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UNIT 8. ATOMIC STRUCTURE AND PROPERTIES OF SUBSTANCES

PHYSICS AND CHEMISTRY 4º ESO Physics and Chemistry Department. UNIT 8. ATOMIC STRUCTURE AND PROPERTIES OF SUBSTANCES. Characteristics of atoms. Historical evolution of atomic theories. Chemical elements. Types of chemical elements. The periodic table.

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UNIT 8. ATOMIC STRUCTURE AND PROPERTIES OF SUBSTANCES

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  1. PHYSICS AND CHEMISTRY 4º ESO Physics and Chemistry Department UNIT 8. ATOMIC STRUCTURE AND PROPERTIES OF SUBSTANCES

  2. Characteristics of atoms Historical evolution of atomic theories Chemical elements Types of chemical elements The periodic table Internal structure of the matter The covalent bond The theory of the chemical bonding The ionic bond The metallic bond UNIT 8. ATOMIC STRUCTURE AND PROPERTIES OF SUBSTANCES Concepts 4º ESO – PHYSICS AND CHEMISTRY

  3. 1. HISTORICAL EVOLUTION OF ATOMIC THEORIES What is matter made up of? All matter is made up of atoms. 1.1. Ancient Greek ideas on matter (5th century B.C.) First atomic hypothesis (Democritus and Leucippus, 5th century B.C.): They proposed that matter was made up of discrete, tiny and indivisibleparticles called atoms. Aristotle (4th century B.C.): All the chemicals substances are made up of the combination of 4 basic elements: Water, air, earth and fire. 4º ESO – PHYSICS AND CHEMISTRY The Greek ideas about matter lasted for more than 2000 years.

  4. 1.2. Dalton’s atomic theory (1.808): the first atomic theory Matter is made up of atoms, tiny, indivisible, and indestructible particles. There are two types of chemical substances: 1. Elements: It is a simple substance that is made up of identical atoms in size, mass and other properties. • Atoms of different elements differ in size, mass, and other properties. 2. Compounds: It is a substance made up of different atomscombined in a fixed number. 4º ESO – PHYSICS AND CHEMISTRY In the chemical reactions the atoms are notcreated or destroyed. They only separate or combine with each other in different groups, to form different compounds.

  5. Dalton believed that atoms were small solid spheres. Element: an elementary pure substance which is made up of only one type of atoms and cannot be split up into two or more simpler substances by chemical reactions. Compound: a pure substance which is made up of two or more types of atoms and can be split up into two or more simpler substances by chemical reactions, but no by physical means). It is not a mixture (a mixture is made up of two o more substances that can be separated by physical means).

  6. 1.3. Electrical nature of matter (19th century) Matter and electrical phenomena are intimately related to each other. Although the knowledge of electricity dates back to the earliest civilizations, in many ways the 19th century was the century of electricity. 4º ESO – PHYSICS AND CHEMISTRY Electrolysis: Chemical change in which a substance transforms in its elements when an electric current passes through a solution of that substance.

  7. Static Electricity: It is the change in the electrical state of an object by 1. Contact with a charged object. 2. Rubbing against another object. 3. Induction of a charged object: a charge is created by the influence of a charged object. The Law of Electric Charges 1. Matter is made up of two types of charges: (+) and (). 2. The SI unit of quantity of electric charge is the coulomb, C. 3. A neutral object: the same number of (+) and ()charges. 4. A positively charged object: more (+) than () charges. 5. A negatively charged object: more () than (+)charges.

  8. 6.Two (+) charged objects experience a mutual repulsive force, as do two ()charged objects. 7. (+)charged objects and ()charged objects experience an attractive force • If matter is made up of atoms and atoms are small solid spheres, where are the electrical charges located in matter? • Scientists’ conclusions: Atoms are not indivisible; they have a complex internal structure.

  9. 1.4. THOMSON’S ATOMIC MODEL (1897) During the last quarter of the 19th centurycathode rays were discovered. Thomson studied the nature of cathode rays by the use of cathode ray tube. http://www.youtube.com/watch?v=XU8nMKkzbT8 He determined that cathode rays were a stream negatively charged particles smaller than the atom. He called these particles electrons.

  10. Characteristics of the electron: It is a tiny particle which forms part of all atoms. Negatively electric charge: Smallest negatively electric charge in the Universe. Qe = 1,6  1019 C Qe = 1 Very small mass me= 0,00000000000000000000000000000091 kg me = 9,1  1031 kg

  11. Thomson’s atomic model (plum pudding cake) • A uniform sphere of positively charged matter. • Almost all the mass of the atom is spread throughout the sphere, so the atom has a very low density. • A sphere of positive chargewith almost all the mass of the atom. • Electrons are embedded in the sphere. • The atom is electrically neutral: • no. (+) charges = no. () charges This model explains the static electricity and the ion formation: Positively charged atoms: They lose electrons. Negatively charged atoms: They gain electrons.

  12. 1.5. RUTHERFORD’ATOMIC MODEL (1911) Radioactivity: Spontaneous emission of radiation, either directly from unstable atomic nuclei of some elements (uranium, polonium…) or as a consequence of a nuclear reaction. It was accidentally discovered by A. H. Becquerel (1896). E. Rutherford determined the cause and the nature of radioactivity in 1901: http://www.youtube.com/watch?v=a9O2r2edZBE  Rays: Helium nuclei of electric positive charge (two protons and two neutrons).  Rays: Electrons of electric negatively charge. g Rays: Electromagnetic radiation that has no electric charge (gamma rays).

  13. Electrolysis, cathode rays, and radioactivity show that the atom is not indivisible but a complex system.

  14. Rutherford’s gold foil experiment: This experiment involved the firing of radioactive particles, positively charged a particles, through very thin metal foils (notably gold) and detecting them using screens coated with zinc sulphide. Expected results according to Thomson’s atomic model: the a particles should have passed through the gold foil with only a few minor deflections. This is because the a particles are heavy and the mass and the positive charge in the "plum pudding model" is widely spread.

  15. Rutherford Gold Foil Experiment - Backstage Science - YouTube http://www.youtube.com/watch?v=5pZj0u_XMbc Experiment results: 1. Rutherford found that although the vast majority of particles passed straight through the foil without deflection. 2. Some particles were deflected at large angles. 3. Surprisingly, very few particles even deflected backwards.

  16. Rutherford’s atomic model: The atom is similar to a solar system. It can be divided in two parts: Thenucleus. 1. It is located in the centre of the atom. 2. It is very dense, because it contains almost all of the mass of the atom in a very small volume. 4. It has all the positive charge. The extra-nuclear part. 1. It is most of the space of the atom. 2. It is largely empty. 3. The negatively-charged electrons revolve around the nucleus in closed orbits attracted by its positive charge. Atom size: 10-10 m = 0,0000000001 m. Nucleus size: 10-14 m = 0,00000000000001 m. The atom is 10.000 times larger than the nucleus. The atom is almost empty: Very few a particles are deflected, those that collide with the positive nucleus which occupies a very small fraction of the volume of the atom.

  17. 1.6. BOHR’s ATOMIC MODEL (1913 The atoms of the each element emit a different light when they are excited by heat or electricity. The different colours of the fireworks are an example of this phenomenon. The atoms of the each element emit a different light because they have their own electronic structure of the extra-nuclear part. 1. The atom consists of a small, positively-charged nucleus surrounded by electrons that travel in certain definite circular orbits or shells attracted by the nucleus. 2. Each orbit or shell corresponds to a definite energy and a definite distance to the nucleus in which the electrons are stable. That means that the electrons don’t emit or absorb energy.

  18. 3. The orbits or energy levels are characterized by an integer of the called quantum number, n, which can have values 1, 2, 3, 4…The orbits are numbered as 1, 2, 3, 4..., starting from the nucleus side. Thus, the orbit for which n = 1 is the lowest energy level and the closestorbit to the nucleus. The orbits corresponding to n = 1, 2, 3, 4…, are also designated as K (n = 1), M (n = 2), N (n = 3) … shells. The electrons occupy the lowest energylevel, it is said to be in the ground state. Since, electrons can be present only in these orbits, hence, they can only have energies corresponding to these energy levels, i.e., electrons in an atom can have only certain permissible energies .The atom is quantized.

  19. Each shell can contain a maximum number of electrons given by the expression: 2n2 1st shell (K): 2 e. It is the closest shell to the nucleus with the lowest energy level. 2nd shell (L): 8 e. 3td shell (M): 18 e. 4th shell (N): 32 e. (Up to 7 shells) The filling order is complicated and the 3td shell fills until it gets to 8, and then the 4th shell starts adding electrons until it has 8 electrons. Then the 3td shell fills until it gets to 18.

  20. 4. The e- present in an atom can move from a lower energy level (Elower) to a level of higher energy (Ehigher) by absorbing the appropriate energy. Similarly, an e-can jump from the higher energy level (Ehigher) to a lower energy level (Elower) by losing the appropriate energy. The energy absorbed or lost is equal to the difference between the energies of the two energy levels: ΔE= Ehigher - Elower Electronic Configuration of an atom is the arrangement of electrons in the various shells/orbits/energy levels of an atom starting from the shell 1 of lower energy. E.g.: Cl (2, 8, 7).

  21. 1.6. THE ATOM STRUCTURE Atoms are made up of electrons, protons, and neutrons. Electron (Thomson, 1898): located in the extra-nuclear part. Negative electric charge: Qe = 1,6  1019 C. Unit of negative electric charge smaller than exists: Qe = 1. Insignificant mass: me = 9,1 × 10 31 kg Proton (Rutherford, 1919): located in the nucleus. Positive electric charge: Qp = +1,6  1019 C. Its charge is equal and opposite to that of the electron. Unit of (+) electrical charge smaller than exists. Qp = +1. Very small mass:mp = 1,673 × 10-27 kg mpis 1836 times greater thanme

  22. Neutron(Prediction of Rutherford: 1920; discovery of Chadwick: 1932):located in the nucleus. Without electrical charge. Very small mass: mn = mp = 1,675 × 10-27 kg

  23. Nucleus: central zone of the atom. Protons and neutrons: all the positivecharge and almostall the mass. The number of protons of an atom is fixed and characteristic. Very dense: almost all of the mass of the atom in a very small space with respect to the size of the atom. Extra-nuclear part: external zone of the atom. Almost all the atom is empty. The electrons revolve around the nucleus, attracted by the positive charge of its protons, in only certain allowed orbits. Its electric charge is negative and mass is insignificant.

  24. 2. CHARACTERISTICS OF ATOMS Chemical element: Each type of atom with a characteristicnumber of protons in its nucleus. Atomic number, Z: Number of protons of an atom in its nucleus. It is the identifying characteristic of each chemical element. Nucleons: Particles that make up the nucleus of an atom. They are protons and neutrons Mass number, A: It is the total number of nucleons in the nucleus of an atom. No. of neutrons, N: N = A - Z

  25. Representation of an atom Electronic configuration of an atom: It is the arrangement of e in the various allowed shells/orbits/energy levels. Electrically neutral atom: nº p+ = nº e

  26. Order of filling of e: The e shells are built up in a regular fashion from the first shell to a total of seven shells, each of which has an upper limit to the number of e that it can accommodate. 1. The 1st shell is complete with 2 e 2. The 2nd can hold up to 8 e 3. The 3rd shell fills until it gets to 8 e although it can have a maximum of 18 e 4. The 4th shell starts adding e until it has 8 e 5. Then the 3rd shell fills until it gets to 18 e

  27. Valence shell: It is the outermost shell of an atom. • Valence electrons: Electrons of the valence shell. They determine the chemical properties of an atom. • Valence or valency of an element: no. of ethat it needs or that exceeds to have a stable electron configuration. It determines the number of other atoms with which an atom of the element can combine.

  28. Isotopes: Atoms of the same chemical element, with equal atomic number Z, same no. protons, but different massnumber A, i.e., different no. neutrons, therefore, they have different mass. Natural isotopic abundance: relative amount of each isotope in nature.

  29. Mass of atoms: • Atomic mass: approximately equal to the sums of masses of its protons and neutrons (electron mass is insignificant). • Almost all the mass of the atom is in the nucleus. • The atomic mass is very small: 10-27 - 10-25 kg. The kg is a unit of very great mass for a so small mass. • Unit of atomic mass,u: 1/12 times the mass of a 12C atom. • 1 u = 1,66033  1027 kg = 1,66033  1024 g • m (12C) = 19,9240  1027 kg = 12 u • Relative atomic mass: Ar, atomic mass of an atom of an element obtained by comparison with the atomic mass of the reference atom, the carbon-12 atom. Used apparatus: spectrograph of masses. • Atomic mass of an element: weighted average of the masses of its natural isotopes. Sum of the masses of each isotope multiplied by its relative natural abundance, dividing by 100.

  30. 3. CHEMICAL ELEMENTS Chemical element: a) A pure simple substance which is made up of only one type of atoms and cannot be split up into two or more simpler substances by chemical reactions (O2; N2; H2; He; Au). b) A type of atom which is made up of a variety of particles (p+, n and e), with a characteristic number of protons: Z. Chemical name: name corresponding to each element (gold, silver, bromine…). Chemical symbol: Form of representation of an element.  A capital letter (H, O, N, F…).  A capital letter and another small letter (Br, Zn, Au…). Number of known chemical elements at the moment: 118. Natural chemical elements: 90 Artificial chemical elements (laboratory): 28

  31. How are the elements in the nature: Simple substances: Substances made up of a single type of atoms (silver, iron, aluminium, oxygen…). Chemical compounds: Substances made up of a combination of two or more types of atoms (H2O; NaCl). Distribution of the elements in nature: The Earth: (O, 49,4%), (Si, 25,7%), (Al, 7,5%), (Fe, 4,7%), rest (12.7%). Living beings: (O, 63 %), (C, 20%), (H, 9.9%), N, 2,5%), (Ca, 2,5%), (P, 1,1%), rest (1,0%).  Universe: H(90 %),He(9%),rest(1%).

  32. Discovery of the chemical elements: • Elements known from Antiquity:9. Au, Ag, Cu, Fe, Pb, • Sn, Hg, S, C. • Elements discovered by the alchemists:3. As (1250), • Sb (1450), P (1669). • Elements discovered in the 18th century:20. • Elements discovered in the 19th century:50. • Elements discovered in the 20th and 21st centuries: 36.

  33. 4. THE PERIODIC TABLE Periodic Table: Arrangement of all the chemical elements to facilitate their study. Historical antecedents 19th Century: Great discovery of a great no. of chemical elements and their compounds, with varied physical and chemical properties: Families of elements with many similarities. Criteria of classification of the elements: 1. Similarities of physical/chemical properties of elements and its compounds. 2. Relationships between physical/chemical properties and some characteristics of the atoms (atomic mass).

  34. First attempts of classification of the known elements: 1. Metals and non-metals: Aspect and physical properties. 2. Döbereiner’s Triads (1817): He classified the elements into groups of 3 elements on the basis of their atomic masses with similar chemical properties. When elements were arranged in order of their increasing atomic mass, the atomic mass of the middle element was approximately the arithmetic mean of the other 2 elements of the triad.

  35. 3. Newlands’ Law of Octaves (1869). He arranged all the elements known at the time into a table in order of increasing relative atomic mass and similar properties. He found that each element was similar to the element 8 places further on.

  36. 4.Mendeleev (1869) and Meyer (1870): The properties of the elements they are not arbitrary, they vary periodically with their atomic masses.  Criteria of periodic arrangement of the elements:  Increasing atomic mass: Horizontal rows from left to right. Similar properties: Vertical columns.  Gaps in the table: Prediction of unknown elements, their masses and their properties. Defects of the arrangement: Inadequate position of H.  Inversion of the order of increasing atomic masses to maintain the properties of a column. There was no position for Lanthanides and Actinides. Diffuse separation between metals and non-metals.

  37. PRESENT PERIODIC SYSTEM Moseley (1912): The ordering of the elements by their spectra of the X-ray emissions coincided with the ordering of the elements by their atomic numbers, Z. PERIODIC LAW: the physical and chemicalproperties of the elements are periodic function of their atomic numbers. The elements are arranged in order of increasing atomic numbers, the elements with similar properties recur after regular intervals. The periodic repetition is called periodicity. Origin of the regularity: The physical and chemicalproperties of the elements are related to the arrangement of electrons in the valence shell. Thus, if the arrangement of electrons in the valence shell of the atoms is the same, their properties will also be similar. Authors: Werner and Paneth.

  38. PRESENT CRITERIA OF THE ARRANGEMENT OF THE PERIODIC TABLE • Increasing atomic number: From Z = 1, for H, increasing • in a unit from left to right and from up to down. • Two discontinuities, in the La (Z = 57), and in Ac (Z = 89). • 2. Groups: Columns (vertical rows)of elements with the • same no. of electrons in itsvalence shell. • Similar chemical properties. • 18 Groups. They are numbered from left to right, from • number 1 to number 18. • Special names for some groups: Group 1 = Alkalines. • Grupo 17 = Halogens. Grupo 18 = Noble Gases. • 3. Periods:Horizontal rowsof elements, with the same no. of electronic shells with electrons. • 7 Periods: 1st Period: 2 elements. 2nd and 3rd Periods: 8 • elements each one. 4th and 5th Periods: 18 elements in • each period. 6th Period: 32 elements. 7th Period: more • than 19 elements.

  39. 5. TYPES OF CHEMICAL ELEMENTS METALS CHEMICAL ELEMENTS CIENCIA CIENCIA NOBLE GASES SEMI-METALS NON-METALS

  40. METALS 1.Solids (room temperature), highmelting and boilingpoints. 2.A characteristic brightness. 3.Opaque (it doesn’t allow all light to pass through). 3.Metals feel cold to the touch. 4.Goodthermal and electricalconductors. 5.Malleable (Malleability: property that enables a material to deform by compressive forces. It can be stamped, hammered, forged, pressed, or rolled into thin sheets.) 6.Ductile (Ductility: property that enables a material to stretch, bend, or twist without cracking or breaking. This property makes it possible for a material to be drawn out into a thin wire). 7.Tough (Toughness: property that enables a material to withstand shock and to be deformed without rupturing). 8.Located on the left and the middle of the PeriodicTable. 9.Most of the chemical elements of the Periodic Table.

  41. NON-METALS 1.Solids, liquids or gases at room temperature. 2.Lowmelting and boilingpoints. 3.They do not have characteristic brightness. 4.Badthermal and electricalconductors. 5.Located on the right of the Periodic Table. SEMI-METALS 1.Intermediate characteristics between metals and non-metals. 2.Located between metals and non-metals: B, Si, Ge, As, Sb, Te, Po, and At. NOBLE GASES 1.18thGroupof the Periodic Table. 2.They are all gases at room temperature. 3.They are inert.

  42. 6. INTERNAL STRUCTURE OF THE MATTER What is matter made up of? Are there different types of matter? There are millions of different chemical substances It is made up of 118 different types of atoms They can combine with each other

  43. 7. INTERNAL STRUCTURE OF THE MATTER • Electronic configuration of an atom: arrangement of electrons in the various shells of an atom. Stable simple substances Monoatomic gases Inert (unreactive) They don’t react with other elements Noble gases 8 ein the valence shell He: 2 ein the valence shell

  44. they don’t have 8 e in the valence shell Unstable atoms They combine with each other to have 8 e in the valence shell Rest of the elements They form chemicalbonds with other atoms LEWIS THEORY OF THE CHEMICAL BOND (1916) • The atoms of the elements become more stable by formation of chemical bonds with other atoms. • A chemical bond: the electrical attraction force between the atoms in a molecule or a crystalline network, by means of cession, gain or sharing of e between atoms, so that both obtain a more stable electronic configuration: the noble gas electron configuration (8 ein the valence shell except for He with 2 e): The octet rule (Expections: B and 3rd Period).

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