could not be divided. They imagined it to be a solid particle. • Democritus called nature’s basic particle an atom based on the Greek word meaning “indivisible” ATOM

13. Foundations of Atomic Theory • Virtually all chemists in the late 1700s accepted the modern definition of an element as “a substance that cannot be further broken down by ordinary chemical means”. • Clear that elements combine to form compounds that have different chemical and physical properties than those elements that form them. • 1790s – study of matter revolutionized by new inventions – tools allowed scientists to measure very small masses with accuracy never achieved before. • This allowed chemists to discover some very important laws.

14. Story of the Atom • The analytical balance scale was invented in the 1700’s. This tool allowed scientists to measure very small masses with accuracy never achieved before. This allowed chemists to discover some very important laws. • Democritus and Aristotle’s idea were not supported by experimental evidence and thus were remained in speculation until the eighteenth century.

15. Conservation of Mass • The Law of Conservationof Mass(Law of Conservation of Matter) states that mass(matter) is neither created nor destroyedduring ordinary chemical or physical changes. Oxygen + Hydrogen  Water

16. Conservation of Mass • Soon lead to the assertion that regardless of where or how a pure chemical compound is prepared, it is composed of a fixed proportion of elements. Oxygen + Hydrogen  Water

17. Conservation of Mass

19. Definite Proportions • The Law of Definite Proportions states that a chemical compound contains the same elements in exactly the same proportionsby mass regardlessof the sizeof the sample or the source of a compound.

20. Multiple Proportions • The Law of Multiple Proportions states that if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.

21. Multiple Proportions

22. Story of the Atom • In 1808, John Dalton proposed an atomic theory that described atoms smallest particles of elements.

23. Story of the Atom • Dalton’s model pictured atoms as small, indivisible particles similar to the ancient Greeks. His model fit experimental evidence at the time(law of conservation of mass, law of multiple proportions, etc.).

24. Dalton’s Theory • All matter is composed of atoms. • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. • Atoms cannot be subdivided, created, or destroyed.

25. Dalton’s Theory • Atoms of different elements combine in simple whole-number ratios to form chemical compounds. • In chemical reactions, atoms are combined, separated, or rearranged.

26. Modern Atomic Theory • By relating atoms to mass, Dalton turned Democritus’sidea into a scientific theory – one that could be tested by experiments. • Not all aspects of Dalton’s atomic theory have proven to be correct: • Today we know that atoms are divisible into even smaller particles • We know that a given element can have atoms with different masses (isotopes – element with the same number of PROTONS but a different number of NEUTRONS) • Atomic theory has been MODIFIED to fit new data/information • Aspects that have NOT Changed: • All matter is composed of atoms • Atoms of any element differ in properties from atoms of another element

27. Section 2 Objectives • Be able to define: atom, proton, neutron, electron, electron cloud, nuclear forces. • Be able to describe the properties of cathode rays that led to the discovery of the electron. • Be able to summarize the experiments of Rutherford that led to the discovery of the atomic nucleus. • Be able to list the properties of protons, neutrons, and electrons.

28. Story of the Atom • Although John Dalton thought that atoms were indivisible, investigators in the late 1800s proved otherwise. It became clear that atoms are actually composed of several basic types of smaller particles and that the number and arrangement of those particles determined the atom’s chemical properties.

29. Story of the Atom • Atoms: • Today’s definition: the smallest particle of an element that retains the chemical properties of that element. • Atoms are put together a certain way and are made up of subatomic particles • They have a core we call the nucleus – very small region located at the center of every atom • Nucleus of every atom is made up of at least one POSITIVELY charge particle (proton) and usually one or more NEUTRAL particle (neutron) • Surrounding the nucleus is a region occupied by NEGATIVELY charged particles (electrons) • This region is very large compared to the nucleus

30. Story of the Atom • John Thomson demonstrated, in 1897, that atoms contained smaller, negatively charged particles. They were later called electrons. Atoms were no longer viewed as solid particles with no parts.

33. Story of the Atom • Experiments revealed: • Cathode rays were deflected by a magnetic field in the same manner as a wire carrying electric current (negative charge) • The rays were deflected away from a negatively charged object • Thomson was able to measure the ratio of the negative charge of cathode-ray particles to their mass – found this ratio was always the SAME • These negatively charged “objects” were later called electrons. Atoms were no longer viewed as solid particles with no parts.

34. Story of the Atom • Thomson imagined the atom to be like a plum pudding. Electrons were like the scattered plums and the pudding was thought of as positively charged matter(all atoms are neutral).

35. Story of the Atom • In 1911, Ernest Rutherford’s experiments showed that atoms had a central core called a nucleus.

37. Rutherford’s Experiment

38. Story of the Atom • Rutherford suggested that negative electrons orbiteda positively charged nucleus. He could not explain how this occurred.

39. Nucleus • Atoms are put together a certain way. They have a core we call the nucleus. • All atomic nuclei are made of TWO kinds of particles – protons and neutrons. • Except Hydrogen nucleus

40. Protons • Inside the nucleus we find protons and neutrons. • Protons are positively chargedparticles, equal in magnitude to the negative charge of the electron

41. Neutrons • Neutrons are neutral, they have no charge. • Atoms are neutral because they contain equal number of protons and electrons • Hydrogen has a single proton nucleus with a single electron moving about it.

42. Question • What forces are holding the nucleus together? Gravitational? Electrostatic? Magnetic?

43. Nuclear Forces • Generally – particles that have the SAME electric charge will repel one another. • When two protons are extremely close to each other, there is a strong ATTRACTION between them – they help stabilize the nucleus

44. Nuclear Forces • Nuclear forces are short range forces of attraction that exist between protons and neutrons in the nucleus. • Neutron – proton • Neutron – neutron • Proton – proton

45. Size of Atoms • Atoms are extremely small. Atomic radii are on the range from about 40 to 270 picometers(pm). • 1 pm = 10-12 m • 1 pm is to 1 cm as 1 cm is to 103 km(about 600 mi)

46. Size of Atoms • Region occupied by the electrons as an electron cloud – a cloud of NEGATIVE charge • Radius of an atom is the distance from the center of the nucleus to the outer portion of this electron cloud

47. Section 3 Objectives • Be able to define: atomic number, isotope, mass number, nuclide, atomic mass unit(amu), average atomic mass, mole, Avogadro’s number, molar mass. • Be able to describe how the terms atomic number and mass number apply to isotopes.

48. Section 3 Objectives • Be able to determine the number of protons and neutrons in a nuclide when given the identity of the nuclide. • Be able to state how the terms mole, Avogadro’s number, and molar mass are related.

49. Section 3 Objectives • Be able to solve problems involving mass in grams, amount of moles, and number of atoms of an element using conversion factors(dimensional analysis).

50. Atomic Number • All atoms are composed of the same basic particles, but not all atoms are the same. Atoms of different elements have different numbers of protons & atoms of the same element have the same number of protons.